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Extrusion- part 1

Caroline SchauerDepartment of Materials Science and Engineering

Drexel University

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The Book of Extrusion

Chris Rauwendaal

Polymer Extrusion

Hanser Publishers

New York (1990)

ISBN 3-446-16080-9.

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Definition of Extrusion

The meaning of extrude means topush out which describes the process

In addition to polymers many different

materials are formed into profiles viaextrusion

Metals

Ceramics Foodstuffs

Pasta, sausages, cereals and some sweets

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Two basic categories of extruders

Batch (discontinuous) Ram extruder

Positive displacement pump based on pressuregradient term of equation of motion

Reciprocating ram or plunger to propel materialthrough die

Used to extrude intractable polymers Ultra-high MW polyethylene

Solid state polymers

Preparation of rubber preforms Seen in making automobile bumpers or

bottles

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Continuous

Rotating piece

Disc, drum, screw(s) to develop a steady flow

of material Screw extruder

Viscosity pump, pressure gradient term

and deformation of fluid

Seen in wire coating

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What does it look like?

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Schematic of extrusion line

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Plasticating Extruder If the extruder is fed solid chips or beads, a

melting operation is normally achieved a fewdiameters downstream of the feed inlet-called

plasticating

Melt Extruder If the extruder is feed molten polymer or fluid

Mixing Extruder dissimilar polymers

polymer plus another fluid

Polymer plus pigment or filler

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Tasks of a plasticizing extruder

Transport solid pellets or powder from

the hopper to the screw channel

Compact the pellets and move them

down the channel

Melt the pellets

Mix the polymer into a homogeneousmelt

Pump the melt through the die

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The zones along the screw

Can be up to 24 feet long!

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Three Zones- three different screwsections

Solids conveying zone

Melting or transition zone

Metering or pumping zone

Screws can be custom made-big business $$$

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Feeding system

We want smooth controlled flow. Typical problems

are arching, funnel flow (and piping). Important parameters

Bulk density

Compressibility

Internal coefficient of frictionbetween the plastic particles

External coefficient of frictionbetween plastic and hopper

Particle size and distribution

Circular hopper is better than square hopper

Temperature control (cooling) in the feeding zoneis important- occurs at the neck (throat) of thehopper to prevent softening and compaction of

feedstock

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Vertical Feed Hopper

Relies on gravity to push pellets through

Most common type of hopper

Minor fluctuations in feed rate can be

accommodated by the compression

occurring as the feed progresses down the

barrel

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Other types of hoppers

If more accurate and constant rate of feed isdesired, a dosing unit feed hopper is used-usually a controlled rate screw or conveyingbelt assemblies above the main hopper

Vibrating hoppers Prevents compaction of cohesive feedstocks-

leads to blockages known as bridges

Crammer hoppers

Force non free-flowing materials into the extruders Vacuum hoppers

Minimize air entrapment in the feedstock

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Solid Conveying ZoneCompaction

Drag Induced Conveying (Archimedean transport) Plastic moves forward from rotation of screw due to friction

with the barrel wall and not the friction with the screw.

Analogy is a nut on a screw. If the nut is free to rotate it will

not move up the screw. If the nut is held the nut movesforward.

We want high friction with the barrel

Pressure drop in the feeding zone is very small in

conventional extruders, except if a grooved barrel(for maximum friction) is used

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Grooved Feed (Barrel)

Usually optional ($)

Advantages: higher throughput@low RPM

better stability, and

ability to process very high MWconventional extruders at low

RPM/high p ressure have low th roug hpu t

Disadvantages:

complexity...

higher motor load and wear

high pressures in the grooved

region, and the screw design hasto be adapted (need strong barrel)

Feed extruders have now been developed that incorporate anadjustment mechanism that allows the depth of the grooves tobe changed

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Solid ConveyingModel

Darnell & Mol; Tadmor & Klein;

depthchannel

thflight wid

anglehelixscrew

diameterscrew

diameterbarrel

densitysin4

tan

s

b

22

h

e

D

D

ehDDNDm

feed

sbb

f

f

f

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Reduce friction on Screw Internal screw heating

Apply a coating to the screw or a surfacetreatment. PTFE impregnated nickel/chrome plating

Titanium-nitride or Boron-nitride

Tungsten-disulfide (WS2)

Advantage of a low friction coating Improves conveying along screw

Reduces tendency of plastic to build up on

screw surface, is easier to clean Reduce pressure drop

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Starve Feeding

Starve Feeding

Method of feeding the extruder where the plastic is metered intothe extruder at a rate below the flood feed rate.

