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2005 10:43 Uhr Seite 1

INJECTION MOULDING
Pocketbook
INJECTION MOULDING – Pocketbook

Demag Plastics Group

Demag Ergotech GmbH

Altdorfer Str. 15
D-90571 Schwaig
Tel. +49 911/50 61-0
Fax +49 911/50 61-265
E-Mail: info-dpde@dpg.com
www.dpg.com
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Operating instructions
for NC4 control system

No other publication enjoys such a long tradition as a key When the Emergency Stop button is pressed the machine shuts
source of information as the “Injection Moulding Pocketbook”. down immediately. This includes
The many requests we have for copies of the booklet from the
pump motor – Off
injection moulding industry shows that our booklet is providing
a source of valuable information for moulders in overcoming cylinder heating – Off
problems arising in day-to-day operation.
mould heating – Off
The emphasis in this publication is not so much on technological
developments. It is rather the total concept of optimisation of Each of the following functions is switched on by pressing
the injection moulding machine, which includes the evaluation the green keys:
and selection of process parameters and the elimination of sur- pump
face defects that forms the central focus of this handbook.
cylinder heating
We should like to thank Martin Bichler, Guenter Seibold, Ansgar
Jaeger, Reinhard Gottschild, and Dr. Sabine Pahlke for their active mould heating
support.
When the corresponding red buttons are pressed these functions
are switched off.

Start button:
When the Start button is pressed in “semi-automatic“ and
“automatic“ modes, this initiates the automatic machine cycle.
In “semi automatic” mode the machine runs for only one
cycle. The Start button must be pressed to initiate each cycle.
In “automatic” mode the machine runs continuously.

Attention!
Start-up can only occur when the following conditions have
been met:
mould fully open
9
hydr. ejector back
cores moved out
Injection Moulding Pocketbook
Special publication from the Demag Plastics Group metering stop reached
Demag Ergotech GmbH
5th edition 08/2004, circulation 2,000
Copyright © 1996
Id. No.: WA gb 08/04 01 2T PP

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The injection moulding process The injection moulding process

Over the past few decades the injection moulding process, and Basics
1 all its associated processes, has advanced further than almost It is important to maintain constant environmental conditions. 1
any other manufacturing process and grown to incorporate the Avoid doors being left open, running ventilators or heating units
production of many more products. The advantages are clear: in the immediate vicinity of the machine, if possible.
favourable material All equipment in the production plant must be regularly maintai-
ned. This includes the machine, mould and all peripheral units.
lower energy consumption for moulding due to lower
processing temperatures For safety reasons, the following must be observed during
production:
direct route from raw material to end product
(single-stage operation, no secondary finishing) Work to be carried out on the open mould only when
the pump is switched off
There are a whole host of influencing factors which combine to
create cost-effective, high quality injection moulding production Gloves and safety goggles to be worn and a copper rod
which, when correctly selected and managed, all play a part in to be used when working on the hot runner
producing a first-class injection-moulded product.The factors All safety mechanisms on the machine to be checked
which influence injection moulding production are classified as at regular intervals
follows:
Setting up a machine should not just be a matter of following
1. Man tables and formulae, but each value should be considered logi-
Motivation, qualification, flexibility, experience cally and analysed.
2. The injection moulding machine Attention should be drawn to the basic difference between toggle-
Ergonomics, efficiency, accuracy, reliability, correct design, type and hydraulic direct lock injection moulding machines. In
monitoring options comparing the mould-opening strokes specified for equal-size
3. The mould toggle and hydraulic machines, it is invariably found that larger
Plastics-oriented component and gate design, thermal design, opening strokes are claimed for the hydraulic clamp. The point
rigidity, maintenance to be noted, however, is that this does not involve an increase in
the daylight between the platens, in other words, the maximum
4. The material opening stroke can be utilised only with the minimum mould
Correct choice, purity, pre-drying, only minor batch variations height. The useful opening stroke is smaller the greater the mould
5. Peripherals height – this also goes for a two-platen machine. But, actually, it
Temperature control units, hot runner control is the larger moulds that do need long opening strokes. Being a
“quasi-closed system”, the toggle clamp – with its larger daylight
6. Environment – provides the same opening stroke for every possible mould
Safety, environmental influences height. There are adequately long opening strokes available here
which, except for rare cases, accommodate all applications.

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The injection moulding process The initial setting of an

injection moulding machine

2.1 Preliminary check list

1
Part to be moulded
Have we produced this moulding before?
On which machine?
2
Is setting data already available on hard copy,
floppy disk etc.?
How many mouldings are required?
By when?
Is special measuring equipment required?
Material, dimensions and weight of moulding?

