Desmopan TPU Processing

7/28/2019 Desmopan TPU Processing

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Plastics Business Group

Processing and machining

Desmopan (TPU)


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Product description 4

The main advantages of Desmopan 5

General remarks 6

2.1 Form supplied 6

2.2 Storage 6

2.3 Pre-treatment of the granules 6

2.4 Post-treatment of the finished articles 8

2.5 Coloring 8

2.6 Additives 9

2.7 Occupational hygiene and environmental information 92.7.1 Air extraction 9

2.7.2 Waste disposal 9

Processing by injection molding 10

3.1 General 10

3.2 Processing parameters 12

3.2.1 Temperature settings for cylinder and mold 12

3.2.2 Plastication 13

3.2.3 Injection pressure, holding pressure, back pressure,

injection speed 143.2.4 Cycle times 14

3.2.5 Demolding 15

3.3 Regrind usage 15

Tools for injection molding 16

4.1 Mold design 16

4.2 Gating 16

4.3 Hot runner technique and hot runner nozzles 19

4.4 Flow characteristics of the mold 22

4.5 Mold venting 22

4.6 Shrinkage 23

4.7 Demolding 24

4.7.1 Cavity surface 24

4.7.2 Drafts 24

4.7.3 Ejectors 24

4.8 Defects in injection molding 25

2

Contents

1.

3.

4.

2 .


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8.

3

Processing by extrusion 26

5.1 General 26

5.2 Screw design 28

5.3 Processing parameters 30

5.3.1 Temperature setting for the barrel and die 30

5.3.2 Screw speed 30

5.4 Adapters and extrusion dies 31

5.4.1 Adapters 31

5.4.2 Melt pump 31

5.4.3 Extrusion dies 32

5.5 Cooling and calibrating the extrudate 34

5.6 Extruded articles 345.6.1 Tubing 34

5.6.2 Sheathing of electric cables, ropes and connecting hoses 36

5.6.3 Profiles 36

5.6.4 Flat film 37

5.6.5 Blown film 37

5.6.6 Extrusion coating 38

5.6.7 Coextrusion 38

5.6.8 Extrusion blow molding 38

5.7 Defects in extrusion 39

Machining and fabrication 40

6.1 Bonding 40

6.2 Welding 40

6.2.1 Hot air and nitrogen welding 40

6.2.2 Hot plate welding 40

6.2.3 Heated tool and heat impulse welding 40

6.2.4 High-frequency welding 41

6.2.5 Friction welding 41

6.2.6 Vibration welding 41

6.2.7 Ultrasonic welding 41

6.3 Machining 42

6.3.1 Sawing 42

6.3.2 Drilling 42

6.3.3 Turning 42

6.3.4 Milling and planing 43

6.3.5 Punching 43

6.3.6 Thread cutting 43

Index 44

Range of products and Bayer service 46

5.

6.

7.


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100

101 10

210

310

4

70A 75D Shore hardness

MPa

Elasticitymodulus

4

1. Product description

Rubber

Desmopan

Polyamid 6 and 66

ABS

PC

POM

PA-GF; PC-GF

Desmopan is the trade name for Bayersrange of thermoplastic polyurethanes (TPUs). On the

basis of its excellent property profile, Desmopan can be

categorized as a high-grade thermoplastic elastomer

(TPE), bridging the gap between rubber and traditional

thermoplastics.

Desmopan, the link between

rubber and plastic


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5

High abrasion resistance

High elasticity over the entire

hardness rang

Excellent low-temperature

impact strength

Flexibility over a wide

temperature range

Freedom from plasticizers

Excellent resistance to oils,

greases and many solvents

Good resistance to weathering

and high-energy radiation

Pleasant tactile properties

Weldable and bondable

Easy coloring

Easy recycling

Excellent rot resistance

(special grades)

The main advantages of Desmopan


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Moisture

content

1

Storage period

2 3 4 5 7

0,6

0,4

0,3

0,2

Ether-based

Ester-based

00

Moisture absorption ofDesmopan granules (at 23 C/50 % r.h.)

Days

%

2.3 Pretreatmentof the granules

TPU absorbs moisture

from the air. The extent

and rate at which this hap-

pens depends on the raw

material type, hardness

and climate (Figs. 1 and 2).

2.1 Form suppliedDesmopan is supplied as

natural colored cylindrical

or lentil-shaped granules.

Depending on the particu-

lar grade, the color ranges

from transparent/clear and

whitish opaque to white.

The product can be sup-

plied in quantities of be-tween 25 kg and 1,000 kg,

depending on the grade.