The screw channel is partially empty in the first few diameters of

the extruder.

Results in very little pressure buildup in the plastic and as a

result very little frictional heating and mixing.

Effectively reduces the length of the extruder, e.g. a 25:1 L/D

extruder may have an effective length of 21 L/D with the first 4

diameters partial

Used on high speed twin screw extruders.

Reduces motor load, melt temperature, and useful when addingseveral ingredients simultaneously through one feed port from

several feeders.

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Melt Zone (Plasticizing)

Solid bed shrinksand a melt poolform.

It is important toknow wheremelting starts andends.

1-2=delay zone

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FOR EFFIECIENT USAGE

THE SCREW MUST MATCH

THE BEHAVIOR OF THEMATERIAL

I.e., need a di fferent screw for each material...

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Melting Zone

Two sources of heat

Barrel heat conducts from heaters through barrel and to melt

Viscous heating caused by shearing of melt

Drag induced melt removal

Melted material is dragged away by rotation of screw Thin melt film is essential to proper melting

Similar to a stick of butter melting in frying pan; best if movedaround

Melt thickness determined from flight clearance. Larger flight

clearance results in thicker melt film. Important to keep flight clearance small

Increase in barrel temperature may cause viscosity to dropcausing viscous dissipation to drop and less efficient melting.Thus, increase in barrel temp can reduce melting efficiency.

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Tadmors Melting Model

Gives an estimate of the melting zone, X.

Shows that if the screw diameter is taperedthen X becomes smaller.

Also highest melting efficiency (shorterlength) is with 90 helix angle but not good forconveying since 90 means that conveyingcapability is zero. Good range for helix angleis between 20 to 30.

More complex/accurate models exist (FEM)but are rarely necessary.

b=barrel, s=screw, m=melt

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Metering Zone

The most important zone: pressure isgenerated to push the plastic through the die

Analysis via characteristic curves.

First order analysis - assumptions: Newtonian fluid

Steady state flow

Viscosity is constant

No slip at the wall

infinite channel width

negligible channel curvature

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Metering Zone

The movement of plastic depends on whetheris sticks to barrel or screw. Analogy is a nut on a screw. If the nut is free to rotate it

will not move up the screw (sticks to screw). If the nut isheld the nut moves forward (sticks to barrel).

Reality is a bit more complicated: Three flow components:

Drag flow due to rotation of screw Pressure backflow due to pressure increase along

screw Leakage backflow due to pressure increase along the

screw. Total Flow profile takes into account the three

flow components

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p

NOMECLATURE

n=angular velocity (RPM) W=channel width (h

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Geometry of

screw

p

A D

A

BC

D

F

ff

ff

f

costan

preciselymoreor

costan

tan

eDW

DCDW

DCBp

C B

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Drag Flow Along the Helix

2

tan

cos

)(

WhVQ

D

p

nDV

h

yVyv

bzD

bz

bz

f

f

f

W

hF

FhWV

Q

d

dbz

D

571.01

2

d

Actually more accurately

bzV

geometry factor

F~1 if h

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DRAG FLOW IN METERING ZONE

ff

dff

ff

cossin2

tancos2

1

costan

22

2

hnDF

Q

FheDnDQ

eDW

dD

dD

p

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Pressure Backflow Along the Helix

fh

fh

f

h

23

3

3

sin12

sin12

sin

12

L

pDh

L

phD

zd

dpWhQP

The screw forces the

melt forward anddevelops a pressureTherefore there isbackflow along the helix

due to pressure differential

P

zFeeding Melting Metering

Qp

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Pressure Backflow Due to Leakage

