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Advanced applications of numerical modelling techniques for clay extruder design.

KANDASAMY, Saravanakumar.

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KANDASAMY, Saravanakumar. (2013). Advanced applications of numerical modelling techniques for clay extruder design. Doctoral, Sheffield Hallam University (United Kingdom)..

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Advanced Applications of Numerical Modelling Techniques for Clay Extruder Design

Saravanakumar Kandasamy

A thesis submitted in partial fulfilment of the requirements of Sheffield Hallam University for the degree of Master of Philosophy

April-2013

AcknowledgementI would like to offer my sincere thanks to Sheffield Hallam University-United

Kingdom, for offering me the opportunity to pursue this research work and

providing me with adequate resources required to complete this research

work. I would like to thank Dr. Abhishek Asthana, Dr. Andrew Young,

Dr. Francis Clegg and Prof. Graham Cockerham for their enduring support

and guidance in completing this research work. I also thank the CAD

technicians Mr. John Stanley and Mr. Steve Brandon, for their support.

I also would like to offer my gratitude to Prof. Alan Smith, Prof. Doug

Cleaver and all the other non-teaching staff members at Materials and

Engineering Science Research Institute (MERI), for their timely support and

guidance.

I am grateful to the board of directors at Group Rhodes Limited-United

Kingdom, for offering me this wonderful opportunity of undertaking a

research work at their esteemed workplace. I would like to thank Mr. Mark

Ridgway-OBE, whose vision for developing technically superior products and

interests in research and development helped in establishing a strong

platform for undertaking this research work. I would like to thank Mr. Barry

Richardson, whose ideas and zest for knowledge created this research

requirement and also helped in building strong and focused objectives for

this research work. I also would like to thank Mr. Ian Ridgway and Mr. Peter

Anderton, for their support in providing adequate resource for completing this

project work.

I would like thank the design, sales and manufacturing team at Group

Rhodes Limited and a special thanks to Mr. Dave Pearson, Mr. Kevin Hall,

Mr. Glynn Dixon, Mr. Mick Tinker and Mr. Edwin, for sharing their knowledge

and experience in the field of clay extrusion and supporting with required

scientific data required to complete this research work.

I also would like to thank the engineering and production team at

M/s Hepworth Wavin Limited- United Kingdom, M/s Dreadnought Tiles-

United Kingdom, M/s Ibstock Bricks Limited- United Kingdom, M/s HansonI

Brick Limited-United Kingdom and M/s Blockley's Limited-United Kingdom,

for their interest and technical contributions made to this research work.

Last but not the least; I would like to thank my parents and all my friends for

their support offered during this research work.

PrefaceA major portion of the research work discussed in this report was completed

through Knowledge Transfer Partnership (KTP) programme

(Ref.No:KTP007670), between Sheffield Hallam University (SHU), United

Kingdom (U.K) and Craven Fawcett Limited (C.F Ltd) - a part of Group

Rhodes Limited, U.K.

KTP is a U.K government initiated programme intended to support mainly the

small and medium scale business sectors in the U.K. It focuses on improving

their business prospects, either by solving any technological or management

issues existing in their business structure or to improve their product quality

and introduce new products. The main aim is to increase the

competitiveness and create healthy business prospects within the economy.

The required objectives of a KTP programme will be achieved by

establishing a short term partnership between a Higher Educational

Institution and a company registered in the U.K. The aim and objectives of

the project will be defined clearly by the members of participating

organisation and will be achieved through a working member, called an

Associate.

Established in the year 1836, Sheffield Hallam University is one among the

top 50 higher education institutions in the U.K, to undertake research works

in the subject of engineering. It has dedicated research institutions and lab

facilities for carrying out world class research works under the supervision of

academic experts from various areas of mechanical and materials

engineering. It also possesses a dedicated team of academics and experts

to support industrial partnership based projects and research works in the

field of engineering.

Craven Fawcett Limited, established in the year 1843, is a subsidiary

company of Group Rhodes Limited. It specialises in design and

manufacturing of clay working machines, which has its application mainly in

heavy clay structural ceramics industry. The range of products offered by

them includes box feeders, grinding mills, mixers, conveyors and extruders.

Being an ISO 9001 certified organisation and a well reputed company in U.K

and worldwide, it places a greater emphasis on design, and material

selection for the components of their products, optimising the production

process and time and improving the quality and efficiency of their products.

Combined de-airing type (Vacuum type) extruder is a specialised product of

C.F Ltd. and being a market leader in this segment, the management has a

keen interest in introducing and using advanced computer aided techniques

such as Computational Fluid Dynamics and Finite Element Analysis to

improve their current designs and to fast track the development of new

extruders and its components. Through this they are intended to achieve a

better and energy efficient extruders, for the use of ceramic industries. Since

the company did not have any experience and expertise available in-house

to accomplish this, a KTP programme was established and the research

work was undertaken to meet the required objectives. This report

summarises the research work undertaken and accomplishments towards

the company's intended requirement.

IV

AbstractCeramic materials play a vital role in our day to day life. Recent advances in

research, manufacture and processing techniques and production

methodologies have broadened the scope of ceramic products such as

bricks, pipes and tiles, especially in the construction industry. These are

mainly manufactured using an extrusion process in auger extruders. During

their long history of application in the ceramic industry, most of the design

developments of extruder systems have resulted from expensive laboratory-

based experimental work and field-based trial and error runs. In spite of

these design developments, the auger extruders continue to be energy

intensive devices with high operating costs. Limited understanding of the

physical process involved in the process and the cost and time requirements

of lab-based experiments were found to be the major obstacles in the further

development of auger extruders.

An attempt has been made herein to use Computational Fluid Dynamics

(CFD) and Finite Element Analysis (FEA) based numerical modelling

techniques to reduce the costs and time associated with research into design

improvement by experimental trials. These two techniques, although used

widely in other engineering applications, have rarely been applied for auger

extruder development. This had been due to a number of reasons including

technical limitations of CFD tools previously available. Modern CFD and FEA

software packages have much enhanced capabilities and allow the modelling

of the flow of complex fluids such as clay.

This research work presents a methodology in using Herschel-Bulkley's fluid

flow based CFD model to simulate and assess the flow of clay-water mixture

through the extruder and the die of a vacuum de-airing type clay extrusion

unit used in ceramic extrusion. The extruder design and the operating

parameters were varied to study their influence on the power consumption

and the extrusion pressure. The model results were then validated using

results from experimental trials on a scaled extruder which seemed to be in

reasonable agreement with the former. The modelling methodology was then

extended to full-scale industrial extruders. The technical and commercial

V

suitability of using light weight materials to manufacture extruder components

was also investigated. The stress and deformation induced on the

components, due to extrusion pressure, was analysed using FEA and

suitable alternative materials were identified. A cost comparison was then

made for different extruder materials. The results show potential of significant

technical and commercial benefits to the ceramic industry.

VI

Contents

Acknowledgement.................................................................................................... I

Preface................................................................................................................... Ill

Abstract....................................................................................................................V

List of figures........................................................................................................... X

List of tables..........................................................................................................XX

Chapter-1 Introduction........................................................................................ 1

1.1 Bricks........................................................................................................ 2

1.2 ............... 2

1.3 Objectives................................................................................. ............... 2

1.4 Research methodology........................................................... ............... 3

1.5 Previous works........................................................................ ............... 3

1.6 Thesis outline........................................................................... ................4

Chapter-2 Review of existing work for ceramic extrusion............. ................5

2.1 Introduction.............................................................................. ................6

2.2 Modelling and simulation of extruder system...................... ................6

2.3 Design and performance evaluation of extruders.............. ............. 13

2.4 Clay-Water rheology............................................................... ............. 24

2.5 Conclusion............................................................................... ............. 28

Chapter-3 CFD modelling of clay extruder...................................... ............. 29

3.1 Introduction.............................................................................. ............. 30

3.2 Fundamental classification of fluids...................................... ............. 30

3.3 Process of CFD modelling..................................................... ............. 36

3.4 CFD modelling of extruder..................................................... ............. 40

3.4.1 Geometry creation............................................................................ 40

3.4.2 Geometry discretisation....................................................................41

3.4.3 Boundary conditions......................................................................... 45

VII

3.4.4 Solver settings.................................................................................. 47

3.5 Experimental validation of CFD modelling...........................................51

3.6 CFD modelling of a scaled extruder......................................................56

3.7 Experimental study of clay rheology.....................................................59

3.8 Performance assessment of extruders with different diam eters 61

3.9 Performance assessment of a 500 mm extruder................................. 71

3.9.1 Effect of varying feed rate on performance of extruder.................71

3.9.2 Effect of varying auger speed on performance of extruder...... 75

3.9.3 Effect of varying pitch distance on performance of extruder.... 79

3.9.4 Effect of varying die shapes on performance of extruder.........83

3.9.5 Effect of varying number of split worms on performance of

extruder..........................................................................................................88

3.10 Performance assessment of a 600 mm extruder............................. 93

3.10.1 Effect of varying feed rate on performance of extruder.......... 93

3.10.2 Effect of varying auger speed on performance of extruder... 97

3.11 Conclusion..........................................................................................101

Chapter-4 Finite Element Analysis of clay extruder.....................................102

4.1 Introduction:............................................................................................103

4.2 FEA of clay extruder components........................................................103

4.2.1 Barrel.................................................................................................103

4.2.2 Distance piece................................................................................107

4.2.3 L iner..................................................................................................111

4.2.4 Auger.................................................................................................114

4.3 Conclusion..............................................................................................118

Chapter-5 Conclusion and future directions................................................. 119

5.1 Conclusion..............................................................................................120

5.2 Future directions.................................................................................... 121

VIII

References.......................................................................................................... 123

Appendix-A......................................................................................................... 129

Appendix-B..........................................................................................................175

Appendix-C..........................................................................................................182

Appendix-D......................................................................................................... 204

IX

List of figuresFigure 2-1 Extrusion pressure at various length of extruder.............................8

Figure 2-2 Dynamic pressure at various length of extruder..............................9

Figure 2-3 Dynamic pressure variation with respect to auger speed .............. 9

Figure 2-4 Clay velocity at various lengths of extruder....................................10

Figure 2-5 Viscosity profile for Bingham and Casson model flu ids ................11

Figure 2-6 Stress induced on die mandrel during wet clay extrusion............ 12

Figure 2-7 Effect of auger pitch variation on extruder performance...............15

Figure 2-8 Performance characteristics profile for a typical auger.................15

Figure 2-9 Pressure waves experienced in auger with half flights .................17

Figure 2-10 Typical pressure distribution in an extruder..................................18

Figure 2-11 Effect of extrusion rate on die pressure ........................................ 18

Figure 2-12 Forming pressure profile under normal condition ........................19

Figure 2-13 Effect of increasing clay stiffness on extrusion pressure ........... 20

Figure 2-14 Effect of decreasing clay stiffness on extrusion pressure 20

Figure 2-15 Effect of changing die geometry on extrusion pressure............. 21

Figure 2-16 Effect of changing feed rate on extrusion pressure .................... 21

Figure 2-17 Effect of die shape on extrusion pressure and power.................22

Figure 2-18 Effect of die shape on quality of extruded product...................... 23

Figure 2-19 Viscosity of pure clay sewer paste .................................................24

Figure 2-20 Viscosity profile of a typical shear thinning fluid...........................26

Figure 3-1 Newtonian flu ids.................................................................................30

Figure 3-2 Pseudoplastic fluids........................................................................... 32

Figure 3-3 Visco plastic flu ids ............................................................................. 33

Figure 3-4 Dilatant fluids...................................................................................... 34

Figure 3-5 Thixotropic fluids.................................................................................34

Figure 3-6 Rheopectic flu ids ................................................................................35

Figure 3-7 Visco-elastic fluids............................................................................. 35

Figure 3-8 Flow physics features in CFD ...........................................................37

Figure 3-9 CFD modelling process flow diagram ..............................................39

Figure 3-10 430 mm extruder- Auger volume-1................................................42

Figure 3-11 430 mm extruder- Auger volume-2................................................42

Figure 3-12 430 mm extruder - Clearance volume........................................... 43

X

Figure 3-13 430 mm extruder - Die/ extruder mouth volume........................ 43

Figure 3-14 430 mm extruder- Liner volume....................................................44

Figure 3-15 430 mm extruder components and die assembled view...........44

Figure 3-16 Moving volumes..............................................................................47

Figure 3-17 Stationary volumes........................................................................ 47

Figure 3-18 Scaled extruder...............................................................................52

Figure 3-19 Experimental set up layout...........................................................52

Figure 3-20 Scaled extruder-auger shaft.........................................................56

Figure 3-21 clearance.........................................................................................56

Figure 3-22 Scaled extruder-transition piece.................................................. 56

Figure 3-23 Scaled extruder-auger shaft meshed.......................................... 57

Figure 3-24 Scaled extruder-clearance meshed.......................... .................. 57

Figure 3-25 Scaled extruder- transition piece meshed...................................58

Figure 3-26 Parallel plate viscometer-Anton Parr (MCR301)........................59

Figure 3-27 Apparent viscosity vs. Strain rate of clay- measured

experimentally........................................................................................................60

Figure 3-28 Static pressure contour (full view)-430 mm Case 1...................62

Figure 3-29 Static pressure contour (sectional view) - 430 mm Case 1.......63

Figure 3-30 Static pressure profile-430 mm Case 1........................................63

Figure 3-31 Flow velocity during extrusion (sectional view)- 430 mm Case I

.................................................................................................................................64

Figure 3-32 Molecular viscosity vs. Strain rate- 430 mm Case 1..................65

Figure 3-33 Residual convergence-430 mm Case 1.......................................66

Figure 3-34 Mass flow rate convergence- 430 mm Case 1............................66

Figure 3-35 Extrusion pressure and Energy consumption vs. Diameter

(Case-1)...................................................................................................................67

Figure 3-36 Static pressure contour (full view)-430 mm Case I I ..................68

Figure 3-37 Static pressure contour (sectional view)- 430 mm Case II.......68

Figure 3-38 Static pressure profile-430 mm Case II.......................................69

Figure 3-39 Flow velocity during extrusion (sectional view)- 430 mm Case II

.................................................................................................................................69

Figure 3-40 Molecular viscosity vs. Strain rate-430 mm Case I I .................... 70

Figure 3-41 Extrusion pressure, Energy consumption vs. Diameter (Case-11)

.................................................................................................................................70XI

Figure 3-42 Static pressure contour (full view) - feed rate 10 kgs'1.............. 72

Figure 3-43 Static pressure contour (sectional view) - feed rate 10 kgs'1.... 72

Figure 3-44 Static pressure profile- feed rate 10 kgs'1................................... 73

Figure 3-45 Flow velocity during extrusion (sectional view)- feed rate 10 kgs'1

................................................................................................................................ 73

Figure 3-46 Molecular viscosity vs. Strain rate- feed rate 10 kgs'1................ 74

Figure 3-47 Extrusion pressure, Energy consumption vs. Feed rate ............ 74

Figure 3-48 Static pressure contour (full view) - auger speed 10 rpm 76

Figure 3-49 Static pressure contour (sectional view) - auger speed 10 rpm76

Figure 3-50 Static pressure profile-auger speed 10 rpm................................. 77

Figure 3-51 Flow velocity during extrusion (sectional view) - auger speed 10

rpm.......................................................................................................................... 77

Figure 3-52 Molecular viscosity vs. Strain rate - auger speed 10 rpm ..........78

Figure 3-53 Extrusion pressure, Energy consumption vs. Auger speed .......79

Figure 3-54 Static pressure contour (full view)-pitch dist. 246.13 mm........... 80

Figure 3-55 Static pressure contour (sectional view)-pitch dist. 246.13 mm 80

Figure 3-56 Static pressure profile-pitch dist. 246.13 mm............................... 81

Figure 3-57 Flow velocity during extrusion (sectional view)-pitch dist. 246.13

mm.......................................................................................................................... 81

Figure 3-58 Molecular viscosity vs. Strain rate-pitch dist. 246.13 m m .......... 82

Figure 3-59 Extrusion pressure, Energy consumption vs. Auger pitch

distance..................................................................................................................83

Figure 3-60 Types of die design investigated...................................................84

Figure 3-61 Static pressure contour (full view)-die type-11............................... 85

Figure 3-62 Static pressure contour (sectional view)-die type-11.................... 85

Figure 3-63 Static pressure profile-die type-11...................................................86

Figure 3-64 Flow velocity during extrusion (sectional view)-die type-ll.........86

Figure 3-65 Molecular viscosity vs. Strain rate- die type-ll........................... 87

Figure 3-66 Extrusion pressure, Energy consumption vs. Die design........... 87

Figure 3-67 Types of split worm design investigated.......................................89

Figure 3-68 Static pressure contour (full view)-two split worms..................... 89

Figure 3-69 Static pressure contour (sectional view)-two split worms........... 90

Figure 3-70 Static pressure profile-two split worms......................................... 90

Figure 3-71 Flow velocity during extrusion (sectional view)-two split worms 91XII

Figure 3-72 Flow pattern with no split worm .....................................................91

Figure 3-73 Flow pattern with one split w orm ................................................. 91

Figure 3-74 Flow pattern with two split worms................................................ 92

Figure 3-75 Molecular viscosity vs. Strain rate-two half flights....................... 92

Figure 3-76 Extrusion pressure, Energy consumption vs. Split worm s.........93

Figure 3-77 Static pressure contour (full view) - feed rate 8.1 k g s 1.............. 94

Figure 3-78 Static pressure contour (sectional view) - feed rate 8.1 k g s 1... 95

Figure 3-79 Static pressure profile- feed rate 8.1 kg s1................................... 95

Figure 3-80 Flow velocity during extrusion (sectional view)-feed rate 8.1 kgs'1

................................................................................................................................ 96

Figure 3-81 Molecular viscosity vs. Strain rate- feed rate 8.1 k g s 1............... 96

Figure 3-82 Extrusion pressure, Energy consumption vs. feed rate.............. 97

Figure 3-83 Static pressure contour (full view) - auger speed 15 rpm ...........98

Figure 3-84 Static pressure contour (full view) - auger speed 15 rpm ...........98

Figure 3-85 Static pressure profile- auger speed 15 rpm ................................ 99


rpm .......................................................................................................................... 99

Figure 3-87 Molecular viscosity vs. Strain rate- auger speed 15 rpm 100

Figure 3-88 Extrusion pressure, Energy consumption vs. auger speed 101

Figure 4-1 430 mm extruder barrel geom etry............................................... 104

Figure 4-2 430 mm extruder barrel- load applied..........................................104

Figure 4-3 Stress induced in barrel @ 2.6 MPa load .....................................105

Figure 4-4 Deformation in barrel @2.6 MPa loa d ......................................... 106

Figure 4-5 430 mm extruder distance piece geometry...................................107

Figure 4-6 430 mm extruder distance piece- load applied ............................ 108

Figure 4-7 Stress induced in distance piece @ 2.6 MPa load...................... 109

Figure 4-8 Deformation in distance piece @2.6 MPa load...........................110

Figure 4-9 430 mm extruder liner geometry.................................................... 111

Figure 4-10 430 mm extruder liner - load applied .......................................... 111

Figure 4-11 Stress induced in liner @ 2.6 MPa load......................................112

Figure 4-12 Deformation in liner @ 2.6 MPa load .......................................... 113

Figure 4-13 430 mm extruder auger shaft geometry......................................114

Figure 4-14 430 mm extruder auger shaft - load applied.............................. 114

Figure 4-15 Stress induced in auger shaft @ 2.6 MPa load..........................115XIII

Figure 4-16 Deformation in auger shaft @ 2.6 MPa load............................ 116

Figure A-A- 1 500 mm extruder volumes and mesh generated ..................130

Figure A-A-2 600 mm extruder volumes and mesh generated ...................130

Figure A-A-3 Static pressure contour (full view)-500 mm Case 1............... 131

Figure A-A-4 Static pressure contour (sectional view)-500 mm Case 1...131

Figure A-A-5 Static pressure profile -500 mm Case 1....................................131

Figure A-A-6 Flow velocity during extrusion (sectional view)-500 mm Case I

............................................................................................................................. 132

Figure A-A-7 Molecular viscosity vs. Strain rate-500 mm Case 1.................132

Figure A-A-8 Static pressure contour (full view)-600 mm Case 1.................133

Figure A-A-9 Static pressure contour (sectional view)-600 mm Case 1.....133

Figure A-A-10 Static pressure profile -600 mm Case 1.................................. 134


............................................................................................................................. 134

Figure A-A-12 Molecular viscosity vs. Strain rate-600 mm Case..1..............135

Figure A-A-13 Static pressure contour (full view)-500 mm Case I I 135

Figure A-A-14 Static pressure contour (sectional view)-500 mm Case II... 136

Figure A-A-15 Static pressure profile -500 mm Case II..................................136

Figure A-A-16 Flow velocity during extrusion (sectional view)-500 mm Case

II........................................................................................................................... 136

Figure A-A-17 Molecular viscosity vs. Strain rate-500 mm Case I I 137

Figure A-A-18 Static pressure contour (full view)-600 mm Case I I 137

Figure A-A-19 Static pressure contour (sectional view)-600 mm Case II... 138

Figure A-A-20 Static pressure profile -600 mm Case II..................................138


II........................................................................................................................... 138

Figure A-A-22 Molecular viscosity vs. Strain rate-600 mm Case I I 139

Figure A-A-23 Static pressure contour (full view) - feed rate 15 k g s 1 139

Figure A-A-24 Static pressure contour (sectional view) - feed rate 15 k g s 1

..............................................................................................................................140

Figure A-A-25 Static pressure profile- feed rate 15 k g s 1.............................140

XIV

Figure A-A-26 Flow velocity during extrusion (sectional view)-feed rate 15

kg s1..................................................................................................................... 140

Figure A-A-27 Molecular viscosity vs. Strain rate- feed rate15 k g s 1 141

Figure A-A-28 Static pressure contour (full view) - feed rate 25 kgs'1 141

Figure A-A-29 Static pressure contour (sectional view) - feed rate 25 kgs'1

.............................................................................................................................. 142

Figure A-A-30 Static pressure profile- feed rate 25 kgs'1........................... 142

Figure A-A-31 Flow velocity during extrusionfsectional view)-feed rate 25

kg s1......................................................................................................................142

Figure A-A-32 Molecular viscosity us. Strain rate- feed rate 25 kgs'1.......... 143

Figure A-A-33 Static pressure contour (full view) - feed rate 30 kgs'1......... 143


............................................................................................................................. 144

Figure A-A-35 Static pressure profile- feed rate 30 kgs'1.............................144


k g s 1..................................................................................................................... 144

Figure A-A-37 Molecular viscosity vs. Strain rate- feed rate 30 kgs'1 145



............................................................................................................................. 146



kgs'1..................................................................................................................... 146




..............................................................................................................................148



kgs'1..................................................................................................................... 148


Figure A-A-48 Static pressure contour (full view) - auger speed 15 rpm.... 149

Figure A-A-49 Static pressure contour (sectional view) - auger speed 15 rpm

..............................................................................................................................150XV

Figure A-A-50 Static pressure profile- auger speed 15 rpm..........................150

Figure A-A-51 Flow velocity during extrusion(sectional view)-auger speed 15

rpm........................................................................................................................150

Figure A-A-52 Molecular viscosity vs. Strain rate - auger speed 15 rpm ... 151



.............................................................................................................................. 152


Figure A-A-56 Flow velocity during extrusion (sectional view)-auger speed 20

rpm........................................................................................................................152




............................................................................................................................. 154

Figure A-A-60 Static pressure profile- auger speed 25 rpm.......................154


rpm....................................................................................................................... 154




..............................................................................................................................156

Figure A-A-65 Static pressure profile- auger speed 40 rpm........................ 156


rpm....................................................................................................................... 156




...............................................................................................................................158



rpm........................................................................................................................ 158


Figure A-A-73 Static pressure contour (full view)-pitch 338.012 mm 159

Figure A-A-74 Static pressure contour (sectional view)-pitch 338.012 mm 160XVI

Figure A-A-75 Static pressure profile-pitch 338.012 m m ............................ 160

Figure A-A-76 Flow velocity during extrusion(sectional view)-pitch 338.012

mm........................................................................................................................160

Figure A-A-77 Molecular viscosity vs. Strain rate-pitch 338.012 mm .......... 161

Figure A-A-78 Static pressure contour (full view)-die type-l..........................161

Figure A-A-79 Static pressure contour (sectional view)-die type-1.............. 162

Figure A-A-80 Static pressure profile-die type-1............................................. 162

Figure A-A-81 Flow velocity during extrusion (sectional view)-die type-1... 162

Figure A-A-82 Molecular viscosity vs. Strain rate- die type-1........................ 163

Figure A-A-83 Static pressure contour (full view)-die type-ill....................... 163

Figure A-A-84 Static pressure contour (sectional view)-die type-lll............ 164

Figure A-A-85 Static pressure profile-die type-ill........................................... 164

Figure A-A-86 Flow velocity during extrusion (sectional view)-die type-lll. 164

Figure A-A-87 Molecular viscosity vs. Strain rate- die type-lll.....................165

Figure A-A-88 Static pressure contour (full view) - feed rate 11.8 kgs'1 165

Figure A-A-89 Static pressure contour (sectional view) - feed rate 11.8 kgs'1

166

Figure A-A-90 Static pressure profile- feed rate 11.8 kgs'1...........................166

Figure A-A-91 Flow velocity during extrusionfsectional view)-feed rate 11.8

kgs'1...................................................................................................................... 166

Figure A-A-92 Molecular viscosity vs. Strain rate- feed rate 11.8 kgs'1.......167

Figure A-A-93 Static pressure contour (full view) - feed rate 19 kgs'1......... 167


168

Figure A-A-95 Static pressure profile- feed rate 19 kgs'1.............................. 168


kgs'1...................................................................................................................... 168

Figure A-A-97 Molecular viscosity vs. Strain rate- feed rate 19 kgs'1.......... 169



............................................................................................................................... 170

Figure A-A-100 Static pressure profile- auger speed 30 rpm........................170

Figure A-A-101 Flow velocity during extrusionfsectional view)-auger speed

30 rpm................................................................................................................... 170XVII

Figure A-A-102 Molecular viscosity vs. Strain rate- auger speed 30 rpm ..171

Figure A-A-103 Static pressure contour (full view)-scaled extruder-T1.......171

Figure A-A-104 Static pressure contour (sectional view)-scaled extruder-T1

.............................................................................................................................. 172

Figure A-A-105 Flow velocity during extrusion (sectional view)-scaled

ext rude r-T1 ..........................................................................................................172

Figure A-A-106 Molecular viscosity vs. Strain rate-scaled extruder-T1.......172

Figure A-A-107 Static pressure contour (full view)-scaled extruder-T2.......173

Figure A-A-108 Static pressure contour (sectional view)-scaled extruder-T2

............................................................................................................................. 173


extruder-T2..........................................................................................................174

Figure A-A-110 Molecular viscosity vs. Strain rat e-scaled extruder-T2 174

Figure A-B- 1 Stress induced in barrel @1.8 MPa load ...............................176

Figure A-B- 2 Deformation in barrel @1.8 MPa load.................................... 177

Figure A-B- 3 Stress induced in distance piece @1.8 MPa load..................178

Figure A-B- 4 Deformation in distance piece @1.8 MPa load ...................... 178

Figure A-B- 5 Stress induced in liner @1.8 MPa load....................................179

Figure A-B- 6 Deformation in liner @1.8 MPa load ........................................ 180

Figure A-B- 7Stress induced in auger shaft @1.8 MPa load.......................... 180

Figure A-B- 8 Deformation in auger shaft @1.8 MPa load............................ 181

Figure A-C- 1 Energy consumption pattern of U.K brick industries..............184

Figure A-C- 2 Typical brick making process flow diagram ............................ 186

Figure A-C- 3 Classification of clay mineral groups ....................................... 187

Figure A-C- 4 Quarries for brick clay in U.K .................................................... 188

Figure A-C- 5 Quarry operated with mechanical extraction process............189

Figure A-C- 6 Hand moulding process............................................................. 191

Figure A-C- 7 Mechanized soft moulding machine ........................................ 192

Figure A-C- 8 Typical De-Boer soft mud moulding machine.........................192

Figure A-C- 9 Soft moulding machine-Aberson type...................................... 193

Figure A-C- 10 Vacuum extruder.....................................................................194

XVIII

Figure A -C -11 Hydraulic press type tile making machine............................195

Figure A-C- 12 Typical cutting system used in a brick production line 199

Figure A-C- 13 Tunnel dryer............................................................................201

Figure A-C- 14 Tunnel kiln-Type 1....................................................................202

Figure A-C- 15 Tunnel kiln-Type 2 ...................................................................202

Figure A-D- 1 Piston extruder...........................................................................206

Figure A-D- 2 Europresse extruder..................................................................207

Figure A-D- 3 Electrophoretic extruder........................................................... 208

Figure A-D- 4 Vacuum extruder-Centex model.............................................. 212

Figure A-D- 5 Mixing chamber.........................................................................213

Figure A-D- 6 Components of an extruder system.........................................214

Figure A-D- 7 Auger geometrical parameters................................................ 217

Figure A-D- 8 Vacuum extruder pressure profile............................................ 219

XIX

List of tablesTable 3-1 Craven Fawcett extruders for brick making..................................... 40

Table 3-2 Extruder mesh details........................................................................ 45

Table 3-3 Variables for Herschel- Bulkley's model..........................................49

Table 3-4 Experimental analysis results-trial 1 ................................................ 54

Table 3-5 Experimental analysis results-trial 2 ................................................ 55

Table 3-6 Herschel- Bulkley's model values for scaled extruder CFD analysis

................................................................................................................................ 58

Table 3-7 Result comparison for scaled extruder............................................. 59

Table 3-8 Data set for varying extruder diameter and moisture content

analysis.................................................................................................................. 61

Table 3-9 Data set for varying feed rate analysis............................................. 71

Table 3-10 Data set for varying auger speed analysis.................................... 75

Table 3-11 Data set for varying pitch distance analysis.................................. 79

Table 3-12 Data set for varying die design analysis.........................................83

Table 3-13 Data set for varying split worm analysis.........................................88

Table 3-14 Data set for varying feed rate analysis........................................... 94

Table 3-15 Data set for varying auger speed analysis.................................... 97

Table 4-1 Stress results-barrel.......................................................................... 105

Table 4-2 Deformation results- barre l.............................................................106

Table 4-3 Manufacturing cost comparison for extruder barrel.....................107

Table 4-4 Stress results-distance p iece ...........................................................108

Table 4-5 Deformation results- distance piece.............................................. 109

Table 4-6 Manufacturing cost comparison for distance p iece .......................110

Table 4-7 Stress results-liner........................................................................... 112

Table 4-8 Deformation results-liner...................................................................113

Table 4-9 Stress results-auger shaft...............................................................115

Table 4-10 Deformation results-auger shaft.................................................... 116

Table 4-11 Manufacturing cost comparison for auger.................................. 117

Table A-C- 1 Various shaping techniques and their applicability............... 198

Table A-D- 1 Extruder classification based on process parameters 210X X

1.1 BricksCeramic products like bricks, pipes and tiles have been used extensively in

the construction industry for many years. The demand for ceramic products

especially bricks have rapidly increased over the past few decades due to

the excessive growth in population. This burgeoning demand has opened up

a huge market potential for ceramic industries to thrive upon. In order to

utilise the market potential to its full capacity, the brick industry needs to

overcome some key challenges like better and efficient production methods,

reduction of energy usage during manufacturing and reduced impact on

environment through sustainable operation. The ceramic industry, compared

to its predecessors has made significant and laudable changes in terms of

production techniques and machines used. The modern industry is

incorporated with completely automated production process and looks

entirely different from how it was in the olden days. Energy efficiency in its

operation is still an arduous task that needs to be accomplished. It requires

an integrated effort from all the entities embedded in its entire supply chain,

which includes raw material suppliers, other major systems and equipment

providers. Brick industry, being energy intensive, faces an increasing

pressure from the government and environmental organisations for reducing

its environmental impact, by cutting down its energy consumption and

emissions. This in turn has increased the scope for further research works in

this field and a definite need to identify key areas in the brick manufacturing

process and improve their performance.

1.2 AimThe main aim of this research work is to assess and improve the design of

auger extruders used in clay extrusion process using computational fluid

dynamics (CFD) and Finite Element Analysis (FEA).

1.3 ObjectivesThe main objectives of this research work includes,

• Conduct a thorough literature search on previously completed

research works in the clay extrusion process.

2

• Investigate suitable CFD techniques to model the clay extrusion

process.

• Analyse the flow parameters like pressure and velocity for various

designs and operating conditions.