For sampling purposes,

steel drums with a content

of 30 kg can be supplied.

6

Desmopan can be

processed on the

equipment normally

used for processing

thermoplastics.

The most important

processing

techniques are:

Injection molding

Extrusion

Blow molding

2. General remarks

2.2 StorageDesmopan should be

stored in cool, dry condi-

tions. Temperatures above

40 C should be avoided.

Optimum processing is

ensured within approx.

6 months after delivery.

Fig. 1

Fig. 2

Moisturecontent

Storage period

0 122 4 6 8 10 min 16

0,10

0,06

0,04

0,02

0

0,05

%

0 1

Ether-based Desmopan

Ester-based Desmopan

Threshold value foroptimum processing

0,1

0


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Drying time

0 0 3015 45 60 75 90 105 120 min 150

0,20

0,16

0,12

0,08

0,04

%

0,14

0,10

0,06

0,02

Moisturecontent

0,05

Drying kinetics for Desmopan granules

7

To ensure trouble-free pro-cessing and avoid any loss

of quality, we recommend

drying to a moisture con-

tent of 0.05 %.

If the granules are too

moist, blisters or streaks

can occur on the surface

of the finished compo-

nents. The extrudate is no

longer smooth and glossybut foamy and gassy.

A frequent cause of de-

fects is also the use of un-

dried functional concen-

trates. These batches

should be separately

pre-dried and have a mois-

ture content 0.05 %. Such

levels can be reliably

reached in conventional

dry air and circulating airdryers (Fig. 3).

Depending on the hard-

ness, the recommended

drying temperatures are

between 80 and 110 C,

with drying times of 1 to 3

hours. Better drying can be

achieved in a shorter time

with dry-air dryers (Fig. 4).

Dried, hot granules should

not be left to cool down in

the open air. They must be

stored in dry containers

that can be re-sealed. The

machine hopper must be

kept covered over.

Fig. 4

Operation of a dry-air drierFig. 3

A = Dry airB = Return airC = Fresh airD = Waste air


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Non-return valve

Screw tip

Designed to fit nozzleMetering zone

4 d

2.75 mm

3.50 mm

4.00 mm

4.50 mm

10

Due to the high shearstress, short-compression-

zone screws are unsuit-

able. The high plasticizing

energy needed for TPU re-

quires a high torque for the

screw drive. Insufficient

torque leads to fluctua-

tions in the screw speed

and thus to non-uniform

homogenizing.

To a limited extent, highercylinder temperatures may

yield better results, al-

though there is a risk of the

material overheating. The

nozzle and cylinder head

should be designed in such

a way that there are no

dead corners in which the

material can become

lodged and thus become

thermally damaged.

3.1 GeneralOptimum processing of

Desmopan is only possible

on screw-type injection

molding machines. Well

plasticated, homogeneous

melts can be produced

with single-flighted three-

zone screws of normal

length. If a high plasticiz-

ing capacity (throughput)

is needed, longer screws

can be used (Fig. 5).

3. Processing by injection molding


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Compression zone6 d

Feed zone8 10 d

Compression = 2:1; Length 18-20 d

Flight depths for 45 mm




5.50 mm

7.00 mm

8.00 mm

9.00 mm

1 D

11

Accurate temperaturecontrol for the cylinder and

nozzle heating system is

essential.

Care must be taken that

the nozzle is heated evenly

over its entire length. Only

in this way can local over-

heating or possible freez-ing of the melt be pre-

vented.

Molten Desmopan is nei-

ther corrosive nor abra-

sive. For this reason, there

is no need for any special

steel alloy or armor-plating

of the screw.

Injection molding screw for processing Desmopan

Fig. 5

Injection molded gear shift knobsFig. 5a


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12

3. Processing by injection molding

Fig. 6

ture ranges for the individ-

ual Desmopan grades can

be found in the relevant

product information

sheets.

Fig. 6shows guide values

for the settings for cylinderand nozzle heating in rela-

tion to the Shore hardness.

3.2.1 Temperaturesettings forcylinder and mold

Injection unit

Desmopan should be

processed at melt temper-

atures of between 190 and220 C. With some hard

grades, a melt temperature

of up to 240 C may be

needed. The melt tempera-

3.2 Processing parametersMoldThe mold temperature has

a major influence on the

quality of the surface and

the demolding behavior. It

also affects shrinkage and

internal (frozen-in) stress-

es in the final component.

Normally, mold tempera-

tures of 20 - 40 C will be

used, but with some modi-fied Desmopan grades and

with glass fiber reinforced

Desmopan, mold tempera-

tures of up to 60 C will beneeded to ensure optimum

surface quality.

