ME VI ü úextruder), the output would be maximum, i.e. drag flow only: 2. If the end is closed, Q=0...

εκεηώζεηο Μαζήκαηνο «Ρενινγία & Μνξθνπνίεζε Πνιπκεξώλ Τιηθώλ»

Α.Γ. Παπαζαλαζίνπ, Αλνημε 2017

MEΡΟ VI

ΔΚΒΟΛΖ ΠΟΛΤΜΔΡΧΝ (POLYMER EXTRUSION)



ΣΗ ΔΗΝΑΗ Ζ ΔΚΒΟΛΖ?

• ΜΗΑ ΑΠΌ ΣΗ ΚΤΡΗΔ ΓΗΔΡΓΑΗΔ ΣΖΝ ΒΗΟΜΖΥΑΝΗΑ ΠΟΛΤΜΔΡΧΝ

• ΤΝΔΥΖ ΓΗΔΡΓΑΗΑ ΜΔ

ΜΔΓΑΛΖ ΔΤΔΛΗΞΗΑ ΟΟΝ ΑΦΟΡΑ ΣΟ ΣΔΛΗΚΟ ΠΡΟΗΟΝ

• ΤΥΝΑ ΔΊΝΑΗ ΣΟ ΠΡΧΣΟ ΣΑΓΗΟ Δ ΜΗΑ ΔΗΡΑ ΓΗΔΡΓΑΗΧΝ ΜΟΡΦΟΠΟΗΖΖ

Δ ΠΟΗΑ ΠΟΛΤΜΔΡΖ ΔΦΑΡΜΟΕΔΣΑΗ

• Primary Uses are Thermoplastics:

– LDPE, LLDPE, HDPE, ABS, PC, PS, Nylon,

PVC, PP

– Melt Index and Density should be matched to

application

• Some uses for Elastomers and Thermosets

– Important to watch age of material and

processing conditions





ΔΗΓΖ ΔΚΒΟΛΖ ΠΟΛΤΜΔΡΧΝ

• Compounding

– Pellets for future use

• Blown Film

– Bags, film ….

• Cast Film

– Plastic Food Packaging

• Sheet

– Foam Trays, packaging via

thermoforming


• Compounding

– Pellets for future use

• Blown Film

– Bags, film ….

• Cast Film

– Plastic Food Packaging

• Sheet

– Foam Trays, packaging via thermoforming

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• Pipe and Tubing

– PVC Pipe; Garden Hoses

• Extrusion Coating

– Paper Milk Cartons with Plastic Coating

– Wire and Cable Coating

– Underground Cables

• Monofilament

– Fishing Line, Ropes



ΤΝ-ΔΚΒΟΛΖ

• Allows Opportunity for Several Layers with Different Properties

• All Extruders for Each Material Goes into Common Die

• Die Design Determines Division of Layers

The history of extrusion goes back to Archimedes and before BUT modern developments based on understanding of the physical phenomena are less than 50 years old.

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Ο ΒΑΗΚΟ ΜΟΝΟΚΟΥΛΗΟ

ΔΚΒΟΛΔΑ

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9

• Advantages of Single Screw:

– Low Cost

– Straightforward Design

– Reliability

• Disadvantages of Single Screw:

– Mixing is not very good (for some applications)

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ΘΔΡΜΑΝΖ ΚΑΗ ΦΤΞΖ

• Heating

– Bring to startup temperature

– Maintain desired temperatures

• Cooling

– Water or Air Cooled

– To shutdown an extruder quickly

– To cool down when the polymer overheats

– To keep from bridging in the feed throat

– To keep from melting in the grooved feed



ΔΝΓΟ-ΚΟΥΛΗΑ ΘΔΡΜΑΝΖ ΚΑΗ ΦΤΞΖ

• Cartridge Heaters to heat from both sides

• Fluid Heating and Cooling

– to control melt temperature

– to prevent melting in the feed zone

– to increase pressure generation in feed



ΔΠΗΠΛΔΟΝ ΔΞΟΠΛΗΜΟ

• ΤΣΖΜΑΣΑ ΣΡΟΦΟΓΟΗΑ

– Gravimetric versus RPM-based

– Type of hopper

• ΠΗΝΑΚΑ ΔΛΔΓΥΟΤ – ΠΑΡΑΚΟΛΟΤΘΖΖ ΛΔΗΣΟΤΡΓΗΑ

• ΑΝΣΛΗΔ (GEAR PUMPS)