fh

d

ffh

df

fh

d

f

tan12

costan12cos

cos12cos

322

3

revolutiononealong3

L

p

e

D

eD

LpD

e

pDQL

There is also backflowdue to pressuredifferential throughthe screw clearance

width

QL

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TOTAL FLOW

fh

ff

f

h

df

h

ff

23

22

3222

322

sin12

cossin2

1

tan

12

sin

12

cossin

2

1

L

pDhhnD

L

p

e

D

L

pDhhnD

QQQQ LPD

For more exact solution see Osswald book, 4.1.3 (RED)

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The amount of material pumped through the die isrelated to the pressure at the end of the screw. Ingeneral for a linear fluid:

For example for a cylindrical channel die:

Die Characteristic

pQ h

g

dieL

PRQ

h

8

4

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The amount of material pumped through the die is equalto the amount of material pushed through the screw:

Throughput independentof viscosity (temperature)

Operating Point

ppN h

g

h

Diecharacteristic

Screwcharacteristic

OperatingPoint

N

Q

p

hN

Np hg

NQ g

g

h

g

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Through putindependent ofviscosity (temperature)

Pressure proportionalto viscosity

(l inear visco us model)

Viscosity (Temperature) Effects

N

Q

p

hN

hlow

hhigh

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Channel depth (screw) effects

N

Q

p

hN

sLDh

hD

f

ff

23

22

sin12

cossin2

1

Deep channel

Narrowchannel

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Die effects

N

Q

p

hN

Less restrictive die(e.g., large diameter,

thick sheet)

More restrictive die(e.g., small diameter

thin sheet)die

die

L

RL

PRPQ

8

84

4

g

h

h

g

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Uniformity is highly desired.(especially in cases such asthin sheets).Problems are caused byvariations of the pressure

as a result of feednon-uniformity, variationof RPM, randomness, etc.

Example:A long die minimizes swellingbut is less sensitiveto RPM variation thana short die

Dimensional Uniformity

N

Q

p

hN

Less restrictive die(e.g., short land length)

More restrictive die(e.g., long land length)

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Summary of rules

Solid conveying zone

Channel depth H Solids conveying rateincreases with channel depth until a point

(usually 0.1-0.15 x D) then decreases Helical angle between 0 and 90 noconveying usually between 15-25 withmost common 17.66

Number of flights p increasing the numberof flights reduces the rate of solidsconveying

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Summary of Rules Plasticating zone

Helix angle no optimal helix angle for melting

Melting rate is proportional to square root of solid bed width(X)0.5

The width of the solid bed is at a maximum at the beginningof the melt zone and tapers off as melting proceeds. Thus

the highest melting rate occurs at the start of the melt zone Flight clearance, d=: standard clearance is 0.001D

Wear of screw and barrel detrimental effect in theplasticating zone

Compression zone resulting from reduced channel depth,

tends to widen the solid bed and increase the rate of melting Multiple flights Barrier flight screw

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Summary of Rules

Total length-typical L/D ratios 20:1 to 30:1 for thermoplastics

15:1 to 20:1 for elastomers

Longer L/D for high melt throughputs

Feed zone typically 4-8 D in length

Longer zones for hard, high melting point polymers

Metering zone Typically 6-10 D

Shallower channels, longer zones for restrictive dies and lowviscosity melts or to generate higher melt temperatures andimprove distributive mixing

Shorter zones, deeper channels for relatively open dies,thermally sensitive polymers and high viscosity melts

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Mixing extruders

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Optimization of screw design

There are many ways to optimizescrew

helix angle,

channel depth, width, etc.

Criteria can be

output

mixing

power

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O ti t t

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Optimum output may mean

bad mixing

High pressure flowresults in recirculationof the molten polymer =better mixing but less

output.

clearance)neglibleforvalid

-ratiothrottle(

tan

6

2

NDL

ph

Q

Qr

sD

Pd

f

h

Mi i i i l t d

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Mixing in single screw extruders

Specialty Mixing Sections - Screw

Desirable characteristics for mixingsection

Minimum pressure drop with forward pumping

capability Streamlined flow and no deadspots

Barrel surface wiped completely with nocircumferential grooves

Operator friendly and easy to install, run,clean,etc

Easy to manufacture and reasonably priced.