With thick-walled articles,

cooling down to approx.

5 C can bring a reduction

in cycle time.

Temperature profile according to hardness range

C

C

C

190 to 200 200 to 230 190 to 210 170 to 200 160 to 180

190 to 220 200 to 220 200 to 220 180 to 210 170 to 200

220 to 240 230 to 250 220 to 240 210 to 230 210 to 230


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13

3.2.2 PlasticationFor plastication, the speed

should be selected in such

a way that the peripheral

velocity of the screw does

not exceed 0.3 m/s. The

metering stroke should be

between 1 D and 4 D.

Fig. 8

If the shot volume is verylow in relation to the ca-

pacity of the cylinder, the

dwell time of the melt in

the plasticating unit will be

very long indeed. This

could result in thermal

damage to the melt (Fig. 8).

Fig. 7shows the maximumspeeds for various screw

diameters.

Practical experience has

shown that a 30 - 75 % ca-

pacity utilization of the re-

spective cylinder is bene-

ficial.

Fig. 7

Normal screw diameters0 30 90 150

min-1

100

60

20

S

peed

mm60

40

80

120

200

160

140

Speed at V = 0.2 m/secSpeed at V = 0.3 m/sec

Screw speed range as a function of diameter

Breakdown of the TPU meltin the processing cylinder at a melt temperature of 220 C

TPU 90 Shore A

Dwell time of the melt in the cylinder

Elongation

atbreak

500

0

40

30

25

00 1 10 15 min 20

%

2 5

MPa

350

300

200

400

250

Tearstrength

Elongation at breakTear strength

70 to 85 Shore A

85 to 95 Shore A35 to 50 Shore D

50 to 74 Shore D

heated20 - 40 C

Shore hardness


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Molds for Desmopan

should be made of the

same kind of steel as is

used for molding thermo-

plastics. Simple molds for

small production runs can

also be made of aluminum

alloys.

For prototype trial molds,inserts of casting resin or

pressure die-cast metal

could even be used.

4. Tools for injection molding

The following types of

mold are suitable for pro-

cessing Desmopan:

Two-plate mold

Three-plate mold

Split mold

Positive mold

Multi-daylight mold

Hard thermoplastics

Desmopan

4.1 Mold design

The following types of gate

are commonly used for

Desmopan:

Edge gate

Film gate

Diaphragm gate

Pinpoint gate

Ring gate

Sprue gate

Tunnel gate

Hot runner gate

The gates, runners and

sprues should be 25 - 50 %

larger than with hard ther-

moplastics (Fig. 12). Signifi-

cant pressure drops in the

gating system should be

avoided.

Design of a sprue bushingFig. 12

4.2 Gating

Taper angle (4 )

Spruelength

max.

150mm


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17

As far as the runners are

concerned, the flow chan-

nel must be designed in

such a way that the full di-

ameter of the runner isused and that it is posi-

tioned in one or both

halves of the mold (Fig. 13).

In multi-cavity molds, e.g.

two-plate or three-plate

types, the runners should

be arranged in such a way

that the flow paths are all

roughly the same

length(Fig. 14).

Runners for multi-cavity moldsFig. 14

Runner cross sections Fig. 13

Wrong Right


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18


Pin-point gates must havea weakened point on the

gate cross section to en-

sure a clean tear-off. Large

pin-point gates must not

involve any jetting, other-

wise squeeze marks can

occur on the component.

With axially symmetric

parts, it may be useful to

work with ring-type or di-

aphragm gates to prevent

the formation of flow lines.

Mold filling and venting

must be kept under tight

control (Fig. 15). A film gate

is an advantage with large

flat, long parts, as the mold

is optimally filled (Fig. 16).

A tunnel gate is the best

solution if the gating point

is not visible (Fig. 17).

Gate forms Fig. 15

Clothes hanger-type film gateFig. 16

Cross section A-B

Ring gate Diaphragm gate

3 - 6 Pin-pointor film gate

Weakened point0.5 - 0.1 mm


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19

Hot runner feed systems

are becoming increasing

popular in the processing

of thermoplastics. With

Desmopan, too, this tech-

nique is being used more

and more often. Fig. 18 lists

some of the main criteria

for this method.