Mould
Where is the mould stored?
Does the mould need any repairs or have these been dealt
with?
How can it be transported and lifted into the machine?
Which clamping devices are required to fix the mould
in the machine?

Comparison of mould opening strokes in toggle Have the following parameters been checked to establish
and hydraulic systems the suitability of the mould on the proposed machine?
1. mould fixing dimensions
2. centring device
3. shot weight
We hope you enjoy reading this booklet and wish
you every success in the operation of your injection 4. ejector rods to fit ejector coupling (connecting dimensions)
moulding machine.
5. nozzle radius and bore and corresponding sprue bush size
6. additional equipment (core pullers etc.)

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The initial setting of an The initial setting of an

injection moulding machine injection moulding machine

Are peripheral units required such as temperature control 2.2 Preparing the machine
units, cooling units, hot runner controllers, belt conveyors?
2.2.1 Setting up the clamping unit for Demag
Are the fittings on the cooling water connections on the toggle machines 125 to 2000
machine and the mould compatible?
2 Attention! All mould adjustments to be made in 2
Has the cooling water region of the mould been leak-tested? set-up mode only
(For pressure and speeds see screen page 10 on NC4 operator
Machine
panel)
Is the proposed machine available for the production target
1. Extend the toggle. The ACTUAL value for mould stroke
date?
must be “0”.
Is the maximum clamping force sufficient?
2. Using the “Mould height” function keys, set platen distance
Has the necessary maintenance work been carried out? slightly greater than the mould height.

Has the machine been running problem-free lately? 3. Move the moving platen to maximum opening distance.

Is the appropriate screw cylinder available (cylinder head 4. Attach the mould securely to the lifting gear. The mould
volume, injection pressure)? must hang straight. Make sure that the mould halves cannot
slide apart.
Material
5. Protect the machine tie bars from damage during mould
Is there sufficient material for the job? installation.
Where is the material stored? 6. Position the mould on the fixed platen, centre and attach.
Does the material need to be pre-dried? If the mould is to be fixed using mould clamps, ensure a
proper fit.
Is there a supply of masterbatch, if required?
7. Extend the toggle. Mould stroke on the OPERATOR PANEL
must indicate “0”. Take care that the ejector rod moves into
the ejector coupling without being forced. Now by using
mould height adjustment move the moving mould half until
platen contact is made. Clamping force is now “0” kN.
8. Tighten the mould half on the moving platen. Remove safety
strap from mould, if used. Connect the ejector rod with the
ejector coupling using the slide mechanism.

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The initial setting of an The initial setting of an

injection moulding machine injection moulding machine

9. Open the mould far enough to allow the moulding to fall 2.2.2 Setting up hydraulic clamps on Demag machines
out safely. An accurate setting of the opening stroke is 25 to 120
made later when optimising the injection moulding process.
Attention! All mould adjustments to be made
10. Enter clamping force. When the Start key is pressed the in set-up mode only
2 clamp unit moves automatically to approx. 75% of the set 2
value of the clamp force. In automatic mode, when clamp 1. Move clamp unit to maximum opening distance.
force control is fitted, clamp force is regulated in stages to 2. Attach the mould securely to the lifting gear. The mould
100% of the pro-selected value. If necessary, clamp force must hang straight, Make sure that the mould halves cannot
can be in creased or decreased using the “Mould height” slide apart.
function key.
3. Protect the machine tie bars from damage during mould
11. Now move the clamp unit in set-up mode until platen con- installation.
tact is made and read off the ACTUAL value for mould
stroke. The stroke point for “Mould protection end” must 4. Position the mould on the fixed platen, centre and attach.
be set approx. 0.5 mm higher than the ACTUAL value dis- If the mould is to be fixed using mould clamps, ensure a
played, in order to be able to lock the mould. proper fit.

12. The speeds and change-over points for the mould and the 5. Move the clamp unit until platen contact is made, taking care
ejector must be compatible with the specification of the that the ejector rod moves into the ejector coupling without
mould (see comments in chapter on Cycle Sequence). being forced.

13. When clamp force is set, tighten the clamps up on the 6. Set mould height using the program switch. Actual mould
mould. If necessary, heat the mould beforehand. stroke is indicated as 2 mm.
7. Tighten the mould half on the moving platen. Remove safety
strap from mould, if used. Connect the ejector rod with the
ejector coupling using the slide mechanism.
8. Enter required clamp force.
9. To achieve clamping pressure, stroke point “Mould protection
end” must be approx. 0.5 mm higher than the set mould
height.
10. The speeds and change-over points for the mould and the
ejector must be compatible with the specification of the
mould (see comments in chapter on Cycle Sequence).
11. When clamp force is set, tighten the clamps up on the
mould. If necessary, heat the mould beforehand.