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Distributive Mixing Sections

Plastic melt subjected to significant shearstrain

Flow should be split frequently with

reorientation of melt Types

Cavity mixers

Pin mixers

Slotted flight mix

Variable channel depth mixers

Variable channel width mixers

Di t ib ti Mi i S ti

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Distributive Mixing SectionsCavity Transfer Mixer

Screw section and barrel section contain hemi-sphericalcavities

Advantages: Good mixing capability

Disadvantages

No forward pumping capability and is pressure consuming Reduces extruder output and increases temperature buildup

Streamlining is not very good, high cost, high installation $$

Barrel not completely wiped during processing

Di t ib ti Mi i S ti

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Distributive Mixing SectionsPin Mixer

Pin mixers are common and come in many sizes and shapes

Circular, square, rectangular, diamond-shaped

On screw or on barrel

Advantages: Good mixing capability

Disadvantages Pins cause restriction and reduce extruder output

Pins create regions of stagnation at the corner of pin and rootof screw

Di i Mi i S

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Dispersive Mixing ScrewBarrier-type / Maillefer Screw

Solid and melt are separated into two channels:

The solids channel becomes progressively shallower, forcingthe unmelted pellets against the barrel for efficient frictionalmelting, until it finally disappears into the back side of theprimary flight.

As the solids are pressed agaist the barrel the melt flows intothe melt channel which is deeper than the primary flight.Because the melt channel is deep, it causes low shearand reduces the possibility of overheating the meltedpolymer.

Di i Mi i S

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Dispersive Mixing ScrewFluted Mixing Section

Material passes through a narrow gap of barrier flightswhere mixing takes place.

flutes may have helical orientation

Leroy Union Carbide (straight flights)

No forward pumping capability and thus high pressure drop Inefficient streamlining at entry and exits

Most common for single screw extruders

Poor Helix angle design of 90

Di i Mi i S

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Dispersive Mixing ScrewStatic Mixers

Only shear (noelongation)

Pressure drop

Di i Mi i S

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Dispersive Mixing ScrewCRD Mixing Section

The first mixing device developed using numerical techniques. Introduced in 1999, it has been used successfully to replace other screws

Specifically designed to generate strong elongational flows. Elongationalflow is more effective in breaking down agglomerates and droplets thanshear flow.

It combines both distributive and dispersive mixing capability. The CRD mixer is designed to force the material through the high stress

regions several times to achieve a fine level of dispersion.

Twin Extruder

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Twin Extruder

Does not rely onfriction

Flow field complex

Highly efficient

mixing Self-cleaning

Co-rotating mostpreferred than

counter-rotating EXPENSIVE

Di t ib ti Mi i

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Distributive Mixing

Based on intenseshearing which: inceases interfacial

area

decreases local

dimensions (striationthickness)

Large strains are notenough if orientation

of inhomogeneitydoes not intersect flow lines

Di i Mi i

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Dispersive Mixing

Involves: breaking up of agglomerates(e.g., carbon black in rubber)

breaking a secondary immiscible fluid

(e.g., blends)

Distributes it into the matrix

B ki f l t

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Breaking up of agglomerates

Requires high viscosity

Tensile elongation moreefficient than simple shear

2

3 rF gh

B ki f Fl id d l t

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Breaking up of Fluid droplets

Immiscible phasetends to be spherical(but is takes time)

Intense shearing

transform a sphereinto a filament thatbreaks through aRayleigh instabilityinto smaller droplets

Coalescence worksagainst it

Time

B ki f Fl id d l t

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Breaking up of Fluid droplets

Capillary number

t=stress,R=radius of dropletss=surface tension

Breakup when capillarynumber reaches critical

value

Note the difference between

shear and elongation flow

S

RCa

s

t

2:droplet; 1:matr ix

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Mixing Devices

Batch mixers Banbury

In extrusion room

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Degassing

Degassing is done on a vented extruder vent port in barrel

Special design to insure there is zero pressure under vent

Eliminates volatiles

Most common volatile is water.