• Assess the performance of the clay extruder with changes in design.

• Investigate alternate designs and materials to improve the

performance of the extruders and reduce their capital costs.

• Experimentally validate the results obtained from the applied CFD

modelling technique.

1.4 Research methodologyThe objectives of this research work were achieved in three stages:

1. The first stage was dedicated to the use of computational methods for

determining the extrusion pressure and the power requirement of

extruders for various design and operational parameters.

2. The focus in the second stage was on experimental tests to assess

the performance of a miniature scaled extruder. The results obtained

from the experiments were used to validate the computational

methodology used in first stage.

3. The third stage of this research focused on using FEA to predict the

stresses induced on extruder components during the process of

extrusion, for various materials. It also looked at the costs and

technical benefits that could be achieved by using alternate materials.

1.5 Previous worksA similar effort was made by Jonathan Headley in 2009 and Alex Poyser in

2011, MSc. students at Sheffield Hallam University. In their work, both of

them have used CFD techniques to study the flow characters of the clay and

water system during the process of extrusion and assessed the performance

of extruders. A detailed review of their works and the results obtained are

discussed in Chapter-2.

3

1.6 Thesis outlineThis report is divided into five chapters suitably to give the reader a clear

picture about the need for design improvements of extruders used in brick

industries and the use of CFD, FEA based numerical modelling technique to

accomplish that.

A brief introduction is presented in Chapter 1, detailed review of existing

research in the modelling of extruders, experimental studies and clay

rheology is presented in Chapter-2. Experimental validation of the numerical

modelling approach and assessing the performance and flow parameters of

extruders and clay extrusion process using the CFD technique is presented

in Chapter 3. Assessing mechanically induced stresses using FEA

technique, potential alternative cost effective and light weight materials for

improving the efficiency of extruders is presented in Chapter 4. Conclusions

and suggestions for the future research work in this area are presented in

Chapter 5.

A brief review on the prospect of brick industries and brick manufacturing

process is presented in Appendix C.

Design, functional and process requirements of vacuum type de-airing

extruder and the association of flow parameters to the performance of the

system is reviewed in Appendix D.

4

Chapter-2 Review of existing work forceramic extrusion

2.1 IntroductionThe aim of this chapter is to provide a comprehensive review of scientific

works undertaken by academic researchers and industrial professionals,

focused on studying the flow parameters of clay and assess the performance

of extruders using numerical and empirical methods. The results obtained

and conclusions drawn from their studies are presented and discussed. The

review is based on three key areas that are necessary to build and simulate

a CFD model successfully; that includes numerical modelling methods for

simulating clay extrusion or a ceramic shaping process, experimental studies

conducted to assess key performance variables (like extrusion pressure)

involved in ceramic shaping process and works related to rheological

characters of clay-water system.

Even though there are different types of mechanical systems, which are

termed as extruders, were used in the process of shaping, discussed briefly

in Appendix- D, henceforth in this report the term extruders commonly refer

to auger extruders, unless and until specified. The extruder system

considered for this research work is vacuum type de-airing extruder, falls

under the category of stiff extruders used in the heavy clay structural ceramic

industries.

Due to the limitation in the availability of published works, that specifically

discuss the simulation of the extrusion process and design assessment of

extruders using CFD based numerical modelling technique, most of the work

discussed here do not have direct relation to this research work. However it

presents the reader with various scientific approaches and methods that

were used and how significant those works were to the methodology used

and results obtained from the numerical modelling approach undertaken

through this research work.

2.2 Modelling and simulation of extruder systemZhang et al. (2011) have investigated the process of clay extrusion in a de

airing type extruder, using CFD technique. In their research work they

investigated the velocity of the clay material, during the process of extrusion,

along the entire length of the auger and have assessed the variation of clay

velocity along the radial and longitudinal direction within the extruder

chamber. They have also studied the effect of varying moisture contents and

the auger speed on the velocity of the clay within the extruder chamber. In

their work they have used a Bingham Fluid model to represent the flow

physics of clay and water mixture and have assumed the flow process to be

isothermal and laminar. The effect of gravity and inertial force were not

accounted for in their model. Using a 3-D model with an unstructured T-grid

mesh, they have solved their model in FLUENT-CFD solver and have

presented their results.

It is understood from their work that the velocity of clay particles varies both

along the longitudinal and radial directions of an extruder chamber, during

the process of extrusion and also depends upon the moisture condition of the

clay.

They have also predicted from their model that the velocity of clay near the

wall zones (both at the hub's outer edge and barrel's inner edge) is almost

zero and the maximum value is observed in the middle (area between hub

and the barrel); which is demonstrated by the formation of an oval shaped

pattern for the velocity of clay at different sections of the auger.

The formation of the secondary flow zone (a circular flow pattern), as

discussed by them- demonstrates the plastic and elastic properties

possessed by the clay during extrusion. The change from elastic zone to

plastic zone is subjected to shear force experienced from the extruder

components.

They have concluded from their study that the radial velocity is an important

component for the mixing and plasticity of the material and the axial velocity

is important for discharge rate. They have also mentioned that both these

velocity components are influenced by the moisture content in the clay

material used.

Hedley (2009) attempted to study the flow of clay through full scale de-airing

type vacuum extruders using CFD technique. In his work he has used a 3-D,

multiphase laminar flow approach and Herschel-Bulkley's fluid model to

define the flow physics of the clay. He has assessed the dynamic pressure7

developed during extrusion and velocity of clay in the direction of extrusion;

with respect to various pitch length and speed of auger. He has used

unstructured T-grid mesh elements to mesh the components of extruder and

solved the model using FLUENT solver. In order to achieve a good quality

mesh and avoid complexity while meshing the geometry, he has used a

simplified geometry (uniform rectangular cross section) for the auger and

neglected the effects of barrel and liner geometry. Using a constant density

value for the clay material, the model has been solved with the effect of

gravity. From his work it is understood that the pressure during extrusion

rises gradually from the inlet of the auger and reaches a maximum value at a

certain length of the auger and further down along the length of the auger the

pressure reduces as the material approaches the exit area, as shown in

Figure 2-1.

Pressure gradient along the length of screw 1 and 2

300

250

£ 200 «^ 150 wV)2 100 Q.

50

0

.

- * - ..—t ‘ ' Vly.J

r . p ' . *'V ,-jr *' ; . -•*/» I**J

t-'

—- • ~ : ■- ;

♦ Screw 1• Screw 2

200 400 600 800 1000 1200 1400 *600

Screw length (mm)

Figure 2-1 Extrusion pressure at various length o f extruder

[Source: Hedley, 2009]

Also the dynamic pressure varies at different sections of auger with respect

to the change in pitch length and speed of auger, as shown in Figure 2-2 and

2-3.

8

Dyn

amic

p

ress

ure

(P

a)

Effect of pitch length on pressure gradient along the screw

« Sere* 3

■ Screw 4

Screw 5

Screw 6

0 200 400 600 800 1000 1200 1400 1600

Distance along the sscrcw

Figure 2-2 Dynamic pressure at various length of extruder


Affect on the magnitude of dynamic pressure acting on the screw hub and spiral as RPM increases

250

re"t 200a>UI 150

S' 100EreI 50 O

0

Figure 2-3 Dynamic pressure variation with respect to auger speed


The same trend was observed in the velocity as well, shown in Figure 2-4.

5 RPM = 15 screw hub ■ RPM = 22.5 screw hub□ RPM = 15 spiral front face□ RPM = 22.5 spiral front face

Screw component at specified RPM

9

Effect of velocity magnitude of the clay over the length of the screw

♦ Screw 1 ■ Screw 2

Screw 3

Screw 4

* Screw 5

• Screw 6

+ Screw 7

- Screw 8- Screw 9

Screw 10— Poty. (Screw 7)

0 200 400 600 800 100C 1200 1400 1600

Screw length (mm)

Figure 2-4 Clay velocity at various lengths of extruder


The results and discussions presented in his work, clearly indicates that the

dynamic pressure and the velocity of clay observed during extrusion is

influenced by the pitch length and speed of the auger.

Poyser (2011) attempted to use CFD technique to assess the performance

of lab-scale model of an extruder system. Using a 3-D steady state, single

phase laminar flow model approach with Herschel-Bulkley's fluid model for

clay, he has assessed the performance of the scaled extruder. In his model,

he has used unstructured T-grid mesh to discretize the geometry and Fluent-

CFD solver to solve the model. From the results obtained through his work,

he has suggested that the use of unsteady state method in CFD modelling

could help to gain a better understanding of the flow process within an

extruder system.

Handle (2007) has discussed about the application of simulation in ceramics.

He has reviewed about numerical simulation of ceramic extrusion using CFD

technique, and has presented various governing equations that typically

represent the flow physics of ceramic materials. The author proposes that

the ceramic material exhibits visco-plastic behaviour and is expected to take

0 7

I & ■o3

0 6

0 5

0 3

0.2

0 1

0

10

the form of either a Bingham or Casson model. Figure 2-5 shows typical

viscosity profiles of materials that follow the above mentioned fluid models.

,x1oP

(0 ‘ CL 'P->%*</> O .8 1*>i—(C<1)x:<o L

Bingham

«BCasson

0 2 4 I5 3 1shear rater [s’ ]

Figure 2-5 Viscosity profile for Bingham and Casson model fluids

[Source: Handle, 2007]

[Note: Unit for Shear viscosity is Pa.s, it is misprinted as Pa in the above picture]

Continuity equations for mass, momentum and energy, proposed by the

authors are based on incompressible, Bingham fluid model. The reason for

including the energy equation in the numerical model is because the

viscosity of ceramic material is temperature dependent. He recommends that

the accurate definition of ceramic material properties like density, viscosity

and specific heat capacity at constant volume and specific heat conductivity

is a vital part in ceramic extrusion process simulation.

Bouzakis et al. (2008) have investigated the stress distribution on the

surface of a die mandrel, during the process of extrusion, using experimental

and numerical modelling techniques. Using Finite Element Method (FEM)

based numerical simulation (DEFORM); they have assessed the clay sliding

velocity; various stress elements and its distribution on the surface of the

mandrel. They have also compared the results obtained with the

experimental results. Figure 2-6 shows the investigated model and results

obtained.

11

Supporting pdMandrel

Die with mandrel used for the study

Figure 2-6 Stress induced on die mandrel during wet clay extrusion

[Source: Bouzakis et al. (2008)]

Through the experimental and numerical model results, they have derived a

characteristic equation that represents the rigid- viscoplastic behaviour of wet

clay, observed during extrusion. Based on the assumptions they made to

include the frictional factor during extrusion, they suggests that the flow

pattern of the rigid viscoplastic material like clay, is not effected by the friction

on the wall surfaces and the stress induced on the die wall depends on the

speed of extrusion .

Doltsinis and Schimmler (1998), using FEM, have investigated the process

of ram extrusion used in making ceramic tubular components. In their work,

considering the ceramic paste to be a viscous compressible fluid, they have

developed a suitable numerical model to represent the flow features of the

material. Using an analytical approach to determine material parameters

12

Sliding Velocity of elay-dbtribution pattern on mandrelFlow stress (Mpa]

1 0 30 0 40 0 5 0 0 6 0

Flow stress observed in clay column

[rrm/scc A = 180 00r s ?io noC - 74(1 UO U = ii/U U J E = 3COOO F = 33000 G =200 00

required for the numerical model they have predicted the flow velocity of the

material within the barrel, die and the tool. By applying the developed FE

model to an actual industrial scale system and through the results obtained,

they have concluded that the FEA is adequate enough to represent the flow

of such viscous materials and such computational methods can be used for

modelling ceramic extrusion process to a higher degree of appropriateness.

Discussion:-

The efforts undertaken by professionals in various scientific communities, to

apply numerical modelling and simulation as a tool to model the clay

extrusion process, clearly indicates that there is an indisputable need for

such tools in the ceramic industries. With the availability of wide range of

fluid flow models and modelling techniques that are suitable, as illustrated

above, there is inadequate evidence on the applicability of a particular

numerical modelling technique and methodology suitable for auger extrusion

process. Though Zhang et al. (2011), Hedley (2009), Poyser (2011), have

attempted to use CFD to model the auger extrusion process and assess the

performance of an extruder, their methodology does not really account for all

the major features of an auger extrusion process. For instance, in all their

work, the material density is considered to be a constant, which is not true in

a real scenario. Also they have not given much importance to the clearance

volume between the auger and the barrel in their model, which is considered

to have a major influence on the extrusion pressure and the material flow.

The modelling technique and methodology used in this research work has

taken into consideration of additional factors like change in density,

temperature and temperature dependant properties that influences the

process of extrusion and performance of an extruder. A detailed description

about the CFD modelling approach undertaken in this research is presented

in Chapter 3.

2.3 Design and performance evaluation of extrudersJohnson (1962) studied the design parameters of variable pitch or variable

volume augers that influence the performance of an extruder system used in

sewer pipe production using experimental methods. Combining both

13

geometrical and experimental methods, he has analysed the influence of

auger diameter, pitch and conditions of raw material on the extruder

performance. He has proposed that the determination of Displacement

Volume Ratio (DVR) (function of pitch of the auger) of augers using

mathematical methods is a significant approach in studying and comparing

their performance.

The result obtained through his work indicates that the volumetric efficiency

of a variable extruder increases when the size of the extrudate increases,

even if the type of clay remains the same. He suggests that the efficiency of

an extruder system depends on extrusion pressure, clay particle size and

design modifications to the pitch and diameter of an auger. Suitable

considerations to these parameters at the design stage could result in a

more efficient system.

Lund et al. (1962) have studied the operating characteristics of augers used

in pipe clay extrusion, with respect to various design parameters at specific

moisture content of clay. In their work they have assessed the performance

of constant and variable pitch augers. They have also determined the validity

of scaled extruder results when extrapolating it to a full scale system. Based

on the design data available for the augers used in production and using an

empirical approach, they have designed experimental augers and assessed

their performance. Using the approach of calculating DVR value to compare

the performance of auger system, as discussed by Johnson (1962) and by

employing a special device to maintain the consistency of the clay, they have

assessed the extrusion rate, power consumption; die pressure and internal

radial barrel pressure for constant and variable pitch auger systems. Figure

2-7 shows the effect of varying the displacement volume on the performance

characters of augers for a constant pitch auger and Figure 2-8 shows the

characteristic curves of the various experimental augers used in their study.

14

l / l 6 " BA R R LL G L E A i^A g.C E ,- S O F T - AG ED - D E A IR E D

4 0

0.6

3 5>4

12 -

02 0POWER __CONSUMPTION 16 RP*M

2 510-

2 0BARREL S T R E S S -16 RPpm

0 5EXT. R ATE - 2 6 RPUA

DISPLACEMENT VOLUME,

Figure 2-7 Effect of auger pitch variation on extruder performance

[Source: Lund et al. (1962)]

AUGER NUM BER PO W ER - 4 2 RPM

POWER - 2 6 i RPM

POWER - 16 IR P M

2 IB 'l

Si2 Oo

EXT. RATE 4 2 RPM

EXT R ATE — 2 6 RPMzo10o£EI-

EXT. RATE — 16 RPMTHRUST-26 RPW* OR STIFF CLAY THRUST-16RPNM OR SOFTCLAY

aUJ*Oa.

(£UJ

XUJ

BARREL STR-ESS - 2 6 RPM BARREL S T R ttS S — 16 RPM

D ISPLACEM ENT VOLUM E /R E V . (DVR.

Figure 2-8 Performance characteristics profile for a typical auger

[Source: Lund et al. (1962)]

From the results obtained through their work on constant pitch auger, it is

understood that the increase in auger speed and decrease in DVR (pitch)

increases the extrusion rate. Also that power consumption is a function of

15

auger speed and clay consistency. Barrel stress increases with increase in

auger speed, clay stiffness and clay particle size.

The results obtained through their work on variable pitch auger indicate that

the extrusion rate for a variable volume or variable pitch auger is higher than

that of a constant pitch auger. Also the compression ratio (ratio of change in

volume between successive auger flights) of variable pitch auger influences

the extrusion rate. They have also noted that changes in the tip volume of an

auger also influence the extrusion rate.

In both the cases, they have noted that extruding clay with smaller particle

size resulted in an increased extrusion rate and better flow character,

compared to extruding clay with large particle size. This also confirms to the

suggestion by Norton (1954).

Seanor and Schweizer (1962) have investigated about mechanical and

physical factors that affect auger design and its performance. They have

suggested that the co-efficient of friction is an important factor that has

significant effect on auger's performance. Also in order to have a better flow,

the clay contacting surface in an auger should be sufficiently sloped to

achieve better sliding for the clay, which enhances its flow. Hence they

believed that reducing the pitch of auger will reduce the co-efficient of friction

and will lessen the augers performance. This contradicts the above

discussed results, presented by Lund, et al. (1962). They had also

postulated suitable design modifications for the leading face of an auger

(working face of an auger which is subjected to stress and wear is called the

leading face of an auger), to enhance the performance of a new auger and

increase its life, right from installation. Since they did not validate their

suggestions with any experimental results and also the co-efficient of friction

varies with respect to clay stiffness, clay material and auger material, it is

hard to include it at the earlier stages when designing an auger.

They have also studied the effect of adding half pitch augers or wings or half

flights, to the tip of main auger system. Through investigating the

performance of the extruder system by having single, double and triple wings

at the end of the main auger, they have suggested that having wings in the

16

tip ensures smooth and uniform feeding of clay to the die section from

extruder and ensures uniform pressure distribution over the entire area of

die, as shown in Figure 2-9. Also an auger with three wings performs more

efficiently than augers with single and double wings, when it is ensured that

the die is mounted properly.

4 SECONIDuration 3\ litensity \ 180°

Seci

SINGLE WING

90°± SecsIntensity

Duration IDOUBLE WING

Ir tensity 60° Durption l|Sec.

120° 240° ____DEGREES OF ROTATION

360'TRIPLE WING

Figure 2-9 Pressure waves experienced in auger with half flights

[Source: Seanor and Schweizer, 1962]

Parks and Hill (1959) have developed mathematical equations for the

purpose of designing augers and die for extrusion application. Through

performing experiments in clay like plastic material with specific moisture

content, they have developed a mathematical representation for calculating

extrusion rate for auger and die section. They have also mentioned that the

extruder system comprising the barrel, auger and die, is divided into different

zones based on the functions they perform at different stages of extrusion

process and the pressure during extrusion varies across each of these

zones, as shown in Figure 2-10.

17

Toed

D t l14 ] l-J—( b )

{ D ieC on vey ing ( | )

M e t e r in g

Atm os - pheric

Figure 2-10 Typical pressure distribution in an extruder

[Source: Parks and Hill, 1959]

It is understood from their mathematical model that the extrusion rate at

auger section is a function of outside diameter of auger, depth of auger

channel, helix angle, clay material and speed of auger. Whereas the

extrusion rate at die section is a function of pressure and it has linear relation

as shown in Figure 2-11.

Die Hole Die Thic

D iam . - O :kn ess - I "

25“ y

\\

\

0 2 4 6P ressu re ( Ib ./s q . in .) x IO - 2

Figure 2-11 Effect of extrusion rate on die pressure

[Source: Parks and Hill, 1959]

It is clearly understood from their results that the pressure increases as the

extrusion rate increases in the die section. They suggests that, though this

linear relationship curve was not obtained for an actual clay material, but still

it holds a good representation of what happens in clay extruding augers.

Handle (2007) suggests that the pressure developed within the extruder and

die has greater influence on the quality of extruded product and performance

18

of extruder. He has discussed the effects of changing geometric, process

and operating parameters on the extrusion or pressure developed during an

extrusion process. The results presented by him show, under normal

circumstances the pressure profile for an extruder system will be like as

shown in Figure 2-12.

length of nozzle length of cylinder

o oSSP'

pressure generatorpressure consumer

RSP1

length of backlog

Figure 2-12 Forming pressure profile under normal condition


As mentioned earlier it is clear that the pressure within the extruder unit rises

gradually from a lower value to a peak value at a certain length of auger and

then it gradually decreases within die section to attain ambient conditions.

The author describes these functions as pressure generator and pressure

consumer. It is also understood from the above figure that the maximum

extrusion pressure is experienced at the tip of the extruder. This pressure

profile is similar to the other theories about extrusion pressure proposed by

other authors, whose works were discussed earlier in this chapter.

According to him, modification to clay moisture content, die (nozzle)

geometry and feed rate has a significant effect in the extrusion pressure

formation and distribution within the extruder and die system. The various

pressure profile observed for such changes, suggested by him is shown from

Figure 2-13 to 2-16.

19


o o•RSPl!


P3

A A1length of backlog

Figure 2-13 Effect of increasing clay stiffness on extrusion pressure


length of norzle length of cylinder

o o;r s p RSP2i RSP3

V

pressure generatori

!

I

I

RSP1 RSP3

length of backlogi

Figure 2-14 Effect of decreasing clay stiffness on extrusion pressure


20


o& x > o

0 /v\ RSP2 / \r s p i ;V Y-v S

pressure generatorp re ss u re

I/A1 RSP2IRSP1

length of backlog

Figure 2-15 Effect of changing die geometry on extrusion pressure



& % f fO OA

\ R S P 2 / \r s p i ;


R 5P 2IRSP1

tenglh of backlog

Figure 2-16 Effect of changing feed rate on extrusion pressure


21

The effects of changing process, operating and design parameters on the

extrusion pressure, as discussed by Handle (2007), clearly indicates that the

performance of an extruder system depends on one or more independent

variables. It is also evident that the process of experimental analysis, to

study the effect of each such change consumes time and resource.

Kocserha and Kristaly (2010) have theoretically and experimentally

investigated the effect of die shape on the performance of an extruder

system and on the quality of extrudate. They have used a Bingham fluid

model for representing the flow parameters of clay in their theoretical

evaluation. They suggest that the optimization of extruder component

geometries or rotation speed of the auger have beneficial effects on

extrudate quality and power consumption. They also suggest that the

extrusion pressure depends on rheology of the clay. The plastic flow

character of clay throughout the entire cross section of the die is considered

as an important factor to avoid crack formation that occurs during lateral

processing of the extrudate. The results obtained from their work for a

specific clay water mixture proportion demonstrates, a) the effect of die

shape on extrusion pressure and power consumption at different auger

speeds, shown in Figure 2-17, b) the effect of die shape on the physical

properties of extrudate, shown in Figure 2-18.

w 2.5 -

0.5-

Rotation, 1/min

Extrusion pressure Vs Auger speed for various die shapes

Power consumption Vs Auger speed for various die shapes

■ Spherical R25

■Cone

850-

i 800 ■

I 750-

I 700-

| 650 - | 600-

| 550-

| 500-

§ 450 - | 400-

o 350 -

300 -35

Rotation, 1/min

Figure 2-17 Effect of die shape on extrusion pressure and power

[Source: Kocserha and Kristaly , 2010]

22

40.00

35.00

“ 30.00 .c£ 25.00 £" 20.00

15.00—it—Spherical R25

^H-Cone - O - Torus R25

10.00

5.00

0.0015 35 55

Rotation, 1/min

13

12.5

12

2 11.5

Spherical R25

- ♦ -C o n e

-O —Torus R2510.5

105515 35

Rotation. 1/min

Strength of extrudate Vs Auger speed for various die shapes

Density of final product Vs Auger speed for various

die shapes

1.84

■S 1.82 -

| 1.76

0 1.74 - -♦ -S p h e rica l R25

-♦ -C o n e

-O -T o ru s R25c 1.72 -

Rotation. 1/mln

Water absorption rate of extrudate Vs

Auger speed for various die shapes

Figure 2-18 Effect of die shape on quality of extruded product

[Source: Kocserha and Kristaly, 2010]

It is understood form their work that any change made to the geometrical

parameters of the extruder components not only affects the performance of

the extruder, but also the physical characters of the product.

Discussion:-

The work undertaken and the results obtained by various authors, as

presented above, clearly illustrates that an optimised design of extruder

components, die and material properties of clay plays a vital role in

determining the performance of an extruder system. Most of their works

focused to determine the optimised design requirement has resulted from

time and cost consuming experimental works and none of them considered

using computer based modelling techniques to reduce cost and time.

However the valuable results and suggestions for various design changes,

acquired from their work, were used to justify the results obtained from the

computer based modelling work presented in this report.

23

2.4 Clay-Water rheologyThe rheological properties of clay-water system, has been a subject of

interest in different fields of engineering for many years, that includes for

example soil, civil engineering, and ceramics etc. A number of research

works have been undertaken to develop mathematical models to predict and

understand the flow physics of clay-water system. Some of those key works

and significant findings were useful in choosing a suitable flow model used in

the CFD modelling work undertaken through this research work and are

discussed here.

Amin et al. (2009) have discussed their experimental work on optimizing the

mixing variables that influences the rheology of clay sewer pipe paste

(Aswan clay-found in Upper Egypt). In their work they have clearly illustrated

the effect of water content in a clay water system on the viscosity, as a

function of shear rate, shown in Figure 2-19.

500

2500

£ 2000

-fc'mI> 1500

S

% water = 25 j

Vo water - 27

% water — 30

% w a te r — 32

°/n w a ter — 35

% water = 37

Vo water = 40

250 300

Shear rate ( s' 1 )

Figure 2-19 Viscosity of pure clay sewer paste

[Source: Amin et al, 2009)]

The result obtained by them is for a pure clay water mixture, with the particle

size of 0.2 mm. They suggest that additives like grog or any adhesive to the

pure form of clay will alter the above shown results. Also the mathematical

model that fits well to predict the above shown results, as suggested by them

is the Bingham model (Equation 2.1).

t = k.y + t 0 2 .1

24

Where, r= shear stress (Pascal), y = strain rate (s'1), k= consistency index

(Pa.sn), x 0= yield stress (Pascal). (When x > t 0 flow & x < t 0 solid)

The values of the constants k and x0 are said to vary with respect to water

content. The results obtained from their work indicates that when the clay is

soft (more water content), it tends to yield quicker and the viscosity attains a

lower value in less time, compared to stiffer clays. Also the value of k and x0

dictates the initial viscosity values and the flow curves of a fluid based on

Bingham model.

Ormsby and Marcus (1963) have discussed the variation of clay viscosity

with respect to the size of clay particle. Through their work they have noticed

that the flow curve for various types of clays varies with respect to particle

size, even when the amount of moisture is maintained to the same level.

They suggest that when clay added with 50% of water to the weight, 1)

behaves like a Newtonian fluid for particle size with 44-10, 10-5, 5-2 micron

fractions, 2) behaves like a pseudoplastic fluid for 1-0.5 and 0.5-0.25 micron

fractions and 3) like a dilatant fluid for 2-1 micron fractions. They have also

observed dilatant behaviour for clay water mixture, even at lower percentage

of water content. It is clear from their work that one should account for the

particle size of clays as well, while determining or choosing a value for the

variables associated with the rheology of clay.

Al-Zahrani (1997) has developed a generalised mathematical model to

predict the viscosity as a function of shear rate for non-Newtonian fluids. He

claims that the model is suitable to predict the behaviour of shear thinning

fluids like clay water, polymer melts, paints and paper pulps etc. and is better

than the traditionally used Power law and Herschel-Bulkley's model. The

mathematical models proposed by him are shown in Equation 2.2 and 2.3.

25

Where, t= shear stress (Pa), A, B= Constants, n=model index and y= shear rate (s'1)

The results obtained by using his model to predict the viscosity of a gelex

polymer fluid is shown in Figure 2-20.

6

5

4

3

2

1

O

100 200O 300 400 500 700600

Figure 2-20 Viscosity profile of a typical shear thinning fluid

[Source: Zahrani, 1997]

He claims that the predicted result using his model is accurate when

compared to the experimental results and suggests it to be an alternate and

improved approach to Herschel-Bulkley's model. The key things to be noted

from his work includes, the viscosity profile of a shear thinning fluid as a

function of shear rate and suggestion about the suitability of Herschel-

Bulkley's model in predicting the shear thinning fluid rheology.

Maciel et al. (2009) have studied the physical and rheological properties of

Kaolinite clay and water mixture using Herschel-Bulkley's model. They

suggest that material, like clay-water mixtures, could be well represented by

Herschel-Bulkley's viscoplastic non-linear rheological model. Their study was

focused to develop behaviour laws for predicting the flow behaviour of mud

found in torrential lavas. Based on the experimental and mathematical model

results obtained from their work, they suggest that the flow characters of

Kaolinite clay and water systems predicted using Herschel- Bulkley's model

was in good agreement with the measured values. They also suggest that

Herschel-Bulkley's model is better for predicting the yield stress (deformation

of the fluids) experienced at lower shear rates than the Bingham model,

which is good for fluids yield at high shear rate.

26

Nelson and Andrews (1959) have experimentally investigated the forces

required to shear plastic clay (Florida Kaolin), both within its own structure

and at clay-metal surface interface. They suggest that, in addition to the

basic factors like type of clay material and water content, the shearing of

plastic clay is also influenced by pressure distributed within the clay and

speed of rotation of metal surface that comes in contact with the clay.

Results obtained through their investigation indicate that the pressure

distribution in a clay water system is a function of yield value and the force

required to shear plastic clay increases with increase in pressure to a certain

extent and remains constant. It also increases with the speed of the metal

surface with which the clay encounters.

Mahajan and Budhu (2008) have proposed an analytical model to

determine shear viscosity of clay-water system (Kaolin clay), using Casson's

Model. They suggest that it is applicable for mixtures with very low water

content. The results obtained through their work indicate that the shear

viscosity reduces with increase in percentage of water content. They also

suggest that the accurate prediction of viscosity of clay water system using

numerical model depends on the rheological model used.

Andrade et al. (2010) have developed a mathematical model for evaluating

the clay plasticity. Comparing their model with experimental results, they had

confirmed that their model gives a more accurate approach in obtaining the

plasticity for wide range of ceramic materials, with different mineral and

moisture content. From the results obtained through their work, it is

understood that the plasticity value of clay varies with respect to its mineral

contents, even if the moisture content remains the same.

Discussion

It is evident from the above information that the flow physics of clay-water

system have been studied for many years. The research activities

undertaken and results obtained clearly indicate that the flow characteristic of

clay-water system varies with respect to the type of clay, additives, particle

size and moisture content. It also influences the performance of the machine

that it encounters. From various mathematical models used to represent

27

highly viscous materials like clay water mixture, the choice of an appropriate

numerical model, that suits the problem of investigation, depends upon

experimental and availability of other resources.

2.5 ConclusionThus a review of previously completed works relevant to the subject of

interest in this research was presented in this chapter. The various

methodologies used, results obtained, their advantages and disadvantages

were briefed clearly for further understanding and also to acquire substantial

validation to the methodology and modelling technique used in this research

work.

28

Chapter-3 CFD modelling of clay extruder

29

3.1 IntroductionThis chapter presents a brief review about the basic classification of fluids

and available numerical models for modelling the viscosity of non-Newtonian

fluids (exhibited by the clay-water mixture). It also reviews the basics about

CFD modelling technique. The CFD modelling approach used in this

research work is discussed, explaining the background concepts involved in

modelling various physical processes involved in the clay extrusion.

Experimental validation of the modelling approach, results obtained from

various CFD simulations along with the evaluation of performance characters

for various design and operating conditions of the extruder are presented

and discussed.

3.2 Fundamental classification of fluidsFundamental classification of fluids includes Gases- substances that deform

under shear stress and Liquids- substances that continuously deform under

shear stresses. The dependency of continuous deformation of liquids

subjected to shear stress is an inherent property of the substance and this

has led to further classification of fluids,

1. Newtonian fluids: The fluids that have a constant viscosity or deform

linearly to the applied shear stress, as shown in Figure 3-1, are called

Newtonian fluids.

Y

Shear stress vs. Strain rate Viscosity vs. Strain rate

Figure 3-1 Newtonian fluids

[Source: Brookfield Engineering, 2010]30

Newtonian fluids are commonly agreed to obey the Navier-Stokes

equation and the best curve fit mathematical model, accepted and used

widely to describe the flow of such substances is shown in

Equation 3-1.

duT = #t— = / t * y - - 3 . i

du . 1Where p= Shear viscosity (Pa.s), — or y = Rate of shear (s )uy

2. Non-Newtonian fluids: Fluids that do not obey the basic

principles of Newtonian fluids are commonly described as non-

Newtonian fluids. The flow of such liquids is subjected to shear

stress and is influenced by more than one factor under certain

circumstances. There are various types of such fluids that exist in

nature. The three basic categories under which these types of

fluids are grouped include a) time independent non-Newtonian

fluids, b) Time dependant non-Newtonian fluids, and c) Visco

elastic fluids.

a. Time-Independent non-Newtonian fluids: The rate of shear for such

type non-Newtonian fluids depends only on the instantaneous value of

the shear stress and is independent of time. It is also referred as non-

Newtonian viscous fluids [Wilkinson,1960].Depending on the function

of rate of shear to the applied shear stress, the different types of fluids

grouped under this category includes I) Pseudoplastic fluids or Shear-

thinning fluids II) Visco-Plastic fluids or Bingham plastics III) Dilatant

fluids or Shear thickening fluids.