4.3 Hot runnertechnique andhot runnernozzles

Tunnel gate with lenticular feedFig. 17

Demands on the hot runner systemFig. 18

1. Flow technology

Optimum rheological design:

- Minimal rise in temperature-

due to shear

- Tolerable shear rates(at flow restrictions< 5,000 s-1)

- Low pressure drop (openflow channels should bepreferred to annular crosssections)

2. Temperature control

Good temperature controland precise temperaturemeasurement:

- Adequate number of control

circuits

- Position thermocouple wheremax. temperatures occur

- Good thermal separationbetween cold injectionmolding tool and hot runner

- Uniform temperature overthe entire length of therunner

3. Mechanical aspects

Factors to taken into accountin the design of a hot runner:

- Injection pressure

- Clamping, sealing andbearing forces

- Thermal expansion

- Surface of runner polished

- Runner diameter < 7 mm:Pressure increase

- Runner diameter >11 mm:Long dwell time


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20

Fig. 19

Fig. 20

Fig. 21

Hot runner nozzles

Type 1: Open nozzlefor direct gating

Open nozzle withoutplastic insulating cap

Not very common for pro-

cessing TPU, because of

poor thermal separation,

resulting in shiners, halo-

ing, sticking and material

drooling (Fig. 19).

Open nozzle with plasticinsulating cap

The insulating cap and

cooling system lead to

better thermal separation

(Fig. 20).

Open nozzle withtorpedo

The narrow annular slitleads to excessive shear.

Normally unsuitable for

TPU (Fig. 21).



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21

Fig. 22

Fig. 23

Wrong

Type 2: Open nozzlewith sprueThis system is used pri-

marily for large molds (sin-

gle/multiple cavity)

The particular advantages

of this construction are its

low pressure losses and

good thermal separation

(Fig. 22).

Type 3: Nozzle withneedle valveA clean gating point can

be placed directly on the

component. This gating

system is characterized by

effective heat insulation

and low pressure losses

(Fig. 23).

Right


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22

The flow behavior of

Desmopan is basically the

same as that of other ther-

moplastics. The length of

the flow path is dependent

on the melt temperature,

the wall thickness of the

part to be filled, the injec-

tion speed and the rheo-

logical properties of the

material. The injection

speed can be varied ac-

cording to the machine

and the technical circum-

stances.

Fig. 24shows the flow path

of Desmopan as a function

of melt temperature.

Particularly with thick-

walled parts of Desmopan,

good venting of the mold

cavities is essential. At the

parting line, grooves of

0.02 to 0.04 mm in depth

and 5 mm in width have

proved suitable (Fig. 25). If

the area in which the air is

compressed is not in the

area of the mold parting

line, adequate venting can

also be achieved through

pins and inserts with ap-

propriate play.

Fig.25


Venting guidelines

4.4 Flow characteristics of the mold

4.5 Mold venting

Fig. 24

160

170

180

190

200

C

220

Melttemperatu

re

0

Flow path

100 200 300 400 500 mm 700

Length of flow path as a function of temperatureSpecimen: Rectangular spiral mold, 2 x 10 mmInjection pressure: approx. 900 bar

Hard

96Sho

reA

Soft

85Sho

reA

Ground channelfor air venting0.1 mm

Ventilating channelsat intervals of ap-

prox. 30 mm

Mold

Full venting


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transverse longitudinal

Shrinkage

Hard

Medium

Soft

R-TPU

Desmopan

0 0,2 0,4 0,6 0,8 1,0 % 1,4

23

Comparison of the shrinkage ranges with Desmopan Fig. 264.6 ShrinkageIt is only possible to fix the

shrinkage data for mold

design for thermoplastic

polyurethanes within cer-

tain limits because the

shape of the article, its

wall thickness and the pro-

cessing conditions all ex-

ert a significant influence

on shrinkage. As a roughguide for mold design, a

shrinkage of approx. 1 %

can be assumed.

Minor differences in size

are balanced out by the

good elastic deformability.

Post-molding shrinkage is

greater with soft

Desmopan grades and

thin-wall articles than it is

with hard grades and

greater wall thicknesses.

Fig. 26gives an idea of the

extent of overall shrinkage.

Mold sealing area

0.020.04 mm deep

4 T l f i j ti ldi


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24

Fig. 28

Fig. 29

Com-pressedair


4.7.3 EjectorsFor TPU, the surfaces of

the ejectors should be as

large as possible to avoid

any deformation of the fin-

ished article (Fig. 28).

4.7 Demolding

DraftFig. 27

5

4.7.1 Cavitysurface

A mold cavity surface

roughness of 0.5 - 0.6 m

reduces demolding forces

and aids ejection with

Desmopan resins.

4.7.2 DraftMold drafts should be at

least 5, particularly for

components made of soft

Desmopan grades. Stag-

gered draft improves re-

lease from the mold wall

(Fig. 27).

The high elasticity ofDesmopan allows the de-

molding of undercuts and

hollow articles. Blow

moldings can be blown off

the core using com-

pressed air (Fig. 29).

