Using Advanced Materials and Advanced Processing Technologies to provide solutions

Savings through Understanding and Controlling Energy Usage in Polymer Processing

Gerry McNally, CSci MSc FIOMM FSPE Facilitator/Director of Polymer Research,

Innovation and Competence Northern Ireland Polymers Association

Challenges for the NI Polymer Industry Sector

NIPA/ Invest NI Collaborative Programme 1. Materials – costs and lack of substitutions, green polymers, materials availability

2. Energy Costs – issues associated with costs and availability and improved energy management within companies – NI 2nd highest energy costs in Europe (Montenegro)

3. Collaboration – Issues directly addressing the B2B industry/academia interface inhibiting collaboration - particularly inhibiting SME involvement 4. People – Issues associated with staff recruitment, lack of qualified graduates, staff retention, training and up-skilling

5. Processing – Issues related to new processes, challenges of using new materials, improved process control - inhibiting innovation

6. Legislation - recycling, REACH, WEEE and H&S

7. Marketing, end user demands, trading conditions, imports.

Current Sources of Energy Usage in Polymer Processing

Operation of machinery and ancillary equipment – 90% total energy

bill

Heating a polymer materials (which have excellent insulation properties) and conveying the polymer melt at correct viscosity to forming tools to high quality for a wide range of applications manufacture products.

Mission To manufacture products with excellent performance and appearance at most competitive cost

Vitally important to gain more knowledge on processing & polymer viscosity

Challenges –we use a wide range of processing machines and polymers – with different melting temperatures- different viscosities- processes -

5.

Challenges for the NI Polymer Industry Sector

NIPA Initiative for Energy Cost Savings 1. Energy Costs – issues associated with costs (a) Established BPF Climate Change Levy reductions for NIPA companies (b) NIPA Energy Basket - Bergen Energy –

2.. Improved Energy Management within NIPA Companies (a) 1st Energy workshop in Jan 2014 inhibiting (b) 2nd Cost saving workshop today

3. Establish NIPA Innovation Vouchers with PPRC on additives and process monitoring with automatic control for energy reduction

4. NIPA/Invest NI Planned activities over next 1-2 months – (a) Immediate- assistance available to establish Energy management strategies within selected NIPA Companies (b) Establish a range of demonstration plants in firms to bench mark and improve on energy efficiency –

Polymer processing -Complex Science and Engineering Field To manufacture products with performance and appearance at most competitive cost

Use correct polymer and process using optimum processing conditions

To achieve optimum processing conditions involves knowledge of engineering and scientific disciplines

1. Solids Handling and Solids feeding

2. Design -- wide variety of dies, IM tools, extruder screw designs etc

3. Heat transfer -

4. Fluid flow -

5. Aerodynamics -

6. Cooling and development of morphology and crystallinity

7. Micro structural development will affect mechanical performance

8. Development of crystalline structure simultaneously during cooling, cooling rate orientation biaxial

9. Understanding of the effect of additives on crystalline development

10. We use a wide variety of processing technologies

We use Advanced Processing technologies to process advanced materials

Advanced Polymer Processes

Blown FilmProfile ExtrusionTube and PipeSheet ExtrusionCast FilmExtrusion blow mouldingMultilayer co-extrusionCompounding

Injection mouldingMulti-shot moulding Mesh/Netting

Typical of Energy Cost in Polymer Processing Site

Operation of machinery and ancillary equipment – 90% total energy

bill

Energy Usage In Extrusion Blow Moulding Unit Processes

Energy Usage in Sheet Extrusion Unit Processes

Energy Usage in Injection Moulding Unit Processes All Electric – 30% Energy savings over Hydraulic

Energy Use at a typical Profile Extrusion Plant

Comparison of Average Specific Energy Consumption, kWhr/kg /hr

SEC dependent on; Unit Processes Production rate Polymer Type

Current Sources of Energy Usage in Polymer Processing

Operation of machinery and ancillary equipment – 90% total

energy bill

Materials and energy costs are greatest expense to companies

Polymer Processing (motors and barrel heating ) 66%

Compressed air 10%

Chillers 10%

NIPA Invited Speakers today on;

Chillers, Heaters, Smart heat barrels and screws

Challenges –we use a wide range of polymers – with different melting temperatures- different viscosities- processes -

•

Polymer Materials To manufacture products with performance and appearance at most

competitive cost

We process correct polymer using optimum processing conditions.