• ΤΣΖΜΑΣΑ ΜΔΣΑΓΟΖ ΚΗΝΖΖ



Extruder Heads and Adapters

ΔΠΗΠΔΓΔ ΚΔΦΑΛΔ ΔΚΒΟΛΖ

(FLAT EXTRUSION DIES)

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Schematic of a spider leg tuning die

Schematic of a cross-head tubing die used in film blowing

Schematic of a spiral die

Tubular Dies

ΠΗΡΑΛ ΚΔΦΑΛΔ ΔΚΒΟΛΖ

(SPIRAL EXTRUSION DIES)

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ΠΑΡΑΜΔΣΡΟΗ ΠΟΤ ΔΛΔΓΥΟΝΣΑΗ ΚΑΣΑ ΣΖΝ

ΛΔΗΣΟΤΡΓΗΑ

• Entered By Operator

– Set-Point temperatures along barrel and die

– Rotational speed of screw

• Output from Process

– Melt pressure before & after screenpack

– Temperature of the polymer melt at die

– Actual temperatures along barrel and die

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ΓΔΧΜΔΣΡΗΚΑ ΥΑΡΑΚΣΖΡΗΣΗΚΑ ΚΟΥΛΗΑ

The “standard” screw

• L ~20-30D

• Feed section ~ 4-8D

• Metering section ~6-10D

q =17.66o (E=1D)

• W =1D

• Hfeed ~0.15-0.2D

• Hf/Hm ~2-4





ΛΔΗΣΟΤΡΓΗΚΑ ΥΑΡΑΚΣΖΡΗΣΗΚΑ ΣΟΤ

ΚΟΥΛΗΑ

Screw ofDiameter Outer

Length Flighted Ratio L/D

Depth Metering

Depth Feed Ratio nCompressio



Diameter Effect

Typical Extruder Output Versus Diameter

0.1

1

10

100

1000

10000

0.1 1 10

Diameter, inches

Outp

ut,

pph

L/D Effect

Increasing L/D:

– More shear heat can be uniformly generated

without degradation

– Better mixing opportunities

– Greater Residence Times

Screw ofDiameter Outer

Length Flighted Ratio L/D



ΓΗΔΡΓΑΗΔ ΚΑΣΑ ΜΖΚΟ ΣΟΤ

ΚΟΥΛΗΑ



Feed Section

PURPOSE:

– Supply plastic at a uniform rate and pressure to

the other sections of the screw

– Compress the solids into solid bed (by

difference between barrel and screw friction)

– Allows air to be pressured back to hopper

– Be able to withstand high torque loadings

Problems in feeding will manifest themselves as air

entrapment in melt, melting inconsistencies and irregular

extrudate rate

Ζ ΕΧΝΖ ΜΔΣΑΦΟΡΑ ΣΔΡΔΧΝ (ΕΧΝΖ ΣΡΟΦΟΓΟΗΑ – Solids Conveying Zone)

Η ΖΩΝΗ ΜΕΤΑΦΟΡΑΣ ΣΤΕΡΕΩΝ (ΖΩΝΗ ΤΡΟΦΟΔΟΣΙΑΣ – Solids Conveying Zone)

How the solid pellets convey????

Barrels: rough surface (sometimes intentionally grooved) Screws: smooth (polished) surface

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25 Rheology-Extrusion - Univ. Thessaly

2015



•

– Solid region approximated by a rigid

plug in contact with all sides of

channel

– Channel depth is constant

– Neglect flight clearance

– Coefficient of friction (COF)

function of temperature but not of

pressure

– No gravity, no density differentials

in plug

ΑΝΑΛΤΗ ΕΧΝΖ ΣΡΟΦΟΓΟΗΑ

Fr=W*dz*P*fs



sin

sins bM HWpv

q

q

1 22

1 2exp

1

so b s

af W H zP z P f f

W Ha

Darnell & Mol (1956):

Max (M) when fs is small and fb is large

1

2 2 2

2

1arcsin

1

s s

s

f k f k

fq

2ln 1s

b o b

fH P Hk

f z P f W

)tan( q

ΑΝΑΛΤΗ ΕΧΝΖ ΣΡΟΦΟΓΟΗΑ

sin

Lz

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0.000 0.111 0.250 0.429 0.667

Ms[k

g/h

r]

fs/fb

Ο ρυθμός μεταφοράς των στερεών σε σχέση με το λόγο fs/fb.