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The initial setting of an The initial setting of an

injection moulding machine injection moulding machine

2.3 Setting the injection unit 2.4 Starting production

Follow instructions in the operating manual to change When all settings have been checked the machine can be switch-
the screw cylinder. ed to the “semi-automatic” program. To enable the machine
cycle to commence once the Start key has been pressed, the fol-
2 1. Enter the material-related temperatures required for the
lowing start conditions must be fulfilled:
2
cylinder heating zones and for flange temperature control.
Mould open stop reached Ejector back
2. Turn on water supply to the machine.
Metering Stop reached (dose manually beforehand and,
3. Switch on cylinder heating.
if necessary, depending on the type of material, purge the
4. Set reference point for injection unit. All heating zones must material a few times). If one or more of the start conditions
be up to SET temperature and the mould must be locked. are not met, alarms will be raised on the Operator panel.

5. In set-up mode, move the nozzle until it makes contact with As a rule, no monitoring functions or tolerances should be set
the mould. Then set to zero using program switch “Reference during the start-up phase.
point IU”.
The machine can be switched to “fully automatic” after a few
6. Check nozzle radius centring and dipping depth. cycles, once the mouldings are being ejected and falling clear.
At this point process optimisation can begin (more detailed
7. Enter nozzle contact pressure, strokes and speeds for the
information can be found in Chapter 5 “Process Optimisation
injection unit.
on the injection moulding machine”). The following sequence
8. Enter metering stroke according to the necessary shot weight. is recommended:
Calculate, if need be, taking into account the necessary melt
optimise metering
cushion.
optimise injection speed
9. Enter injection pressure, injection speed, follow-up pressure,
follow-up pressure time, cooling time, back pressure and determine follow-up pressure and follow-up pressure time
screw speed. See Chapter 4.1 “Processing Guidelines”.
limit injection pressure
10. Switch on program switch “Change over to follow-up
determine cooling time
pressure dependent on volume” (pN volume).
ensure smooth operation of the clamping unit
11. Enter stroke point for “Follow-up pressure start”. Follow-up
pressure start should occur at around 80 to 90 % of the shot optimise clamping force
volume. As a rule, we recommend that a mould filling study
carry out checks on mouldings
be made on new moulds to determine the exact change-over
point. In this case, follow-up pressure should be set to “0”.
12. If necessary, set decompression to release the pressure of melt
in the cylinder if an open nozzle is used.

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The initial setting of an Notes

injection moulding machine

When the mouldings have reached the required quality standard

and the cycle time is satisfactory, the important parameters can
be monitored by setting tolerance limits using process control.
Save the set machine data by storing the programme on floppy
2 disk. In addition a hard copy should be made. 2

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The cycle sequence The cycle sequence

on a Demag machine on a Demag machine

3.1 Closing the clamping unit Operating sequence

Assuming that the machine is a standard model of the Extra,
Fig. 1 Compact, Concept or System Series, the cycle will proceed as
follows: (see Fig. 1)
All Start conditions must be met to enable the clamp unit to
be started (in semi- or fully automatic operation). (See Fig.1)
The clamp unit moves from Pos. [1] “Mould open Stop”
3 to Pos. [2] on high pressure and at speed “Mould close V1”. 3
At Pos. [2] “Mould close” there is a change of speed to
“Mould close V2”.
At Pos. [3] “Mould close” there is a change of speed to
“Mould close V3”.
Pos. [3] should be set so that speed V3 comes into effect
at the very latest by the start of reduced mould clamping
pressure at Pos. [4].
If Pos. [3] is set after Pos. [4] there will be an automatic
change over to V3 at Pos. [4].
Pos. [4] – “Mould protection start” – reduced mould clam-
ping pressure begins. This switch over point should occur
30-60 mm before platen contact or, in the case of a sliding
splits mould, before the angled dowel moves into the splits.
Reduced mould clamping pressure should be set just high
Start conditions:
enough for the mould to close.
Mould open stop
On platen contact – Pos. [5] – the high pressure must be
Hydraulic ejector back stop switched on again by the position point “Mould protection
end” to achieve the set clamping force.
Guard door closed
At the same time as the mould closing movement “Mould
Cylinder up to temperature
protection time” (determined empirically”) starts at Pos. [4]
Start key depressed and should not have finished by Pos. [5]. Otherwise, the
cycle will be interrupted. (Exception: activation of “Mould
protection repeat” program).