In order to achieve this we use a wide variety of polymers with different chemical structures and additives

1. Commodity polymers -- PEs PP PS PVC

2. Engineering polymers --PA ABD POM PC Peek PPS PET PBT PVdf

3. Thermoplastic Elastomers -- (TPEs) TPOs PU Silicones

4.. Co-polymers -- LLDPEs, block and random PP/PE copolymers, ABS

5. Polymer Blends

6. Wide range of additives to improve processing and product performance and appearance

7. Wide range of different molecular weight polymers and MWD( catalyst type)

8. These polymers have different melting temperatures

9. Wide range of melt viscosities

We use Advanced Materials to provide solutions

Melting/Processing Temperatures Commodity Polymers

Polymer Melting Temp Processing Temperature

LDPE 110ºC 190ºC

LLDPE 120ºC 210ºC

HDPE 135ºC 220ºC

PP 165ºC 230ºC

EVA 100ºC 170ºC

PP/PE Copolymers

120ºC 200ºC

PVC 180ºC 190ºC

Melting/Processing Temperatures Engineering Polymers

Polymer Melting Temp Processing Temperature

Nylon 6 180ºC 260ºC

PET 230ºC 270ºC

PEEK 265ºC 360ºC

PC 150ºC 280ºC

PBT 220 ºC 270ºC

PA 66 230ºC 275ºC

PPS 190ºC 350ºC

Specific Energy Consumption of Polymers

Dependent on Polymer thermal characteristics Heat transfer coefficients, thermal conductivity, specific heat, enthalpy of melting etc. Semi -crystalline Polymers PP, PEs, Nylons, PET etc.

Amorphous Polymers Polystyrene, PVC, PC etc.

Heat transfer to the polymer in an extruder • Extruder Motor • Screws• Barrel• Heater bands• Breaker Plate• Screen Packs• Melt temperature/ pressure

• Heat Transferred by both conduction and extruder screw shear

.c

Heater bandsScrewBreaker Plate

and Screen Pack

Die

Metering

section

Compression

section

Feed sectio

n

Feed

Hopper

Drive

Barrel

Extruder zones

Feed sectionThis zone accepts the granules from the hopper, preheats them and conveys them to the next section.

The screw depth in this section is constant

Compression sectionThe screw depth decreases in this section squeezing any air back out through the hopper and giving a

melt free from porosity.

Metering sectionThis section homogenises the melt and meters it through to the die at a constant rate, with uniform

temperature and pressure. The screw depth is constant.

Mechanism of Polymer Flow in a single screw extruder

Feed Section

In the first, or solids conveying, zone of the extruder the solid polymer particles are compacted together in the screw channel by the rotating action of the screw to form a solid bed of material.

Compression Section

At the start of the next extruder section, the plastication (melting) zone, the barrel heaters cause a thin film of molten polymer to form in the gap between the solid bed and the barrel wall. The melt film is subjected to intense shearing in the thin gap, causing a rapid temperature rise in the material.

The generated heat melts the solid bed within a short distance of the start of melting.

Metering Section

In the last zone of the extruder, the metering section, the polymer melt flow is stabilized in the shallow screw channels, and finally the material passes out through the die on the end of the machine

The extruder conveys a well mixed polymer melt with a constant viscosity to forming dies tools etc.

Barrier Screws

Barrier screws have a second flight added which splits the channel into two; a solids channel and a melt channel. The screw’s feed channel connects to the solids channel and the melt channel connects to the metering section.

At the beginning of the barrier section a barrier flight is introduced into the screw channel. The clearance between the barrier flight and the barrel is generally larger than the clearance between the main flight and the barrel. The barrier clearance is large enough so the polymer melt can flow over the barrier; but it is too small for solid particles to pass over. This causes a phase separation with the solid bed on one

side and the melt pool on the other.This design ensures better melting and also increases mixing capabilities

Polymer Melts are non-Newtonian Fluids

Many fluids not ideal.

Viscosity varies with shear rate

Therefore the term viscosity must be related to a particular shear rate

Polymer melts are pseudoplatic Fluids (Time independent)

1.Viscosity decreases with increasing shear rate. *

2.Examples.

3.Shear Thinning – (Explanation)

4.Various flow regimes in pseudoplastic fluids.

•Apparent viscosity μa read from rheogram.

Polymer Melt Flow

Typical rheogram showing the effect of shear rate on polymer viscosity

( shear thinning)

Typical shear ratesRotational 0 sec-1 Extrusion 100-300 sec-1Injection 1000-4000 sec-1

•

Experimental Characterisation of Non – Newtonian Fluids

1.Tube Viscometry.

2.Rotational viscometry.

- Cone and plate.

- Concentric cylinders.

3.Melt flow indexer (MFI).

4.Melt rheometer - Single barrel -- Dual barrel.

5.Torque rheometer.

6.Dynamic rheometer.

Melt Flow Indexers1. Description of equipment.

2. Different operating conditions for different polymers.

3. MFI is defined as the weight in grams extruded in 10 minutes g/10min

4. Extruded through a standard capillary at standard temperature and load.

5. Limitations but useful for grading polymers.

6. 190oC PEs -- 210oC PP --300 PC

Dual Capillary Rheometers

The most versatile of all rheometer for polymer rheology; shear rate range up to 10-6 sec-1.

Description of equipment.

Shear stress, shear rate and temperature control.