Mass Flow Rate of the solid bed as a function of the ratio fs/fb:

Max (M) when fs is small and fb is large 5/15/2017

29 Rheology-Extrusion - Univ. Thessaly

2015



Solids Conveying: COF

Barrel COF Effect on Conveying

Soilds Conveying Rate versus

Coefficient of Friction on the Barrel for Soarnol EVOH

0

50

100

150

200

250

300

350

400

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Coefficient of Friction

So

lid

s C

on

ve

yin

g R

ate

,

pp

h a

t 1

00 R

PM

Dependency of COF

COF Depends On:

– Temperature

– Pressure

– Velocity (Screw Speed)

COF Measurement

– SPR-18 Term Model

– Place plastic in between metal for barrel and

metal for screw and measure COF (via torque).



0,000

100,000

200,000

300,000

400,000

500,000

600,000

0 0,001 0,002 0,003 0,004 0,005 0,006 0,007 0,008

H [m]

Ms

[k

g/h

r]

Ο ρυθμός μεταφοράς των στερεών σε σχέση με το βάθος του

καναλιού.



Feed Section - Screw Length

Length of feed section can be negligible to 1/2

the length of screw

– Industry Standard = 5 Diameters

INCREASING LENGTH:

– Increase output of the screw

– Decrease available mixing time downstream

Feed Section - Channel Depth

Solids Conveying Rate versus Channel Depth for

Various Back Pressures

0

2

4

6

8

10

12

14

16

18

20

0.4 0.5 0.6 0.7 0.8 0.9 1

Channel Depth, inches

Solid

s C

onveyin

g R

ate

, in

3/s

P1/P0 = 1

P1/P0 = 100

P1/P0 = 200

P1/P0 = 500



Solids Conveying - Feed properties:

Bulk Density

Bulk Density and

Compressibility

BULK DENSITY

– Density of the plastic including the air voids

between the particles

– Typically 20 - 40 lb/ft3

– < 10 lb/ft3, then extrusion on conventional

extruder is no longer possible

Screw Design For Bulk Density

Bulk Density Design Rules

– Bulk Density > 1/2 Solid Density

• Feed Channel = 0.1 - 0.2 D

– 1/3 Solid < Bulk Density< 1/2 Solid Density

• Deeper feed Channel Required

– Bulk Density< 1/3 Solid Density

• Crammer Feeder Needed



Solids Conveying - Feed properties:

Compressibility

Bulk Density and

Compressibility

COMPRESSIBILITY

– Difference in percent between bulk density of

loose particles and bulk density of packed

particles

– > 20%, polymer is considered “non-free-

flowing”

– Measure by “Hand Clump” Test

Bulk Density and

Compressibility

Free flowing:

•No clump in hand squeeze

test

•Angle of Repose < 45°

Non-free flowing:

•Compressibility > 20%

•Easily broken clump in hand

squeeze test

•Angle of Repose > 45°

Bridge in Hopper:

•Compressibility > 40%

•Hard clump in hand squeeze test

Difficult to feed a compressible powder



Feed Section Design

Feed Section - Channel Depth

SUMMARY OF COVNEYING SPEED

VERSUS CHANNEL DEPTH:

– Parabolic Shape to curve - therefore, optimum

depth can be chosen

– Pressure is a key variable - Increased pressure

generation comes from a shallower depth

Feed Section - Helix Angle



Feed Section Design

Feed Section - # of Flights

E ffe ct o f F ee d C h an n el D ep th o n S o lid s C o n ve yin g

R a te

0

5

10

15

20

25

30

0 .1 0 .15 0 .2 0 .25 0 .3 0 .35

C h ann e l D ep th , in ch es

So

lid

s C

on

ve

yin

g R

ate

, c

c/s

S in g le F l ig h t

D o u b le F lig h t

*Increasing # of Flights, decreases Solids

Conveying

Torsion Factor

• Feed Section produces the most pressure, and

greatest possibility of breaking screw

• TORSION Measurement:

3

1

zul

motormax

N

P

5500

3D5.0H

Where:

Hmax = maximum feed depth, inches

D = Diameter, inches

Pmotor = Power rating of the motor, horsepower

N = screw speed, rpm

zul = allowable shear stress of metal, psi

4140 Tensile 237,500 psi Yield 182,000 psi



Screw channel cross section

Ζ ΕΧΝΖ ΣΖΞΔΧ (Melting Zone)

Solids bed in an unwrapped screw channel

Predicted (Tadmor Model) and experimental solids bed profile

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“Barrier” Screw



“Basic” Extruder Analysis

• 1D Isothermal Newtonian flow between

parallel plates

– One plate moving (screw surface)

– Other plate stationary (barrel inner surface)

DP caused by constriction near the die

Conclusion: The flowrate is the sum of the drag flow and

of the pressure-driven flow

Now, let’s (conceptually) unwind the channel, and turn it into….A CHANNEL between two flat plates (assume the screw is stationary and THE BARREL ROTATES):

The barrel moves with Vb=πDN where N rotational speed of screw (e.g. RPM) and z the downchannel direction.