Wrong Right

Small roundejectors

Large-areaejectors


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4.8 Defects in injection molding

25

Defect Possible causes

Streaks on the surfaceof the article

Granules damp (plasticated melt foams up); melttoo hot (melt is of very low viscosity, blistering onthe surface of the article)

Matt surface Melt too cold

Distinct weld line Melt too cold; injection speed too slow; moldtemperature too low; too much external releaseagent

Squeeze marks andlines Jetting due to unsuitable mold design

Flash Melt temperature too high, injection pressure toohigh; injection speed too high; locking force toolow; mold cavity not tight

Sink marks Holding pressure too low, holding pressure timetoo short; no holding pressure effect due to small

gate cross section; air in the cavity; inadequateventing; excessive wall thickness differences onthe part

Gas bubbles Back pressure too low (air is entrained in themelt); overheated melt; granules damp

Separations Melt temperature too low; impurities; incompati-

ble blend of different TPU grades

5 Processing by extrusion


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5. Processing by extrusion

Conventional thermoplas-

tic processing machines

and tools can be used in

Desmopan extrusion. The

downstream units must be

optimized for the typical

properties of TPU.

The Desmopan pellets andany functional concen-

trates must be dried before

processing to a moisture

content of 0.05 %. See

Sections 2.3 and 2.5.

Blending with regrind andcombining of different

batches is not recom-

mended.

Single-screw extruders

are normally used for ex-

truding Desmopan. Vented

barrels are unsuitable.

Heated, grooved feed

throats (Fig. 30)ensure

higher, more uniform

throughput.

26

Desmopan

grades in thehardness range between

70 Shore A and 52 Shore D

are particularly suitable

for extrusion applications.

The following products

can be extruded from

Desmopan:

Tubing

Cables

Tubular filmProfiles

Sheathings

Flat and blown film

Blow moldings

Coatings

5.1 General


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27

Fig. 30

Fig. 31

Molten Desmopan is nei-ther corrosive nor abra-

sive, which means there is

no need for a special steel

alloy or armor-plating of

the screw. The drive rat-

ings shown in Fig. 31

should be adhered to. Any

additional torque means

that processing can be

carried out at lower tem-

peratures, making for high-er dimensional stability of

the emerging melt.

Grooved feed throat

Screw diameter

90

60

40

25

15

Driverating

30 45 60 90 120

Minimum drive rating as a function of screw diameter

0

kW

mm

5 Processing by extrusion


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28

5.2 Screw designSingle-flighted three-sec-

tion screws with a length

of approx. 22 to 32 D and

constant pitch have

proved successful for pro-

cessing Desmopan. Fig. 32

shows the features of a

screw suitable for pro-

cessing Desmopan.

Extruder screw for processing Desmopan


Metering zone

7-10 D

Compression zone

7-10 D

Compression





2.5 mm

3.0 mm

4.5 mm

6.0 mm

Constant taper screws(PVC screws) and barrier

screws (e.g. Maillefer sys-

tem) can also be used.

Short-compression screws

are not suitable for pro-

cessing TPU.

Heating of the screw is not

necessary.

Shearing and mixing sec-

tions are not needed for

homogenizing Desmopan,although it may be an ad-

vantage to use mixing sec-tions if particularly high

color dispersion is needed,

for example with thin film

or coatings. The shearing

section (Fig. 33)and mixing

section (Fig. 34)should be

designed in such a way

that the energy input is as

low as possible. Dead

spots must be avoided un-

der all circumstances.

Fig. 32


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29

Toothed disk mixing section

Spiral shear section Fig. 33

Fig. 34

Feed zone

8-10 D

3:1; Length 2232 D

7.5 mm

9.0 mm

13.5 mm

18.0 mm

1 D



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30


5.3.1 Temperaturesetting for thebarrel and die

The extrusion tempera-

tures for Desmopan are in

the range between 160 and

220 C. The melt tempera-

ture ranges for the rele-vant Desmopan grades

can be found in the pro-

duct information sheets.

5.3 Processing parameters

Fig. 35gives approximate

temperatures for heating

the barrel and die.

The level of gloss on the

article surface can be

influenced by the die

temperature. Low temper-

atures produce matt

surfaces and high temper-atures glossy surfaces.

5.3.2 Screw speedIn addition to the tempera-

ture, the screw speed also

exerts a major influence on

the quality of the extrudate.

Low screw speeds mean

that the melt has to spend

a long time in the extruder,

with the result that it may

become damaged by heat.