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The cycle sequence The cycle sequence

on a Demag machine on a Demag machine

3.2 Injection and follow-up pressure phase Operating sequence

Fig. 2 When start conditions have been met (see Fig. 2) the injection
unit moves forward to Pos. [8] on speed “lU forward V1”.
At Pos. [8] there is a change over to speed “lU forward V2”.
The injection unit now moves forward on speed V2 until the
cylinder nozzle makes contact with the sprue bush on the
mould Pos. [9].
3 Nozzle contact pressure now starts to build. When the given
3
nozzle contact pressure is reached, this initiates injection.
The set values for “Injection pressure” and “Injection speed”
are also required.
Injection stages – 10 max. “Follow-up pressure start” at Pos. [10] initiates stroke depen-
Follow-up pressure stages – 10 max. dent change-over from injection pressure to follow-up pres-
sure. Alternatively, the change-over to follow-up pressure can
occur depending on time or pressure.
If it is necessary to inject at varying speeds, the machine can
operate on up to 10 different injection speeds. The speeds
and stroke-dependent change-over points required can be set
on the “Injection profile” page.
The follow-up pressure phase is operative from Pos. [10] to
Pos. [11]. If follow-up pressure needs to be stepped, this can
be set on the “Follow-up pressure profile” page.
A reading for the actual melt cushion can be taken from the
Process Optimisation page.

Start conditions: The tolerances are set on the “Process control” page.

Clamp force reached

Guard door closed
Injection unit guard door closed
Cylinder up to temperature
Metering Stop and Screw back' reached

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The cycle sequence The cycle sequence

on a Demag machine on a Demag machine

3.3 Metering, screw and injection unit back after Operating sequence
metering
When the "Follow-up pressure times" have finished,
Fig. 3 “Cooling time” begins. Metering (melt processing) begins at
Pos. [12] when “Delayed metering” (Time) is over. Fig. 3.
Metering begins at “Screw speed” Stage 1 and “Back
pressure” Stage 1 and ends at “Metering Stop” Pos. [13].
It is possible, however, to operate on up to 6 different screw
3 speeds and 6 different screw back pressures per cycle. The
3
relevant change-over points can be set on the “Metering
profiles” page.
Next, if set, comes screw decompression with “Screw back
after metering” up to Pos. [14].
Metering – 6 stages max., If the program “lU back after metering” is switched on,
Back pressure – 6 stages max. the injection unit can be moved back on 2 speeds.
When time “lU back delayed” has elapsed, the injection unit
moves back on speed “lU back V1”. At Pos. [15] there is a
change over to the second speed “lU back V2”. The injection
unit now moves back on speed V2 as far as Pos. [16] “lU
back stop”.

Start conditions:
All activated follow-up pressure times have elapsed
Delayed metering has finished
“Screw back before metering” has been completed, if set
“IU back after metering” program

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The cycle sequence The cycle sequence

on a Demag machine on a Demag machine

3.4 Opening the clamping unit Operating sequence

When start conditions have been met (Fig. 4) the clamping
Fig. 4
unit opens from Pos. [17] to Pos. [18] on speed “Mould
open V1”.
The slow speed facilitates the gentle demoulding of parts
from the fixed mould half.
With a sliding splits mould the change-over point “Mould
3 open V1-V2” up to Pos. [18] should only be activated after
3
the angled dowel is clear of the splits.
The clamping unit then moves to Pos. [19] on speed
“Mould open V2”.
At Pos. [19] there is another change-over from speed “Mould
open V2” to “Mould open V3” to ensure smooth running of
the machine.
The machine runs on this speed to Pos. [20] “Mould open
stop”.
The entire opening stroke occurs at high pressure.

Start conditions:
Metering stop
“Screw back after metering” is completed
Injection unit back stop
Cooling time is finished

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Concise material science Concise material science

4. Concise material science Polypropylene, PP

4.1 Processing guidelines for the most important Structure:
plastics Partially crystalline

This chapter sets out basic, relevant data for the treatment and Density:
processing of the most important plastics. 0.91-0.93 g/cm3
Thermal, optical, mechanical properties:
Material Page Material is harder and more heat resistant than PE, but is less
resistant to low temperature (special low-temperature resistant
PP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 grade available). Particularly suitable for hinges. Hard, non-fragile,
excellent dielectric properties, non-toxic, not odour-proof.
PE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4 Chemical properties:
4
PS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
resistant to
ABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 acids, alkaline solutions, salt solutions, alcohol, petrol, fruit juices,
oil, milk
SAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
not resistant to
PA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 chlorinated hydrocarbons, avoid contact with copper, slight
POM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 tendency towards stress cracking
Material identification:
PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
PP is highly flammable, drips and continues to burn; burns
PMMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 brightly with blue core, strong smell of paraffin (tar-like).