Plastics can tolerate about 0.1% moisture

Some hygroscopic plastics degrade when exposed to heat and

moisture (Polyester, Polycarbonate, nylon and polyurethane)

Two stages:

Diffusion based transport of gas from inside the granule tothe surface. Depends on monomer and morphology

Convective transport throught the pores towards the back ofthe screw (hopper) or vents.

Both temperature dependent

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Portion of Wei Suns talk on Tissue

Engineering pertaining to extrusion(real world example)

Extrusion Part 2

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Scaffold

Construction

Cell

Seeding

Separated

process

Current Limitations in Scaffold Guided Tissue

Engineering

Can we load cells

simultaneously with the

scaffold construction?

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Limitations of current fabrication techniques

Indirect Fabrication:Casting, salt leaching etc.

Difficult to build scaffold with complex architecture;

Can not deliver bioactive species

Direct Fabrication: SFF Solid Freeform FabricationSLAStereolithography, SLS - Select Sintering

LOMLaminated Object Manufacturing

FDMFused Deposition Modeling, and 3DP3D Printing

Harshheat and chemical environment

Not biocompatible to deliver bioactive medium

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Research on Development of Biopolymer Deposition

System

A viable manufacturing process that allows a controlled

deposition of biopolymer and bioactive medium for

freeform fabrication of 3D functional and bioactive

tissue substitutes

Right material/medium

Right amount

Right time/position

Right Structure

(multi-nozzle)

(drop-on-demand)

(controlled deposition)

(Physical and chemical reaction)

Overview of Biopolymer Deposition for Freeform Fabricationof 3D Tissue Scaffolds/Constructs

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40 layers, 275 micro strand pattern, 38 micro single strand

Multi-nozzle systems:

Precision extruding Solenoid-actuated Piezoelectric

Pneumatic syringe Pneumatic spray

Biopolymer: Hydrogel-Alginate/Chitosan

Fibrin PCL

Cells:

Endothelial Cardiomyoblasts (H9C2) Fibroblast

Chondrocytes Osteoblasts Smooth muscle cells

Cell deposition, cellular thread, cell pattern vascular network

US Provisional Patent #: 60/520,672

International Patent #: PCT/US2004/015316

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Micro-valvesdeposition

Processing control

Board

XYZ Mechanism

Motion ControllerMulti-channel

Signal Generator

Servo Drives

Tool Path File

MotionCommands

System Configuration

Material DeliverySystem

Motion Parameters

Data ProcessSystem

Heterogeneous fabrication

MaterialDeposition

System

Design ModelInput

Motion ControlSystem

Data interface

tissue substitutes Imaging and Monitoring System

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Drop-on-demand deposition Continuing deposition

Two Deposition Modes

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Features

Microvalve Nozzle System

Pressurized MiniExtruder

Solenoid

Microvalve

Piezoelectric

Nozzle

PneumaticMicrovalve

Deposition Mode Continuous Continuous/Droplet Droplet Continuous/Droplet

Operation/

Control

Rotating screw gear

via motor

Frequency pulse of

voltage

Frequency pulse of

voltage

Frequency pulse of

air pressure

Key Process

Parameters

Pressure and Speed

TemperatureMaterial

Nozzle diameter

Deposition speed

Pressure

Frequency pulseMaterial

Nozzle diameter

Deposition speed

Pressure


Nozzle diameter

Deposition speed

Pressure


Nozzle diameter

Deposition speed

Operating Rangelimitations

Screw speed < 1rps

Temperature

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Basic process parameters Materials (melting point)

Driven pressure and speed

Temperature

Diameter of Nozzle

Deposition speed

Pressurized Extruder Microvalve

motor

Heating bands

Nozzle tip

Material inlet

Thermal couple

Sc

rew

Worm-gear set

Average pore size:~ 200 mm

Smallest strut: 100 mmMaterial: Poly-e-Caprolactone (PCL)