Pseudoplastic fluids: In such fluids, the rate of shear is not linear to

the applied shear stress, the viscosity decreases with increase in shear

rate and it becomes linear only at a very high shear rate, as shown in

Figure 3-2.

31

T *1i \

A B


Figure 3-2 Pseudoplastic fluids

[Source: Brookfield Engineering, 2010]

The viscosity values are termed as Zero shear viscosity and infinite

shear viscosity. The mathematical models that best describes the

behaviour of such fluids include,

Power law model= t = kyn 3.2

Where k = Flow consistency index (Pa.sn), n=power law index (<1 for shear thinning fluids)

Where p 0lPoo= Zero and infinite shear viscosity (Pa.s), X = time

constant, n=flow index.

The other, not widely used models include the Prandtl, Eyring, Powell-

Eyring and Williamson.

Viscoplastic fluids: These type of fluids when subjected to shear

stress will start to flow only after a certain value of stress is reached.

This value is commonly described as yield stress and beyond this value

the flow could be linear or non-linear as shown in Figure 3-3.

Carreau Model= ~ —~Ho-Hoo

Cross model= °°H-Hoo _ iHo —Hoo l + ( * Y x y )

32

A BStrain rate vs. Shear stress Viscosity vs. Strain rate

Figure 3-3 Visco plastic fluids


Viscoplastic fluids that have a linear profile after the minimum yield

stress are called as Bingham plastic fluids. Mathematical models

commonly used to describe the behaviour of such fluids include,

Bingham plastic model=x - t0 = K y 3.5

Herschel-Bulkley's model= t = t0 + kyn — 3.6

Where r 0=minimum yield stress threshold (Pa),

And, Cross model-another type of recommended mathematical model,

for studying the behaviour of such fluids.

Dilatant fluids: It is similar to Pseudoplastic fluids [Wilkinson 1960]. In

this type of fluids, the fluid viscosity increases with rate of shear, as

shown in Figure 3-4. Clay slurries, candy compounds and sand-water

mix are few examples.


Figure 3-4 Dilatant fluids


It is suggested that even power law model could be used to model such

fluids, with flow index value greater than unity [Wilkinson 1960].

b. Time-dependent non-Newtonian fluids: The rate of shear and shear

stress, for such type of non-Newtonian fluids, are functions of time.

Such type of complex fluids is further divided into a) Thixotropic fluids-

characterised by decreasing apparent viscosity or shear stress with

respect to time, when subjected to constant rate of shear. As shown in

Figure 3-5. b) Rheopectic fluids - characterised by increasing apparent

viscosity or shear stress with time, when subjected to constant rate of

shear. As shown in Figure 3-6.

--------------------------> t

Figure 3-5 Thixotropic fluids


34

1]A

------------------------------ > t

Figure 3-6 Rheopectic fluids


c. Visco-elastic fluids: This type of fluids exhibits both elastic characters

like solids and viscous character like fluids, as shown in Figure 3-7.

The suggested mathematical model that represents the behaviour of

such fluids is Maxwell's model, shown in Equation 3.7.

Where, G = rigidity modulus (Pa), t= Rate of shear stress (Pa).

Through the knowledge gained from the classification of fluids, basic working

principle of extruders and various scientific works completed previously, it is

sensible to consider the clay-water system as a non-Newtonian fluid and

exhibits a Visco-plastic fluid or shear thinning fluid character. Its behaviour

could be summarised as, the mixture when subjected to a shear force does

not deforms readily until it reaches as particular value and this value is

tFigure 3-7 Visco-elastic fluids


35

termed as the minimum yield stress threshold. Once this value is attained, it

continuously deforms under the action of shear stress to the extent where

the viscosity reduces to a very low value and remains constant (at this point

the fluid is set to have reached the Newtonian fluid flow regime). Herschel-

Bulkley's model, discussed above along with other available mathematical

models for non-Newtonian fluids, which includes the functions representing

both yield stress region and constant viscosity region, proves to be the best

suitable model for clay like materials. Due to its extensive use in various

fields for studying clay-water rheology and recommended for CFD modelling

of clay like materials [Ansys-Fluent 12.0 user's guide 2010], in this

research work it was decided to use Herschel-Bulkley’s fluid model to

simulate the process of clay extrusion and assess the performance of

extruder using CFD.

3.3 Process of CFD modellingThere are three different types of numerical modelling techniques commonly

used in engineering applications: a) Finite Difference Methods (FDM) b)

Finite Element Method (FEM) and c) Finite Volume Method (FVM). The

fundamental difference between all these techniques is based on the way a

functional variable is represented and with the process of discretisation

[Versteeg and Malalasekera 1995]. CFD is one of the computational

techniques used for solving internal and external fluid flow problems and

associated heat transfer phenomenon. The three common equations

involved in any CFD model are equations for conservation of mass,

momentum and energy. Irrelevant to the nature of problem, these equations

will always be included in the model; additional equations in the model will

depend upon the nature of the problem investigated. The various types of

flow physics that can be modelled and investigated using CFD is shown in

Figure 3-8.

36

| Viscous Fluid

Convection

Fluid

TurbulentLaminar Radiation

Steady

Conduction

Heat TransferInviscid Fluid

T ransient/Unsteady

Compressible (Panel Method)

External (Airfoil, Ship)

Internal (Pipe, Channel)

Compressible (Air, Acoustic)

Incompressible (Water, Low speed air)

Computational Fluid Dynamics & Heat Transfer

Figure 3-8 Flow physics features in CFD

[Source: Jiyuan Tu et al, 2013]

Major steps involved in any CFD modelling process includes,

1) Pre-processing: Generating suitable CAD geometry to represent the

domain or domains of interest and meshing. Meshing is defined as

discretizing the domain or the CAD geometry into suitable finite number of

volumes using any standard mesh generating software. GAMBIT and ICEM-

CFD are some of commonly used meshing software. In this stage, the

physical and chemical phenomenon to be modelled and boundary conditions

will be defined. The boundary conditions can be even defined or altered in

the next step of the modelling process. Gambit was used for meshing the

extruder geometries investigated in this research.

2) Solver setting: A suitably meshed geometry will then be imported to a

solver, where appropriate numerical techniques, flow equations and

variables for solving the problem will be defined. This is required for solving

the physical or chemical phenomenon of a flow process defined earlier.

Examples of commercially available solvers for the application of CFD

problems includes FLUENT, STAR-CD, CFX, FLOW 3D, PHOENICS and

37

FEMLAB and all these solvers are based on FVM technique. In this research

work the extruder model was solved using Ansys- FLUENT 12.0.

3) Post-processing: The primary function in a post processing stage is

reviewing the results obtained from the solver. For example pressure,

velocity and temperature distribution in a flow regime. Recent advancements

in the capability of computer graphics, has enhanced this process and

proves to be more useful tool in communicating the results of a solved flow

problem to end users.

A flow diagram that briefs the various stages involved in a complete CFD

analysis is shown in Figure 3-9.

38

Geometry creation

(2-D or 3-D CAD model of the flo w domain)

Meshing

(Di scretisi ng the domai n usi ng 2-D or 3-D

structured or unstructured grids or mesh and

define boundary conditions)

Quality of mesh

Check the quality

and quantity of the

mesh, w .r .t. solution

and computational

Solver

(I m port the m eshed ge om etry i nto th e solver

and define the required flo w equation, type of

analysis and set the vari abl es accordi ng to the

convergence requirem ent)

Convergence and residual monitoring Solution

dependency on

the mesh

refinem ent

required to be

evaluated

Solution

converged(Is there a significant

convergence noted in

residuals fo r certain

iterations or time steps)

Result evaluation

(Pictorial or graphical representation of the

results fo r fu rther study)

Figure 3-9 CFD modelling process flow diagram

39

3.4 CFD modelling of extruderThe methodology used to set up the flow problem of clay extrusion and

assess the performance of an extruder in the CFD solver is described below

in this section. The process of set up remains the same for all the CFD

analysis discussed in this report.

3.4.1 Geometry creationThe various standard sizes of extruders designed and manufactured by C.F

limited, for the process of ceramic extrusion (mainly bricks) is provided in

Table 3-1.

Machine Size (Extruder diameter)

CENTRIM 406.40 mm (-1 6 inch)

CENTEX430 mm (-1 6 inch) ,

500 mm (-19.68 inch)

60F 422.27 mm (-16.625 inch)

90BD 488.95 mm (-19.25 inch)

Table 3-1 Craven Fawcett extruders for brick making

The Centex series of extruders are the most widely used extruder system by

many of C.F customers. Considering the feasibility in obtaining any valuable

field based data to validate the numerical model investigated in this research,

it was considered to be sensible approach to model and assess the

performance of CENTEX type machines. Flence the various sizes of full

scale extruders from CENTEX series, considered for the investigation

includes 430 mm, 500 mm and 600 mm. The 600 mm extruder is an

extended version of the 500 mm extruder, targeted for higher productivity

rate. Proposed for a specific requirement, it was the first of its kind that the

company were intending to manufacture and the design engineers were very

keen to obtain performance comparison data with respect to its

predecessors. So the 600 mm extruder was also included in this numerical

modelling work and its performance was assessed and compared.

40

The domains of interest include barrel liner, auger with shaft (collectively

called as extruder) and die. The required 3-D geometry of the components

was created using Autodesk-lnventor and Pro-Engineer Wildfire.

3.4.2 Geometry discretisationThe 3-D CAD model of the extruder geometries created in the above step

were discretised using Gambit. The different types of surface mesh elements

available in Gambit are Quad-generates only quadrilateral elements; Tri-

generates only triangular elements, Quad-Tri-generates quadrilateral and

triangular elements at the required areas. The different types of surface

mesh schemes available in Gambit are Map- generates structured grid of

mesh elements, Sub-map- generates a structured grid of mesh elements in a

suitably converted unmappable face, Pave-generates structured or

unstructured mesh elements, Tri-Primitive-generates mapped quadrilateral

elements and Wedge primitive- generates a triangular mesh element for

wedge shaped elements. The different types of volume mesh elements

available in Gambit include Hex, Hex/Wedge, Tet/Hybrid and types of

volume mesh schemes include Map. Sub-map, Tet-Primitive, Cooper,

Stairstep, T-grid and Hexa core [Gambit-2, 2001].

The option of treating the entire geometry as a single volume and generating

a uniformly distributed mesh with suitable size was considered to be a

complex process, due to the nature of the shape of various components.

Hence the system was sub divided into different zones namely, 1) Auger

volume-l, 2) Auger volume-ll, 3) Clearance volume, 4) Die /Mouth piece, 5)

Liner volume. As discussed earlier, based on the available computing power

and solution requirement, unstructured volume mesh with 4-node tetra

hedral mesh elements and t-grid hybrid meshing scheme was used for

meshing the auger, die and liner geometry, and a structured hex mesh for

the clearance volume. The various fluid volumes along with the mesh

generated for a 430 mm extruder, used for the investigation, are shown

below.

41

1) Auger volume-1: Fluid volume around the auger shaft, shown in Figure 3-

10 .

Figure 3-10 430 mm extruder- Auger volume-1

2) Auger volume-2: Solid volume around the auger shaft, shown in Figure 3-

1 1 .

Figure 3-11 430 mm extruder- Auger volume-2

3) Clearance volume: Small gap between the auger shaft and the liners,

shown in Figure 3-12. A structured hexahedral mesh was generated for this

volume.

42

Figure 3-12 430 mm extruder - Clearance volume

4) Die or mouth piece: A round shaped die design was used during the initial

investigation and is shown in Figure 3-13. The geometric details of the other

die shapes used in this research work are available in section 3.9.4.

Figure 3-13 430 mm extruder - D ie/ extruder mouth volume

5) Liner volume: The design and choice of material for liner depends on the

requirement and type of clay extruded. It varies with respect to size of

extruders and sometimes varies even for the same size. The factors that

influence the design include the clay material, production rate and

manufacturing feasibilities. The extruders modelled and investigated in this

research work have different liner designs. Suitable mesh size, meshing

element and meshing scheme was chosen with respect to the design.

Meshed liner geometry of a 430 mm extruder used in the investigation is


43

Figure 3-14 430 mm extruder- Liner volume

The final geometry of a 430 mm extruder, with assembled fluid volumes is

shown Figure 3-15.

Figure 3-15 430 mm extruder components and die assembled view

The meshed geometries of 500 mm and 600 mm extruder are available in

Appendix A - section I. Table 3-2 summarises the details of mesh generated

for various extruders investigated in this research.

44

Extruder sizeAuger and Liner volume

mesh elements

No. of cell

elements

430 mm Tetra hedral,Tgrid-Hybrid 956,143

500 mm Tetra hedral,Tgrid-Hybrid 1,312,961

600 mm Tetra hedral,Tgrid-Hybrid 1,545,053

Table 3-2 Extruder mesh details

3.4.3 Boundary conditionsThe choice of boundary condition for various elements of the geometry

depends on the flow problem being studied and there are 22 different types

of boundary conditions available in GAMBIT, suitable for various flow

problems. It is recommended to choose an appropriate boundary condition

such that it gives an accurate or a fair representation of the real condition.

Due to the lack of availability in previous experimental data and knowledge of

flow physics that occurs in an extruder, it was tedious to choose a precise

boundary condition. However from the various scientific works discussed in

Chapter 2, it was considered pressure inlet or velocity inlet or mass flow rate

for the inlet of an extruder system and for the outlet of die either pressure

outlet or outflow as an appropriate choice of boundary conditions. During the

initial stage of the research, 1) pressure inlet, pressure outlet and 2) velocity

inlet-pressure outlet boundary conditions were used to run the simulation.

Since satisfactory results were not obtained when compared with actual

scenarios, a different approach was undertaken.

It was decided to use mass flow rate for the inlet section of the extruder and

outflow boundary condition for the outlet section of the die. The two main

reasons behind this are,

1) The size of an extruder system is always determined by the number

of bricks to be extruded per hour and the shape of the outlet section of

die is based on the shape and size of the brick. Other components like

liners and barrel chamber are scaled suitably to meet the extrusion

rate requirement.

2) A significant amount of real time data was available for variables

like extrusion rate, compacted and un-compacted clay density, for

45

various size of extruders investigate in this research work. These

facilitated in using sensible values for the boundary condition and

compare the results obtained from the CFD analysis with real time

data.

Wall boundary condition was used for all the other geometrical features,

where fluid volume interacts with solid volumes. Interface boundary condition

was used for connecting surfaces between two fluid zones or components of

extruder, through which transfer of fluid from one to other occurs.

Simulations completed during the initial stage of investigation, using these

boundary conditions, yielded results that were in good agreement to actual

scenarios. Furthermore the solver was stable and a better convergence of

residual was noted for a significant number of iterations, compared to the

other boundary conditions mentioned earlier.

The extruder system is sub-dived into moving and stationary

zones/components. In order to understand the actual flow process and

assess the performance of the system, it was considered that representing

these features in the numerical model is an essential requirement. FLUENT

has different types of in-built modelling features that help to model and

simulate such kind of systems. Dynamic mesh modelling is one such feature

that allows users to specify moving and deforming fluid zones or stationary

fluid zones that exist within a single flow domain (refer to section 3.4.4.2 for

further details). In order to be able to use this feature at the solver stage, it is

necessary to discretise the domain suitably and specify the features of

various zones clearly at this stage of the process. In this research work, the

solid volume of the auger and the fluid volume around the auger were

defined as moving zones and the remaining components were defined as

stationary zones, shown in Figure 3-16 and Figure 3-17.

46

Auger fluid volume

Auger solid volume

Figure 3-16 Moving volumes

Figure 3-17 Stationary volumes

3.4.4 Solver settings

3.4.4.1Flow modelling

Solver settings generally depend upon the flow physics that is being

investigated. So it is necessary to have some preliminary understanding

about the type of flow occurring in the domain of investigation, before setting

up the problem in the solver.

In comparison to Newtonian fluids, there is lack of a standard method or

procedure for determining the Reynolds number of non-Newtonian fluid

flows. Wilkinson (1960) has discussed about the formula used for

calculating the Reynolds number for the flow of time-dependent non-

Newtonian fluids through a pipe channel, both in a laminar and turbulent flow

regime. However considering the highly viscous nature of the material and

speed of the auger, it was clearly understood that the material exhibits

laminar flow throughout the entire length of the extruder and die sections. So

an unsteady state, single phase, laminar flow model with pressure based47

solver and coupled algorithm for pressure-velocity coupling was assigned to

the model. Though the pressure based solver is predominantly used to solve

incompressible flow problems, it is also recommended for solving mildly

compressible flow [Ansys 12.0-User's guide, 2009], as occurs in the case

of clay extrusion.

The generalised form of conservation equations for mass and momentum

solved by FLUENT, for both compressible and incompressible laminar flow

problems are shown in Equations 3.8 and 3.9.

^ + V . ( p v ) = S m 3 . 8

Where, Sm= mass added to the continuous phase, p= density, v=velocity

vector.

— ( p v ) + V . ( p v ! v ) = - V p + V . (T) + p g + F 3 . 9d t '

Where, p=static pressure, f=stress tensor, pg=gravitational force and

F=external body force.

3.4.4.2 Dynamic mesh modellingIt was mentioned earlier that the extruder system comprises of both

stationary and moving zones and the geometry was discretised suitably to

reflect these properties. Using the moving and deforming mesh modelling

feature available in FLUENT, the moving and stationery zones of an extruder

system were defined in the solver.

Dynamic meshes are used in problems where boundaries move rigidly with

respect to one another, may exhibit linear or rotary motion. It can also be

used for deflecting and deforming boundaries (example: balloon, artificial

wall) [Fluent -6.3 user guide]. The mesh generation will be based on the

moving boundary conditions. This feature is used to model flows that involve

change in domain shape with respect to time, due to moving boundaries. The

mesh updates every time step based on new positions of the moving

48

boundary. The different methods by which the solver updates the mesh of

moving boundaries at each time step includes,

• Smoothing method-spring based method, Laplacian method and

boundary layer method.

• Dynamic layering method.

• Local remeshing.

The choice of the mesh updating method depends upon the type of problem,

computation and solution requirements.

3.4.4.3 Material definition and Viscosity modellingAssigning material properties to the discretised fluid and solid volume is the

next and important step in the process of solver settings. As mentioned

earlier, it was decided to use Herschel-Bulkley's model with shear rate

dependent feature to model the viscosity of wet clay used in the extrusion

process. Since clay is not a standard type of fluid that is commonly

encountered in many flow scenarios occurring in the field of engineering, its

properties are not readily available in FLUENT solver. Thus the required

variables of Herschel-Bulkley’s model, relevant for wet clay were added to

the existing material database. Table 3-3 shows the different variable inputs

required for a typical Herschel-Bulkley’s model.

Variables

Consistency Index (k) (Pa.sn)_____Power law index (n)

Yield stress threshold^,) (Pa)

Critical shear rate(C.S.R) (yr) ( (s'1)Table 3-3 Variables for Herschel- Bulkley's model

The above mentioned variables vary with respect to the particle size,

moisture and raw material content of clay. These variables can be related to

each other as shown in Equation 3.10.

= kycn 3.10

The major mineral content found in clays used for making bricks in U.K. is

Kaolinite and widely used size of the clay particle is <2 mm. The uniqueness49

in the mineral content and size of clay particles and the available

mathematical model facilitated in choosing a few sets of values for Herschel-

Bulkley’s model variables, for representing the (kaolinite) clay with different

moisture content. The values of r 0, k, y c and n used in this research work, for

representing clays with moisture content ranging from 7-14% on wet basis

(typical range for clay used in stiff extrusion process), is presented later in

this chapter along with the results of various CFD simulations.

Herschel-Bulkley’s model combines the effect of both Power law fluids and

the Bingham plastic fluids. The viscosity at each time step during an

unsteady state process is determined using the Equations 3.11 or 3.12,

depending upon the y value. [Ansys-Fluent 12.0 user's guide 2010].

For y>yc

For y<Yc,

( 2 “ % c )

T) — t 0 : 1- k [ ( 2 — n ) + ( n - 1 ) t - 3 . 1 2Yc Yc

Where, y = D : D - - 5 . 1 3

Where, D=rate of deformation tensor, rj= viscosity.

3.4.4.4 Temperature dependent properties modellingExtrusion in actual scenario is a non-lsothermal process. The heat generated

during the flow of wet clay through the auger, barrel enclosure and die,

because of frictional forces, is understood to attain a significant value during

stiff extrusion process and also influences the quality of extruded material

and the flow process. The energy equation along with viscous heat

dissipation feature available in the FLUENT was used to model this

phenomenon. The properties of the extruded clay column that are subjected

50

to variation with respect to change in temperature include compacted

density, thermal conductivity and specific heat capacity.

The density (bulk density) of the wet clay that enters the extruder system

varies significantly with respect to the clay column that leaves the extruder

system. In a stiff extrusion process, the density of compacted and un

compacted wet clay typically falls in the range of 1602 kgrrf3 to 1742 kgm'3

[Walker,2012] and the rise in temperature falls in the range of 50°C to 60°C.

These values could be even higher if dies with a single or multiple core is

used. Since such die designs were not considered in this research work, it is

not discussed any further. This change in density along with thermal

conductivity and specific heat capacity of the wet clay was expressed as a

linear function with respect to the temperature rise, experienced during the

extrusion process. Due to the lack of availability of proper material data and

experimental works on the thermal conductivity and specific heat capacity of

wet clay, suitable values were obtained from the work completed by Robie

and Hemingway (1991) and Michot et al. (2008).Though the values

discussed by these authors do not specify the moisture content of the clay,

suggested values were used as a guidance to calculate the values required

for the CFD modelling work undertaken in this research.

3.5 Experimental validation of CFD modellingThe CFD modelling technique for assessing the performance of an extruder

system, discussed above was validated by modelling and comparing the

numerical results with experimental results of a lab scale extruder.

The experimental investigation of performance characters of a lab scale

extruder are discussed in this part. A lab scale extrusion unit with an extruder

of diameter 75 mm was used for the investigation and is shown in Figure 3-

18.

51

Figure 3-18 Scaled extruder

Experimental set up

The extrusion pressure was measured using a special type of pressure

sensor, power consumption using an ammeter and vacuum pressure using a

vacuum gauge. A schematic representation of the experimental set up used

for the investigation is shown in Figure 3-19.

Ammeter

Pug mill

Extruder DiePower Drive unit

Vacuum gauge

Pressuresensor

Transitionpiece

Figure 3-19 Experimental set up layout

52

Extrusion pressure and power consumed by the lab scale extruder was

measured for two different extrusion scenarios (two different clays with

different moisture content). The operating parameters used and results

obtained from the experimental investigation are summarised below.

Trial: 1

In this case, clay from M/s Hanson Brick Limited, Desford, U.K. was used for

the investigation. The actual moisture content of the clay obtained from the

source was assessed based on dry and wet method, and then suitable

amount of water was added per unit mass of clay sample to achieve a

moisture content of 12-13% on dry basis (recommended moisture content

level for stiff extrusion process). Suitable care was taken to prevent

significant loss of moisture content during the experiment. The extrusion

pressure and current consumption was recorded at a point when the

extruded mass of clay reached the right amount of stiffness (2.6 in the

Penetrometer scale). The power consumed was calculated using the current

reading obtained during extrusion and applying the standard formula. Table

3-4 summarises the measured values.

Die used for Trail: 1

Parameters Measured value

Moisture content of the clay Wet basis-11-12%, Dry basis 12-13%

Auger speed 19 rpm

Vacuum pressure -20 mm mercury. (-2666.6 Pa)

Penetrometer scale reading 2.6

Current readingsBefore feeding clay - 2.5-2.6 Amps,

During feeding and when clay reached a certain level in vacuum chamber- 3.1

53

Amps to 3.5 Amps,During continuous extrusion, with right

stiffness- 3.9 Amps.Current consumption by extruder

alone, during extrusion.0.3 to 0.4 Amps

Voltage 415 Volts.

Power consumed by extruder

unit alone, during extrusion.124.5 Watts

Extrusion rate 0.013 to 0.015 kgs'1

Extrusion pressure 13-14 bar

Temperature change in the clay

Initial temperature 296 K and final

temperature of extruded clay 301K (five

degree rise)

Uncompacted density of clay 1298 kgm'3

Compacted density of clay 2270 kgm'3

Table 3-4 Experimental analysis results-trial 1

Trial: 2

In this case, clay from river Humber U.K. was used for the investigation.

Since the clay obtained from the source contained more amount of moisture

content of approximately about 25-30% on wet basis, the sample was

directly used for the experimental investigation, without further addition of

water. The required parameters were then measured and calculated using

the same procedure, as discussed above in Trial: 1. Table 3-5 summarises

the measured values.

54

Die used in Trial:2

Parameters Measured value

Moisture content of the clay Wet basis 25-30%

Auger speed 19 rpm

Vacuum pressure -13 mm mercury. (-1733.19 Pa)

Penetrometer scale reading 2.3

Current readings

Before feeding clay - 2.8 Amps,

During feeding and when clay reached a

certain level in vacuum chamber-

3.2 Amps to 3.3 Amps,

During continuous extrusion, with right

stiffness- 3.4 Amps to 3.5 Amps.

Current consumption by extruder

alone, during extrusion.0.1 Amps

Voltage 415 Volts.

Power consumed by extruder

unit alone, during extrusion.57.5 Watts

Extrusion rate * 0.01014 kgs'1

Extrusion pressure 5.8 bar to 6.0 bar

Temperature change in the clay

Initial temperature 293 K and final

temperature of extruded clay 297 K (four

degree rise)

Uncompacted density of clay 1200 kgm'3

Compacted density of clay 2150 kgm'3

Table 3-5 Experimental analysis results-trial 2

55

3.6 CFD modelling of a scaled extruderThe Performance assessment of the scaled extruder using CFD modelling

technique is discussed in this part of the report.

CAD modelling and discretisation of scaled extruder

3-D CAD model of the scaled extruder components used for the investigation

is shown from Figure 3-20 to 3-22.

Figure 3-20 Scaled extruder-auger shaft

Figure 3-21 clearance

Figure 3-22 Scaled extruder-transition piece

56

The generated CAD model was meshed in Gambit using suitable meshing

schemes for individual components. Tetrahedral / hybrid mesh elements and

T-grid meshing scheme was used to mesh the fluid volume around the auger

shaft and the total number of cell elements obtained was 310,552. The

meshed geometry is shown in Figure 3-23.

Figure 3-23 Scaled extruder-auger shaft meshed

Uniform hexagonal mesh elements with cooper scheme were used to mesh

the clearance volume. The total number of cell elements obtained was

11,778 and the meshed geometry is shown in Figure 3-24.

Figure 3-24 Scaled extruder-clearance meshed

Hex/wedge shaped mesh elements with cooper scheme were used to mesh

the transition piece. The total number of cell elements obtained was 502,199

and the meshed geometry is shown in Figure 3-25.

57

Figure 3-25 Scaled extruder- transition piece meshed

A similar boundary condition and modelling approach, used to model the full

scale extruder, was used to complete the pre and post processor solver

settings of scaled extruder modelling. In the earlier part of this chapter, it was

discussed that the moisture content of clay determines the variable values in

a Herschel-Bulkley’s model and also the performance of an extruder system.

Since in Trial: 1 and Trial: 2 two different clays with different moisture content

was used, the values for Herschel-Bulkley’s model were chosen

appropriately. Table 3-6 summarises the values used for the variables of

Herschel-Bulkley’s model in CFD analysis.

Herschel-

Bulkley's model

variable

Trialil values Trial:2 values

k (Pa.sn) 5206.95 3200

n 0.32 0.2

To (Pa) 6500 3516

C.S.R (s'1) 2.1 1.6

Table 3-6 Herschel- Bulkley's model values for scaled extruder CFD analysis

The values for clay used in Trail: 2 were set to a lower value due to the soft

nature of clay, and such soft clay materials are normally used in soft

extrusion process. Since extruders manufactured by C.F Ltd, for the purpose

of stiff extrusion are sometimes used for soft extrusion process as well, it

was considered to be a useful investigation with the identified CFD

methodology and compare the numerical model results with experimental

results.

The results of CFD analysis for extrusion scenarios Trial: 1 and Trial: 2 are

available in Appendix A- section XII & XIII. Table 3-7 shows results of the

extrusion pressure and power consumption by the scaled extruder under the

two extrusion scenarios, determined experimentally and using CFD analysis.

Process parameters Experimental results CFD results

Trial-I

Extrusion pressure 13-14 bar 13.4 bar

Power consumption 124.5 Watts 114.06 Watts

Trial-ll

Extrusion pressure 5.8-6.0 bar 5.84 bar

Power consumption 57.5 Watts 47 watts

Table 3-7 Result comparison for scaled extruder

3.7 Experimental study of clay rheologyThe most important determinant factor in selection and use of an appropriate

flow model to simulate the process of clay extrusion and assess the

performance of extruders numerically is the shear thinning behaviour of the

clay-water system. In order to demonstrate the shear thinning behaviour of

the clay and to further support the choice of flow model used in this research

work, an attempt was made to study the rheological characters of wet clay by

measuring the viscosity, using oscillatory test in a parallel plate viscometer

(Make: Anton Parr, Model no: MCR301), shown in Figure 3.26.

Figure 3-26 Parallel plate viscometer-Anton Parr (MCR301)59

The viscosity of clay sample used in Trial: 2 experimental work was

measured. The accuracy of the measured results when using a parallel plate

viscometer depends upon the contact established between the sample

surface and measuring plate surface of the instrument (It consists of a

stationary and a moving plate). A gap of 2 mm is recommended to be an

optimised gap between the plates, to get sensible results [Mezger, 2006]. In

order to satisfy this criterion, clay samples with a diameter of 50 mm,

thickness between 2-3 mm and surface free from disparities was prepared.

Values for G' (G-prime) and G " (G-double prime) were measured to identify

suitable frequency value for oscillatory test and then by varying the plate gap

from 2 mm to 2.19 mm, values for the complex modulus, storage modulus,

loss modulus and damping factor were measured and a graphical plot for

Apparent viscosity vs. Strain rate was obtained for the clay sample and is


Clay with 25%-30% water

- KKFS- gap 2.

- KKFS- gap 2.

KKFS- gap 2.

KKFS- gap 2.

- KKFS- gap 2.

02-Plate 17 mm

03-Plate17mm

■04-Plate186mm

■05-Plate17mm

-06-Plate 0 mm

19800 19200 18600 18000 17400 16800 16200 15600 15000 14400 13800 13200 12600

•5T 12000 1140010800

= . 10200 £? 9600 g 9000 <j> 8400> 7800£ 7200£ 6600 2. 6000 3 - 5400

4800 4200 3600 3000 2400 1800 1200

600 0

A p p aren t V isco s ity Vs S train R ate (1/s)

Strain Rate (1/s)

Figure 3-27 Apparent viscosity vs. Strain rate of clay- measured

experimentally

60

The viscosity profile obtained through the viscometer experiment clearly

indicates the shear thinning nature exhibited by wet clay and also

demonstrates the change observed in viscosity value when it is subjected to

a uniform shear. This viscosity profile determined experimentally, when

compared with the CFD analysis results proves the point that, the clay exhibit

shear thinning behaviour during extrusion and is well represented by the flow

model and its variables used in the CFD model.

The use of the CFD modelling technique, discussed above, to assess the

performance characters of full scale extruders is presented further in this

chapter.

3.8 Performance assessment of extruders with

different diametersThe performance of an extruder system varies significantly with respect to

particle size and moisture content of clay. Extruder’s diameter varies with

respect to extrusion rate or number of bricks to be produced per hour and

moisture content varies with respect to strength requirements and extruding

ability of clay. In this part of the research work, the effect of varying the

diameter of an extruder and clay moisture content on the performance

parameters like extrusion pressure (static pressure) and power consumption

during the process of extrusion were investigated using CFD. The variation

of performance parameters was assessed for extruders of size 430 mm, 500

mm and 600 mm, using two sets of Herschel-Bulkley's model values.

Operating parameters used in the CFD model are shown in Table 3-8.