Excessive screw speedsalso lead to thermal de-

Temperature profile according to hardness range Fig. 35

composition due to fric-tion. Speeds of between

15 and 50 rpm are recom-

mended for extruding

Desmopan.

70 to 92 Shore A170 to 170 to 170 to 170 to 170 to 170 to 170 to 160 to

210 200 200 200 210 200 190 180

180 to 180 to 180 to 180 to 180 to 180 to 180 to 180 to

220 210 210 210 220 210 200 200

92 to 95 Shore A

40 to 53 Shore D

Shore hardness

Heated20 to 40 C


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31

5.4 Adapters and extrusion dies

5.4.1 AdaptersIt is important to have ade-

quate controlled heating of

the die adapters and con-

necting flanges. With un-

heated flanges, so much

heat may be dissipated

that the temperature in thisarea drops too heavily. The

flow channels must be de-

signed so as to encourage

good flow (i.e. without any

dead spots), and the cross

section should be geared

to the mass flow rate.

5.4.2 Melt pumpA microprocessor-con-

trolled gear pump for the

melt raises the output and

improves overall quality in

the extrusion of profiles or

tubes of very low dimen-

sional tolerance. The meltpump also compensates

for any extruder-related

problems such as output

fluctuations and incorrect

pressure/temperature ra-

tios. The basic principle is

In long adapters, static

mixers have proved useful

for maintaining transverse

mixing as they ensure

greater uniformity of tem-

perature and color disper-

sion in the melt. The use of

strainer disks with and

without a screen pack is ofcourse also a possibility

(Fig. 36).

Fig. 36

that the melt pump breaks

down the extruder output

into smaller, volumetrically

controlled individual flows

and conveys them at a

very accurate rate.

Example of a strainer disk with a screen pack

Melt



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g y

Spider-type die

32

Fig. 38

Fig. 375.4.3 Extrusiondies

As far as the dies are con-

cerned, the same flow and

heating guidelines apply

as for adapters.

Desmopan can be

processed with side-fed

dies (Fig. 37), spider-type

dies (Fig. 38), flat-film dies

(Fig. 39)and flat-film coex-trusion dies (Fig. 40).

The tools must allow a uni-

form flow front and be

equipped with an easily

centered die with a paral-

lel guide (die land).

Side-fed die (tubular film production)


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Fig. 39

Fig. 40

33

Coathanger-type manifold for flat-film die

Flat-film die



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34

5.5 Cooling andcalibrating theextrudate

When the melt leaves the

die, it has low dimensional

stability. It should therefore

be cooled as close as pos-

sible to the die without in-

fluencing the temperature

control at the head of the

die. Water baths, waterspray jets, air showers or a

combination of these sys-

tems can be used for cool-

ing. To prevent any defor-

mation of the extrudate

while still in a plastic state,

cooling should be carried

out gently. The length of

the cooling section will de-

pend on the type of article,

wall thickness and take-off

speed. The final tempera-

ture should be 40 C.

Calibration systems suchas sizing/draw plates,

floating plugs and vacuum

5.6 Extrudedarticles

5.6.1 TubingTubes can be manufactured

from Desmopan either hor-

izontally or vertically. The

horizontal arrangement is

usually selected where the

pipes/tubes cannot be de-flected around corners be-

cause of their hardness

and size.

Low-friction calibrationFig. 41

calibration can only be

used with TPU if a lubricat-

ing film builds up between

the extrudate and the cali-

brating surface.

Fig. 41 shows a vacuum

low-friction calibrator.

Mandrel

Die

V Vacuum Water inlet Water outlet


35/48

Vertical manufacture is

recommended for the pro-

duction of thin-walled

tubular film that is wound

up flat.

So that the bubbles do not

collapse on leaving the die

and so that no dimensional

fluctuations occur, a con-

stant supply of calibrating

air must be passed

through the die to inflatethe tube and keep it in

shape.

Pre-cooling with air

Tube extrusion lineFig. 42

Fig. 43Fig. 42shows a tube extru-

sion line.

When extruding thin-

walled tubing, it is an ad-

vantage to pre-cool it in-

tensively with air. The flow

of air solidifies the surface

so that the subsequent wa-

ter cooling cannot make

any marks on the tube (Fig.

43).

For the take-off unit, con-veyor belts or rubber-cov-

ered caterpillar take-off

units give good results.

35

Mandrel

Die

Tube

Air

Pre-

cooling



36/48

5.6.2 Sheathing of electric cables, ropesand connecting hoses

36

Dies extending beyond the

head should be heated.

The mandrel through

which the product to be

sheathed is passed should

be adjustable in the axial

direction to allow the sur-

face quality of the sheath

to be influenced. The actu-al sheathing process is

carried out by the pressure

or tubular process (Fig. 44).