Shear rate

Shear stress

Viscosity

Single capillary – corrections. Rabinowitch and Bagley correction factors

Therefore if you know (i) dimensions of your die/tool channels

(ii) Pressure (p) and (iii) Throughput (Q gms /sec) then you know viscosity of the polymer melt

3

4

r

Q

L

pr

2

LQ

rp

Q

r

L

rp

842

43

Factors Affecting Viscosity1. Temperature.

2. Pressure.

3. Molecular weight.

4. Molecular weight distribution.

5. Additives.

Effect of temperature on viscosity Viscosity decreases with increasing temperature – density lower – more

intermolecular space available.

1. Some polymers are more sensitive to temperature change than others – activation energy of flow.

2. Arrhenius relationship: U = A eE/RT.

3. Williams Landel and Ferry – Viscosity of a polymer at a certain temperature is related to Tg.

1. See Activation Energy table.

• Equation WLF Log

g

g

TT

TTU

66.51

44.1713

Effect of Molecular Weight on Viscosity.

1. The most important effect controlling viscosity.

2. The longer the chain, the more intermolecular contact and entanglements.

3. Beuche Relationship between melt viscosity and molecular weight ;: Uo = K mw3.4.

4. With increasing shear rate, 3.4 decreases as increases

5. Molecular weight distribution

Effect of Additives on Viscosity

Plasticisers and flow promoters ( liquids waxes ) decrease the viscosity of polymer melts

Viscosity decreases with increasing content – density lower – more intermolecular space available

Flow promoters - 1- 3%

Plasticised PVC 5- 40% -plasticiser level related to shore hardness

Extrusion processing conditions

Vitally import to achieve correct viscosity of polymer melt before the die

Normally achieved by in house trails to establish SOP

Barrel and die temps and barrel pressures Melt temperature/ pressure

Well established SOP conditions so no change ??

However perhaps we can still achieve correct viscosity in a much more energy efficient way

.c

Heater bandsScrewBreaker Plate

and Screen Pack

DieDrive

Barrel

Mica Band Heaters (used on dies) They consist of a nickel chromium resistance wire (80% nickel, 20% chromium) wound onto a mica sheet and protected by a metal sheath made of brass, steel or stainless steel.

Ceramic heaters (used on barrels)A nickel chromium resistance wire (80% nickel, 20% chromium) or any other adequate resistive material is coiled and inserted into articulated ceramic knuckles. A heat shield located in between ceramic knuckles and the outside metal sheath protects the outside structure of the band heater while directing the heat to the centre of the heater.

Aluminium or bronze cast band heatersOne or more tubular heaters are coiled into a cylindrical or half-cylinder shape and cast into bronze or aluminium.

Those heaters are designed for applications in difficult environments and applications requiring very good reliability and good heat distribution.

Cartridge heaters are used when it is not possible to use band or cast heaters, i.e. in clamp rings, adaptors Care should be taken that the heater fits tightlyinto the slot otherwise it can easily burn out

Conventional Heaters

Conventional temperature thermocouples

• Melt temperature is usually measured by thermocouples situated• against the actual melt in ports drilled through the barrel and die walls.• The tip of the probe is flush with the barrel and die surface• in order to reduce hang-up degradation and wear on the• thermocouple. • It should be noted that the melt temperature reading• will be related to the temperature of the surrounding• metal surface. • The melt temperature towards the centre of the • melt stream will usually be a few degrees higher.

• Must be well positioned and mounted

• Pressure transducers

• Melt pressure is usually measured by transducers situated against • the actual melt in ports drilled through the barrel and die walls.• By fitting pressure probes before and after the breaker plate• it is possible to constantly measure the differential pressure • and hence the degree of blocking or contamination of the screens.• Alarms can be set to shut down the machine in cases of high pressure

Energy saving in extrusion heater bands

Barrel and die heaters most important condition controlling

viscosity

RMG USA New Mica Heater bands with ceramic fibre filled insulation- less heat escapes to air savings of approx

20-30% on power consumption

New - Rex TCS products

Bonded ceramic fibre insulation

savings of 60% on energy

Induction heating Xalloy RMG USA

Injection moulding not yet on extrusion

Reducing energy in extrusion processes new developments locally

1. By Improved on-line automatic Extrusion Control system

2. Preliminary system funded by and developed at PPRC 2011 -2012 (Bo Kha, Clarke, McNally )

- real time using pressure measurements and algorithms to develop software and automatic control

3. By Supercritical additives to reduce processing temps by up to 20-30oC

NIPA Innovation Voucher – commencing January 2014 – NIPA Process capability SIG

Summary

Commence company Energy strategy and monitoring protocols immediately

Investigate improved energy efficient barrel heater bands

Improve overall insulation of barrel and dies

Formation of NIPA Energy SIG to research develop improved energy efficient processing

Industrial R&D programme Invest NI

Closing Information