Extruder

Size

Feed

rate

(kgs1)

Auger

speed

(rpm)

Herschel-Bulkley's model value

Case-I Case-ll

430 mm 15 30 k=4908 Pa.sn

n=0.5

t 0=8500 Pa

C.S.R=3 s'1

k=5206.95 Pa.sn

n=0.32

t 0=6500 Pa

C.S.R=2.1 s 1

500 mm 19 30

600 mm 11.8 22.5

Table 3-8 iData set for varying ex truder diameter and moisture content

analysis61

The two data sets used for the variables in the Herschel-Bulkley’s model

represent uncompacted clay with different moisture content. (Value I

represents harder clay and value II for softer clay). Results obtained from the

CFD analysis of 430 mm extruder are summarised below, the results of 500

mm and 600 mm extruders are available in Appendix A from section II to V.

CFD Simulation results of 430 mm extruder with Herschel-Bulkley's

model value-1

Extrusion pressure:

Pressure developed during the extrusion process, along the entire length of

the extruder and die section, obtained from the CFD analysis is shown in

Figure 3-28 and 3-29. The value varied from -605 kPa at the inlet section to a

maximum of 3.4 MPa. (34 bar), observed at the tip of the auger shaft and

further downstream the pressure reduced to an average value of 2.57 MPa.

(25.7 bar) at the outlet.

[Note: The negative value of extrusion pressure observed at the inlet

section of the extruder as discussed above and in other CFD results

discussed further in this chapter is a result of the numerical evaluation

on the vacuum pressure value i.e. set as the inlet boundary condition.

The physical meaning of the negative pressure value is a vacuum

condition exists at the inlet section.]

3.40e+0B 3.21 e+OB 3 07e+062.938+062 78e+062 64e+06 2.50e+06 2.36e+06 2.22e+06 2.08e+06 1.94e+06 1,80e+06 1 65e+06 1.51e+06 1 37e+06 1 23e+06

I 1 09e+06 9 48e+05 8 078+05 6 66e+05 5 25e+053 83e+Q5

.■ 2 42e+05

' -6 05e+05

Contours of Static Pressure (pascal) (T im e=2.0240e+00)

Figure 3-28 Static pressure contour (full view)-430 mm Case I

62

2.78e+0B2B4e*062.50e+062 38e+0B2 22e+082 09e»06I 84e+06t BOe+OB1 65e+081 51e+081.37e+081 23e+061 D9e+069.48e+05B 07e+056.68e+055 25e+053 83e+05242e+D51 Ule+05•4 03e+04-1 82e+05-3 23e<-05■A B4e+05■6 05e+Q5

Contours of Static Pressure (pascal) (Time=2.0240e+00) Oct 2 7 .2 01 '

Figure 3-29 Static pressure contour (sectional view) - 430 mm Case I

Extrusion pressure values discussed above and the profile shown in

Figure 3-30, clearly indicates the trend of pressure developed inside the

extruder and die section during the extrusion process This data obtained

through the numerical simulation confirms the results discussed by [Bender

and Handle,1982] and [Handle,2007].

(Note: The results of trend in pressure development during the process

of extrusion, discussed in this report refer to the pressure development

trend observed in the direction of extrusion.)

3.50e-*06

3 00e+06

2 50e-*06

2 CD e+06

1 50e+06

1 00e+06

5 00e+05

0.00e+00

-5.00e+O5-0.6 -0 5 -0 4

Position (m)

StaticPressure

(pascal)

Static Pressure (Time=2 5050e+00)

Figure 3-30 Static pressure profile-430 mm Case I

63

Material Flow pattern:

857e-01 8 17e-01 7 .70e-O1 7.36O-01 0.94e-O1 0 530-01 6 12©-01 5720-01 5310-01 4 900-01 4 49e-01 4.08e-01 3.67O-01 3 27e-01 2 86e-01 2 45e-01 2.04e-01 1.63e-01

The flow pattern and velocity of clay during extrusion, at various sections of

extruder and die, obtained from the CFD analysis is shown in Figure 3-31. In

the direction of extrusion the average value observed for velocity at outlet

section of die was 0.47 ms'1. It is understood from the results that the

material tends to deform continuously under the action of shear as it

proceeds down from the inlet. It is also clear from the results that, when

moving along the radial direction the material near the hub and middle of the

auger gap tends to flow faster than the material near the liners. This confirms

that the liners are restricting the clay from rotating along with the shaft and

also it facilitates it to move in the direction of extrusion. This data obtained

through numerical simulation confirms with results discussed by Zhang et

al., 2011.

C ontours o f V e loc ity M agn itude (m /s) (T lm e= 2 .0240e+00 )

Figure 3-31 Flow velocity during extrusion (sectional view)- 430 mm Case I

Viscosity profile:

Shear thinning behaviour of clay during the process of extrusion was verified

by plotting a graph with molecular viscosity against strain rate (shear rate) at

different sections of extruder and die. The profile for molecular viscosity vs.

strain rate at the outlet, obtained from the CFD analysis is shown in Figure 3-

32.

64

MolecularViscosity(kg/m-s)

1.00e+04

8.00e+03

6 00e+03

4 00e+03

2 00e+03

0 00e+0020 30 40

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=2,0240e+00) t

Figure 3-32 Molecular viscosity vs. Strain rate- 430 mm Case I

Convergence monitoring:

The accuracy and validity of the solution in any CFD analysis is ensured by

monitoring the convergence of residuals and other problem relevant process

parameters like mass flow rate, velocity components, co-efficient of drag and

pressure components. In this research work it was accomplished through

monitoring the convergence of residuals and mass flow rate at the outlet. It

was very hard to acquire a complete converged solution and hence the

iteration was stopped when the monitored residuals convergence stayed

constant for a certain number of iterations and results were obtained. Figure

3-33 and 3-34 shows the results obtained in this case for convergence

monitoring.

65

1e-02

1e-03

1e-04

1e-06

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Iterations

Scaled Residuals (Time=2.0240e+00)

Figure 3-33 Residual convergence-430 mm Case I

Mass -13 0000FlowRate

(kg/s) -14.0000

-150000

-1600000 0000 0 2500 0 5000 0 7500 1 0000 1 2500 1 5000 1 7500 2 0000 2 2500

Flow Time

Convergence history of Mass Flow Rate on outlet (Time=2.0240e+00) Oc

Figure 3-34 Mass flow rate convergence- 430 mm Case I

The results of convergence monitoring obtained from other CFD analysis are

similar to the case presented above and hence these results were not

discussed for other cases of CFD analysis presented later in this chapter.

The energy required to extrude per unit mass of clay was calculated for each

case using the torque value at the auger section, obtained from the CFD

analysis. A graph was plotted to analyse the trend of variation in maximum

pressure and energy required during the extrusion process, with respect to

change in diameter of extruder, shown in Figure 3-35.

66

Pressure and Energy consumption @ respective design condition vs Diameter of a u g e r, for Clay Type-1

430 500 600

10

12

- 6

-- 4

- - 2

■o

S *Q -> O*

§1 C **“o 9 o w

2 *UJ

Diam eter of auger (in m m)

■Pressure Vs Diameter of auger

-Energy consumed to extruder per Kg. of clay Vs Diameter of auger

Figure 3-35 Extrusion pressure and Energy consumption vs. Diameter

(Case-1)

The general trend clearly indicates that the pressure and energy

consumption during extrusion varies significantly with respect to design (size)

and operating parameters (speed and feed rate) of an extruder, even if the

type and moisture content of clay material remains the same.

CFD Simulation results of 430 mm extruder with Herschel-Bulkley's

model value-ll

Extrusion pressure:

Pressure developed during extrusion in a 430 mm extruder, with respect to

change in clay moisture content is shown in Figure 3-36 and 3-37.The

pressure varied from a minimum value of -334 kPa at the inlet section to a

maximum of 1.98 MPa (rounded off to 20 bar), observed at the tip of the

auger shaft and further downstream the pressure reduced to an average

value of 1.47 MPa (14.7 bar) at the outlet. In comparison to the case

discussed earlier, the pressure developed during the extrusion of softer clay

is lower than the pressure developed for the harder clay.

67

I

1 98e+0B 1 67e+06 1 78e+0B1 70e+B61 62e+B6I 53e+06 1 45e»0B 1 37e+86 t 28e+08 1 2fle+86 1 12e+061 03e+86 9.51e+05 8 68e+05 7.84e+05 7 01e+05 6 18e+05 5 34e+B5 4.51e+85 3 68e+052 84e+052 01e+85 1 18e+B53 45e+04 -4 88e+B4 -1 32e+B5 -2 15e+05 -2 99e+05 -3.82e+05

Contours of Static Pressure (pascal) (Time=2.0250e+00) Or

Figure 3-36 Static pressure contour (full view)-430 mm Case II

t 98e+B6 1 B7e+08 1 78e*08 1 7Be»061 B2t+06 t 53e+861 45e+061.37e+B6 1 28e+08 I 20e+06 1 12e+0B1 03e+08 9 5!e+05 8 68e+B5 7 84e+B5 7 flle+85 6 18e+B5 5 34e+05 4 51e+B5 3 68e*B52 84e-*05 2 0le+05 1 18e+B5 345e*B4 -4 88e*04 -1 32e+05 -2 15e*05 -2 99e*05 •3 82e*05

Contours of Static Pressure (pascal) (Time=2.0250e+00) Oct 26. 2(

Figure 3-37 Static pressure contour (sectional view)- 430 mm Case II

The trend observed in extrusion pressure, developed during extrusion is

shown in Figure 3-38. No significant variation was noted when compared

with the earlier case.

68

Position (m )

Static Pressure (Time=2.0250e+00) <

Figure 3-38 Static pressure profile-430 mm Case II


The flow pattern and velocity of clay observed during extrusion is shown in

Figure 3-39. In the direction of extrusion the average value observed for

velocity at outlet section of die was 0.47 ms'1. A significant difference in

material deformation pattern and in velocity was noted within the auger and

barrel section, for softer clay when compared with harder clay. It indicates

that the softer clay deforms more uniformly, observed along the radial

direction, compared to the harder clay, when subjected to equal shear force.

1 IBe+00 1 10e+00 1 06e+001 02e+00982e-019.41e-01 9 0Qe-01 8.59e-01 8.19e-0l 7 78e-017 37e-018 966-01 6 55e-01 6 14e-01 5 73e-D1 5 32e-01 4 91e-0l 4 50e-01 4 09e-013 68e-013 27e-012 86e-01

2 46e-012 05e-01 1 B4e-01 1 23e-018 19e-024 09e-02 0 00e*00

Contours of Velocity Magnitude (m/s) (Time=2.0250e+00) Oct 2 6 ,2C

Figure 3-39 Flow velocity during extrusion (sectional view)- 430 mm Case II

Viscosity profile:

The profile of shear thinning behaviour of clay at the outlet section of die is

shown Figure 3-40. It also indicates that the softer clay deforms more easily

than the harder clay when subjected to shear.

1 OOe+04

8 00e+03


6 0 0 e *0 3

4 00e+03

2 00e*03

30 40

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (T im «=2.0250e+00)

Figure 3-40 Molecular viscosity vs. Strain rate-430 mm Case II

The graph shown in Figure 3-41 indicates the trend of variation in energy

required to extrude per unit mass of clay and maximum pressure developed

during extrusion with respect to size of extruder, for softer clay.

Pressure and Energy consumption @ respective design condition vs Diameter of auger, fo r Clay Type-ll

6.005.35

4.29 t S 3.43 o *

+* c^ c n i 'O O

24.3

1.71 3 “-ri

0.00c430 500 600

Diam eter of auger (in m m)

-Pressure Vs Diameter of auger

-Energy consumed to extrude per Kg. of clay Vs Diameter of auger

Figure 3-41 Extrusion pressure, Energy consumption vs. Diameter (Case-11)

The general trend in energy requirement and maximum pressure developed

during extrusion remained the same for both hard and soft clay extrusion. It

70

is clearly understood from the graphs, that irrespective of the extruder size,

the extrusion pressure and power required for extruding clays with high

moisture content will be low compared with extruding harder clay. The

extrusion pressure increases with respect to increase in the size of extruder

even for the clay with same moisture content, but not necessarily the power

required in all cases. It also clearly demonstrates the effect of changing

moisture content of clay on the performance of extruder.

3.9 Performance assessment of a 500 mm extruderThe effect of varying design and operating parameters on the performance of

a 500 mm extruder system was investigated in this part of the research,

using CFD. The results obtained from the CFD analysis are summarised

below.

3.9.1 Effect of varying feed rate on performance of extruderThe effect of changing the feed rate of uncompacted clay, on the

performance of a 500 mm extruder was investigated in this part. The other

parameters like the die design, extruder design, clay material, size, clay

moisture content and auger speed were kept constant. Table 3-9

summarises the operational parameters and material properties used in the

CFD analysis.

Extruder Size

Feed

rate

(kgs1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

500 mm Varying 30

k=5206.95 Pa.sn

n=0.32

r o=6500 Pa

C.S.R=2.1 s'1Table 3-9 Data set for varying feed rate analysis

The performance characters were assessed for the following feed rates 10

kgs'1, 15 kgs'1, 19 kgs'1, 25 kgs'1, 30 kgs'1, 40 kgs'1 and 50 kgs'1. The results

obtained from the CFD analysis are summarised below.

71

Extrusion Pressure:

Pressure developed during extrusion in a 500 mm extruder with 10 Kgs'1 of

feed rate is shown in Figure 3-42 and 3-43. The pressure varied from a

minimum value of -150 kPa at the inlet section to a maximum of 2.68-2.78

MPa (rounded off to 28 bar) observed at the end of auger shaft and reduced

to an average value of 2.13 MPa (21.3 bar) at the outlet.

Contours of Static Pressure (pascal) (Tlme=4.4200e-01) Oi

Figure 3-42 Static pressure contour (full view) - feed rate 10 kgs'1

2.04e+06 194e+06 1.848+06 1 74e+06 1 65e+06 1 55e+08 1 45e+06 1.35e+06 125e+06 1.15e+08 1 05e+06 9.47e+05 8.47e+05 747e+05 6.4Be+05 5.48e+05 4 48e+05 3.48e+05 249e+05 t.49e+05 4 93e+04 -5 05e+04 -1 50e+05

2448+06

2 248+062 14++062.048+06194e+061 B4e+061 74e+061B5e+061 55e+061.45e+061.358+061.25e+061 15e+061.058+069.47e+05B47e+05747e+05B.46e+055 48e+054 488+05348e+052 498+05149e+054 93e+CM-5 05e+04-1 50e+05

Contours of Static Pressure (pascal) (Time=4.4200e-01) Oct 10.2011

Figure 3-43 Static pressure contour (sectional view) - feed rate 10 k g s 1

The trend of pressure development within the extruder section, observed

during extrusion is shown in Figure 3-44.

72

StaticPressure

(pascal)

1.50e+06

1.00e+06

5.00e+05

0.00e+00

-5 00e-H35-1 -0.9 -0 8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

Position (m)

Static Pressure (Time=4,4200e-01) I

Figure 3-44 Static pressure profile- feed rate 10 k g s 1


The flow pattern and velocity of clay observed during extrusion at various

sections of extruder and die, in a 500 mm extruder with 10 kgs'1 feed rate is

shown in Figure 3-45. In the direction of extrusion the average value

observed for velocity at outlet section of die was 0.32 ms'1.

118e-*»1 14fr*O0 1.09e+001.D5e+009 98e-01 9.51e-01 9 03e-01 9 56e-0f8 08e-01 7 Ble-01 7.13e-01 6 .66e-01 6.18e-01 5.71e-01 5 23e-01 4 75e-01 4.28e-013 BOe-01 3.33e-012 85e-01 2 38e-01 1 9D6-01 143e-019 51e-024 75e-02 0 00e+00

Contours of Velocity Magnitude (m/s) (Time=4.4200e-01) Oct 10.201

Figure 3-45 Flow velocity during extrusion (sectional view)- feed rate 10 k g s 1

Viscosity Profile:

The profile of shear thinning behaviour of clay observed at the outlet section

of die in a 500 mm extruder with 10 kgs'1 feed rate is shown in Figure 3-46.

73

The viscosity value was observed to be higher at lower mass flow rate when

compared with higher mass flow rate.

7 00e+03


4 00e«-03

2 00e+03

1 00e+030 5 10 15 20 25 30

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (T im e=4.4200e-01) C

Figure 3-46 Molecular viscosity vs. Strain rate- feed rate 10 k g s 1

The results of CFD analysis, for feed rates 15 kgs'1, 19 kgs'1, 25 kgs'1,

30 kgs'1, 40 kgs'1 and 50 kgs'1 is available in Appendix A-section VI.

The trend of variation in maximum extrusion pressure and energy required in

extruding per unit mass of clay, with respect to change in feed rate of clay for

a 500 mm extruder is shown in Figure 3-47.

500mm extruder Pressure and Energy consumption Vs Mass flow rate/Feed rate @ constant speed of 30 rpm, for Clay type-ll

3.20

2.84 at

2.49 | f

2.13 * 2

1.78 | o

o o- 0.71 *2|-60.36 • |

iu1 0.00

Mass flow rate/ Feed rate (in Kg/sec)

500mm extruder Pressure Vs Mass flow rate/Feed rate @ constant speed of 30 rpm

500mm extruder- Energy consumed to extruder per Kg. of clay vs Mass flow rate/Feed rate @ constant speed of 30

_ rom_____________

30

25

202 ^153 fJ 10 U> S I

IS do>- o

5cm3 a | 2 0 .E m2 > cn m-5 2 73

-10-15

Figure 3-47 Extrusion pressure, Energy consumption vs. Feed rate

74

3.9.2 Effect of varying auger speed on performance of

extruderThe effect of varying auger speed on the performance characters of a 500

mm extruder was investigated in this part. The other parameters like the die

design, extruder design, clay material, size, clay moisture content and feed

rate were kept constant. Table 3-10 summarises the operational parameters

and material properties used in the CFD analysis.

Extruder Size

Feed

rate

(kgs1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

500 mm 19 varying

k=5206.95 Pa.sn

n=0.32

t0=6500 Pa

C.S.R=2.1 s"1

Table 3-10 Data set for varying auger speed analysis

The performance characters were assessed for the following auger speeds-

10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, 40 rpm and 50 rpm. The results


Extrusion Pressure:

Pressure developed during extrusion in a 500 mm extruder with auger speed

of 10 rpm is shown in Figure 3-48 and 3-49. Negative pressure was

observed at the outlet and at the tip auger section of the extruder. The

maximum pressure observed was 192 kPa (1.92 bar) at the inlet section,

which indicates that the speed of the auger is not sufficient enough to induce

the required shear force for the clay to deform and resulting in clay being

stopped at the inlet section.

75

152e+05

l.24e+055.68e+Q4-1.1le+04-7.88e+04-147e+05-2.14e+05-2.82e+05

-3.50e+05

-4.18e+05

-4.85e+05

-5.53e+05

-6.21e+05

-6.89e+05

-7.56e+05 -8.24e+D5

-8.92e+D5

-9.60e+05

-1.03e+06

-1.10e+06

-1 16e+06

Contours of Static Pressure (pascal) (Ttme=2.6040e+00)

Figure 3-48 Static pressure contour (full view) - auger speed 10 rpm

3.71e*M -1-Sle+W -8 29e+04 -111e+05-1.59e+05-2.086+05-2.54e+05 -3 02e+05 -3.5Oe+05 -388e+05 -4.48e+05 -4 93e+05 -541e+05 -589e+05 -6.37e+05 -B85e+05 -7 33e+05 -780e+05 -8 28e+05 -8 76e+05 -9 24e+05 -9 72e+05 -1 02e+08 -1.07e+06 -1 12e+06 -1 t6e+06

Contours of Static Pressure (pascal) (Time=2.6040e+00) Sep 28,:

Figure 3-49 Static pressure contour (sectional view) - auger speed 10 rpm

The trend of pressure development observed within the extruder section,


76

StaticPressure

(pascal)

-4

-6 00e+05

-8.008+05

-1 00e+06

-1 20e+06-1 -0 9 -0.8 -0.7 -0.6 -0.5 -0 4 -0.3 -0 2 -0 1 0

Position (m)

Static Pressure (Time=2.6040e+00)

Figure 3-50 Static pressure profile-auger speed 10 rpm


The flow pattern and velocity of clay observed during extrusion, at various

sections of extruder and die, in a 500 mm extruder with auger speed of 10

rpm is shown in Figure 3-51.

Jpffi r jg *:9 29e-018 93e-u 18 57e-010 226-017 88e-017 50e-0l7.14e-016.79e-01643e-016 07e-0l5.72e-015 38e-015 00e-014 64e-014.29e-013 93e-0t3.57e-0l3.21e-012 86e-u12 50e-012 14e-0l1 79e-011 43e-011 07e-0i7 14e-023 57e-020 00e+00

Contours of Velocity Magnitude (m /s) (Tim e=2.6040e+00) Sep 28.


rpm

77

Viscosity profile:


of die in a 500 mm extruder with auger speed of 10 rpm is shown in Figure 3-

52.

6 00e+03

5.0ue+03

4.00e+03MolecularViscosity(kg/m-s) 3 00e+03

2 00e+03

1 OOe+03

0 00e+0020 25 30 35

Strain Rate (1/s)

Molecular Viscosity vs Strain Rate (Time=2 6040e+00)

Figure 3-52 Molecular viscosity vs. Strain rate - auger speed 10 rpm

The results of CFD analysis, for auger speed of 15 rpm, 20 rpm, 25 rpm,

30 rpm, 40 rpm and 50 rpm are available in Appendix A-section VII.


extruding per unit mass of clay, with respect to change in auger speed for a

500 mm extruder is shown in Figure 3-53.

78

500 mm extruder pressure VS RPM @ constant extrusion rate

- * -5 0 0 mm extruder- Energy consumed to extruder per kg. of clay Vs RPM @ constant extrusion rate

Figure 3-53 Extrusion pressure, Energy consumption vs. Auger speed

The trend clearly indicates the effect of varying auger speed on the

performance of an extruder. It is also understood that, depending upon the

moisture content of the clay, an optimum auger speed is necessary to induce

the required amount of shear in the clay for generating sufficient extrusion

pressure at specified extrusion rates.

3.9.3 Effect of varying pitch distance on performance of

extruderThe effect of increasing and decreasing the pitch distance of the auger on

the performance characters of a 500 mm extruder was investigated in this

part. The other parameters like the die design, barrel design, auger speed,

clay material, size, clay moisture content and feed rate were kept constant.

Table 3-11 summarises the operational parameters and material properties

used in the CFD analysis.

Extruder Size

Feed

rate

(kgs'1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

500 mm 19 30

k=4908 Pa.sn n=0.5

t 0=8500 Pa C.S.R=3 s'1

500 mm Extruder Pressure and Energy consumption vs RPM(@ constant extrusion rate, for Clay type-ll

2.97

2.64.2!

22.31*= i5 515W _Q

■65S&

0.99 >>rs a*

0.66 2 c l

Auger RPM

Table 3-11 Data set for varying pitch distance analysis

79

The performance characters were assessed for augers with following pitch

distances 246.13 mm, 292 mm and 338.012 mm. The results obtained from

the CFD analysis are summarised below.

Extrusion Pressure:

Pressure developed during extrusion in a 500 mm extruder with 246.13 mm

auger pitch distance is shown in Figure 3-54 and 3-55. The pressure varied

from a minimum value of -5.2 kPa at the inlet section to a maximum of 4.02

MPa (40.2 bar) observed at the end of auger shaft and reduced to an

average value of 2.92 MPa (29.2 bar) at the outlet.

3 iee+oe3,QQe+06 2 84e+062.68e+062 52e+062.36e+06 2.20e*06 2.048+06 1 88e+06 1 72O+06 1.560+06 1 40©+06 1 24©+061 08e+06 9 220+05 7.620+05 6 020+05 4 410+052 810+05 1 21©+05 -3 91e+04 -1 99©+05 -3 60e+05 -5 20©+05

Contours o f Static Pressure (pascal) (T im e =2 .5 3 50 e +0 0 )

Figure 3-54 Static pressure contour (full view)-pitch dist. 246.13 mm

3490+06ML.1t* Q.

3.160+063 000+06

2 20e+062.048+061 8 8 0+O61.720+061.560+061400+061 248+061 O80+O69 22e+057 62e+056 02e+054 41©+052 810+051 21©+05-3 918+041 990+05

-3 60e+05-5200+05

Contours of Static Pressure (pascal) (Time=2.5350e+-00) Nov 03, 201

Figure 3-55 Static pressure contour (sectional view)-pitch dist. 246.13 mm

80



StaticPressure(pascal)

4 008+06

3 50e+G6

3 0 0 e+06

2 50e+06

2.00e+06

1.50e+06

1 00e+06

5.00e+05

000e+00 -5 00e+05

-0 9 -0 8 -0.7 -0 6 -0,5 -0.4 -0.3 -0 2 -0 1 0

Position (m)

Static Pressure (Time=2.5350e+00) I

Figure 3-56 Static pressure profiIe-pitch dist. 246.13 mm

Material flow pattern:


sections of extruder and die, in a 500 mm extruder with 246.13 mm auger

pitch distance is shown in Figure 3-57. In the direction of extrusion the

average value observed for velocity at outlet section of die was 0.59 ms'1.

iContours of Velocity Magnitude (nVs) (Time=2.5350e+00) Nov 03, 201

Figure 3-57 Flow velocity during extrusion (sectional view)-pitch dist. 246.13

mm

81

9.94e-01

9.18©-018.80*4)18.41*4)18 03e-017.656-017.270-016 .886-016.508-016 .126.015.74e-015 .350-014 .970-014 .590-014.21e-013 826-013 448-013 06e-012 .680-012 290-011 916-011 536-011 150-017 65e-02382e-020 000+00

Viscosity profile:


of die in a 500 mm extruder with 246.13 mm auger pitch distance is shown in

Figure 3-58.


5.00O+03

4 .0 0 e + O 3

3.00e+03

2.006+03

1.008+030 5 10 15 20 25 30 35 4 0 45

S tra in R a te (1 /s )

Molecular Viscosity vs. Strain Rate (T im e=2.5350e+00)

Figure 3-58 Molecular viscosity vs. Strain rate-pitch dist. 246.13 mm

The results of CFD analysis for augers with pitch distance of 292 mm are

available in Appendix A- section II and for 338.012 mm distance in Appendix

A- section VIII.


extruding per unit mass of clay, with respect to change in auger pitch

distance for a 500 mm extruder is shown in Figure 3-59.

82

500 mm extruder Pressure and Energy consumption vs Auger pitch distance @ constant extrusion rate and RPM, for Clay type I

3 2w -a w c at £

t \3 S'E —■- at2 > n a)

41

40

39

2.5940.22.58

38 2.54

2.52

2.50

2.48

2.46

2.44

2.42

2.40

37

36

35

34

33

32

31

2A1

246.136 292 338.012

4)U _ 3 O) *: *$ ^o* * cTJ O% > £ n3 oJ2 t-i °O o? >-

CUJ

Auger pitch distance (in mm)

-500 mm extruder Pressure vs Auger pitch d istance@ constant extrusion rate and RPM

-500 mm extruder- Energy consumed to extrude per Kg. of clay vs Auger pitch d is ta nce© constant extrusion rate and RPM

Figure 3-59 Extrusion pressure, Energy consumption vs. Auger pitch

distance

The observed trend in the change of performance characters clearly

indicates that reducing pitch distance does not influence the performance

characters of an extruder significantly compared to increasing pitch distance.

3.9.4 Effect of varying die shapes on performance of extruderThe effect of varying the design of die outlet on the performance characters

of a 500 mm extruder was investigated in this part. The other parameters like

the auger design, barrel design, auger speed, clay material, size, clay

moisture content and feed rate were kept constant. Table 3-12 summarises

the operational parameters and material properties used in the CFD analysis.

Extruder Size

Feed

rate

(kgs'1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

500 mm 19 30

k=4908 Pa.sn

n=0.5

t0=8500 Pa

C.S.R=3 s’1

Table 3-12 Data set for varying die design analysis

83

The performance characters of the extruder were assessed with respect to

three different types of die design, shown in Figure 3-60.

Die Type- Die Type-ll

Die Type-!

Figure 3-60 Types of die design investigated

The above shown die designs are intended to produce clay columns with

different cross sections used by C.F Ltd, in different applications. The results


Extrusion pressure:

Pressure developed during extrusion in a 500 mm extruder with die type-ll is

shown in Figure 3-61 and 3-62. The pressure varied from a minimum value

of -616 kPa at the inlet section to a maximum of 3.54 MPa (35.4 bar) and

reduced to an average value of 2.79 MPa (27.9 bar) at the outlet. The

maximum extrusion pressure developed during extrusion remained constant

even within the die section until the outlet, where the actual reduction

occurred. In the other die designs a gradual decrease in extrusion pressure

was observed along the entire length of the die section.

84

3 54e-*06 3.33e+06 3 12e-»06

■Contours of Static Pressure (pascal) (Time=2.4750e-HII0)

Figure 3-61 Static pressure contour (full view)-die type-ll

Mmys_ ;w r #V'

Contours of Static Pressure (pascal) (Tim e=2.0000e+00)

Figure 3-62 Static pressure contour (sectional view)-die type-ll



85

5 00e-KJ5

-5.00e+05-1 -0.9 -08 -07 -0.6 -0.5 -0 4 -0.3 -0.2 -0.1 0

Position (m)

J 00e+065 0 g hj6

2.00e+06

1 50e+06

1.00e+06

StaticPressure

(pascal)

0 00e+00

Static Pressure (Time=2 OOOOe-KXI)

Figure 3-63 Static pressure profile-die type-ll


A significant change was observed in the flow pattern and the exit velocity

values with respect to the die shape and die outlet flow area. The flow

pattern and velocity of clay observed during extrusion, at various sections of

extruder and die, in a 500 mm extruder with die type-ll is shown in Figure 3-

64. In the direction of extrusion the average value observed for velocity at

outlet section of die was 0.74 ms'1.

l .2 0 e -0 0

1 I3 e *0 01 06e+009 86e-019.15e-01

8.45e-017 .74e-01 f-

7 .04e-01 I

6 .34e-01 *-

5 .63e-01

4 93e-01

4 22e-01

3.52e-012 82e-01

I 1 41e-017.04e-020 00e+00 #

Contours of Velocity Magnitude (m/s) (Time=2 OOOOe-tOO)

Figure 3-64 Flow velocity during extrusion (sectional view)-die type-ll

86

Viscosity profile:


of die in a 500 mm extruder with die type-ll is shown in Figure 3-65.

M o le c u la rV is c o s ity(k g /m - s )

2 00®+03

1 ,00®+03

O .O O e + O O

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time-2.0000e-*-00) Ju

Figure 3-65 Molecular viscosity vs. Strain rate- die type-ll

The results of CFD analysis, for the other types of die design are available in

Appendix A - section IX.

The trend of variation in average pressure observed at the outlet section of

the die and energy required in extruding per unit mass of clay, with respect to

change in die design for a 500 mm extruder is shown in Figure 3-66. It is

understood from the results that the cross sectional area at the outlet and the

profile of a die has significant effect on the performance characters of an

extruder.

500mm Extruder-Pressure and Energy consumption Vs Die type, with costant extrusion rate and RPM, for Clay type-l

27 97

2.622 *

Type 1 Type 2 Type 3 Die-type

2.70

2.68

2.65

2.63

4>TJ _

E 05

o * ** c •o * >. E n 3 o *2 « -

§ ° O CDp »_ a! * c °- LU

2.60

-500mm Extruder Pressure Vs Die type with costant extrusion rate and RPM

-500mm Extruder- Energy consumed to extrude per Kg. of clay vs Die type with constant extrusion rate and RPM

Figure 3-66 Extrusion pressure, Energy consumption vs. Die design

87

3.9.5 Effect of varying number of split worms on performance

of extruderThe effect of adding split worms or half flight at downstream side of an auger

shaft is understood to have significant effect on the material flow, extrusion

pressure and power consumption in an extruder system [Seanor and

Schweizer, 1962]. The effect of varying the number of split worms on the

performance characters of a 500 mm extruder was investigated in this part

using CFD analysis. The other parameters like the die design, auger pitch,

barrel design, auger speed, clay material, size, clay moisture content and

feed rate were kept constant. Table 3-13 summarises the operational

parameters and material properties used in the CFD analysis.

Extruder Size

Feed

rate

(kgs1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

500 mm 19 30

k=4908 Pa.sn

n=0.5

t 0=8500 Pa

C.S.R=3 s'1

Table 3-13 Data set for varying split worm analysis

The performance characters of the extruder were assessed for three different

cases, which includes 1) auger shaft with no split worm, 2) auger shaft with

one split worm and 3) auger shaft with two split worms. The position and

orientation of the worms on the auger shaft were as shown in Figure 3-67.

