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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
Flight depths for 65 mm
Flight depths for 85 mm
Flight depths for 100 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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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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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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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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4. Tools for injection molding
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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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).
4. Tools for injection molding
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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
4. Tools for injection molding
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. Tools for injection molding
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
5. Processing by extrusion
Metering zone
7-10 D
Compression zone
7-10 D
Compression
Flight depths for 45 mm
Flight depths for 60 mm
Flight depths for 90 mm
Flight depths for 120 mm
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
5. Processing by extrusion
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30
5. Processing by extrusion
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
5. Processing by extrusion
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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
5. Processing by extrusion
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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
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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
5. Processing by extrusion
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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
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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
5. Processing by extrusion
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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.
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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
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6. Machining and fabrication
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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.
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8. Range of products and Bayer service
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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
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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
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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