With the pressure tech-

nique, a non-circular sub-

strate can be topped up to

produce a circular cross

section. With the tubular

process, a coating of even

thickness is applied, which

largely adjusts to the given

cross section.

Adhesion of the Desmopanextrudate to the carrier

material essentially de-

pends on which sheathing

process is used. Good ad-

hesive strength can gener-

ally be achieved by the

pressure method. On the

other hand, the tube/pipe

extrusion method allows

easy peeling off of the

sheathing. By applying a

vacuum to the mandrel,

adhesion can be adjusted

to suit requirements. It is

important to have a dry,

grease-free substrate, oth-erwise blistering and ad-

hesion problems may occur.

Fig. 45shows a cable

sheathing head.

5.6.3 ProfilesDesmopan can be used to

extrude profiles with a

wide variety of different

geometries. The aim

should be to keep the wall

thickness as uniform as

possible.

With major variations in

wall thickness, the cross

sections of the die must bedesigned in such a way

that a uniform melt front is

formed.

Fig. 44Sheathing dies

Pressure die

Tubular die

Fig. 45Sheathing of electric cables


37/48

37

5.6.4 Flat filmFlat film extrusion is gener-

ally used for film thick-

nesses greater than

approx. 0.5 mm. Both the

chill-roll process and the

take-off calender are suit-

able. In the case of the

calender, the first flight

land clearance must be

adjusted so that the film ispolished on both sides. If a

matt surface is required,

matted PTFE-coated rollers

or rollers covered with

silicone rubber should be

selected. The roll tempera-

tures should be between

5 and 40 C.

5.6.5 Blown filmWith the blown film

process, film can be pro-

duced with a thickness of

between 0.02 and approx. 1

mm. The addition of func-

tional concentrates (e.g.

antiblocking agents)

makes the entire handling

process easier. Fig. 46

shows a blown film line.

Fig. 46

Blown film extruder



38/48

38

ishes and simultaneouslybonds the still plastic melt

film to the substrate. The

level of adhesion differs

from one substrate to an-

other and can be improved

with the aid of suitable ad-

hesion promoters.

5.6.6 Extrusioncoating

Woven and nonwoven fab-

rics can be coated with

Desmopan. The film, ex-

truded with a flat-film die,

is applied directly to the

substrate. A calender pol-

Fig. 47Extrusion blow molded bellows

5.6.8 Extrusionblow molding

The production of blow

moldings is possible with

specially developed

grades of Desmopan using

familiar techniques. Either

blown film dies or accumu-

lator heads can be used.

Fig. 47shows extruded

bellows components.

5.6.7 CoextrusionThrough the coextrusion of

Desmopan with hard ther-

moplastics, the range of

properties and the number

of possible applications for

the resultant articles can

be extended. Desmopan

improves the scratch

resistance, has pleasant

tactile properties and insu-lates against noise.

The coextrusion process

can also be used to apply

hot-melt adhesives to flat

and tubular film of

Desmopan.


39/48

39

5.7 Defects in extrusion

Defect Possible causes

Material lackshomogeneity

Incorrect screw geometry; temperature toolow; screw speed too high, use of regranulat-ed scrap; different grades or batches mixedtogether; cold areas in the die or adapter

Rough surface Die too cold, granules moist, incompatible ordamp masterbatch

Surface striation Deposits at the edge of the die; flash at thedie, poor color distribution; lubricant

Streaky surface Moisture, die land too long; lubricant; over-heating

Bubbles in the extrudate Moisture; melt temperature too high;residence time too long

Sink marks Uneven cooling; poor wall thickness distribu-tion; poor centering

Weld lines Melt temperature too low; poor pressurebuild-up in the die

Dimensional inaccuracies Uneven take-off speed; pulsating melt stream;poor centering; unfavorable die land

Irregular conveying Irregular feed of granules; incorrect melt tem-perature; lubricants

Low melt stability Melt temperature too high; moisture

Sticking or blocking Melt temperature too high

Melt fracture Melt temperature too low; output too high


40/48


41/48

6. Machining and fabrication


42/48

6.3.3 Turning

6.3.2 Drilling

6.3.1 Sawing

42

6.3 MachiningSharp cutting tools are

needed for Desmopan.

Hard Desmopan grades

can be machined in the

same way as polyamides,

but with soft grades (< 90

Shore A), the tough, elastic

nature of the material must

be taken into account.

Desmopan can be ma-chined on the machines

normally used for metal

and woodworking.