88

One split w ormMo split worm

Two split worms

Figure 3-67 Types of split worm design investigated

The results obtained from the CFD analysis for auger shaft with two split

worms are summarised below.

Extrusion pressure:

Pressure developed during extrusion in a 500 mm extruder with two split

worms at the end of auger shaft is shown in Figure 3-68 and 3-69. The

pressure varied from a minimum value of -237 kPa at the inlet section to a

maximum of 3.79 MPa (rounded off to 38 bar) observed at the end of auger

and reduced to an average value of 2.72 MPa (27.2 bar) at the outlet.

3.79*406 3.59*406 3.39*406 3.19*406 2.98*4062 79*4 -0 6 ^2 5 8 * 4 0 6 2 .3 8 *4 -0 6 2 .1 8**-0 6 1 .9 8 *4-0 6 1 .7 8 *4-0 6 1 .5 7 *4-0 61 .3 7 *4 -0 6 , . 11 1 7 *4 -0 69 .7 1 *4 -0 5

5 .6 8 *4 -0 5 -3 .6 7 *4 -0 5

1 1.65*4-05

I -3.61*404

* -2.37*405

Con to u rs o f S ta tic P res su re (p a s c a l) (T im e = 2 .5 0 0 0 e 4-0 0 )

Figure 3-68 Static pressure contour (full view)-two split worms

89

3.79e+06

3.59e+063.39e*063.19e*D6

2.98e+062 78e+062.58e+06

2 38e*06

2.18e+06

1.98e+06

1.78e+06

1.57e+06

1.37e+06

1.17e+06

9.71 e+05

7.69e+05

5.68e+05

3.67e+05

1.658+05

-3.61 e+04

-2.37e+05

Contours of Static Pressure (pascal) (Time=2.5000e+00)

Figure 3-69 Static pressure contour (sectional view)-two split worms

The trend in the pressure developed during extrusion was linear and similar

to the other cases, as shown in Figure 3-70. The pressure distribution at the

exit of extruder or at the inlet section of the die was observed to be more

uniform, when compared with other cases.

3.00e+06

2.50e+06


2.00e+06

i.°0e+06

5.00e+05

0 .0 0 e+ 0 0

-5.008+05-1 -0 9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

Position (m)


Figure 3-70 Static pressure profile-two split worms



sections of extruder and die, in a 500 mm extruder with two split worms at

the end of the auger shaft is shown in Figure 3-71. In the direction of

90

extrusion the average value observed for velocity at outlet section of die was

0.6 ms'1.

1 236*00 1 16e*001 09e*<30 1 02e*00 9 53e-01 8 85e-01

Contours ofVelocity Magnitude (m/s) (Time=2.5000e+00)

Figure 3-71 Flow velocity during extrusion (sectional view)-two split worms

The effect of split worms on the flow pattern at the exit section of extruder

was also analysed and a significant change was observed. The flow pattern

observed at the exit section of extruder with respect to number of split worms

in the auger shaft is shown from Figure 3-72 to 3-74.

106^00101e*00963e-019.12e-©1 8.61*01 811*01 7 60*01 709*01 659*01 6 08*01 557*01 507*01 4 56*01 4 05*01 3 55*01 3 04*01 2 53*01 203*01 152*01 101*01 507*02 C00**90

1 35e+QO 1 30e+0Q I 25e+QQ 1 20e+Q0 1 156+00 1 10e+0G 1,06e+001 01e+00 9.61 e-01 9 I3e-01 8 65*018 17e-01 7.69e-01 7.21*01 6 72*01 6 24*01 5 76e-01 5.28*01 4.80*01 4 32*01 3.84*013 36*012 88*01 2 40*01 1 92*01 1 44*019 61*024 80e-02 0 00e+00

Contours o f Velocity Magnitude (rrVs) (Time=2 5000e+00)

Figure 3-72 Flow pattern with no

split worm

Contours of Velocity Magnitude (m/s) (Time=2 5050e+00)

Figure 3-73 Flow pattern with one

split worm

91

114e*0C I09e»00 1 05e*0C1 OOe*OC9 576-01 9116-018 656-01 8206-01 7.746-01 7 296-01 6 836-01 6.386-01 5 926-01 5476-01 5016-01 4 55e-0l

106-C'3 646-01 3 196-012 736-01 2 28e-01 1.826-01 137e-019 116-02 4556-02 000e-00

Contours of Velocity Magnitude (m/s) (Time=2.5000e+00)

Figure 3-74 Flow pattern with two split worms

Viscosity prof He:


of die in a 500 mm extruder with two split worms is shown in Figure 3-75.

6 0 0 *4 0 3


5 00*4-03

4 00*+03

3 .0 0 *+ 0 3

2 0 0 *+ 0 3

1 0 0 *4 0 315 20 2 5 30

Strain Rate (1/s)

M o le cu la r V isco s ity vs . S tra in R a te (T im e * 2 5 0 0 0 *4 0 0 )

Figure 3-75 Molecular viscosity vs. Strain rate-two half flights

The results of CFD analysis for auger with no split worms are presented in

Appendix A - section IX (b) and for auger with one split worm are presented

in Appendix A - section II.

The trend of variation in maximum pressure developed during extrusion and

energy required in extruding per unit mass of clay with respect to number of

split worms in an auger shaft, for a 500 mm extruder is shown in Figure 3-76.

92

500 mm extruder-Pressure and Energy consumption Vs No.of Split womrs @ constant extrusion rate and RPM, for Clay type-1

2.72

2.68 * _

2.65 £ f

2.61

2.58 i f ;

2.54.54

o O)2.47 > ;*

2.44 £ o.1U

2.400 2

No.of split worm at the auger

■500 mm extruder Pressure developed and powerconsumption VS No.of splitworms

-500 mm extruder- Energy consumed to extruder per Kg. of clay Vs No.of splitworms

Figure 3-76 Extrusion pressure, Energy consumption vs. Split worms

It clearly indicates that the addition of split worm at the end of auger shaft

influences the extrusion pressure but not the power consumption, confirms

with the recommendations of Seanor and Schweizer (1962) from the ir work.

3.10 Performance assessment of a 600 mm extruderThe effect of varying the design and operating parameters on performance

characters of a 600 mm extruder system, without varying the type of clay

was investigated in this part of the research, using the CFD modelling.

3.10.1 Effect of varying feed rate on performance of

extruder

The effect of increasing the feed rate of uncompacted clay, in a 600 mm

extruder was investigated in this part. The other parameters like the die

design, extruder design, clay material, size, clay moisture content and auger

speed were kept constant. Table 3-14 summarises the operational

parameters and material properties used in the CFD analysis.

93

Extruder Size

Feed

rate

(kgs’1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

600 mm Varying 22.5

k=5206.95 Pa.sn

n=0.32

t0=6500 Pa

C.S.R=2.1 s'1

Table 3-14 Data set for varying feed rate analysis

The performance characters were assessed for the following feed rates 8.1

kgs'1, 11.8 kgs'1 and 19 kgs'1. The results obtained from the CFD analysis

are summarised below.

Extrusion pressure:

Pressure developed during extrusion in a 600 mm extruder with a feed rate

of 8.1 kgs'1 is shown in Figure 3-77 and 3-78. The pressure varied from a

minimum value of -228 kPa at the inlet section to a maximum of 3.15 MPa

(31.5 bar) observed at the end of the auger shaft and reduced to an average

value of 2.7 MPa (27 bar) at the outlet.

—-ij 3.15e+06

(| 2 98e+G6| 2.81 e+G6

2.64e+06 2 47e+062.31 e+06 2.14e+06

1 97e+06 1 80e+06

1 63e+06

1 46e+06 1 29e+06

1 12e+06 9 54e+05

7.85e+05

k* * 1 6.17e+05

4 48e+05 2.79e+05

1 10e+O5

-5 89e+04 -2.28e+05

Contours of Static Pressure (pascal) (Time=2 6750e+00)

Figure 3-77 Static pressure contour (full view) - feed rate 8.1 k g s 1

94

3.15e+Q62.98e+Q62.81 e+06

2 6 4 e+06 2 47e+062.31 e+06 2 14e+06

1 97e+06 1 80e+06

1 63e+06

1 46e+06 1 29e+061 12e+06 9 54 e+05

7 8 5 e+05 6.17e+05

4 48e+052 79e+05

1 10e+05

-5 8 9 e+04 -2.28e+05

1 ITT

I__I

rContours of Static Pressure (pascal) (Time=2 6750e+00)

Figure 3-78 Static pressure contour (sectional view) - feed rate 8.1 kgs-1



-1 -0.8 -0.6 -0 4

Position (m)


3 00e+06

2 50e+06

2 00e+06

1 50e+06

1 0 0 e+06

5 00e+05

0 00e+00

-5.00e+05

Static Pressure (Time=2.6750e+00) I

Figure 3-79 Static pressure profile- feed rate 8.1 kgs'1



sections of extruder and die, in a 600 mm extruder with 8.1 kgs'1 feed rate is

shown in Figure 3-80. In the direction of extrusion the average value

observed for velocity at outlet section of die was 0.07 ms'1.

95

9 916-01

9 42e-018 92e-01

8.43e-01

7.93 e-01

7 43e-01

6 9 4 e-01

6 44 e-01

5.95e-01

5.45e-01

4 96e-01

4 4 6 e-01

3 9 6 e-013 47 e-01

2.97 e-01

2.48e-01

1 98 e-01

1 49 e-01

9.91 e-02

4 96e-02

0 00e+00

r n : . 1 1

I I 1 T J

rContours of Velocity Magnitude (m/s) (Time=2 6750e+00)

Figure 3-80 Flow velocity during extrusion (sectional view)-feed rate 8.1 kgs-1

Viscosity profile:


of die in a 600 mm extruder with 8.1 kgs'1 feed rate is shown in Figure 3-81.

120e-*-O4

1.10e+04

Molecular iooe+o4 Viscosity (kg/m-s) 9 00e+03

8.00e+Q3

7CX)e+03

6.00e+03

5 00e+030.5 1 1.5 2 2.5 3 3.5 4

Strain Rate (1/s)

Figure 3-81 Molecular viscosity vs. Strain rate- feed rate 8.1 kgs'1

The results of CFD analysis, for feed rates 11.8 kgs'1 and 19 kgs'1 are

available in Appendix A- section X.


extruding per unit mass of clay, with respect to change in feed rate of clay for

a 600 mm extruder is shown in Figure 3-82.

96

Sheffie ld Hallam U n iversity

A .iB .o r,

T itle /T hesis 2 ^ 0 f i ^ ^

Degree Py\ D f i j-( I L o S o QC- fvl U M £ iS ( c.C i-^Y ear: *—

2 - ^ 13

C opyr ight Declaration

Consultation for Research or Private study for Non Commercial PurposesI recognise that the copyright in this thesis belongs to the.author.I undertake not to publish either the whole or any part of it, or make a copy of the whole or any substantial pai t of it, without the consent of the author.I recognise that making quotations from unpublished works under 'fair dealing for criticism or review' is not permissible.

Consultation for Research or Private study for Commercial PurposesI recognise that the copyright in this thesis belongs to the author.I undertake not to publish either the whole or any' part of it, or make a copy of the whole or any part of it, without the consent of the author.I recognise that making quotations from unpublished works under 'fair dealing for criticism or review' is not permissible.

Readers consulting this thesis are required to complete the details below and sign to show they recognise the copyright declaration.

Date | Name and Institution /Organisation (in block letters)

Signature

600 mm extruder Pressure and Energy consumption Vs Mass flow rate/Feed rate @ constant speed of 22.5 rpm, for Clay Type-ll

3.14

8.1 11.8 19

7.034)TS _P »

5.86 S *<Kn *

4.69 ~ c-U 13,l i3.52

2.34 | 5o 9O U)1.1/ U) i_0.00

LUMass Flow rate/Feed rate (in Kg/sec)

-600 mm extruder Pressure Vs Mass flow rate/Feed rate ©constant speed of 22.5 rpm

-600 mm extruder- Energy consumed to extrude per Kg. of clay Vs Mass flow rate/Feed rate @ constant speed of 30 rpm

Figure 3-82 Extrusion pressure, Energy consumption vs. feed rate

3.10.2 Effect of varying auger speed on performance of

extruderThe effect of varying auger speed on the performance characters of a 600

mm extruder was investigated in this part. The other parameters like the die

design, extruder design, clay material, size, clay moisture content and feed

rate were kept constant. Table 3-15 summarises the operational parameters

and material properties used in the CFD analysis.

Extruder Size

Feed

rate

(kgs1)

Auger

speed

(rpm)

Herschel-Bulkley's

model value

600 mm 11.8 varying

k=5206.95 Pa.sn

n=0.32

t 0=6500 Pa

C.S.R=2.1 s '1

Table 3-15 Data set for varying auger speed analysis

The performance characters of the extruder were assessed for the following

auger speeds- 15 rpm, 22.5 rpm and 30 rpm. The results obtained from the

CFD analysis are summarised below.

97

Extrusion pressure:

Pressure developed during extrusion in a 600 mm extruder with an auger

speed of 15 rpm is shown in Figure 3-83 and 3-84. The pressure varied from

a minimum value of -181 kPa at the inlet section to a maximum of 1.97 MPa

(19.7 bar) observed at the end of the auger shaft and reduced to an average

value of 1.54 MPa (15.4 bar) at the outlet.

1 9 7 e -0 6 1.86e+06

1 758+061 65e+06

1 5 4 e -0 6 1 43e+06 1 32e+06 1 22e+06 1.11 e+06

1 00e-»06 8 94e+05

7.87e+05 6 .79e+05

5.71 e+05

4 6 4 e *0 5 3 5 6 e -0 5

2 49e+05 1.41 e *0 5 3 .38 e+04

-7 38 e *0 4

-1.81 e+05

Contours of S tatic Pressure (pascal) (T ime=2 6800e+00)


1 7584061 65e-*06 I 54e-*061 43e406 1.32e406 1 22e406 1.11e406 1.00e406 8.94e405 7.87e405 6.79e405 5.71e4054.64e-*053.5694052.498405 1 41e405 3 38e404 -7 ^ e 4 0 4 -1 81e405

Contours of Static Pressure (pascal) (Time=2 6800e400)




98

3 00e+06

2 50e+06

2.00e+06

1 50e+06

1 00e+06

5.00e+05

0 00e+00

-0.8 -0 6

Position (m)


Figure 3-85 Static pressure profile- auger speed 15 rpm



sections of extruder and die, in a 600 mm extruder with auger speed of

15 rpm is shown in Figure 3-86. In the direction of extrusion the average

value observed for velocity at outlet section of die was 0.13 ms'1.

6 6 2 e-01

6.29e-01

5.96e-01

5 6 3 e-01

5 3 0 e-01

4 97e-01

4 6 4 e-01

4 30e-013 .97 e-01

3 64 e-01

3.31 e-012 .98 e-01

2 .65 e-012 .32 e-01

1 99 e-01

1 66e-01

1.32 e-01

9.93e-02

6.62e-02

3.31 e-02

0 00e+00

I 1 1 1

l i r

Contours of Velocity Magnitude (m/s) (Time=2 6800e+00)


rpm

99

Viscosity profile:


of die in a 600 mm extruder with an auger speed of 15 rpm is shown in

Figure 3-87.

t 5" ‘V i ‘■•r;• Sr •'■34. 1

1.00e+04

Molecular ViSCOSity 8.00e+03 (k g /m -s )

6.00e+03

4.00e+03

Z00e+030 1 2 3 4 5 6 7 8

Strain Rate (1 /s )

Figure 3-87 Molecular viscosity vs. Strain rate- auger speed 15 rpm

The results of CFD analysis, for auger speed of 22.5 rpm are available in

Appendix A- section X (a) and 30 rpm are available in Appendix A -section

XI.


extruding per unit mass of clay, with respect to change in auger speed for a

600 mm extruder is shown in Figure 3-88.

100

600 mm Extruder Pressure and Energy consumption vs rpm @ constant extrusion rate, for Clay type-ll

■o w * >. E J2

015 22.5

Auger-rpm30

-600mm extruder pressure vs RPM ©constant extrusionrate

-600mm extruder- Energy consumed to extrude per Kg. of clay Vs RPM @ constant extrusion rate____________

Figure 3-88 Extrusion pressure, Energy consumption vs. auger speed

Similar to the 500 mm extruder, the trend observed for variation in

performance characters of a 600 mm extruder with respect to change in

auger speed indicates that the increase in speed will increase the pressure

and energy requirement of an extruder system to a certain extent.

3.11 ConclusionPerformance assessment of extruders using CFD technique along with

experimental validation of the methodology and fluid model used was

presented in this chapter. The ability to use CFD technique to design a clay

extruder system and the advantages that could be gained within the heavy

ceramics industries has clearly been demonstrated through the results

obtained.

101

Chapter-4 Finite Element Analysis of clayextruder

102

4.1 Introduction:In this part of the research work, mechanically induced stress and strain on

the components of a 430 mm extruder were assessed using FEA technique.

Components investigated include barrel, liner, distance piece and auger.

Based upon the maximum extrusion pressure expected under actual working

conditions, the component were assessed for two different load conditions

1) 1.8 MPa and 2) 2.6 MPa.

Stress and deformation induced with respect to applied load were

investigated for three different materials, which include A) Structural steel

(Grade BS EN 10025 Fe 430A), B) Grey Cast Iron (GCI) (Grade: EN-GJL-

250) and C) Austempered Ductile Iron (ADI) (Grade GJS-1400-1). Structural

steel is the most commonly used material by C.F Ltd to manufacture the

majority of extruder components. GCI and ADI are alternate material chosen

to be investigated through this research work, to identify their technical and

commercial suitability for manufacturing extruder components. In recent

years ADI has been proven to be a highly useful material for heavy clay

industrial applications [Da and Jincheng, 2000], [Chowdhury et al., 2010]

[Ductile Iron Society, 2012], due to its excellent wear resistant properties

and light weight. The technical suitability of these alternate materials was

analysed using FEA results for stress and deformation induced due to

extrusion pressure and the commercial feasibility was analysed by

comparing the cost to manufacture with existing and alternate materials. The

finding are summarised below.

4.2 FEA of clay extruder components

4.2.1 BarrelThe stress and deformation induced by the pressure developed during

extrusion, on the barrel was assessed in this part.

Geometry:

The Barrel geometry used for investigation is shown in Figure 4-1.

103

Figure 4-1 430 mm extruder barrel geometry

Load and boundary condition:

The geometry was suitably meshed using tetrahedral mesh and investigated

for two different load conditions, 1) 2.6 MPa and 2) 1.8 MPa. Pressure load

was applied on all the inner surfaces of the barrel and fixed support condition

on the appropriate surfaces, as highlighted in the Figure 4-2.

ise.co «« oi

Figure 4-2 430 mm extruder barrel- load applied

Stress and deformation results:

Values of equivalent stress, obtained for different materials from the analysis,

with respect to applied load conditions are summarised in Table 4-1.

104

Material

Max. Von-Misses

stress value, load-

2.6 MPa

Max. Von-Misses

stress value, load-

1.8 MPa

Structural steel 59.03 MPa 40.87 MPa

GCI 59.938 MPa 41.496 MPa

ADI 60.164 MPa 41.652 MPa

Table 4-1 Stress results-barrel

There was no significant change observed in stress distribution pattern

across the component with respect to applied load conditions. The results of

FEA for applied load of 2.6 MPa is shown in Figure 4-3. The results of FEA

for the applied load of 1.8 MPa is available in Appendix B- section I.

H

a) Structural steel b) GCI

c) ADI

Figure 4-3 Stress induced in barrel @ 2.6 MPa load

105

The strain induced in the barrel was investigated by analysing the

deformation pattern in the direction of extrusion. The results obtained are

summarised in Table 4-2.

MaterialMax. deformation,

load-2.6 MPa

Max. deformation,

load-1.8 MPa

Structural steel 0.071 mm 0.049 mm

GCI 0.129 mm 0.089 mm

ADI 0.088 mm 0.061 mm

Table 4-2 Deformation results- barrel

There was no significant difference noted in the deformation pattern, for both

the load conditions. The deformation pattern observed in barrel for applied

load of 2.6 MPa is shown in Figure 4-4 and the results for applied load of 1.8

MPa is available in Appendix B- section II.

?vit/)ttt im


Figure 4-4 Deformation in barrel @ 2.6 MPa load

106

The stress and deformation results obtained from the FEA clearly indicates

that, barrel made up of any of the following materials Structural Steel, GCI or

ADI, will be able to withstand the stress induced during extrusion, without

breaking during operation. The material currently used by C.F Ltd is

Structural Steel and its cost of manufacturing was compared with the cost of

alternate materials used in FEA and is summarised in Table 4-3.

Material Cost per piece (in £'s)

Structural steel 6475.00

GCI 3886.00

ADI (cost with pattern) 6680.00

ADI (cost without pattern) 4380.00

'able 4-3 Manufacturing cost comparison for extruder barrel

It is understood from the preliminary investigations that ADI could be used

as an alternate material of construction for extruder barrels. GCI is not

recommended, even though it is cheaper than the other materials, due to its

limitations in manufacturing certain geometrical features.

4.2.2 Distance pieceDistance piece is an intermediate component used to connect the extruder

with the die. The stress and deformation induced by the pressure developed

during extrusion, on distance piece was assessed in this part.

Geometry:

Distance piece geometry used for the investigation is shown in Figure 4-5.

Figure 4-5 430 mm extruder distance piece geometry107



for two different load conditions, applied to the inner surfaces. Pressure load

was applied to appropriate inner surfaces and fixed constraints on the

required external surfaces as shown in Figure 4-6.

Or tfe«4-24Mp*4<»d2 :Ftrtd Support T wm I «2V01/20U 13.J4

9 Pressure: 2.6 MPj

Figure 4-6 430 mm extruder distance piece- load applied

Stress results:



Material

Max. Von-Misses

stress value, load-

2.6 MPa

Max. Von-Misses

stress value, load-

1.8 MPa


GCI 52.403 MPa 36.279 MPa

ADI 52.314 MPa 36.217 MPa

Table 4-4 Stress results-distance piece

There was no significant change observed in the stress distribution pattern

across the component with respect to applied load conditions. The stress

distribution pattern on the distance piece, for applied load of 2.6 MPa is

shown in Figure 4-7 and the results for the applied load of 1.8 MPa is

available in Appendix B- section III

1 0 8

I.QO (mm)


c) ADI

Figure 4-7 Stress induced in distance piece @2.6 MPa load

The strain induced in the distance piece was investigated by analysing the




load-2.6 MPa

Max. deformation,

load-1.8 MPa


GCI 0.0579 mm 0.0401 mm

ADI 0.0394 mm 0.0273 mm

Table 4-5 Deformation results- distance piece

There was no significant difference noted in the deformation pattern, for both

the load conditions. The deformation pattern observed in liner for applied

load of 2.6 MPa is shown in Figure 4-8 and the results for applied load of 1.8

MPa is available in Appendix B- section IV.

a) Structural steel b) Grey cast iron

c) ADI

Figure 4-8 Deformation in distance piece @ 2.6 MPa load

The material currently used by C.F Ltd is Structural Steel and its cost of

manufacturing was compared with the cost of alternate materials used in

FEA and is summarised in Table 4-6.


Structural steel 2445.00

GCI 1680.00

ADI 2170.00

Table 4-6 Manufacturing cost comparison for distance piece

110

It is clearly understood form the preliminary investigation that both ADI and

GCI have design and cost benefits and can be used as an alternate material

for manufacturing extruder distance piece.

4.2.3 LinerThe stress and deformation induced by the pressure developed during

extrusion, on liners was assessed in this part.

Geometry:

Liner geometry used for the investigation is shown in Figure 4-9.

Figure 4-9 430 mm extruder liner geometry



for two different load conditions, applied to the inner surfaces. Pressure load

was applied to appropriate inner surfaces and fixed constraints on external

surfaces as shown in Figure 4-10.

F«t«i Support

2V9U2QU U: 15

■ PrUMrtt 7* MPl n f Support

Figure 4-10 430 mm extruder liner - load applied

111

Stress results:



Material

Max. Von-Misses

stress value, load-

2.6 MPa

Max. Von-Misses

stress value, load-

1.8 MPa


GCI 3.431 MPa 2.375 MPa

ADI 3.441 MPa 2.387 MPa

Table 4-7 Stress results-liner

The stress distribution pattern on the liner, for the applied load of

2.6 MPa is shown in Figure 4-11 and the results for the applied load of 1.8

MPa is available in Appendix B- section V

JWt/SfUM.H


c) ADI

Figure 4-11 Stress induced in liner @ 2.6 MPa load

112

The strain induced in the liner was investigated by analysing the deformation

pattern in the direction of extrusion. The results obtained are summarised in

Table 4-8.


load-2.6 MPa

Max. deformation,

load-1.8 MPa


GCI 0.0004 mm 0.0003 mm

ADI 0.0002 mm 0.0002 mm

Table 4-8 Deformation results-liner

The deformation pattern observed in liner for applied load of 2.6 MPa is

shown in Figure 4-12 and the results for applied load of 1.8 MPa is available

in Appendix B- section VI.


c) ADI

Figure 4-12 Deformation in liner @ 2.6 MPa load

113

4.2.4 Auger

The stress and deformation induced by the pressure developed during

extrusion, on the auger shaft was assessed in this part.

Geometry:

Auger geometry used for the investigation is shown in Figure 4-13.

Figure 4-13 430 mm extruder auger shaft geometry



for two different load conditions. Pressure load was applied on the all the

faces of worm and auger shaft and fixed constraint at one end of the shaft as


m * m >•

Figure 4-14 430 mm extruder auger shaft - load applied

114

Stress results:



Material

Max. Von-Misses

stress value, load-

2.6 MPa

Max. Von-Misses

stress value, load-

1.8 MPa


GCI 4.131 MPa 2.860 MPa

ADI 13.345 MPa 9.238 MPa

Table 4-9 Stress results-auger shaft

The stress distribution pattern on auger shaft, for applied load of 2.6 MPa is

shown in Figure 4-15 and the results for applied load of 1.8 MPa is available

in Appendix B- section VII'

U!« US.M


Figure 4-15 Stress induced in auger shaft @ 2.6 MPa load115

The strain induced in the auger shaft was investigated by analysing the




load-2.6 MPa

Max. deformation,

load-1.8 MPa


GCI 0.009 mm 0.006 mm

ADI 0.198 mm 0.137 mm

Table 4-10 Deformation results-auger shaft

The deformation pattern observed in auger shaft for applied load of 2.6 MPa

is shown in Figure 4-16 and the results for applied load of 1.8MPa are

available in Appendix B- section VIII.


c) ADI

Figure 4-16 Deformation in auger shaft @ 2.6 MPa load

116

nnxm \i i

The material currently used by C.F Ltd for manufacturing auger is a special

type of alloy material developed in house, designated as CF-28. Material with

equivalent mechanical property was used in FEA. In actual scenario, during

the process of manufacturing, the casted auger has to be heat treated in

order to attain the recommended hardness value of =60 HRC. Hence in

order to have a fair comparison of manufacturing cost, the heat treatment

cost for alternate materials was required. Due to amount of time and cost

involved in obtaining this cost, it was decided to make a comparison without

heat treatment cost and it is summarised in Table 4-11.


Chrome steel 311.00

GCI 200.00-223.00

ADI 227.00-266.00

Table 4-11 Manufacturing cost comparison for auger

It is evident from the above discussion that the alternate materials

considered for manufacturing of augers, possess both design and

commercial advantages.

Clay being a very abrasive substance, the hardness value of the auger is

considered to be very critical to withstand the wear caused by the clay and

also increase the life of auger, in order to make the system to be cost

effective.GCI is not recommended by the users and design engineers, due to

its brittle nature at the early stages of installation. ADI alloy is lighter and

cheaper than the steel alloy which is currently used and also proven to be

useful in such applications. ADI, though, has better mechanical

characteristics and costs less than the existing material, the only limitation is

the maximum hardness value that could be achieved through heat treatment

process. As mentioned earlier it is recommended that certain areas of the

auger should have a hardness value of =60 HRC. The maximum attainable

hardness value in an ADI alloy, with the available methods of heat treatment

is 55 HRC, and this increase in hardness is achievable only to a certain

micron depth. However all the augers that are mounted on the shaft are not

subjected to equal pressure and wear. The field data obtained on the wear

117

life of augers indicates that the auger located at the far end of the extruder or

in other words the augers at the end of the barrel chamber is subjected to

excessive wear. Whereas the augers inside the vacuum chamber are

subjected to less wear. This difference in the pattern of wear characters of

auger provides an opportunity for the use of alternate materials for making

augers which are subjected to less pressure and wear. It is evident from the

above discussion that using ADI as an alternate material for making augers

is not only a cost effective option but also could yield other benefits like less

power consumption at the extruder unit and increases the life of augers.

4.3 ConclusionThus the technical and commercial advantage of using alternate light

materials was presented in this chapter. This clearly demonstrates the ability

and advantages of using FEA techniques to improve the design of clay

extruders within heavy ceramic industries.

118

Chapter-5 Conclusion and future directions

119

5.1 ConclusionThe main aim of this research work was to use CFD and FEA techniques to

assess and improve the design of extruders. The key objectives include

identifying suitable CFD methodology to simulate the clay extrusion process,

assessing the performance character of extruders with respect to various

design and operating parameters and investigate alternate materials for

extruder components that could make the extruder more efficient and cost

effective.

The first part of this research work was dedicated to identifying a suitable

flow model and CFD modelling technique, for assessing the performance

characters of a vacuum type de-airing extruder. The extrusion pressure

developed and power consumed by full scale extruders during the extrusion

was predicted using Herschel-Bulkley's fluid flow based 3-D CFD model. The

extrusion pressure, power consumption and the pressure development trend

were then predicted for different designs of extruder under different operating

conditions, using the 3-D CFD model. The results obtained for extrusion

pressure, flow pattern and velocity of clay during extrusion were in good

agreement with the values suggested in the literature and occurring in actual

scenarios. The results obtained from the model for properties like

temperature and density variation were not very satisfactory and need further

investigation.

The results for shear thinning behaviour exhibited by clay during extrusion

was predicted from the CFD model and compared with the experimental

results obtained from various scientific works. The similarity in the viscosity

profile obtained from the model and the literature indicates that Flerschel-

Bulkley’s flow model used in the CFD analysis is well representing the shear

thinning behaviour of clay exhibited during the process of stiff extrusion.

The second part of this research work was focused in validating the CFD

methodology used in the first stage. The extrusion pressure and power

consumed by the lab-scale extruder was measured experimentally and

compared with the results obtained from CFD analysis. The closeness in the

measured values for extrusion pressure and power consumption clearly

120

demonstrates the suitability of using the identified CFD methodology to

model and assess the performance of full-scale extruders.

The third stage of this research work was dedicated to using the FEA

technique to investigate the technical suitability of alternate light weight

materials and the compare the costs of extruders. The FEA results and the

cost of alternate light weight materials indicate that the use of Austempered

Ductile Iron to manufacture extruder components could result in both

technical and commercial benefits. A careful consideration is required at the

design stage in order to identify a proper area for use of this material.

The results obtained from this research work clearly demonstrate that using

CFD and FEA techniques within the process of clay extruder design could be

cost effective and time saving. It helps in reducing the resource and time

required for developing new extruder components, compared with lab-based

development processes.

5.2 Future directions• Performing more trials in the scaled extruder with an improved

experimental set up could help in obtaining further validation of the

CFD methodology used.

• A further investigation in improving the quality of mesh and further

mesh refinement could be beneficial in obtaining a converged solution

and might improve the results in critical areas of extruder sections.

• Experimental works in a controlled environment that focus in

determining the variables used for Flerschel-Bulkley’s model, for clays

with different moisture content could be undertaken. This will enhance

the accuracy of flow parameters predicted by the current CFD

methodology and also reduce time and computing cost.

• A further investigation of suitable CFD based modelling methods that

can predict temperature dependant properties of clay during extrusion

could be helpful in predicting additional flow parameters, involved

during extrusion. It might also open up new areas for investigation.

• Measuring the viscosity of clay with advanced instruments like Ball

measuring system and Building Material cell, could help in obtaining

121

better results and further understanding in the flow characters of clay

when subjected to shear. This could help in making a fair comparison

with the results predicted from the CFD model and make suitable

design changes to enhance the flow of clay in extruders during

extrusion.

122

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Word CountPages 242

Words 35,208

Characters (no spaces) 188,562

Characters (with spaces) 222,469

Paragraphs 2,078

Lines 5,160The count includes textboxes, footnotes & endnotes

128

I. Extruder geom etry

a. 500 mm extruder

%£gEsS&s&.