PPE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Cylinder temperature:

Flange 30- 50 °C / 50 °C*
ABS/PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 MH 1 160-250 °C / 200 °C*
PBT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 MH 2 200-300 °C / 220 °C*
MH 3 220-300 °C / 240 °C*
PET. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 MH 4 220-300 °C / 240 °C*
DH 220-300 °C / 240 °C*
CA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
* These temperature profiles are valid for stroke utilisation of between 35 and
PVC (rigid). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1
PVC (flexible) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

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Concise material science Concise material science

Melt temperature: Re-processing:

220-280 °C Up to 100 % regrind can be processed.
Reduced cylinder temperature: Shrinkage:
220 °C 1.2-2.5 %. Final shrinkage can only be assessed after 24 hours.
Injection pressure: Gating:
There is no build up of very high injection pressure (800-1400 Pin gate or multi-point pin gate, hot runner, insulated runner,
bar), since flow characteristics are generally good. Exceptions ante-chamber; gate at the strongest point of the moulding.
are thin-walled packaging parts. An injection pressure of up to
Machine shut-down:
1800 bar can result on these parts.
No other material is required to follow up. PP is very resistant
Follow-up pressure and follow-up pressure time: to high temperatures.
4 Very long follow-up pressure times are necessary to avoid sink
Cylinder equipment:
4
marks (approx. 30 % of the cycle time). Follow-up pressure
Standard screw; for packaging parts special geometry L:D 25:1
approx. 30-60 % of the required injection pressure.
with shear and mixing section. Open nozzle, non-return valve.
Back pressure:
50-200 bar
Injection speed:
Fast injection speeds are needed (accumulator) for thin-walled
packaging parts. Under other circumstances average injection
speeds suffice.
Screw speed:
Peripheral velocity of up to a maximum of 1.3 m/sec . However,
this should only be set as fast as is necessary for the plasticising
process to finish before cooling time expires.
Recommended min. and max. metering stroke:
0.5-4.0 D metering stroke can be utilised.
Residual melt cushion:
2-6 mm, depending on metering stroke and screw diameter.
Pre-drying:
Not necessary; under poor storage conditions perhaps 1 hour
at 80 °C.

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Concise material science Concise material science

Polyethylene, PE-HD Melt temperature:

220-280 °C
Structure:
Partially crystalline Reduced cylinder temperature:
220 °C
Density:
0.92-0.96 g/cm3 Injection pressure:
There is no build-up of very high injection pressure (800-1400
Thermal, optical, mechanical properties: bar), since flowability is good. Exceptions are thin-walled packa-
Material is flexible to soft, resistant to temperatures up to -40 °C ging parts. An injection pressure of up to 1800 bar can result on
depending on density, impact resistant, indestructible. Good these pads.
dielectric properties, low water absorption, non-toxic, not odour-
proof. Follow-up pressure and follow-up pressure time:
4 Long follow-up pressure times on dimensionally accurate parts 4
Chemical properties: due to relatively extensive shrinkage. Pressure approx. 30-60 %
resistant to of injection pressure.
acids, alkaline solutions, solvents, alcohol, petrol, fruit juices, oil,
milk Back pressure:
50-200 bar. Too little back pressure results in uneven moulding
not resistant to weight or poor pigment dispersion during colouring.
aromatic solvents, chlorinated hydrocarbons, risk of stress crak-
king Injection speed:
Fast injection speed (accumulator) required for thin-walled
Material identification: packaging parts. Otherwise, average injection speed better.
PE is highly flammable, continues to burn when removed from
source of heat, drips. Luminous flame with blue core, smells like Screw speed:
paraffin (snuffed candles). Peripheral velocity of up to a maximum of 1.3 m/sec. However,
this should only be set as fast as is necessary for the plasticising
Cylinder temperature: process to finish before cooling time expires. Required screw
Flange 30- 50 °C / 50 °C* torque is low.
MH 1 160-250 °C / 200 °C*
MH 2 200-300 °C / 210 °C* Recommended min. and max. metering stroke:
MH 3 220-300 °C / 230 °C* 0.5-4.0 D metering stroke can be utilised.
MH 4 220-300 °C / 240 °C* Residual melt cushion:
DH 220-300 °C / 240 °C* 2-8 mm depending on metering stroke and screw diameter.
* These temperature profiles are valid for stroke utilisation of between 35 and
Pre-drying:
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.
Not necessary. Under poor storage conditions, perhaps 1 hour
at 80 °C.