Excessive heat generation

should be avoided and effi-

cient removal of the shav-

ings must be ensured.

Conventional saws can be

used, but, especially when

sawing by hand, saw

blades intended for wood

usually give better results

than metal ones. Only

saws with crossed teeth

should be used.

Clearance angle = 5 - 15.

Effective tool side

rake = 25 - 30

Cutting edge angle = 40 - 60.

Cutting speed,

hard Desmopan

V = 100 - 150 m/min

Cutting speed,

soft Desmopan

V = 300 - 500 m/minAdvance velocity,

s = 0.1 - 0.2 mm/rev.

Tip radius = approx. 0.3 mm

- 0.5 mm.Twist drills with relief-

ground cutting edges

(clearance angle = 12 -

16) and a small twist an-

gle (approx. 30) are rec-

ommended.

Drill tip = 150

Cutting speed V = 40 - 50m/min.

Advance s = 0.01 - 0.03

mm/rev

Care must be taken to pro-

vide adequate ventilation

and to remove the shav-

ings. Cooling may be nec-

essary for deeper holes.

Tools of fast-cutting steel

are suitable for machining

Desmopan. The tools must

cut and not exert pressure.

With large cutting depths,

cooling with compressed

air or drilling oil emulsions

may be necessary.

The following recommen-

dations can be given forthe various mechanical

processes.


43/48


44/48


45/48

8. Range of products and Bayer service


46/48

Polycarbonates

Apec (PC-HT) Polycarbonate with high heat resistance

Makrolon (PC) Polycarbonate

Makrofol/Bayfol (PC)/(PC+PBT) blend Specialty films based on polycarbonateand polycarbonate blends

Styrenics

Novodur/Lustran ABS (ABS) Acrylonitrile/butadiene/styrenecopolymer

Lustran SAN (SAN) Styrene/acrylonitrile copolymer

Bayblend (PC+ABS) Blend of polycarbonate and acrylonitrile/butadiene/styrene copolymers

Triax (ABS+PA) Blend of ABS and polyamide

Cadon (SMA+ABS) blend Blends of styrene/maleic anhydrideand ABS

Centrex (ASA+ASA) blend Acrylonitrile/styrene/butyl acrylatecopolymer

Polyamides and polyestersDurethan (PA6, PA66, Co-PA) Polyamide

Pocan (PBT) Polybutylene terephthalate

Thermoplastic polyurethane

Desmopan/Texin1 (TPU) Thermoplastic polyurethanes

Bayer glass fibers Filler for

Chopped strands (PA, PBT, ABS, PC, PPS, PP, PF)

Milled fibers (PA, PC, PP, PTFE, PU-RRIM)Rovings (GMT)

Polymer raw materials

Bisphenol A (BPA)

Caprolactam (CPL) (Cast PA)

1 Product line of Bayer NA (Bayer Corp. USA)

Range of products, KU EuropePlastics Business Group / Engineering Thermoplastics

46


47/48

All the engineering plastics developed at Bayer have

the full know-how of our development, design and

process engineering services behind them. For more

information contact:

Bayer AG

KU-EU/Information SystemsCustomer Response Desk

Gebude B 207

D-51368 Leverkusen

Tel.: +49 214/30-2 16 16

Fax: +49 214/30-6 12 77

This is also the address to contact for any other

information (brochures, reference data tables,

Application Technology Information brochures/ATIs)on the plastics featured in this general product

brochure, as well as details of custom-tailored

grades developed for specific applications.

Bayer Service for innovative solutions and successfulapplications in virtually all sectors.

47


48/48

Bayer plastics on the Internet: http//www.plastics.bayer.com

Unless specified to the contrary, the values given have beenestablished on standardized test specimens at room tem-perature. The figures should be regarded as guide valuesonly and not as binding minimum values. Kindly note that,under certain conditions, the properties can be affected toa considerable extent by the design of the mold/die, theprocessing conditions and the coloring.

Order-Nr.: KU14202-0102e/6016177Edition: 2001-02Printed in Germany E ek 03

This information and our technical advice - whether verbal,in writing or by way of trials - are given in good faith butwithout warranty, and this also applies where proprietaryrights of third parties are involved. Our advice does not releaseyou from the obligation to check its validity and to test ourproducts as to their suitability for the intended processes anduses. The application, use and processing of our productsand the products manufactured by you on the basis of ourtechnical advice are beyond our control and, therefore, en-tirely your own responsibility. Our products are sold in ac-cordance with the current version of our General Conditionsof Sale and Delivery.

Bayer AGPlastics Business GroupD-51368 Leverkusen

Documents

Desmopan TPU Processing