Figure A-A- 1 500 mm extruder volumes and mesh generated

b. 600 mm extruder

f f i w

M :■ f; M™ ! IIP

: %S&0 S0j! t im ?

m s m

Figure A-A-2 600 mm extruder volumes and mesh generated

130

II. CFD Sim ulation results of 500 mm extruder with Herschel-

Bulkley's model value-1

Extrusion pressure:

4 020+06

3 810+06

3.59©-+06

3.38e+06 3.160+06

2.95©-+06

2.7 3 ©+-06

2.52 ©+-06

2.30©+-06

2.09©+-06

1 .87 ©+-06

1.66©+-06

1 .440+06

1.23e+06

1.01 ©+-06

8 .00e+-05

5.85©+-05

3.70©+-05

1.55©+05

-6 .00e+04

-2.75©+05

1

Contours of Static Pressure (pascal) (T im e=2 .5050e+00)

Figure A-A-3 Static pressure contour (full view)-500 mm Case I

C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 5050e+ -00)

Figure A-A-4 Static pressure contour (sectional view)-500 mm Case I

StaticP ressu re

(p ascal)

4.00e+06

3 50e+O 6

3 00e+O 6

2.50e+06

2 00e+06

1 500+06

1 00e+O6

5 00e+05

0 00e+00

-5 000+0543.9 43 8 43.7 43 6 43.5 43 4 43 3 43 2 43.1 O

Position (m )

S ta t ic P re s s u re (T im e = 2 5 0 5 0 e + 0 0 )

Figure A-A-5 Static pressure profile -500 mm Case I

131


i 1 3e»00 1 07e-oo1 ooe+oo9 33e-018.66e-018 00e-01 _ _7.33e-01

6.66e-01

6.00e-015 33e-01

4.66e-01

4 00e-01

3.33e-01

2.67e-01

2.00e-01

1.33e-01

6.66e-02 O.OOe+OO

Contours of Velocity Magnitude (m/s) (Tim e=2.5050e+00)


Viscosity profile:

7 0 0 e + 0 3

6 .0 0 e + 0 3

Molecular 5.ooe+o3 Viscosity (kg/m-s) 4.ooe+o3

3.00e+ 03

2 .00e+03

1.00e+030 5 10 15 20 25 30 35 4 0 45

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (T im e=2.5050e+00) Ap

Figure A-A-7 Molecular viscosity vs. Strain rate-500 mm Case I

132

III. CFD Sim ulation results of 600 mm extruder with Herschel-

Bulklev's model value-1

Extrusion pressure:

4.71 e+064 .46e+064 21 e+063 9 6 e+063 71e+063 45e+063.20e+062.95e+062.70e+062 45e+062 19e+061 94e+061 6 9 e+061 44e+061 19e+069 34e+056 8 2 e +054 3 0 e +051 78e+05-7 36e+04-3 26e+05


Figure A-A-8 Static pressure contour (full view)-600 mm Case I

4 71e+06

4 4 6 e+064.21 e+06

3 9 6 e+06

3 7 1 e+06

3.45e+063 2 0 e+06

2 9 5 e+06

2 70e+06

2 45e+06

2 19e+06

1 94e+06

1 69e+06

1 44e+06

1 19e+06

9.34e+05

6 8 2 e+054 3 0 e+05

1 78e+05

-7 3 6 e+04

-3.26e+05

s i i i r o n i

■ r r w m

Contours of Static Pressure (pascal) (Time=2 6700e+00)

Figure A-A-9 Static pressure contour (sectional view)-600 mm Case I

133

Position (m )

e+06

4 00e+06

3.00e+06

Static P ressu re 2 00e+06

(pascal)1.00e+O6


Figure A-A-10 Static pressure profile -600 mm Case I


8 95e-08 46s-017.96 e-01 7 46e-01 6.96e-01

6.47e-01

5.97e-01

5.47e-01

4.97e-01

4 48e-01

3 98e-01

I 3 48e-01

I 2 98e-01

I 2 49e-01

| 1.99 e-01

1 49e-01

9.95e-02

4.97e-02

0 00e+00

B E T Till1“ [ T T

____ I f LJr 2

Contours of Velocity Magnitude (m/s) (Time=2.6700e+00)


134

Viscosity profile:

1.10e+04

1 00e+04

Molecular 9.ooe+o3 Viscosity (kg/m-Sj 8 00e+03

7.00e+03

6.00e+03

5.00e+030 1 2 3 4 5 6

Strain Rate (1/s)

Figure A-A-12 Molecular viscosity vs. Strain rate-600 mm Case I

IV. CFD Simulation results of 500 mm extruder with Herschel-

Bulklev's model value-ll

Extrusion pressure:

Contours of S ta tic P ressu re (pascal) (T im e = 2 .5 0 0 0 e + 0 0 )

2 4 3 e + 0 62 3 0 e+0 62 .1 7 e + 0 62 0 4 e + 0 61.91 e+Q61 7 8 e + 0 61 6 5 e+0 61 5 2 e + 0 61 3 8 e + 0 61 2 5 e +061 1 2e +0 69.91 e +058 .60e+ O 57 2 9 e +055 9 8 e+0 54 .6 7 e + 0 53 3 6 e+0 52 0 5 e+0 57 3 5 e +04-5 7 6e + 0 41 8 9 e + 0 5

Figure A-A-13 Static pressure contour (full view)-500 mm Case II

135

2 4 3 e + 0 62 3 0 e + 0 62 1 7 e + 0 6

2 .0 4 e + 0 61 .9 1 e + 0 6

1 7 8 e + 0 66 5 e + 0 6

1 5 2 e + 0 61 3 8 e + 0 6

1 25 e + D 61 1 2 e + 0 69.91 e + 0 58 6 0 e + 0 57 .2 9 e + 0 55 9 8 e + 0 54 6 7 e + 0 53 .3 6 e + 0 52 0 5 e + 0 57 3 5 e + 04-5 7 6 e +041 8 9 e + 0 5

C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .5 0 0 0 e + 0 0 )

Figure A-A-14 Static pressure contour (sectional view)-500 mm Case II

StaticP ressu re

(p ascal)

-1 -0 9 -0 8 -0 .7 -0 6 -0 .5 -0 4 -0 3 -0 .2 -0 1 0

Position (m )

S ta t ic P re s s u re (T im e = 2 5 0 0 0 e + 0 0 ) I

Figure A-A-15 Static pressure profile -500 mm Case II


1 3 5 e-01 6 .7 7 e -02 0 OOe-rOO

: ii '11 CBe-KM

1 01 e + 0 09 47e-01

8 .8 0 e-01 8 12e-01

7 .4 4 e-01 6 7 7 e-01 6 0 9 e-01

5 41 e-014 74e -01

4 06e-013 38e-01

2 71 e-01

C o n to u rs o f V e lo c i ty M a g n itu d e (m /s ) (T im e = 2 5 0 0 0 e + 0 0 )


II136

Viscosity profile:

7.00e+03

6.00e+03

5.00e+03


2 .0 0 e + 0 3

1 .0 0 e + 0 3

0 .0 0 e + 0 01 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=2 5000e+00) Apr

Figure A-A-17 Molecular viscosity vs. Strain rate-500 mm Case II

V. CFD Simulation results of 600 mm extruder with Herschel-

Bulklev's model value-ll:

Extrusion pressure:


2 9 7 e -0 6

2 8 1 e *06

2.65e+06

2 49e+06

2.33e+06

2 1 7e+06

2 01 e+06

1 86e+06

1,70e+06

1.54e+06

1 06e+06

9.00e+057 41 e+05

5 82e + 05

4.23e+05

2 63e + 05

1 04e+055.51 e+04

2.1 4e + 05

Figure A-A-18 Static pressure contour (full view)-600 mm Case II

137

2 97e+OS2.81 e + 0 6 2 6 5 e 4 0 6 2 .4 9 e + 0 6 2 .3 3 e -K )62.170-MD6 2 .0 1 0 4 0 6 1 86e-H36 1 .7 0 0 4 0 6 1 54e406 1 3 8 e 4 0 6 1 2 2 e 4 0 6 1 0 6 e 4 06 9 .0 0 e 4 0 5 7 41 e 4 0 5 5 .8 2 e 4 0 5 4 2 3 e 4 0 5 2 .6 3 e 4 0 5 1 0 4 e 40 5 -5 .51 e 4 0 4 -2 1 4 e 4 0 5

C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .6 9 0 0 e 40 0 )

Figure A-A-19 Static pressure contour (sectional view)-600 mm Case II

-5 00e+O 5-1 4 -1 2 -1 -0 .0 -0 6 -0 4 -0 .2 O

Position (m )

2 00e+O 6

StaticP ressu re

(pascal)

S ta t ic P re s s u re (T im e = 2 6 9 0 0 6 4 0 0 )

Figure A-A-20 Static pressure profile -600 mm Case II


■

9 9 4 e-01 9 44e-018 9 5 e-018 .4 5 e 0 17 9 5 e-017 46e -01

6 9 6 e-01

6 .4 6 e -0 1

5 9 7 e-01

5 .4 7 e-01

4 9 7 e-01

4 4 7 e-01

3 9 8 e-01

3 4 8 e-01

2 9 8 e-01

2 .4 9 e -0 1

1 9 9 e-01

1 49e -01

9 9 4 e -0 2

4 9 7 e -0 2

0 0 0 e + 0 0

C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .6 9 0 0 e 4 0 0 )


II

138

Viscosity profile:


4.00(H-03

2.00e+030 1 2 3 4 5 6

Strain Rate (1/s)

Figure A-A-22 Molecular viscosity vs. Strain rate-600 mm Case II

VI. CFD Simulation results of 500 mm extruder with varying feed

rate:-

a. Feed rate:-15 kgs'1

Extrusion pressure:

2.68a+88 2.54e+08 2.44e+06 2348*06 2 24e+06 2.148+06 2.04e+08 1.838+06 1 83e+08 1.73e+06 1.63e+06 1.53e+0B 1 43e+06 1.33e+08 1.23e+08 1.12e+081 02e+08 8.22e+05 8.20e+05 7 18e+05 6.18e+05 5.17e+05 4.15e+05 3.14e+05 2.13e+05 1.11 e+05 1 01e+04 -9 11e+04 -1 92e+05

Contours of Static Pressure (pascal) (T lm e=5.0400e-01)

Figure A-A-23 Static pressure contour (full view) - feed rate 15 kgs-1

139

2 68e+08 2 54e+0B 2-44e+08 2 34e+082 24e*0B 2 14e+0B 2 04e+081 B3e+081 83e+081 73e+0B 1 83e+0B 1.53C+0B 1 43e+0B 1.33C+06 1.23e+0B 1 12e+06 1 02e+0B 9.22e+05 8 20e+05 7 19e+05 6 18e+05 5 17e+05 4 15e+05 3.14e+05 2 13e+05 1 11e+05 1 01e+04 -9 11e+041 -1 92e+05

m h

Contours of Static Pressure (pascal) (Time=5.0400e-01)


.00e+06

S ta t icP re s s u re

(p a s c a l)

-1 -0 9 -0 8 -0 .7 -0 6 -0 .5 -0 4 -0 .3 -0 .2 -0.1 0

Position (m)

S tatic P re s s u re (T lm e= 5 .0400e-01 )

Figure A-A-25 Static pressure profile- feed rate 15 k g s 1


1 35e*00 1.29e*G0 1.24e«-00 1 19e+001 14e+001 10e+001 05e+001 00e*00 953e-01 9 05e-01 8 58e-018 10e-01 7 62e-01 7 15e-01 6.67e-01 6 19e-01 5 72e-01 5 24e-01 4 76e-01 4 29e-013 81e-Ot3 34e-012 86e-012 38e-011 91e-011 43e-019 53e-024 76e-02 0 00e*00

Contours of Velocity Magnitude (m/s) (Time=5 .0400e-01)


k g s 1140

Viscosity profile:

7 009+03' !' e9T6:006+03

5 00e+03Molecular Viscosi (kg/m

4 000+03

300©+03

2.008+03

1 00e+03

0 00e»0u15 20 25 30

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=5.0400e-01)

Figure A-A-27 Molecular viscosity vs. Strain rate- feed rate15 kgs-1

Results of CFD analysis for feed rate of 19 kgs' 1 are available in Appendix A under Section IV.

a. Feed rate:-25 kgs-1

Extrusion pressure:

2 39e+0B2 27e+062 17e+062 08e+061 98e+061 89e+061 79e+061 70e+0B1.61e+061 61e+06142e+061 32e+061 23e+0B1.14e+061 04e+06947e+058 53e+057 59e+G56 65e+055 7 1 e+054 77e+053 83e+052 89e+051 94e+051 00e+056 25e+03-8 79e+041 82e+052 76e+05

L

Contours of Static Pressure (pascal) (Time=4.2400e-01)

Figure A-A-28 Static pressure contour (full view) - feed rate 25 kgs'1

141

CfflfflEHSSE!239e+08 2.27e*0B 2.17e+O0 2.08e+06 1 98e+08 1.89e+08 1 790+08 1 70e+Q8 1.61e+06 1 51e+0B 1 42e+06 1.32e+08 1.23e+06 1.14e+08 1.04e+06 9.47e+05 8.53e+05 7 59e+05 B.65e+05 5.71e+05 4 77e+05 3.83e+05 2.89e+05 1 94e+05 1 00e+05 6 25e+03 -8 79e+04 -1 82e+05 -2 76e+05

Contours of Static Pressure (pascal) (Time=4.2400e-01) Oct 11. 20


Static 1 2 5 e + 0 6P ressu re

(pascal)

-0 6 -0 .5 -0 .4

Position (m)

S ta t ic P re s s u re (T im e = 4 2 4 0 0 e-01)

Figure A-A-30 Static pressure profile- feed rate 25 kgs'1


Contours of Velocity Magnitude (m/s) (Tim e=4.2400e-01)


k g s 1

142

Viscosity profile:

4.50e+03

4 00e+03

3.50e+03


3.006+03

2.506+03

2.006+03

1 00e+03

5 006+020 10 20 30 40 50 60 70 80

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=4.2400e-01) C

Figure A-A-32 Molecular viscosity vs. Strain rate- feed rate 25 kgs'1

b. Feed rate:-30 Kgs'1

Extrusion pressure:

1,52e+06 1.44e+081 38e+08 t 32e+061 26e+081 20e+06 1 14e+06 1 08e+061 02e+08 959e+05 8 98e+05 8 38e+05 7.78e+05 7 17e+05 657e+05 5 96e+05 5.36e+05 4.76e+05 4 15e+05 3 55e+052 95e+052 34e+05

1 74e+05

1.14e+055 32e+04

-7 14e+03

-6 75e+04

-1 28e+05

-1 88e+05

Contours of Static Pressure (pascal) (Time=5.0400e-01) Oct 17,


143

11 52e+Q8 1 44e*06 1 38e+061 32e*061 26e+08 1 20e*0B 1 14e-*06 1 08e-*-081 02e+06 9 59e+05 8 98e+05 8 38e+05 7 78e+057 17e+05 ; 6 57e+05 \ 5 96e+05 j 5 36e*05 | 4 76e+05 14 15e+05 3 55e+052 95e+05 2 34e*05 1 74e+05 1 14e+055 32e+04 -7 14e+03 -6 75e-*-04 -1 28e+05



1 00e+O6

-1 -0 .9 -0 .8 0 . 7 - 0 6 - 0 5 -0 .4 -0 .3 -0 .2 -0 1 0

Position (m )

S ta t ic P re s s u re (T im e = 5 0 4 0 0 e -0 1 )

Figure A-A-35 Static pressure profile-


feed rate 30 k g s 1

t 52e+Q01 46e+00 141e+001.35e+001.30e+0D124e+001 18e+00 U3e+00 1 07e+00 1.01e+00 9.58e-01 9 01e-01 8.45e-01 7 89e-01 7 32e-01 6 76e-01 6 20e-01 5 B3e-01 5 07e-014 51e-01 3 94e-01 3 38e-012 82e-012 25e-01 1 69e-011 I3e-015 63e-02 0 00e+00

Contours of Velocity Magnitude (m/s) (Time=5.0400e-01) Oct 17. 201


k g s 1144

Viscosity profile:

4.50e+03

4 00e+03

3.50e+03

Molecular 3.ooe+o3Viscosity( k n /m - c l 2.50e+03

1 00e+03

5 00e+020 10 20 30 40 50 60 70 80 90

Strain Rate (1/s)


Figure A-A-37 Molecular viscosity vs. Strain rate- feed rate 30 k g s 1

c. Feed rate:-40 Kgs'1

Extrusion pressure:

6.88e+056 47e+056 IBe+055 84e+055 53e+055 22e+054.90e+054 59e+054 28e+053.97e+053 65e+053.34e+053 03e+052 71e+052.40e+052.09e+051.77e+051 46e+051 15e+05B.33e+045.20e+042 07e+04-1 07e+04-4 20e+047.33e+04

-1.05e+05-1 36e+05-1 67e+05-1 99e+05

Contours of Static Pressure (pascal) (Tim e=5.0400e-01)


145

■ n ^ o iB 89e+u56 47e+u5BIBe+055 84e+055 53e+055.22e+054 90e+054 59e+u54 28e+053.97e+053 65e+053 34e+G53 03e+052.71e+052 40e+052 09e+051 77e+051 46e+051 15e+058 33e+045 20e+042 07e+04-1 07e+04-4 20e+04-7 33e+04-1 05e+05

1 36e+u5-1 67e+05


Figure A-A-39 Static pressure contour (sectional view) - feed rate 40 kgs-1

StaticP ressu re

(p ascal)

S.00e+O5

4 .0 0 e + 0 5

3 .0 0 6 + 0 5

2 .0 0 e + 0 5

1 00e+O 5

0 OOfi +00

-1 0 0 6 + 0 5-1 -0 9 -0 8 -0 .7 -0 6 -0 .5 -0 .4 -0 .3 -0 .2 -0 .1 0

Position (m )

S ta t ic P re s s u re (T im e = 5 .0 4 0 0 e -0 1 ) T

Figure A-A-40 Static pressure profile- feed rate 40 kgs'1


Contours of Velocity Magnitude (m/s) (Time=5.0400e-01) 0 0 17.2011


k g s 1 146

Viscosity profile:

3.506+03

3.006+03


1 0 0 e +03

5 00e+02

0 00e+000 20 40 60 80 100 120

Strain Rate (1/s)


Figure A-A-42 Molecular viscosity vs. Strain rate- feed rate 40 kgs-1

d. Feed rate:-50 Kps'1

Extrusion pressure:

MB

I

3 27e+05 2 31e+05 1 60e+05 8 856+041 706+04-5 446+04 -1 26e+05 -1.976+05 -2 69e+05 -3 40e+05 -4 12e+05 -4 83e+05 -5.556+05 -6 26e+05 -6 97e+05 -7 69e+05 -8 40e+05 -9 12e+05 -9 83e+05 -1 05e+06 -1 13e+06 -1 20e+06 -1.27e+06 -1 34 e+06 -1 41e+06 -1 48e+06 -1 55e+06 -1 63e+06 -1 70e+06

t-5?

Contours of Static Pressure (pascal) (Time=4.8400e-01) Oct

Figure A-A-43 Static pressure contour (full view) - feed rate 50 k g s 1

147

3 27e+05

1 60e+05 8 85e+041 70e+04 -5 44e+04 -1 26e+05 -1 97e+05 -2 69©+05 -3 40©+05 -4 126+05 -4 83e+05 -5 55©+05 -6 260+05 -6 970+05 -7 690+05 -8 40e+05 -9 120+05 -9 83e+05 -1 05©+06 -1 130+06 -1 200+06 -1 27©+06 -1 340+06 -1 410+06 -1 48e+06 -1 55e+06 -1 630+06 -1 70©+06

Contours of Static Pressure (pascal) (Tim e=4 8400e- 01) Oct 18, 2011


-2 00e+05

-4 0 0 e +05

-6 .00e+O 5

-8 0 0 e+ 05

-1 0 0 e+ 06

-1 20e+C 6

•1 40 e+06

-1 60e+O 6

StaticP ressure

(pascal)

- 0 6 - 0 5 -0 .4

Position (m )

S ta t ic P re s s u re (T im e = 4 .8 4 0 0 e -0 1 )



2.15e+00 2.069+00 1 96e+00 1.870+00 1.780+00 1 .680+00 1.590+00 1.500+00 1.400+00 1.310+00 1 .2 2 0 + 0 0 1 . 12 0+ 0 0 1.030+00 9 350-01 8 41 e-01 7 480-01 6 54e-01

K 5 61e-01

" 000e+00

Contours of Velocity Magnitude (nVs) (Tim e=4.8400e-01) Oct 18, 201 ’


kg s 1

148

Viscosity profile:

r

3.00e403

2,50»403

2.006403

M olecularViscosity(kg /m -s)

1.506403

1.006403

5.00e402

0.00640040 60 80 100

Strain R ate (1 /s )

140


Figure A-A-47 Molecular viscosity vs. Strain rate- feed rate 50 kgs-1

VII. CFD Simulation results of 500 mm extruder with varying auger

speed:-

a. Auger speed:-15 rpm

Extrusion pressure:

-1 27e+04

-6 05e+04

-1 08e+05

-1 56e+05

6 OSe+055.61e+05 5 13e+D5 4 65e+05 4.18e+05 3.70e+05 3.22e+05

2 74e+05

2 26e+05

1.79e+05

1.31e+05

8 29e+04

3.51e+04

iS"

a i#!i p

Contours of Static Pressure (pascal) (Time=3.2460e400) Sep 2S

Figure A-A-48 Static pressure contour (full view) - auger speed 15 rpm

149

Contours of Static Pressure (pascal) (Time=3.2460e+00) Sep 29. 2011


: 98 .0 0 e + O 5

7 0Ge+O6

6 O ue+ 05

5 0 0 e+05

StaticP ressure

(pascal) 3 0 0 e+ 05

1 00e+O 5

-1 -0 9 -0 8 -0 7 -0 6 -0 .5 -0 .4 -0 .3 -0 .2 -0 1 0

Position (m)


Figure A-A-50 Static pressure profile- auger speed 15 rpm


750e-017.16e-01079e-O1043e-O10 07e-01 5.72e-01 5.30e-O1 5 00e-01 4 84e-01 4 29e-01 3 93e-01 3 57C-01 3 22e-01 2 86e-01 2 50e-01 2 14e-011 79e-01 1 43e-01

Contours of Velocity Magnitude (m/s) (Time=3.2460e+00) Sep 29. 2011


rpm

150

Viscosity profile:

7 008+03

6 008+03

5.008+03


4.00e+03

3.008+03

2.008+03

1 00e+03

0 00e+0020 25 30 35

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=3.2460e+00)

Figure A-A-52 Molecular viscosity vs. Strain rate - auger speed 15 rpm

b. Auger speed:-20 rpm

Extrusion pressure:

147e+06 1 398+06 1 33e+0B 1 28e+061 22e+081 1Be+06 1 10e+06 1 05e+0B 9 89e+05 932e+05 8 75e+05 8 18e+05 7.60e+05 7 03e+05 646e+05 5 89e+05 5 32e+05 4 75e+05 4 17e+05 3 60e+05 3 03e+05 246e+05 1 89e+05 1 32e+05 7 43e+04 1 72e+04 -4 00e+04 •9 728+04 -1 54e+05

Contours of Static Pressure (pascal) (Time=3.0600e+00) Sep 27


151

I 47e+0BI 39e+u81 33e+061 28e+0BJ 22e+0B1 1Be+061 lOe+OB1 05e+0B

9.32e+058 75e+05B.18e+057 60e+057 03e+05

5 89e+055.326+054 75e+054 17e+053 60e+053 03e+052 46e+05I 89e+051 32e+057 43e+04

L1.72e+04-4 00e+049 72e+04

-1.54e+05

Contours of Static Pressure (pascal) (Tim e=3.0600e+00) Sep 27.


6 OOe+05

0 OOe+OO

1.00e+08

-2 .0 0 8 + 0 5-1 -0 .9 -0 .8 -0 7 -0 .6 -0 5 -0 4 -0 .3 -0 .2 -0 1 0

Position (m)

StaticP ressu re

(p ascal)




Contours of Velocity Magnitude (m/s) (Tlm e=3.0600e+00) Sep 27.


rpm152

Viscosity profile:

6 006+03

5.00e+03

Molecular 4.ooe+03Viscosity(kg/m-s) 3006+03

2 00e+03

1 00e+03

0 5 10 15 20 25 30 35 40 45 50 55

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=3.0600e+00) S


c. Auger speed:-25 rpm

Extrusion pressure:

Contours

202e+06 1 92e+06 1 84e+06 1 76e+06 1 68e+06 1 61e+06 1 53e+06 145e+06 1 37e+06 1 30e+06 1 22e+06 1.146+06 1 06e+06 9 86e+05 909e+05 831e+05 7.54e+05 6 76e+05 5.99e+05 521e+05 4.436+05 366e+05 288e+05 2.11e+05 1 33e+05 555e+04 -2 216+04 -9 96e+04 -1 77e+05

of Static Pressure (pascal)

Yu

(Time=9.6799e-01) Oct 07,2


153

■SUDl&I2 02e*06 1 928+06 1 84e+06 1 76e+06 1 686*-06 1 61e+06 1 53e+06 1 45e+06 1 37e+06 1.308+06 1 22e+061 14e+06„ 1 068+06 986e+05 9 09e+05 8 31e+05 7 54e+05 6 76e+05 . 5 99e+05 5.21e+054 43e+053 66e+052 88e+05 2 11e+05 1 33e+055 55e+04 -2218+04 -9 96e+04 -1 77e+05

Contours of Static Pressure (pascal) (Time=9.6799e-01) Oct 07. 20'


StaticP ressu re

(pascal)

2 00e+06

1 75e+06

1.50e+O6

1 25e+C6

1 00e+O6

7 50e+05

5 0 0 e + 0 5

2 5 0 e +05

0 OOe+OO- 0 6 -0 .5 - 0 4

Position (m )

S ta t ic P re s s u re (T im e = 9 .6 7 9 9 e -0 1 )



1 11O+00 1.060+001 02e+00 980e-019410-01902e-01 8 63©-01 8230-01 7 840-01 7.450-01 7.060-016 67©-01 627©-01 5 880-01 549©-01 5 10©-01 4 71©-01 4 31e-01 3 92©-01 3 53©-01 3 14©-012 74e-012 35e-01 1 96e-01 1 570-01 1 18e-017 84©-023 92©-02 0 00e+00

Contours of Velocity Magnitude (m/s) (Time=9.6799e-01)


rpm

154

Viscosity profile:

7.00e+03

6.00G+03

500e+03

M olecular 4 .000+03 Viscosity(kg /m -s) 3.006+03

2.006+03

1.00e+03

0.00e+0010 15 20 25 30 35

Strain R ate (1/s)

50

Molecular Viscosity vs. Strain Rate (Time=9.S799e-01)


• Results of CFD analysis for auger speed of 30 rpm auger are

available in Appendix A under Section IV.

d. Auger speed:-40 rpm

Extrusion pressure:

2 79e+08

2 64e+06

2 49e+06

2 34e+06

2 I8e+06

2.03e+0B

1 88e+06

1.73e+06

1 58e+06

1 43e+06

1 28e+06

1.13e+0B

9.79e+05

8.29e+05

6 78e+05

5 27e+05

3.77e+05

2 26e+05

7 52e+04

-7 55e+CM

-2 26e+05u

Contours of Static Pressure (pascal) (Time=1,5020e+00)


155

2.79e+0B 2 65e+0B2 54e+0B2 43e+06 2 33e»0B2 22e+0B 2.11e+O0 2.01e+0B 1 .BOe+OB 1 79e*06 1.69e+06 1 58e+06 1 4Be+06 1 37e+06 1 26e+06

I 1 16e»06 1 05e+06 9 44e+058 37e+05

; 7 31e+05 I 6 25e+05

5 18e+05 4 12e+053 06e+05 1.99e*059 29e+04 -1 35e-04 -1 20e*05 -2 26e+D5



-0 .6 - 0 5 - 0 4

Position (m )

S ta t ic P re s s u re (Tirr»e=1 5 0 2 0 e + 0 0 )



t 76e+G0 1 69e+0Q

Contours of Velocity Magnitude (m/s) (Time=1.5020e+00) Oct 03. 20

Figure A-A-66 Flow velocity during extrusionfsectional view)-auger speed 40

rpm156

Viscosity profile:

7 006+03BE

6 00e+03

5 00e+03


4.00e+03

3.006+03

2.006+03

1 006+03

0 006+0015 20 25 30 35

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=1,5020e+00)


e. Auger speed:-50 rpm

Extrusion pressure:

2 12e+06 2.00e+06 1 92e+06 1 84e+061 76e+061 67e+061 59e+0B 1.51e+06 1 42e+06 1 34e+06 1 26e+06 1.18e+06 1 09e+06 1 01e+06 9 27e+058 45e+05 7 62e+05 6 79e+05 5.96e+05 5 13e+05 4.30e+05 347e+05 264e+05 1 82e+059 86e+04 1 58e+04 -6 71e+04 -1 50e+05 -2 33e+05

Contours of S tatic Pressure (pascal) (T im e -2 6790e-01)


157

m2 12e+06 2 00e+08 I 92e*06 I 94e+0B 1 7Be+06 1 67e+06 1 58e+0B 1 51e+06 1 42e+06 1 34e+06 1 28e+06 1 IBe+OB , 1 09e+0B ;1 Ole+06 9 27e+05 845e+05 7 62e+05 6 79e+05 5 9Be+05 5 13e+05 4 3De+05 347e+052 64e+05 1 82e+05 9 86e+04 I 5Be+04 -6 71e+04 -1 50e+05 -2 33e+05

Contours of Static Pressure (pascal) (Time=26790e-01) Oct 05.201


-1 -0 9 -0 8 -0 7 -0 6 -0 5 -0 4 -0 3 -0 .2 -0.1 0

Position (m )

S ta t ic P re s s u re (T im e = 2 6 7 9 0 e -0 1 )


Material flow pattern:3.85e+003.67e+003.54e+003.40e+003.26e+003.13e+00 2.99e+00 2.86e+00 2.72e+00 2.58e+00 2.45e+00 2.31e+00 2.18e+00 2.04e+00 1 90e+00 1.77e+00 1 63e+00 1 50e+00 1 36e+00 1 22e+001 09e+00 9 52e-01 8 16e-01 6 80e-01 5 44e-01 4 08e-012 72e-01 1 36e-01 0 00e*00

Contours of Velocity Magnitude (m/s) (T ime=2 6790e-01)


rpm158

Viscosity profile:

4 50e+03

4.00e+G3

3.50e+03

Molecular 3.00e+03

Viscosity(kg/m-s) 2.50e+03

2 00e+03

1 50e+03

1 00e+03

5 00e+0220 30 40 50

Strain Rate (1/s)

Molecular Viscosity vs Strain Rate (Time=2 6790e-01)


VIII. CFD Simulation results of 500 mm extruder with varying auger

pitch distance:-

a. Pitch distance 338.012 mm

Extrusion pressure:

3 .4 2 e + 0 6

3 .2 3 e + 0 6

3 .0 4 e + 0 6

2 .8 5 e + 0 6

2 .6 6 e + 0 6

2 .4 7 e + 0 6

2 .2 9 e + 0 6

2 .1 0 e + 0 6

1 .9 1 e + 0 6

1 .7 2 e + 0 6

1 .5 3 e + 0 6

1 ,3 4 e + 0 6

1 .1 5 e + 0 6

9 .6 5 e + 0 5

7 .7 7 e + 0 5

5 .8 8 e + 0 5

4 .0 0 e + 0 5

2 .1 1 e + 0 5

2 .2 4 e + 0 4

- 1 .6 6 e + 0 5

- 3 .5 5 e + 0 5Z— 1— x

Y

Contours o f Static Pressure (pascal) (T im e = 2 .5 0 5 0 e + 0 0 )

Figure A-A-73 Static pressure contour (full view)-pitch 338.012 mm

159

3 4 2 e - 0 G

3 .2 3 e + 0 6

■

■ 2.11 e+ 05

2 .2 4 e -0 4

-1 66e-*-05 -3 55 e + 0 5


Figure A-A-74 Static pressure contour (sectional view)-pitch 338.012 mm

0 OOe+OO

-1 -0 9 -0 .8 -0 .7 -0 .6 - 0 5 -0 .4 -0 .3 -0 .2 -0 .1 0

P o s itio n (m )

S ta t ic P re s s u re (T im e=2.5050e-H D 0)

Figure A-A-75 Static pressure profile-pitch 338.012 mm


1 3 6 e -0 0

1 2 9 e + u 0

C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .5 0 5 0 e + 0 0 )

Figure A-A-76 Flow velocity during extrusionfsectional view)-pitch 338.012mm160

Viscosity profile:

9.00e+03

8.00e+03

7.00e+03

6.00e+03

M olecu lar 5.ooe+o3 Viscosity

4.00e+03

3.00e+03

2.00e+03

1.00e+0315 20 25 30


Molecular Viscosity vs. Strain Rate (Time=2.5050e+00)

Figure A-A-77 Molecular viscosity vs. Strain rate-pitch 338.012 mm

• The results of CFD analysis with auger pitch distance 292 mm are

presented in Appendix A- section II.