The down channel velocity component is: Vbz=Vbcosθ=πDNcosθ and: L=z·cosθ

Recall the FLAT PLATE EQUATIONS for drag flow with an opposing pressure flow:

dz

dPHVHWQ

122

3

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Use the helical geometry of the channel:

N = revs per second (rpm/60) of screw

L

Psin

DHcossinHNDQ

Dq

qq 2

322

122

1

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42

If we take into account the leakage flow rate from the small clearance (δ) between the barrel and the screw:

L

Ptan

e

DQL

Dq

12

322

L

Ptan

e

D

L

Psin

DHcossinHNDQ

Dq

Dq

qq

12122

1 3222

322

in our analysis we neglect this term ~ 0

NOTE: 1. If there is no pressure build-up (e.g. no constriction of flow at the end of the extruder), the output would be maximum, i.e. drag flow only:

2. If the end is closed, Q=0 and we may equate drag and pressure flow which gives the MAXIMUM POSSIBLE PRESSURE:

qq cossinHNDQmax

22

2

1

q

Dq

qq

tan

DLNmaxP

L

Psin

DHcossinHND

2

23

22 6

122

1

Since μ is large for polymer melts, extremely large (AND VERY DANGEROUS!!!) pressures can develop.

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μέγιςτη παροχή

μέγιςτη πτώςη πίεςησ

y

x

z

r

n

F

)n(

W

Q

nLmHP

2

1112D 2H

n

C

)n( Q

nLmRP

D

132 13

qq cossinHNDQmax

22

2

1

q

tan

DLNPmax 2

6

For the extruder:

Careful..!! L is the length of the METERING ZONE ONLY!

L

For the DIE (κεφαλή) the pressure drop vs flow rate can be obtained by the usual equations:

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2D Isothermal Analysis of Screw Extruders

• Parallel plate representation

(ι)=άμoλαο ηνπ θνριία, ζρεκαηίδεη

γωλία (ζ) κε ηνλ άμoλα (ρ)

(z)=helical axis

Γηα ζεηηθή ξνή, uι>0

V=πDN

ul=ux*cos(q)+uz*sin(q)



Melt Conveying

simplified flow model - Uz

(z) (y)

Flow in the y-z plane useful for

flowrate predictions

uz(H)=Vz



Melt Conveying – simplified flow

model on x-y plane

(x)

(y)

Vx=Vsin(q)



Melt conveying – simple flow theory

The Ul column shows the velocity perpendicular to the

q-plane (shaded) – in the direction of the screw axis

ux uz

ul=ux*cos(q)+uz*sin(q)

ul



Melt conveying: fluid motion

Pure drag flow No net flow

(circulation only)



Melt conveying – power calculations

?????



Melt Conveying:

geometrical corrections

Effect of finite width of

flow channel Shape factors



Melt Conveying: Effect of clearance ()

Fpn=Fp(1+fL)

And of course (H) is replaced by H- in the FD formula

Pressure gradient in the presence of leackage flow



• Parallel plate vs. annular flow

vs.

(ι)=άμoλαο ηνπ θνριία, ζρεκαηίδεη

γωλία (ζ) κε ηνλ άμoλα (ρ)

(z)=helical axis V=πDN



• Error introduced due

to flat-plate

assumption



Melt conveying: non-Newtonian

fluids



ρεδηαζκόο θαη ιεηηνπξγία εθβνιέα θνριία

Screw and die characteristics for a grooved

feed 45 mm diameter extruder with LDPE

The concept of combining die and screw

characteristic curves to obtain operating points



Dimensionless screw characteristic curves for

conventional and grooved feed extruders



ΑΛΛΔ ΓΗΟΡΘΧΔΗ

• Effect of channel non-

uniformity in z-

direction

– The operating curve

becomes steeper

• Non-isothermal

operation

ME VI ü úextruder), the output would be maximum, i.e. drag flow only: 2. If the end is closed, Q=0...

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Transcript of ME VI ü úextruder), the output would be maximum, i.e. drag flow only: 2. If the end is closed, Q=0...