Designed Scaffold

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0/900 orientation

60/1200 orientation

SEM Characterization

Wang, et al: Precision Extruding Deposition and

Characterization of Cellualr Poly-e-Caprolactone Tissue

Scaffolds, Rapid Prototyping Journal, Vol. 10, Issue 1,

2004. pp. 42-49

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Micro-CT Characterization

Samples S-1 S-2 S-3 S-4

Porosity (%) 39.1 54.9 53.6 44.2

Inter-

Connectivity

(%)

98.16 99.43 99.59 99.04

Darling, A. and Sun, W., 3D Microtomographic Characterization of Precision

Extruded Poly--Caprolactone Tissue Scaffolds, Journal of Biomedical Materials

Research Part B: Applied Biomaterials, V. 70B, Issue 2, pp. 311-317.

Bi l D iti Fl R t M t

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Biopolymer Deposition: Flow Rate MeasurementsCan we drop the right amount materials?

Experimental Set-up

Parameter Value

Pressure (P)8, 10, 12, 14,

16, 18, 20

Microvalve

Frequency (f)

363.6, 444.4,

500, 571.4, 666.6,

800, 1000, 1333.3

Sodium Alginate

Aqueous

Concentrations

(NaAC)

0.1%, 0.4%,

0.75%, 0.85%, 1%

(w/v)

Nozzle

Displacement

Velocity (v)

0 (mm/s)

Nozzle Diameter

(D)2, 3, 4, 5, 7.5 mills

AIRTank

MaterialPressureVessel

100 ml GlassBottle

Sodium AlginateAqueous Solution

Air pressure

Nozzle

PetriDish

Microvalve

MaterialManifold

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1% Sodium Alginate with 4 mills WC Gaiser

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200 1400

Frequency (Hz)

FlowRate(microlitre/second)

8 Psi

10 Psi

12 Psi

14 Psi

16 Psi

18 Psi

20 Psi

Mass Flow vs. Frequency/Pressure on

1% alginate solution with 4 mills solenoid nozzle

High Frequency/Pressure increase the flow rate

Preliminary Results on Deposition Using Solenoid Microvalve

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3% (w/v) Sodium Alginate Aqueous Solution

0

10

20

30

4050

60

70

80

5 15 25 35

Pressure (psi)

Flow

Rate

(microlitre/second)

100 m

150 m

200 m

250 m

330 m

410 m

Flow rate verse pressure under different nozzle diametersfor 3% (w/v) sodium alginate by pneumatic air nozzle

Preliminary Results on Deposition Using Pneumatic Air-Regulated

Microvalve

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04

13

1vR

n

nQ

.

11

0

1

0021

n

nn

n

n

RzP

n

nv

h

g

Using Poiseulle-based non-Newtonian fluid equation

Curve-fitting method to determine the power lawindex n for 3% (w/v) sodium alginate solution

An empirical model to predict the flow rate

)1(.

n

a Kgh

P li i R l D i i U i P i Ai R l d

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Preliminary Results on Deposition Using Pneumatic Air-Regulated

Microvalve

Feasible deposition range for 3% (w/v) sodiumalginate solution

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Syringe MovementSyringe System

Reservoir

Calcium Chloride

Solution (2nd Level)

Sodium Alginate

Solution Deposition

Cross-linked Alginate

Hydrogel (First Layer)

Second Layer

Cross-linked

Alginate Hydrogel

(Second Layer)

Syringe Movement

Syringe System

Reservoir

Calcium Chloride

Solution (1st

Level)

Sodium Alginate

Solution DepositionCross-linked Alginate

Hydrogel

First Layer

Biopolymer Deposition: Simple Geometry FormationCan we form a right structure?