IX. CFD Simulation results of 500 mm extruder with varying die

desiqn:-

a. Die type-l

Extrusion pressure:

3 .5 5 e + 0 6

3 .3 5 e + 0 6

3 .1 4 e + 0 6

2 .9 3 e + 0 6

2 .7 2 e + 0 6

2 .5 1 e + 0 6

2 .3 0 e + 0 6

2 .0 9 e + 0 6

1 .8 9 e + 0 6

1 6 8 e + 0 6

1 .4 7 e + 0 6

1 .2 6 e + 0 6

1 .0 5 e + 0 6

8 .4 5 e + 0 5

6 .3 6 e + 0 5

4 .2 8 e + 0 5

2 .1 9 e + 0 5

1 .1 1 6 + 0 4

-1 .9 7 e + 0 5

4 .0 6 e + 0 5

6 .1 4 e + 0 5

Contours o f S tatic Pressure (pascal) (T im e = 2 .5 0 0 0 e + 0 0 )

Figure A-A-78 Static pressure contour (full view)-die type-1

161

3.55e+063 35e+06 3 14e+06 2 9 3 e +06 2.72e+06 2 5 1 e+06 2 3 0 e + 06

2 0 9 e + 0 6

1 8 9 e + 0 6

1 6 8 e + 0 6

1 47 e + 0 6

1 2 6 e + 0 6

1 05e+O 6

8 4 5 e + 0 5

6 3 6 e + 0 5

4 2 8 e + 0 5

2 1 9 e + 0 5

1.11 e + 0 4

-1 9 7 e + 0 5

-4 .0 6 e + 0 5

- 6 .1 4 e + 0 5


Figure A-A-79 Static pressure contour (sectional view)-die type-1

S ta ticP re s s u re

(p a s c a l)

TffieOEf2.50e+O6

2.00e+06

1 50e+O6

1 00e+06

5 0 0 e + 0 5

-5 0 0 e + 0 5

-1 -0 9 -0 .8 -0 .7 -0 .6 -0 .5 -0 4 -0 3 -0 .2 -0.1 0

P o s itio n (m )

0 00e+O 0


Figure A-A-80 Static pressure profile-die type-1


1 35e+O01 28 e-tOO1 2 2 e+ Q 01 1 5 e + 0 01 0 8 e + 0 0

1.01 e+OO9 .4 6 e -0 1

8 .7 8 e -0 18.11 e -017 .43e -01b.7be-U 1B O8e-O1

5 4 0 e -0 14 .7 3e -01

4 0 5 e -0 13 3 8 e -0 1

2 70e-012 O Je-O I

1 3 5 e -0 16 7 6 e -0 2□ OOe-HJO

C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 5 0 0 0 e + 0 0 )

Figure A-A-81 Flow velocity during extrusion (sectional view)-die type-1

Viscosity /profile:

8 00e+03

7.00e+03

6 .00e+03

5 .00e+03Molecular Viscosity 4.ooe+o3 (kg/m-s)

3 .00e+03

2 .00e+03

1 00e+03

0 .0 0 e + 0 020 40 60 80 100

Strain Rate (1/s)120 140

Molecular Viscosity vs. Strain Rate (T im e=2.5000e+00) Jul

Figure A-A-82 Molecular viscosity vs. Strain rate- die type-1

b. Die type-lll

Extrusion pressure:

3.50e+06

3.29e+06

3.09e+06

2.88e+06

2.68e+06

2.47e+06

2.27e+06

2 06e+06

1.85e+06

1.65e+06

1,44e+06

1,24e+06

1 03e+06

8.26e+05

6.20e+05

4.14e+05

2.09e+05

3.05e+03

-2.03e+05

-4.08e+05

-6.14e+05

Contours of Static Pressure (pascal) (Tim e=2.5000e+00)

Figure A-A-83 Static pressure contour (full view)-die type-ill

163

C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 5 0 0 0 e + 0 0 )

3 50e+063 2 9 e-HJB

3 .0 9 e + 0 6

2 .8 8 e + 0 6

2 68e+Q 6

2 4 7 e + 0 62 .2 7 e + 0 6

2 0 6 e + 0 6

1 8 5 e + 0 6

1 .6 5 e + 0 6

1 ,2 4 e + 0 6

1 0 3 e + 0 6

8 .2 6 e + 0 5

6 2 0 e + 0 5

3 .0 5 e + 0 3

4 0 8 e + 0 5

Figure A-A-84 Static pressure contour (sectional view)-die type-ill

3 .5 0 e + 0 6

3 0 0 e + 0 6

2 5 0 e+06

2 .0 0 e + 0 6

S ta tic P re s s u re 1 50e+o6

(p a s c a l)1 0 0 e + 0 6

5 00e+O 5

0 0 0 e + 0 0

-5 .0 0 e + 0 5-0 .9 - 0 8 -0 .7 - 0 6 -0 .5 -0 .4 -0 .3 -0 .2 -0.1

P o s itio n (m )

S ta t ic P re s s u re (T im e = 2 5000e-+C0)

Figure A-A-85 Static pressure profile-die type-ill


1 0 8 e+ O 0

1 0 1 e+OO 9 46e -01

8 78e-01 8 .1 1 e-01

7 43e-01

6 7 6 e-01 S 08e -01

5 40e-01 4 .7 3 e-01

4 0 5 e-01 3 3 8 e-01

2 70e-01 2 0 3 e-01

1 35e-01

B .7 6 e -0 2 0 OOe+OO

1 .3 5e+ O 0

1 28e+ O 0 1 22e+ O 0

1 15e+O 0


Figure A-A-86 Flow velocity during extrusion (sectional view)-die type-lll164

Viscosity profile:

0 o u tle t

9 .00e+03

8.00e+03

7.00e+03

6.00e+03


3 .0 0 e + 0 3

2 .0 0 e + 0 3

1 0 0 e + 0 30 5 10 15 2 0 2 5 3 0 3 5 4 0 4 5

Strain Rate (1/s)

M olecular Viscosity vs. Strain R ate (T im e = 2 .5 0 0 0 e + 0 0 ) Jul

Figure A-A-87 Molecular viscosity vs. Strain rate- die type-lll

X. CFD Simulation results of 600 mm extruder with varying feed

rate:-

a. Feed rate:-11.8 kgs'1

Extrusion pressure:

2 9 7 e * 0 6

2 8 1 e -0 6

2 65e<-06

2 4 9 e + 0 6

2.33e+06

2 17 e+06

2 01 e+06

1 8 6 e -0 6

1 70e+06

1 S4e+06

1

1

1 06e*06

9.00e+057.41 e+05

5.82e+05

4.23e+05

2.63e+05

1 04e -0 5

-5.51 e+04

-2.1 4e+05


Figure A-A-88 Static pressure contour (full view) - feed rate 11.8 k g s 1

165

2 9 7 e + 0 6

2.81 e + 0 6

2 6 5 e + 0 6

2 .4 9 e + 0 6

2 3 3 e + 0 6

2 1 7 e + 0 6

2 01 e + 0 6

1 8 6 e + 0 6

1 70e+ O 6

1 5 4 e + 0 6

1 .3 8 e + 0 6

1 22e+ Q 6

1 06e+ O 6

9 0 0 e + 05

7.41 e+OS

5 8 2 e + 0 5

4 .2 3 e + 0 5

2 6 3 e + 0 5

1 04e+ O 5

-5 .51 e + 0 4

-2 1 4 e + 0 5


Figure A-A-89 Static pressure contour (sectional view) - feed rate 11.8 kgs-1

• 1 4 -1 .2 •0 .8 - 0 6

P o s itio n (m )

S ta t ic P re s s u re (T im e=2.6900e-+O 0)

Figure A-A-90 Static pressure profile- feed rate 11.8 k g s 1


9 .9 4 e-01

9 .4 4 e -0 1 8 9 5 e-01

8 45e -017 .9 5 e-01

7 .4 6 e-01 6 9 6 e-01

6 46e -01 5 9 7 e-01

5 4 7 e-01

4 9 7 e-01

4 4 7 e-01

3 9 8 e-01

3 .4 8 e-01

2 98e-01

2 49e-01

1 99e -01

1 4 9 e-01

9 9 4 e -0 2

4 9 7 e -02

0 0 0 e + 0 0

L I 1 11r r t i


Figure A-A-91 Flow velocity during extrusion (sectional view)-feed rate 11.8

k g s 1166

Viscosity profile:

1.60e+04

1.40e+04

1.20&+-04

1.00e+04Molecular Viscosity 8 ooe+03 (kg/m-s)

6.00e+03

4 00e+03

2.00e+030 1 2 3 4 5 6 7

Strain Rate (1/s)

Figure A-A-92 Molecular viscosity vs. Strain rate- feed rate 11.8 k g s 1

b. Feed rate:-19 kgs'1

Extrusion pressure:

■ 2 04e+06

1,93e+06

1.81 e+06

1,70e+06

1 59 e+06

1 48e+06

1 37e+06

1 26e+06

1 14e+06

1 03e+06

9 20e+05

8 08e+05

6.97 e+05

5 85e+05

4.73e+05

, 3 62e+05

| 2 50e+05

H1.38e+05

2 67e+04

-8 50e+04

I -1 97e+05


Figure A-A-93 Static pressure contour (full view) - feed rate 19 k g s 1

y< &

167

2 U 4 e + 0 6

1 9 3 e + 0 6

1 -81 e + 0 6

1 70e+ O 6

1 5 9 e + 0 6

1 4 8 e + 0 6

1 37 e + 0 6

I 2 6 e + 0 6

1 .1 4 e + 0 6

1 0 3 e + 0 6

9 2 0 e + 0 5

8 .0 8 e + O 5

6 9 7 e + 0 5

5 .8 5 e + 0 5

4 7 3 e + 05

3.62e-H J5

2 .5 0 e + O 5

1 3 8 e + 0 5

2 .6 7 e + 0 4

-8 5 0 e+ O 4

-1 .9 7 e + 0 5

r j

C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .6 7 5 0 e + O 0 )

Figure A-A-94 Static pressure contour (sectional view) - feed rate 19 kgs-1

-5 0 0 e + 0 5- 1 4 -1 .2 -1 -0 8 -0 6 -0 4 -0 2 O

P o s itio n (m )

StaticPressure

(pascal)

S ta t ic P re s s u re (T im e = 2 6750e-H30)



9 91 e-01

9 42e -01 8 .9 2 e-01

8 43e -01 7 .9 3 e -0 1

7 .4 4 e-01 6 94e -01

6 44e-01 5 .9 5 e-01 5 45e -01

4 9 6 e-01 4 4 6 e-01

3 9 7 e-01 3 .4 7 e -0 1

2 9 7 e-01 2 48e-01

1 9 8 e-01 1 49e-01

9 91 e -02

4 9 6 e-02 0 OOe+OO

1 1 1 ]

C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .6 7 5 0 e + 0 Q )


k g s 1

168

Viscosity profile:

1.60e+04

1.40e+04

1 20e+04

1 00e+04

US t - t : .

Molecular Viscosity s ooe+03 (kg/m-s)

6 00e+03

4 .00e+03

2 00e+034 6 8 10

Strain Rate (1/s)12 14

Molecular Viscosity vs. Strain Rate (Tim e=2.6750e+00) Feb 23. 2011ANSYS FLUENT 12.1 (3d. pbns. dynamesh. lam. transient)

-1Figure A-A-97 Molecular viscosity vs. Strain rate- feed rate 19 kgs

XI. CFD Simulation results of 600 mm extruder with varying Auger

speed:-

a. Auger speed:-30 rpm

Extrusion pressure:

444e+06 3 24e+06 2 35e+06 t 45e+065 55e+05-3 41e+05 -1 24e+0B -2 13e+06 -3 O3e+OB -3.92e+06 -4 82e+06 -5 71e+06 -6.61 e+06 -7 50e+06 -8 40e+06 -9.30e+O6 -1 02e+07 -1.11 e+07 -1 20e+07 -1 29e+07 -1 38e+07 -1 47e+07 -1 56e+07 -1 65e+07 -1 74e+07 -1 83e+07 -1 91e+07 -7 00e+07 -2 09e+07

IContours of Static Pressure (pascal) (Time=1.5100e+00)


169

4 44e*06 3 240*06 2 35©*06 1 45e*065 55©*05 -3 410 *0 5-1 240*06-2 130*06 -3 030*06 -3 92e*06 -4 82e*06 -5 71e*06 -6 61e*06 -7 50e+06 -8 40e *0 6 -9 30©*06 -1 02©*07 -1 110*07 -1 20©*07 -1 29©*07 -1 380*07 -1 47e *0 7 -1 560*07 -1 650*07 -1 74©*07 -1 83e*07 -1 910*07 -2 00©*07 -2 090*07

wr

ST"

M B J/KM1 1

S /

■ . H i

TX— z

Contours of Static Pressure (pascal) (Tim e=1.5100e+00) Oct 31, 2011


■ ' :s d re \*M n f2 - i

StaticP ressure

(pascal)

6 0 0 e +06

5 .0 0 e + 0 6

4 00e+O 6

3 0 0 e + 0 6

2 0 0 e + 0 6

1 0 0 e + 0 6

0 OOe+OO

-1 OO e + 0 6

i

- 0 8 - 0 6

Position (m )

S t a t ic P r e s s u r e (T im e = 1 5 1 0 0 e + 0 0 )

Figure A -A-100 Static pressure profile- auger speed 30 rpm


1.72e+00 1 64e+00 1 58e+00 1 52e+0Q 1 46e+00 1 40e+Q0 1 33e+00 1 27e+00 1 21e+00 1 15e+00 1 09e+001 0 3 e*00 9 71e-01 9 10e-01 8 49e-01 7 89e-01 7 28e-01 6 67e-01 6 07e-015 46e-01 4 85e-01 4 25e-01 3 64 e-01 3 03e-012 43e-01 1 82e-01 1 21e-016 07 e -0 2 0 00e+00

1 1 1 n

l i r tu

Contours of Velocity Magnitude (rrVs) (Tim e=1.5100e+00) Oct 31, 2011

Figure A-A-101 Flow velocity during extrusionfsectional view)-auger speed

30 rpm

170

Viscosity profile:

1.60e+04

1.40e+04

1.20e+04

1.00e+04

M olecular Viscosity 8 ooe+03 (kg /m -s )

6.00e+03

4.00e+03

2.00e+034 5 6 7 8 9 10


Molecular Viscosity vs. Strain Rate (Time=1.5100e+00) O

Figure A-A-102 Molecular viscosity vs. Strain rate- auger speed 30 rpm

XII. CFD Simulation results of Trial:1 experimental set up:-

Extrusion Pressure:

i.2s«+06 . . 1.16«+06

1.07*+06 9.80*405

8.89*405 7.98*405

7.07e+O5

6.16*405 5.25*405

4.34*405 |3.43*405 I 2.52e+051.61*405 ^7.03e+04 -2.06e+O4

-1.12e+05

-2 .03*405 -2.93e+05

-3.84e+05

-4.75e+05

*

L ,

Contours of Static Pressure (pascal) (Time=2.4840e+00) Jan 16. 2012

Figure A-A-103 Static pressure contour (full view)-scaled extruder-T 1

171

■ 1.34e+06 1.256+06 1.16e+06 1.07e+06 9 80e+05 8.89e+05

7.98e+05 7.07e+05 6.16e+05 5.25e+05 4 34e+05 3.43e+05 2.52e+05 1.61 e+05 7.03e+04 -2.06e+04 -1.12e+05 -2.03e+05 -2.93e+05 -3.84e+05 -4.75e+05

IM riY F IT

LContours of Static Pressure (pascal) (Time=2.4840e+00) Jan 16. 2012

Figure A-A-104 Static pressure contour (sectional view)-scaled

extruder-T1

Material flow pattern:1.81 e-01 1 72e-01 1 63e-01 1 54e-01 1 45e-01 1.360-01 1.270-01 1 18e-011 09e-01 9 980-02 9.07e-02 8.17O-02 7 260-02 6 350-02 5 440-02 4.54 e-02 3 63e-022 7 2 0 -02

1 81 0 -0 2 9 .0 7 e -0 3 0.00e+00

C o n to u rs o f V e lo c ity M a g n itu d e (m /s) (T im e = 2 .4 8 4 0 e + 0 0 ) Ja n 1 6 .2 0 1 2


extrude r-T1

Viscosity profile:

\M olecu larV iscosity(kg /m -s )

8.00e+03

6.006+03

4 .00e+03

2.00e+03

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Tlm e=2.4840e+O 0)

Figure A-A-106 Molecular viscosity vs. Strain rate-scaled extruder-T1172

XIII. CFD Sim ulation results of Trial:2 experimental set up

Extrusion Pressure:

5 84e+05

l 545e+055 05e+05

6Be+054 26e+053-86e+053 47e+05

3 07e+052 68e+05

2 28e+05

t 89e+05

1 49e+05

t 10e+05

7 01e+04

3 06e+04-8 97e+034 35e-U4

-8 81e+04

-1 28e+05

- I 67e+ 05

2 07e+05

Y


Figure A-A-107 Static pressure contour (full view)-scaled extruder-T25 84e-05

5450-055 05e+054 669-05

4 26e-05

3860+05

3470-05

3 0 7 e -0 5

2 680-05

2 280+05

1 890-05

1 490-05

1 10e+05 7 01e-043 06e-04

-8 970-03

-4 85e-04

-8 81e-04

-1 280-05

-1 67e-05

-2 07e-05

Contours of Static Pressure (pascal) (Time=2.4000e+00) Mar 02. 201

Figure A-A-108 Static pressure contour (sectional view)-scaled

extrude r-T2

173


v 209e-011980-011880-011.780-01

1670-01

1.570-01

1460-01

1 360-01

1250-01

1 150-01

1 040-01

940O-02

8 360-02 7 31 e-02

6 270-02

5 220-02 4 18e-02

3 13e-022 09e-02

1 04e-02 OOOe-OO

2 X

Contours of Velocity Magnitude im/si (Time=2.4000e+00) Mar 02. 201

Figure A-A-109 Flow velocity during extrusion (sectional view)-scaledextruder-T2

Viscosity profile:

9.50*403

9.00*403

8.50*403

8.00*403

7.50*403

7.00*403

6.50*403

6.00*403

5.50*403

5.00*403

4.50e-K)3


0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Strain Rate (1/s)

Molecular Viscosity vs. Strain Rate (Time=2.4000e+00) It

Figure A-A-110 Molecular viscosity vs. Strain rate-scaled extruder-T2

174

I. Stress distribution pattern in 430 mm extruder barrel-for applied

load of 1.8 MPa


I- tfefid banii 140l-Ut%*W3

i w»l) am

c) ADI

Figure A-B- 1 Stress induced in barrel @1.8 MPa load

176

II. Deformation pattern in 430 mm extruder barrel-for applied load of

1.8 MPa:-


ADI

Figure A-B- 2 Deformation in barrel @1.8 MPa load

III. Stress distribution pattern in 430 mm extruder distance piece- for

applied load of 1.8 MPa:-

23/11/2112 I

a) Structural steel

177

b) GCI

ey&Wiaa

(

Figure A-B- 3 Stress induced in distance piece @1.8 MPa load

IV. Deformation pattern in 430 mm extruder distance piece -for

applied load 1.8 MPa


A

c) ADI

Figure A-B- 4 Deformation in distance piece @1.8 MPa load

178

V. Stress distribution pattern in 430 mm extruder liner- for applied

load of 1.8 MPa:-


Figure A-B- 5 Stress induced in liner @1.8 MPa load

VI. Deformation pattern in 430 mm extruder liner -for applied load of

1.8 MPa:-


179

c) ADI

Figure A-B- 6 Deformation in liner @1.8 MPa load

VII. Stress distribution pattern in 430 mm extruder auger shaft- for

applied load of 1.8 MPa:-


c) ADI

Figure A-B- 7Stress induced in auger shaft @1.8 MPa load

180

VIII. Deform ation pattern in 430 mm extruder auger shaft -for applied

load of 1.8 MPa:-

c) ADI

Figure A-B- 8 Deformation in auger shaft @1.8 MPa load

a) Structural steel

181

Appendix-C

Brick industry and the brick-makingprocess

182

Prospects for global brick industryGlobally the ceramic industry is considered to be among the other major

revenue yielding industrial sectors, which offers significant contribution to the

economy by creating jobs and income. Brick being the favourable

construction material, brick industry shares the major percentage of output

produced within this sector. The global brick production has increased rapidly

over the past few decades, due to increase in demand in the housing market

from both developed and developing countries. Of the various countries that

produce bricks, China remains the largest producer of bricks with an

estimated production of more the 700 billion bricks in 2000 and showing an

increasing trend for the future [CESST, 2000]. India remains in the second

place with more than 140 billion bricks being produced per year [Asian

Institute of Technology, 2003]. The other major producers include USA,

which produced around seven to nine billion bricks during the year 2010

[Madehow, 2012]. Ceramic industries in European Union (EU) do play a

significant role in the global market for producing quality ceram ic products. It

accounts for 25% of the total global production [European ceramic Industry

Association, 2012]. The major producers in EU include U.K, Spain,

Germany, France, Italy, Czech Republic, Poland and Hungary.

Given the scale of production capacities of brick industries globally, it is

clearly understandable that the amount of energy consumed by brick

industries is high. It is also considered to be one among the other major

energy intensive industries that uses fossil fuels, coal and gas for its various

operations.

U.K. Brick industry- future prospect and challengesIn 2010 the U.K brick industry was valued to be £395 million annually, and it

was predicted to rise on an average of 4% over the next five years and is

expected to reach £471 million by 2015 and is expected to grow further in the

future [AMA research limited 2011]. Gas and coal are the major sources of

fuel used in UK brick industries [Department of Technology and Industry-

2006], and the energy consumed by the industry accounts for 1.5% of the

total energy consumed by all manufacturing industries and it is estimated to

183

be approximately 5.4TWh [Brick Development Association, 2011]. It

accounts for more than 30% of the total cost incurred by the industry

[European Ceramic Industry Association, 2012].Though it appears to be

less in value, considering the current global situation on the availability of fuel

sources and the predicted future demand for bricks, it is a very significant

amount.

The other major challenges faced by the brick industries globally and in the

U.K include reduction in the level of energy consumption and pollutants

(mainly C 02, Hydrogen fluorides and particulates) released from its various

processes. Through the use of advanced technologies, improved machines,

operating procedures and energy regulation policies, the modern brick

industries are considered to be more energy efficient compared to what was

available in the early 1970's. A typical energy consumption pattern of UK

brick industries from 1970-2010 is presented in Figure A -C -1.

1 00 ,000 -r

— Total industrial energy in primary energy equivalents

90,000 Total industrial energy consumption

80,000

| 70,000<o>3ST 60,000O0 tf>01 50,000cco§ 40,000<0 «0 3

£ 30,000r -

20,000

10,000

20101970 1975 1985 1990 1995 2000 20051980

Figure A-C- 1 Energy consumption pattern of U.K brick industries

[Source: DECC, U.K 2011]

Though the energy trends indicate that there is a significant reduction in the

energy consumed, the growing concerns about the climate change and

implementation of new environmental legislations has left the UK brick

industries to face a tougher challenge in-terms of reducing the energy usage

184

and its impact on environment. Hence it is worth looking at what makes this

industry energy intensive, which will be dealt with, further in this chapter.

Brick manufacturingThe process of brick manufacturing is a very complex process. It involves the

use of heavy and rugged high performance power consuming machines and

tools, right from obtaining raw materials to the finished product. A simple

overview of the various process involved in the brick manufacturing is

discussed below.

Manufacturing of bricks briefly involves the following key processes:

• Mining raw materials

• Storage of raw materials

• Preparation of raw materials

• Shaping

• Surface treatment

• Cutting

• Drying

• Firing

• Packing and despatch.

Figure A-C- 2 shows a simple schematic representation of various steps

involved in a typical brick manufacturing process.

185

The Process of Brickmaking (extrusion)

botching & mixing d cow «no*j*ial* (lo c ru ae bricfc body mix)

hotdng <oo«nturmetdryw

lunneIM n

Figure A-C- 2 Typical brick making process flow diagram

[Source: Boral Limited 2002]

Mining raw materials

Clay and loam have been used for making bricks and other ceramic products

for over one thousand years. It is formed by erosion and weathering of rocks,

and gets deposited in different places due to the action of water and wind.

Hence the major mineral constituents of clay are rock minerals [Bender and

Handle, 1982]. Depending upon the geographical location and age of

deposit, the mineral and chemical composition of clay varies significantly and

has a major influence on its flow characters during shaping and drying and in

the aesthetics (like appearance and colour) of the final finished products.

Depending upon the raw material used and applications, bricks are broadly

classified into three different types [Petavratzi and Barton, 2007], namely:

• Clay bricks (Burned bricks):- This includes common building brick,

facing brick, glazing brick, fire brick, flooring brick and Hollow brick etc.

• Cementitious bricks: - This includes bricks that are made up of

cementitious material, which gets its hardness by chemical reaction-

Example: - sand lime brick and sewer brick.

186

• Adobe bricks: - These types of bricks are sun dried bricks, unlike burned

bricks which are dried in special chambers called Kilns (will be reviewed later

in this chapter). The major constituent includes calcareous sandy clay or any

alluvial desert clay with good plastic properties.

The chemical composition of typical pure clay will contain the following

substances in respective proportions as indicated [Petavratzi and Barton,

2007].

• Silica (50-60%)

• Alum ina (20-30%)

• Lime (2- to 5%)

• Oxide of iron (5- 6%, but not greater than 7%)

• Magnesia (<1%)

It is clearly evident from the chemical composition that the major constituent

of clay is silicates. Based on the mineralogical composition and presence of

other chemical substances, clay minerals are classified into various groups

as shown in Figure A-C- 3,

SILICATES

Tectosilicates (Framework silicates)* Zeolites* Quartz* Feldspars

Phyllosilicates (Sheet silicates)

Other silicates

1:1 Phyllosilicates Kaolinite-serpentine

2:1 Phyllosilicates

Kaolinite subgroup* Kaolinite* Halloysite* Dickite* Nacrite

2:1 Inverted ribbons♦ Sepiolite• Palygorskite (attapulgite)

Talc- Pyro p hyl I ite Smectitesl I l

Vermiculites Chlorites Micas

Serpentine subgroup♦ Chysotile♦ Antigorite♦ Lizardite♦ etc.

D ioctahedral smectites• M ontm orillonite• BeidelHte• Nontronite

Dioctahedral m icas• Muscovite* ante♦ Phengite» etc.

Trioctahedral smectites Trioctahedral m icas• Saponite • Biotit e• Hectorlte * etc.• Sauconite

Figure A-C- 3 Classification of clay mineral groups

[Source: Punmia and Jain, 2005]

187

The major constituents of pure clay minerals are Kaolin and Shale and small

amount of additives like manganese, barium. Other additives are blended

with clay to produce different colours [Punmia and Jain,2005].

The major mineral constituent of the clay used in making bricks, in the United

Kingdom, includes,

• Kaolinite.

• lllit.

• lllite.

The clay used in brick manufacturing is extracted from "Quarries". Quarry is

a place where natural deposits of clay and mineral occur in significant

proportion, considered to other geographical locations. It is essential to

obtain approval from the government, local authorities and concerned

environmental organisations before setting up a quarry. This is to ensure that

quarrying operation is not affecting the surrounding localities, natural

vegetation and do not possess any risk to humans or animals living in the

nearby areas. Figure A-C- 4 shows the geographical location of various

quarries, currently under operation in the U.K.

Brick clay resources

& \fm- m

Figure A-C- 4 Quarries for brick clay in U.K

[DEFRA, 2007]

188

There are different ways of extracting clay from quarries. Depending upon

the requirement and factors like economic and efficient operation of a quarry,

there are two commonly used methods, namely a) Opencast mining b)

Underground mining. Since open cast mining is accepted to be more

economical compared to the other technique, it is widely used all over the

world to extract clay used in brick making process. A few of the open cast

methods includes Manual Digging, Mechanical extraction, Blasting, Hydraulic

mining [Bender and Handle, 1982].

Mechanical extraction is the most widely used method; a typical mechanical

extraction using an excavator is shown in Figure A-C- 5.

4*l

Figure A-C- 5 Quarry operated with mechanical extraction process

[Source: Iqsgroup]

Storage of raw materials

Clay extracted from quarries will be transported to the brick manufacturing

facilities through suitable modes. Factories operating on a continuous and

mass production process basis should be supplied with ample amount of raw

materials, to meet their demands. Hence most of the brick manufacturing

industries across the world store the ir raw materials within the factory or

nearby area, enabling them for an easy and quick access during production.

This is considered to be another main reason for such industries to be

located near the quarries. There are different ways to store the raw material

and the most widely used includes open-air storage, storage sheds, large

volume feeders and silos.189

Preparation of raw materials

The stored raw material is pre-processed before being used to make bricks.

The pre-processing of brick clays mainly involves reduction of clay particle

size to the required standards, blending of any additives as required for the

products and process and adding or removing moisture to meet the required

standard. The required size for clay particles is achieved by using bespoke

mechanical equipment called pan mill. Size of clay particles and moisture

content are two other important parameters that have influence on the flow

characters of clay water mixture and hence in-order to have a smooth

shaping process and better product, it is important to implement a controlled

strategy at this stage of the production process. Recommended raw material

size is 2-4 pm, before being mixed with water.

The flow character of clay and water mixture, used in brick making process

and in other applications is defined by two variables namely Plasticity Index

and Liquidity Index. The amount of water content determines the plasticity of

clay during shaping process. Depending upon the type of shaping process

the amount of water content varies. A typical stiff extrusion process has 7-

14% of moisture content depending upon the clay type and extruding

technique.

Shaping

Shaping is the next step involved in the brick making process. The required

shape of a ceramic product, like brick, can be obtained through many

techniques using manually operated and completely automated complex

machines, commonly found in modern brick industries. It is a very important

process which determ ines the shape of the ceramic body and also impacts

the further processes involved, before the product is put into its final use.

Based on the raw material conditions and product requirements, the most

widely used and accepted shaping techniques are divided into four types,

namely, Soft mud moulding, Extrusion, Pressing and Casting.

Soft mud moulding

It is one of the oldest and traditional methods of brick making. In simple

terms it could be defined as filling up of lose clay with high plasticity, either

190

mechanically or manually, into a mould made up of wood or metal. Moulds

made of up of wood were widely used. The clay-water mixture used in this

technique is highly plastic, with water content approximately equal to 30% or

even more sometimes, which gives the ability to have a dry shrinkage value

between 6% - 8% [Bender and Handle, 1982], and also required to avoid

insufficient strength of the product. The preferred or recommended plasticity

value of clay water mixture used in this process is 4 mm - 6 mm residual

height in the Pfefferkorn test. (Pefefferkorn test is one among the other

standard testing methods that are widely used and commonly accepted

testing method in ceramic industries to measure the plasticity value of wet

clay) [Wilkinson, 1960].

Ceramic bodies like bricks, made out of soft-mud moulding are amorphous

and solid in nature and offer a good protection during severe cold weather

conditions. The different methods of soft-mud moulding techniques that were

used are as follows,

1. Hand moulding

A typical hand moulding process is shown in Figure A-C- 6.

mrurn

Figure A-C- 6 Hand moulding process

[Source: Bender and Handle, 1982]

2. Mechanized moulding

a. Soft-mud brick moulding machines with loose moulds

191

A typical brick production line with loose moulds setup is

shown in Figure A-C- 7.

Figure A-C- 7 Mechanized soft moulding machine


b. Mould-chain type soft-mud brick moulding

c. Mechanical soft-mud moulding

d. De-Boer soft-mud moulding:-

A typical De-Boer machine is shown in Figure A-C- 8

Mould Washing

Soft Mud Brick Moulding Machine

Figure A-C- 8 Typical De-Boer soft mud moulding machine

[Source: resourceefficientbricks, 2011]

e. The Aberson soft-mud moulding: A typical Aberson soft

moulding machine is shown in Figure A-C- 9.

192

Figure A-C- 9 Soft moulding machine-Aberson type


f. The Hubert soft-mud moulding.