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Concise material science Concise material science

Re-processing: Polystyrene, PS
Up to 100 % regrind can be processed,
Structure:
Shrinkage: Amorphous
1.5-2.5 %, substantial shrinkage, substantial warpage. Final
shrinkage can only be assessed after 24 hours. (After-shrinkage). Density:
1.05 g/cm3
Gating:
Pin gate, hot runner, insulated runner, ante-chamber pin gate. Thermal, optical, mechanical properties:
Relatively small cross sections suffice. Hard, stiff, fragile, very good dielectric properties, low water ab-
sorption, good dimensional stability, crystal clear, brilliant, good
Machine shut-down: pigmentability, no smell or taste.
No other material is required to follow up. PE is very resistant to
4 high temperatures. Chemical properties: 4
resistant to
Cylinder equipment: acids, alkaline solutions, alcohol, grease, oil, salt solutions
Standard geometry for packaging parts; special geometry L:D
25:1 with shear and mixing section; open nozzle, non-return not resistant to
valve. petrol, benzene, large number of solvents, risk of stress cracking
Material identification:
PS is highly flammable, burns bright yellow, produces a lot of
black smoke, and typically smells slightly sweet (styrene).
Cylinder temperature:
Flange 30- 50 °C / 50 °C*
MH 1 160-220 °C / 200 °C*
MH 2 180-240 °C / 210 °C*
MH 3 210-280 °C / 230 °C*
MH 4 220-280 °C / 230 °C*
DH 220-280 °C / 230 °C*
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.

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Melt temperature: Re-processing:

220-280 °C Up to 100 % regrind can be processed.
Reduced cylinder temperature: Shrinkage:
220 °C 0.3-0.6 %
Injection pressure: Gating:
There is no build-up of very high injection pressure (800-1400 Pin gate, hot runner, insulated runner, ante-chamber. Relatively
bar), because material flow is good. small cross sections suffice.
Follow-up pressure and follow-up pressure time: Machine shut-down:
Relatively short follow-up pressure time. Pressure level 30-60 % No other material is required to follow up. PS is resistant to high
of injection pressure. temperatures.
4 Back pressure: Cylinder equipment:
4
50-100 bar. If back pressure is set too low, this can result in
Standard screw
air burns in the melt (displayed as grey or black streaks in the
moulding). Open nozzle
Injection speed: Non-return valve
Generally fast. Stepped depending on shape of moulding. For
thin-walled packaging parts, as fast as possible; some jobs call for
injection with an accumulator.
Screw speed:
Fast screw speeds can be set up to a max. 1.3 m/sec peripheral
velocity. However, plasticising is best carried out slowly to suit
cooling time.
Recommended min. and max. metering stroke:
0.5-4.0 D metering stroke can be utilised.
Residual melt cushion:
2-8 mm depending on metering stroke and screw diameter.
Pre-drying:
1 hour at 80 °C if material has not been properly stored.

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Acrylonitrile-butadiene styrene, ABS Melt temperature:

220-250 °C
Structure:
Amorphous Reduced cylinder temperature:
200 °C
Density:
1.06-1.19 g/cm3 Injection pressure:
1000-1500 bar
Thermal, optical, mechanical properties:
Hard, tough even at -40 °C, good resistance to changes in tempe- Follow-up pressure and follow-up pressure time:
rature, resistance to low temperatures or heat (+100 °C) depen- Relatively short follow-up pressure time. Pressure level 30-60 %
ding on type, limited weather resistance, low water absorption, of injection pressure.
non-toxic, electroplatable. Special purpose material also crystal Back pressure:
4 clear. 50-150 bar. If back pressure is set too low, this can result in
4
Chemical properties: air burns in the melt (displayed as grey or black streaks in the
resistant to moulding).
acids, alkaline solutions, hydrocarbons, oils, fats, petrol Injection speed:
not resistant to Best stepped, slow injection to begin with, then fast (frontal flow).
acetone, ether, ethyl benzene, ethyl chloride, ethylene chloride, Fast injection speed is good for achieving glossy, sparkling sur-
aniline, aniseed oil, benzene faces, a good, strong weld line and only a slight weld line mark.
Venting channels are required on the weld line.
Material identification:
ABS is highly flammable, burns bright yellow, produces black Screw speed:
smoke and typically smells slightly sweet (styrene). Peripheral velocity of 0.6 m/sec is max. setting for screw speed.
However, it is better to set screw speed sufficiently slow so that
Cylinder temperature: plasticising finishes shortly before cooling time expires.
Flange 40- 60 °C / 50 °C*
MH 1 160-180 °C / 180 °C* Recommended min. and max. metering stroke:
MH 2 180-230 °C / 210 °C* 0.5-4.0 D metering stroke can be utilised.
MH 3 210-260 °C / 240 °C* Residual melt cushion:
MH 4 210-260 °C / 240 °C* 2-8 mm depending on metering stroke and screw diameter.
DH 210-260 °C / 240 °C*
Machine shut-down:
* These temperature profiles are valid for stroke utilisation of between 35 and
No more material is required to follow up.
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.