3D Structure Formation

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Structure FormationPressure

NozzleSyringe Movement

rL

v= Nozzle Velocity

R = Radius of Nozzle tip

= Viscosity

= Sear Rate

Q = Volumetric Flow Rate

D= Nozzle Diameter

dp/dz = Pressure Gradient

n = Power Law Index

v

RZP

n

n

n

n

D

n

nn

n

n 15

1

0

1

02113

14

h

g


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Criteria

Velocity < 20 mm/s fordeposition systemdynamic stability

2

4

N

N

ND

Qv

Determining Optimum Nozzle Velocity VN

Tension Compression

Pneumatic Microvalve

Pressure

Syringe

Movement Nozzle

Pneumatic valve spring effect when

valve closes

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Extrusion (part 4)

Caroline SchauerDepartment of Materials Science and Engineering

Drexel University

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Alpine uses cooling as a selling point

Are all vinyl window frames and sashes the same?To just look at them, it's very difficult to see anydifference in quality between various vinyl windows.But there is. Some window manufacturers use lessexpensive compounds and extrusion techniques.

These frames can be very brittle and have a dull blueor gray cast.Alpine products, however, arecomprised of nothing but the finest virgin vinyl (PVC)powder along with the latest water cooling extrusiontechniques to ensure that you get the best framesand sashes possible.

Cooling

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Cooling Air Cooling

5W/m2/ oK natural convection

10-30 W/m2

/o

K Water bath (effective & cheap - temp should be kept const)

1000 W/m2/ Ok

Water Spray (rapid evaporative cooling)

1500 W/m2/ oK

Chill Rolls (large mass and quick heat transfer in thematerial allows for very high cooling rates).

Very effective - depends on material properties/dimensions

The extruded film is cooled while being drawn around two or more

highly polished chill rolls cored for water cooling for exact

temperature control

Requirements depend on throughput

If thickness is large then throughput should be limited

Higher cooling requirements for semicrystalline polymers

C li T k

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Cooling Tanks

Spray cooling tray with super quench option

C li t k f t

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Cooling tank features

Welded stainless steel construction Non-driven stainless steel support rollers

Alternate driven conveyors

Circulation system with reservoir

High efficiency quad spray manifolds

Self contained circulation systems Leak proof recessed lid design

In-line filters and separators

Casters and adjustable floor jacks

Super Quench cooling

ClearView lids

Geared lifters

Self contained blow-off Heat exchanger

Hot water annealing

Th R l f Pl ti P ti

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The Role of Plastic Properties

Molecular Weightaffects viscosity and swelling

Molecular Weight Distributiongives rise to power law

Chain Branchingtension stiffening (increased viscosity) -essential for blow molding

Crystallinity

affects heating/cooling requirements Fibers/Fillers

strong increase of viscosity, die wear, swellingdecreases

Products

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oducts

Pipes

PVC, PP, HDPE, ABS(acrylonitrile/butadiene/styrene)

for generalpurpose / non-pressure

ProfilesPVC, gutters/irrigation/building/plumbingPC and PMMA transparent applications (building, lighting)

Sheet, Flat Film, Coated LaminatesPVC, PC, PMMA

WiresPVC, PE

Coextrusion, and Multi-Layered products

PE (3-layer high barrier films, polyamides), Colorcombinations, Solid/Foam/Solid sandwich.Requires multiple screws and extra care in control

Meshes and GridsPE, PP

Variations on Extrusion

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Matching of rate is not trivial


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Profiles

Defects

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Incomplete melting detected by microscopy under polarized light

Inadequate mixing detected by light microscopy for thin components

Degradation discoloration, spectroscopy

high resident times, high temperature

chemical, thermal, mechanical

Weld zones around spider legs in dies

Contamination metallic slivers, packaging paper etc.

Distortion at exit thermal distortion, excessive orientation

Defects

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Shark Skin (Surface effect)

acceleration of surface at exit of thedie leads to ridged surface

high viscosity / low polydispersitypolymers are susceptible

reduce throughput, higher temperatureadditives

Melt Fracture (through thesection) when wall shear exceeds a critical

value >0.1-0.4MPa

high temperature, low throughput,

lower Mw, external lubricants, diestreamlining help.

In literature they are often not distinguished fromeach other. Current Research topics.

Documents

Extrusion 2012