A few among the main advantages of soft mud moulding includes lower

power consumption compared to extrusion process, can be used for both

small scale and large scale production and has a lower maintenance and

operational cost.

Extrusion

Invented by Schlickeysen, more than 150 years ago [Bender and Handle,

1982], extrusion is the most commonly used shaping techniques in large

scale ceram ic industries for manufacturing bricks, tiles and pipes etc.

Vacuum extruder is one of the recent advancement from its predecessor, de

airing auger and it is an integrated unit that combines more than one

operation involved in the ceramic product manufacturing, like mixing clay

with water to prepare the Mslip"(Plasticised clay), compress the slip to density

the mass and remove any trapped air with the application of vacuum, density

the slip further by forcing it through a chamber with auger shaft and then

produce the required shape of the clay body by forcing it further through the

die or mouth. The die or the extruder mouth resembles the required cross

sectional shape of the final finished product. A typical vacuum type extruder,

used in heavy clay industries, designed and manufactured by Craven

Fawcett Ltd, U.K is shown in Figure A-C- 10.

193

Figure A-C- 10 Vacuum extruder

[Source:-Craven Fawcett Limited, U.K]

The main aim of this research is to study in detail the flow process of wet

clay within the extruder and assess its performance with respect to various

design conditions. Hence a detailed review about the extruders, its

performance characters and the process of extrusion is presented in

Appendix- D.

Pressing

It is another type of ceramic product shaping technique, mainly used to

manufacture tiles and bricks. In simple terms, the final shape of the ceram ic

body is achieved by applying mechanical compaction force to the raw

material placed in an enclosed chamber called a die. A typical hydraulic

pressing machine used for making tiles is shown in Figure A-C- 11.

194

Figure A-C- 11 Hydraulic press type tile making machine

[Source:-American Ceramic Society]

Based on the pressing technique and raw material condition, the pressing

process is classified into the following types,

1. Dry pressing

2. Isostatic Pressing

3. Sem i-dry brick pressing

4. Tile pressing.

The shape and quality of the final product depends upon the pressure

applied to compact the loose mass of clay and it varies with respect to the

techniques used. Irrespective of the technique used, it is required to take a

proper care regarding the pressure applied and die design, to have a better

product. Most of the pressing techniques mentioned above involves three

main steps - 1) filling the loose clay and water mixture (if required) into the

bottom die cavity, usually attached to the bottom of the press, 2) applying

pressure through the top die attached to a ram and 3) removing the formed

product from the bottom die. The removal of final product from the bottom of

die is an important step in pressing, as it often decides the final quality of the

195

product. If care is not taken at the design stage, it could result in major

problems like cracking and irregular shape of final product. The achievable

technical characteristics of the product, speed, simplicity and

inexpensiveness of the overall production cycle has seen pressing technique

to be used widely and extensively in ceramic industries.

Casting

It is similar to the casting technique applied in the manufacturing of metal

components. Ceramic casting is another type of shaping technique, used

mainly for making ceramic components like tableware, sanitary ware and

advanced ceramics. There are different types of casting techniques used in

the ceramic industries [Handle, 2007], namely

1. Slip casting

2. Pressure slip casting

3. Capillary casting in plaster moulds

4. Pressure casting in polymer moulds.

The raw material condition and final product requirements determine the

appropriate type of technique to be used. However the basic principle of

manufacturing is same for all the above mentioned techniques. A suitable

design of mould resembling the shape of the ceramic product will be made

using Plastercine or Polymers or Acrylic or Plaster of Paris or clay and then

the slip will be introduced into the mould. Slip in this case will be more like a

thick liquid. This liquid mass will then be allowed to dry for a sufficient period,

before it is removed. Depending upon the size and thickness of the product,

the drying time varies from hours to days. The main advantages include the

re-usability of the moulds, geometrical accuracy of components produced

and adaptability to large scale production.

Electrophoretic shaping

Invented in the year 1809 [Bender and Handle, 1982], it is a type of

ceramics shaping technique, developed to a commercial scale for special

requirements. This technique involves the use of electric field, applied to the

raw materials, to achieve a preferred orientation of the clay particles in the

196

finished product. Since it is of not much relevance to this research work, it

has not been discussed in this work. However if the reader is interested in

exploring further about this technique, it is recommended to refer the above

stated reference.

Summary of Shaping methods and its applications:

The shaping process in ceramic manufacturing varies widely with respect to

type of raw material, size of the industry and quantity to be manufactured. It

is an energy intense process, which requires a special attention to improve

the overall efficiency of the whole production cycle. Hence engineers and

industrial experts in this sector take an extra care while choosing the

appropriate techniques to meet their requirement. Table A-C- 1 provides the

details of various shaping techniques and their applicability for producing

ceramic components based on the raw material condition and shapes

[Bender and Handle, 1982].

Raw material

condition,

Requirements,

Shapes.

Hand

m

ould

ing

Extr

usio

n

Ram

Pres

sing

Rol

ling,

Mill

ing

Ram

min

g

Dry

pres

sing

Isos

tatic

pres

sing

Elec

trop

hore

si

Cas

ting

Vibr

atio

n

Cohesive

material + + + + + X X + +

processing

Materials with

Low plasticX X - X X ++ + X X X

Material with high

water content+ + - - 0 0 0 + + X

Material with low

water content- + X X + ++ + 0 0 X

Material with high

compact stability- X X X + ++ + - -

Deaerated

materialX ++ + + X + + X

197

Uniform

compaction+ + + X X ++ X -

High throughput + ++ - - -

Non standards

material, in low

numbers

+

+X + + ++ X +

Products with

certain

texturation

+ + + + X X +

Product without

texturation- X + ++

Dimensionally

stable products- X ++ +

Smooth surfaces - + + + + + X + + +

Rough surfaces + X X X X X + X

Massive blocks + ++ + + + - X

Tiles + + + + ++ + + X X

Extruded

products- ++ 0 0 0 X 0

Compacts for

presses & rollers++ X X

Roofing tiles X ++

Holloware - X X X X ++

Tableware + ++ X +

+= Applicable; - = Inapplicable; x=Applicable with certain conditions

Table A-C- 1 Various shaping techniques and their applicability


Surface treatment

It is the process of introducing texturing, glazing, colour and coating to a

ceramic product, to enhance the appearance of the product and make it

appealing. Surface treatment is done mainly to give a specific profile or a

colour to the ceramic products, especially bricks. Coloured bricks, textured

bricks and profiled bricks are a few examples. There are many types of198

surface treatment techniques been developed and used, such as Sanding,

Profiling, Peeling, Colouring, Glazing, Coating, Brushing and Addition of

Combustible materials.

During earlier days, ceramic products with different colours and shapes were

of great appeal to the consumers. This led to the development and

introduction of new techniques in surface treatment, by both small scale and

large scale industries, to capitalise on the demand. But the increase in raw

material cost has led small scale industries to concentrate less on this

process and this factor helped the large scale industries to increase their

market share.

Cutting

With the invention and advent of the extrusion technique in ceram ic-brick

manufacturing, which produces continuous mass of compacted green clay or

wet clay, it was required to introduce a cutting system into the production

process, especially in brick manufacturing, to produce bricks with certain

length and width. The main function of the cutting system is to continuously

cut the compacted mass that comes out of the extruder mouth to the

required size. During the earlier days, it was done manually which is now

replaced by far advanced, efficient and automatic mechanical cutters. A

typical cutter system installed in a brick production line is shown in

Figure A -C -12.

Figure A-C- 12 Typical cutting system used in a brick production line


199

The cutting systems currently used in the ceramic industries are classified

into two main groups -

1. Depending upon the cutting direction- Vertical cutters,

horizontal cutters and segmental cutters.

2. Depending upon the type of cutter and application- column

controlled cutters and fixed cycle cutters.

The most commonly used cutting tool is a thin metal wire of gauge size

varying from 0.5 mm to 1.6 mm, depending upon the thickness of the

compacted clay [Madehow, 2012]. In some special cases knives are used

as a cutting tool. The appropriate cutting system and cutting tool depends

upon the ceramic material processed, speed and economy of the overall

production cycle.

Drying

Drying is defined as the process of removing water or moisture content from

the compacted or shaped ceramic product. Drying is completed before the

ceram ic product is fired to achieve the final colour and strength. Drying also

prevents the development of crack in the product during firing. The process

of drying can be achieved either by applying mechanical forces or using

thermal energy. The most common in practice is drying by using thermal

energy, where a hot medium like gas or air (mostly air) is used to heat the

wet ceramic product under a controlled atmosphere and remove the water in

the form of vapour. It is to be noted that after drying, the ceram ic product still

retains some moisture in it and it is soluble in water. The two common types

of drying system used in the ceram ic industries are Tunnel dryers and

Automatic Chamber dryers. The tunnel drying system is a single stage

process, whereas the automatic chamber drying system involves more than

one stage. Automatic transfer cars are used to transfer the ceram ic product

through the various stages of drying process. A typical tunnel drier is shown

in Figure A -C -13.

200

Figure A-C- 13 Tunnel dryer

[Source: Cereamtechno, 2013]

Firing

Firing is the final process involved in the manufacturing of ceram ic products

used in structural applications. It helps the ceramic product to achieve

required compressive strength, build strong cohesion between the particles

and introduces colouring. Since it is the final process, any additives that are

required to produce a ceramic product with certain features must be added

before the firing stage, mostly at the raw material preparation stage.

The firing of green bricks (wet bricks) vaporises the water content left after

the process of drying and induces chemical reaction that involves production

of gases. Most of the gaseous products are hazardous in nature for both the

environment and to the humans (C02 and Hydrogen Fluoride). Flu gas

treatment is another important area involved in the design of efficient, cost

effective and environmental friendly ceramic industries. Since it is of not

much interest pertaining to this research work, it is not reviewed in detail.

The process of firing takes place in a closed and controlled chamber called a

"Kiln". Since the invention of kilns for firing process there have been many

developments to increase the efficiency and safety of this process. Though

there are different types of kilns, which are operational in ceram ic industries

201

worldwide, one type of kiln which is very common and used in brick

manufacturing is "Tunnel Kilns". Tunnel Kilns are further sub divided into

different types based on the firing arrangement. The features like economical

operation, faster heating time, increased capacity and safe design has

offered the advantage for tunnel kilns to be preferred over the other types.

Typical types of tunnel kilns are shown in Figure A -C -14 and A -C -15.

Figure A-C- 14 Tunnel kiln-Type I

[Source: Shinagawa Refactories, 2013]

Figure A-C- 15 Tunnel kiln-Type 2

[Source: West Lothian Archaeology Group, 2013]

Packing and Dispatch

The final stage involved in ceramic (brick) manufacturing process is storing

the product that comes out of the kiln in an appropriate place and keeping it

202

ready for final inspection and dispatch. Considering the number of products

that are produced, it is physically impossible to check the products

individually for the required quality and hence random visual inspection

techniques are used at every stage during the production process, to make

sure the product meets the required standard. The products that pass the

quality check will then be stored appropriately before being packed and

transported to the end users. The products that fail the quality check are

either re-used along with virgin raw materials for making new products or as

aggregates. So in simple terms, there is no waste of product, but the energy

consumed is still lost and hence products with defects are not preferred by

the industries. Packing involves the use of wooden pallets or boards made

up of plastic, onto which the bricks are arranged in a specific pattern to

ensure that the load is evenly distributed and suitable provisions will be

provided to withstand the weather conditions and avoid damage during

transportation. Mechanical or automatic wrapping machines are w idely used

in packing applications.

ConclusionIt is clearly understood from the above discussion that the ceramic industry,

especially brick manufacturing, involves the use of both heavy and light duty

mechanical and electrical systems to achieve the required objectives.

Considering the demand for bricks and the volume of production, it is

impossible to replace it with a human workforce and also it is not good

practice, hence the use of power consuming machines is inevitable. So for

the longer sustainability of the brick industries in terms of its power

consumption and environmental impact, it is necessary to identify and

undertake suitable developmental work in all possible areas of the

manufacturing cycle on a regular basis. With the availability of advanced

computing methodologies and simulation based techniques, improvement in

certain processes and in design of machines used in brick manufacturing can

be accelerated. This research work is one such effort to demonstrate the

application of CFD and FEA techniques towards improving the process of

brick making in heavy clay industries.

203

Appendix-D

Extruder and the process of extrusion

204

IntroductionShaping is an important function in the process of brick making or in any

ceramic product manufacturing. It is also a major power consuming

processes. Most of the brick industries in the U.K and worldwide uses

combined de-airing type extruder to perform this function. As discussed in

previous chapter, due to certain inherent functional aspects, these types of

extruders are used widely. The aim of this chapter is to review the history of

machines used in extrusion process, general design principles applicable in

the design of combined de-airing auger extruders and the flow parameters

that govern the design and power consumption of extruders together with the

process of shaping.

Developments in extruderA wide variety of mechanical systems have been developed and used for the

purpose of shaping ceramic products since the earlier days. However only a

few of them were very successful in achieving the intended functional

requirements and used widely. This includes the following,

• Piston extruder

• Expression rolls

• Electrophoretic extruders

• Auger extruders

Piston extruders

The use of piston extruders began in the year 1807, with the invention of a

hand operated piston extruder used in making drainage pipes [Handle,

2007]. As the name suggests, the working mechanism of this machine is

mainly based on a piston moving inside a closed chamber that pushes the

clay material through the die or mouth, predominantly in a vertical direction.

The main problems faced with this type of machine includes filling up of raw

material after every cycle of operation and removal of air entrapped in the

raw material. Even though design changes were made to overcome these

problems, to gain acceptance in the ceramic industries for manufacturing

205

structural ceramic products, the piston extruders played a less significant

part in ceramic industries. A simple vertical piston extruder developed and

used in the year 1880 is shown in Figure A -D -1.

Figure A-D- 1 Piston extruder


Expression rolls

The process of extruding a continuous column of clay by pushing it through a

die through a connecting element called a pressure head was born with the

introduction of Expression Rolls in 1830 [Handle, 2007].The first machine

designed by the Englishmen Ainslie [Handle, 2007], served as a blue print

for future machines built using the same principle. Expression rolls capable

of extruding both in vertical and horizontal direction were built and used in

ceram ic industries, especially for making thin tiles. “Europresse” is one of the

most notable developments from the earlier designs of expression rolls. It is

also called as augerless extruder or rotor type extrusion machine. This type

of machine was used for extruding ceram ic product with more than one layer

(multilayer) and each layer will be made up of different or same raw material.

Due its technical advantage and less defect in the extruded product it gained

206

its popularity in fine and advanced ceramic industries. A typical Europresse

type Expression Roll machine is shown in Figure A-D- 2.

m&Ljs

Figure A-D- 2 Europresse extruder


Electrophoretic extrusion

Electrophoretic extruder is similar to Expression Roll machine; it was

introduced and used in ceramic industries by 1977. The machines were built

based on the principle of "Electrophoresis" and is used for special

applications in ceramic industry. Due to the complexity involved in the design

and operation of these machines it was seldom used in the structural

ceramic industries. A typical electrophoretic extruding system is shown in

Figure A-D- 3.

207

Figure A-D- 3 Electrophoretic extruder


Auger extruders

The use of auger extruders in the process of shaping structural ceramic

products began in the year 1855, with the introduction of Carl Schlickeysen's

"Patent Brick Making Machine"- an upright machine for extruding clay

columns [Handle, 2007]. Thereafter, driven by market requirements and

demands, the auger extruders underwent a series of rapid development

processes in various aspects to make it a more operator friendly system and

meet the mass production requirement. Auger extruders capable of extruding

both in vertical and horizontal direction were developed and used for specific

purposes. Even though there were different types of auger extruders

developed and they all can be grouped into the following three categories,

• Auger extruder without de-airing

• Auger extruder with vacuum device installed in extrusion barrel

• Combined de-airing extrusion units consisting of auger extruder,

vacuum chamber and mixer.

Auger extruders can also be classified into different types based on the

process and design features. The various types that fall under such

classification includes,

2 0 8

• Range of application.

• Product to be extruded - bricks, tiles and pipes etc.

• Auger shaft arrangement and direction of column exit- upright

extruder, horizontal extruder, vertical extruder, hinged type extruder.

• Extruder barrel diameter.

• Number of auger shafts- single auger shaft extruder, combined single

auger de-airing extruder, twin shaft extruder, multiple shaft extruder.

• Consistency of the body to be processed.

• Extruder barrel design- cylindrical, conical, combined

(cylindrical/conical), enlarged barrel, expanded barrel, stepped barrel,

noodle barrel.

• Design and mounting of augers-progressive pitch, acute or decreasing

pitch, linear pitch, combined pitch.

• Special extrusion methods-twin layer extrusion, multiple column

extrusion, hot extrusion and vacuum extrusion.

• De-airing device used.

• Design of the extruder elements- auger, housing, infeed device and

barrel liners etc.

• Design of the de-airing mixer.

• Design of combined de-airing extrusion unit- configuration of mixer

and auger shafts, method of connection between the extruder and

mixer and the construction of de-airing mixer.

The most important types in the above said classifications are based on

application and consistency of the body to be processed, which is elaborated

below.

Extruder classification based on application

Based on the shaping effects, body composition, degree of fineness of the

raw material, throughput and extrusion pressure the extruders are classified

into three categories namely, extruders used in heavy clay industries, fine

ceramic industries and advanced ceramic industries. Auger extruder in heavy

clay industries is used for direct shaping process to achieve the final shape

of the product, example brick and pipe. Whereas in fields like advanced

209

ceramics and fine ceramics, it is used for homogenising, de-airing and

improving the plasticity and density of the clay material before the final shape

of product is acquired through other means.

Extruder classification based on body to be processed

The raw material to be extruded varies hugely with respect to products or

even for the same product it might vary in mineral composition and moisture

content. This influences the extrudability of the material and also the function

of the extruder to a greater extent. Based on the moisture content and

pressure developed during extrusion the extruders can be classified into

three categories namely low, medium and high pressure extruders. Table A-

D- 1 provides a rough guide on the classification of extruders based on

process.

Type of extruderLow

pressure

Medium

pressureHigh pressure

Description of extruder Soft Semi-stiff Stiff

Parameter Dimension 1 2 3 4

Moisture

content

%

(dry basis)10-27 15-22 12-18 10-15

Extrusion

pressureBar 4-12 15-22 25-45

up to

300

Penetrometer Nmm"2 <0.20 0.20-0.300.25-

0.450.30

Table A-D- 1 Extruder classification based on process parameters

[Source: Handle, 2007].

It is recommended to refer "Extrusion in Ceramics", mentioned in the

reference section of this report, for more details on the classification of auger

extruders.

De-airing extruderOf the various development works that were undertaken with respect to the

design of an extruder system, the most notable and successful work includes

210

the development of de-airing extruders. De-airing is the process of removing

air particles trapped in the clay-water mixture, before being extruded into

continuous column. This helps to increase the plasticity of the mixture and

extrude a dense mass. Failure to do so will cause problems like lamination,

void formation and blistering. The earlier designs of extrusion system had the

de-airing units located separately from the extruder. This type of design

offered certain process advantages like multiple de-airing and less

sophistication in design. The main disadvantages were blockage, back

pressure and uneven de-airing. This led to the development of combined de

airing extruders or vacuum extruders around 1935 [Handle, 2007]. In simple

terms a vacuum extruder incorporates the mixing, de-airing and extruding

unit in a single system, arranged sequentially. Compare with other earlier

designs of extruders, vacuum extruders possessed a numerous advantages.

Like better efficiency, adoptability for mass production requirement (modern

vacuum extruders are capable of extruding 15000-20000 bricks per hour),

manoeuvrability and quality of extrudate. These factors favoured it to gain its

popularity in structural ceramic industries in a very short time. Based on the

design, arrangement of pug mill, extruder and extruding direction, the

vacuum extruders can be classified into different types. The basic building

blocks of any vacuum extruder include pug mill or the mixing chamber,

primary compression zone, vacuum chamber, extruder, die and drive

system. An overview of each component is presented below. A typical

vacuum extruder designed and built by Craven Fawcett Limited, U.K is

shown in Figure A-D- 4 for the purpose of understanding.

211

De-airing(Vacuum)chamber

Extruder(auger/barrel

Pug mill Primary compression

Figure A-D- 4 Vacuum extruder-Centex model

[Source:-Craven Fawcett Limited, U.K]

Pug mill

Pug mills or the mixing chamber is a semi enclosed metal chamber, mostly

u-shaped, placed before the vacuum chamber. It will be either in line with the

extruder or placed above the extruder (most of the extruders designed and

manufactured by C.F Ltd, have the pug mill aligned parallel to the extruder's

axis of rotation). It is where the right sized clay particles (usually >2 pm and

<4 pm) that comes out of a rotary silos is mixed with water, supplied through

controlled pipe lines. A rotary silo is a rotating drum made up of wire meshes

of different size, used to filter the over sized clay particle. A fairly

homogenised mixture of clay and water is acquired through the rotating shaft

equipped with paddle or knife like structures placed in this chamber. Most of

the machines used in Europe consist of a twin mixing shaft arrangement in

this chamber. Though a 100% homogenised mixture cannot be achieved

through this type of arrangement, it is accepted in the industries as a better

and more efficient system compared to the earlier systems. This type of212

design offers a great flexibility in controlling the moisture content either

automatically or mechanically, with respect to the quality and stiffness of the

extrudate. A typical pug mill with a twin shaft mixer arrangement is shown in

Figure A-D- 5.

Figure A-D- 5 Mixing chamber


Primary compression zone

The connecting element between the vacuum chamber and the mixing unit is

called the primary compression zone, and it is shown in Figure A-D- 4. In

industries this unit is designed with various shapes and accessories attached

to it, depending upon the requirement. In most of the design there will be a

twin conical chamber fitted with small augers in each chamber. The main

function of this unit is to compress the loose wet clay transported from the

pug mill into a mass of substance with medium density called "slip" (as

mentioned in Appendix- C). This helps in creating a bond between the loose

clay and water and removes the trapped air content to a certain extent. The

compressed mass is then cut into suitable lengths using a cutter

arrangement placed at the downstream side of the chamber, in order to

maximise the efficiency of the de-airing process that follows.

De-airing (or) vacuum chamber

The concept of de-airing and the need for it was been discussed earlier in

this chapter. The process of de-airing is achieved by many ways; however in

213

modern combined de-airing and vacuum extruders, this is achieved by using

a vacuum pump mounted on top of an enclosed chamber; typical

arrangement of a vacuum chamber is shown in Figure A-D- 4. The slip, after

being sliced to the required length from the preliminary compression zone is

made to fall into the vacuum chamber by the action of gravitational force; the

vacuum created in this chamber facilitates the air, from the slip, to escape in

the direction of suction. The de-aeration depends on few factors like the

vacuum created, specific surface area of slip and on the duration of the

vacuum [Bender and Handle, 1982]. The de-aired mass of clay will then

enter the charging zone or the extruder section.

Extruder

The extruder used in modern machines is a simplified version of earlier

designs and resulted from the process of continuous development. The

extruder section is sub-divided into two main zones namely a charging and

compression zone. The main elements that contribute to these zones include

auger shaft, barrel, and barrel liners. Figure A-D- 6 shows a typical barrel

and an auger shaft used in one of C.F Ltd's vacuum type de-airing extruder

system.

Barrel Auger and shaft assembly

Figure A-D- 6 Components of an extruder system

Charging zone is where the severed slip from the mixing chamber gets

accumulated before it enters into the compression zone. To ensure a uniform

feed of clay during the process of continuous extrusion, maintaining a certain

level of clay in this zone is important. This is achieved by using sensors and

other suitable means of measuring. An excess accumulation of clay in this

214

zone could cause deaeration problems and cause severe damage to the

machine by means of overloading.

The auger is an integral element between the charging and compression

zones. The slip from the charging zone is carried forward by these augers

and in order to accommodate the uncompacted nature of the clay and

achieve reliable throughput, the diameter of auger in the charging zone will

be slightly larger than the diameter of auger in compression zone. Suitable

design provisions are available in modern extruders, to prevent the clay from

sticking and rotating along with auger (paddle shaft is one such example).

The extended auger shaft from the charging zone is enclosed within a

cylindrical barrel along with liners, which constitutes the compression zone.

The uncompacted mass of clay that enters the compression zone is mixed

well to achieve a good homogenised mixture of clay and water and then will

be pressed together to form a compacted mass. Any air entrapped further

will be removed because of this pressing action and suction pressure created

by the vacuum pump in the charging zone.

Die

The die or mouth is the final element in an extruder system. A continuous

mass of clay is produced because of the rotation of the auger shaft within

extruder section will force the compacted clay to pass through the openings

in the die section. The opening at the downstream side usually resembles

the required cross sectional shape of the extruded product. The earlier

designs of extruder, used in commercial scale include a pressure head,

connecting element that links the extruder with the die (similar to those used

in expression rolls, discussed earlier). The compacted clay will be pushed

into the die or mouth through the pressure head to acquire the intended final

shape of the extruded product. A careful consideration to the flow conditions

and extensive field knowledge has led the design engineers to integrate the

pressure head and die into a single unit. A further brief review about the flow

process and related flow parameters for the die section of an extruder is

presented later in this chapter. Other significant design advancements in the

die design includes dies with core used for manufacturing perforated bricks

215

and hollow blocks etc, and dies with external lubrication arrangement, used

for extruding slip with very less moisture content.

Drive system

The power required to rotate the auger and shafts in the mixing chamber is

obtained through the drive system. The drive system has undergone a series

of many notable developments that includes the use of steam power,

electrical motors and the most recent advancement is the use of planetary

gear boxes. As discussed earlier, the drive system design is another

category for classifying extruders. Most of the modern combined de-airing

type extruder drive system comprises an electric motor combined with a gear

box. The electrical motor (mostly squirrel cage motor, due to the flexibility of

speed control) acts as the primary power source which drives a gear unit,

designed suitably to achieve the required speed with respect to the extrusion

rate required. The electric motor will be coupled to the gear box either

directly or through stepped pulley and belt drive arrangement or through a

clutch system. The gear box will be directly coupled to the shafts in the

extruder and mixing chamber.

Usually a common drive system exists for both the shaft, but there are

extruders with separate drive units for auger and mixing chamber. The

advantage in the latter case is it offers better control of the extrusion process

and reduces complexity in design requirements; the main disadvantage

includes the capital and running cost incurred.

Process of stiff extrusionThe technical aspects of a stiff extrusion process are very sophisticated and

during years of its extensive use in industries, only a very little understanding

has been developed by experts to make any conclusive remarks about the

flow process that occurs inside the auger/barrel and die sections. Smooth

extrusion depends on many factors like the clay particle size, moisture

contents, efficiency of the de-airing system, drive elements and its control

systems, extrusion pressure, die design, pitch and profile of the auger,

clearance between auger tip and the barrel and most importantly the

plasticity of the slip (clay-water mixture).The main performance parameters216

of a de-airing type vacuum extruder includes extrusion rate, extrusion

pressure, material flow velocity at the die section and power consumption.

The geometric and operating parameters that have direct influence on the

performance includes auger speed, auger diameter, uncompacted density of

clay, material of construction of augers and moisture content of the clay. A

brief overview about extruder’s performance characters is presented further

in this chapter.

Extrusion rate

It is quantified by the amount of bricks produced per unit of time (usually rate

per hour). As mentioned earlier in this chapter, modern vacuum extruders

are designed to produce more than 12,000 bricks per hour and this depends

upon two main factors- the auger pitch and plasticity of the clay. Since the

moisture content is controlled by product requirement and other factors, it is

relevant in this context to just to talk about the dependency of extrusion rate

on auger pitch. Figure A-D- 7 shows the various auger geometrical variables

necessary for determining the extrusion rate.

►direction o f extrusion

Figure A-D- 7 Auger geometrical parameters

[Source: Handle, 2007]217

Where,

Ds =Diameter of the auger

f =Flight thickness or auger blade thickness

a =Clearance between the auger and barrel

d =Hub diameter

D =Barrel diameter

h =area of effective gap between hub and barrel

P =helix angle or angle of inclination

S =Pitch distance or effective distance which can be determined

using Equation A.D.1

S = n * D * tan p a — A . D . l

Where, D- diameter of the barrel, pa- Helix angle measured at the tip of the

auger.

Using the above formula, once the auger pitch has been determined, the

swept volume of the auger or the volume of the material discharged per

revolution of the auger shall be determined by Equation A.D.2.

Where, Vs = Swept volume (m3).

The final, volumetric extrusion rate of an auger shall be determ ined using

Equation A.D.3.

Where, Qv= Volumetric discharge rate, n = auger speed in rpm.

It is a common practice in the industries, to express the discharge rate in

terms of mass of clay extruded per unit time. This shall be obtained by

including the density of the final clay column in the above equation as shown

in Equation A.D.4.

Vs = S * h — A.D.2

Where, Qm= discharge rate, p=density of extrudate218

It is clearly evident from the above presented equations that the discharge

rate of an extruder depends on the geometrical and operational parameters

of auger. Hence in actual scenarios the required discharge rate is obtained

by making necessary adjustments to one of the above referred parameters

on a trial and error basis.

Extrusion pressure

Extrusion pressure is another important flow parameter that has a more

significant role in determining the shape, stiffness and quality of the

extrudate (extruded product). The clay material from the charging zone will

flow through the auger convolutions and will fill the extruder and barrel

chamber slowly. The decrease in flow area between the die and auger-barrel

chamber facilitates the material to build up in this zone and imparl pressure

on the extruder and die sections gradually. The extrusion pressure

developed during extrusion depends mostly on the clay moisture content,

extrusion speed, yield point of the material and throughput. The pressure

raises from a negative value (at the entrance of the extruder- charging zone)

to a maximum value at the tip of the auger and then gradually decreases to

reach atmospheric pressure or value equal to the condition at the

downstream side of the die [Bender and Handle, 1982].Figure A-D- 8

shows the pressure profile observed in a typical vacuum type de-airing

extruder.

Figure A-D- 8 Vacuum extruder pressure profile


219

It is clearly understood form the graph that the front side of an auger will

always be subjected to high pressure and in turn a high wear rate occurs.

Hence a greater care is required in designing the auger profile and selecting

suitable material of construction. Even though the pressure is dropping in the

die section, the design should be able to accommodate the stress and heat

induced, due to the loss in pressure. While using dies with core in stiff

extrusion process, the dies are designed with sufficient strength and flexibility

to accommodate any stress and forces induced due to the extrusion process.

Significant scientific works dealing with the flow of clay and assessing the

performance characters of an extruder system is reviewed in Chapter 2.

Power

Stiff extrusion is a high pressure extrusion process; extruders used in this

process are always robustly built to withstand this pressure, stress and wear

induced. This makes them to be a significant power consum ing device used

in brick making process. The power consumption depends upon both

operational and performance characters discussed above. Within the

industries, through repeated lab based experimental works and data

obtained from field, guidelines on power consumption pattern are prepared

for the use of design engineers and it varies with respect to machines and

manufacturers. Due to the complexities involved in the process of extrusion

and extruder design, there is a lack of specific data or an empirical method

that provides an overall picture about the power consumption pattern of any

extruder system.

Quality of extrudate

The quality and nature of the extruded product determ ines the clay

preparation, extrusion technique and equipments required. Stiff extrusion is

renowned for producing complex shapes with sharp edges and smooth

surfaces. The quality of a stiff extruded clay column depends upon one or

many of the process and operational parameters discussed above. A Clay

column with right stiffness and free of defects is what required at the end of

process. The stiffness of the material is determined by the extrusion pressure

and by achieving a suitable extrusion pressure for a given raw material

220

condition, column with unique density and mechanical properties can be

produced through stiff extrusion process (density of the loose clay at the

charging zone will be typically around 1600 kgm'3 and the density of

extruded column varies between 2100 kgm'3 to 2800 kgm'3 [Handle, 2007]).

Predominant problems that occur in the extruded products include texturation

(alignment of clay particles- important for uniform mechanical properties in all

direction), void formation (inclusion of air bubbles, which in turn induces

crack during firing process) and lamination.

ConclusionThe use of extruders and the evolution of vacuum extruders in the brick

industry were reviewed in this chapter. The process and operational

parameters that are necessary to assess the performance of an extruder

system was also reviewed. Through the various facts presented above, it is

evident that the development processes that were undertaken to enhance

the design of the extruder system were through empirical methods or

repeated field trials and there is a lack in application of advanced computing

tools towards the design and development of extruders used in the stiff

extrusion process. Through the introduction of such tools towards the design

and development of extruders will not solve the entire problem and the

challenges faced by the brick industry, it will help to speed up the process in

certain areas that will help in the efficient and sustainable operation.

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