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Pre-drying: Styrene-acrylonitrile copolymer, SAN

To some extent, ABS can be processed direct from the original
bags without pre-drying. Otherwise, pre-dry for 3 hours at 80 °C. Structure:
Damp material causes stripes, streaks or blisters on the moulding. Amorphous

Re-processing: Density:
Providing the material has not already been charred, up to 30 % 1.08 g/cm3
regrind can be added to virgin material. Thermal, optical, mechanical properties:
Shrinkage: Excellent transparency and high gloss, good stiffness and hard-
0.4-0.7 % ness. Good resistance to changes in temperature, good chemical
resistance, good heat resistance.
Gating:
4 Pin gate possible, likewise hot runner. Wall thickness should not Chemical properties: 4
be less than 0.7 mm. resistant to
acids, alkaline solutions, saturated hydrocarbons, mineral oils,
Machine shut-down: vegetable and animal fats
No more material is required to follow up.
not resistant to
Cylinder equipment: concentrated mineral acids, aromatic hydrocarbons and chlori-
Standard screw nated hydrocarbons, ester, ether and ketone

Non-return valve Material identification:

SAN is highly flammable, burns bright yellow, is very smoky and
Open nozzle smells typically of styrene.
Cylinder temperature:
Flange 30- 50 °C / 50 °C*
MH 1 160-180 °C / 180 °C*
MH 2 180-230 °C / 210 °C*
MH 3 210_260 °C / 240 °C*
MH 4 220-260 °C / 240 °C*
DH 220-260 °C / 240 °C*
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.

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Melt temperature: Re-processing:

220-250 °C Providing no charring has occurred during initial processing, up
to 30 % regrind can be added to the virgin material. For high
Reduced cylinder temperature:
quality parts, however, virgin material should always be used.
200 °C
Shrinkage:
Injection pressure:
0.4-0.7 %
1000-1500 bar
Gating:
Follow-up pressure and follow-up pressure time:
In principle, all types of gating systems and hot runners can be
Relatively short follow-up pressure time. Pressure 30-60 %
used
of injection pressure.
Machine shut-down:
Back pressure:
4 50-100 bar. If back pressure is set too low, this can result in
No other material is required to follow up. 4
air burns in the melt (displayed as grey or black streaks in the Cylinder equipment:
moulding).
Standard screw
Injection speed:
Non-return valve
Fast injection speed is good for achieving glossy, sparkling sur-
faces, a good, strong weld line and only a slight weld line mark. Open nozzle
Screw speed:
Max. screw speed equivalent to 0.6 m/sec peripheral velocity.
Screw speed should always be set, however, so that plasticising
finishes just before cooling time expires. Average screw torque
required.
Recommended min. and max. metering stroke:
0.5-4.0 D metering stroke can be utilised.
Residual melt cushion:
2-8 mm depending on metering stroke and screw diameter.
Pre-drying:
If SAN is not stored or transported under the right conditions, it
will absorb moisture. This can cause streaks, stripes or small blis-
ters to appear on the surface of the moulding during processing.

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Polyamide, PA PA 66
Flange 60- 90 °C / 80 °C*
Structure: MH 1 260-290 °C / 280 °C*
Partially crystalline MH 2 260-290 °C / 280 °C*
Density: MH 3 280-290 °C / 290 °C*
1.14 g/cm3 MH 4 280-290 °C / 290 °C*
DH 280-290 °C / 290 °C*
Thermal, optical, mechanical properties:
* Feed performance is most strongly affected by the flange temperatures and
In balanced humidity (2-3 %), very tough. In dry conditions,
the temperatures in zone MH 1. By raising these temperatures, feed perfor-
brittle. Hard, stiff, abrasion resistant, good frictional characte- mance becomes more uniform.
ristics. Good pigmentability, non-toxic, adhesive properties.
Melt temperature:
4 Chemical properties: PA 6 240-250 °C 4
resistant to PA 66 270-290 °C
oils, petrol, benzene, alkaline solutions, solvents, chlorinated
hydrocarbons, esters, ketone Reduced cylinder temperature:
PA 220°C
not resistant to PA 66 250°C
ozone, hydrochloric acid, sulphuric acid, hydrogen peroxide
Injection pressure:
Material identification: 1000-1600 bar; on thin-walled articles with long flow paths
PA is flammable. It continues to burn when removed from source (cable clip) up to 1800 bar.
of heat, drips and blisters, becomes stringy. Blue flame with
yellow rim. Smells like burnt bone. Follow-up pressure and follow-up pressure time:
Normally, approx. 50 % of the resulting injection pressure. Short
Cylinder temperature: follow-up pressure times are sufficient, as the material solidifies
PA 6 relatively quickly. As follow-up pressure decays, so the stress in
Flange 60- 90 °C / 70 °C* the moulding reduces.
MH 1 230-240 °C / 240 °C*
MH 2 230-240 °C / 240 °C* Back pressure:
MH 3 240-250 °C / 250 °C* Set very accurately. 20-80 bar, as excessive back pressure leads
MH 4 240-250 °C / 250 °C* to uneven plasticising.
DH 230-240 °C / 250 °C* Injection speed:
Inject relatively quickly. Ensure that the mould is properly vented,
otherwise charring occurs on the moulding.

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Screw speed: Machine shut-down:

Fast screw speed possible up to 1 m/sec peripheral velocity. No other material is required to follow up. Melt dwell time in the
How-ever, it is better to set the screw speed slow enough, so cylinder is possible up to 20 min, thereafter thermal degradation
that plasticising finishes shortly before cooling time expires. of melt occurs.
Low screw torque required.
Cylinder equipment:
Recommended min. and max. metering stroke:
Standard screw
0.5-3.5 D metering stroke.
Non-return valve
Residual melt cushion:
Small melt cushion (2-6 mm), depending on metering stroke and Open nozzle
screw diameter.
Wear resistant cylinder equipment is required for glass fibre
4 Pre-drying: reinforced materials. 4
Polyamides are hygroscopic, so store in moisture-proof containers.
Close feed hopper! A moisture content of more than 0.25 % is
liable to create processing difficulties. Process directly from canis-
ter, otherwise pre-dry for 4 hours at 80 °C.
Re-processing:
10 % regrind can be added to virgin material.
Shrinkage:
0.7-2.0 PA 6, with 30 % GF: 0.3-0.8%
0.7-2.0 PA 66, with 30 % GF: 0.4-0.7%
Parts with operating temperatures above 60 °C must be annealed.
Annealing cuts down after-shrinkage i.e. the parts are dimension-
ally more stable and have lower stress. Steam treatment works
best. Polyamide mouldings can be checked for stress using solde-
ring fluid.
Gating:
Possible gating systems include pin gate, tunnel gate, film gate,
sprue gate. Blind holes are recommended for cold slugs. PA can
also be processed using a hot runner. The temperature in the hot
runner must be accurately controlled, as the melt solidifies within
a limited temperature range.

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Polyoxymethylene, POM Melt temperature:

205-215 °C
Structure:
Partially crystalline Reduced cylinder temperature:
150 °C
Density:
1.41-1.42 g/cm3 Injection pressure:
1000-1500 bar.
Thermal, optical, mechanical properties:
Hard, stiff, tough, indestructible up to -40 °C, good heat resis- For thick walled technical parts with a wall thickness of 3-4 mm,
tance, good abrasion resistance, good frictional characteristics, injection pressure amounts to approx. 1000 bar; for thin-walled
low moisture absorption, non-toxic. parts it can rise to approx. 1500 bar.
Follow-up pressure and follow-up pressure time:
4 Chemical properties:
Dependent on the wall thickness of the moulding and on mould
4
resistant to
weak acids, weak alkaline solutions, petrol, benzene, oils, alcohol temperature. The longer the follow-up pressure, the less the
shrinkage on the mouldings. Follow-up pressure should amount
not resistant to to approx. 800-1000 bar to achieve a pressure of around 600-
strong acids 700 bar in the mould. Where precision mouldings are concerned,
Material identification: it is useful if injection and follow-up pressure are the same and
Highly flammable, bluish flame, drips and continues to burn, no drops in pressure occur. Extend follow-up pressure time for
smells like formaldehyde. the same total cycle time. Weigh mouldings. When weight sta-
bilises, follow-up pressure time is optimal. More often than not
Cylinder temperature: follow-up pressure time amounts to approx. 30 % of the total
Flange 40- 50 °C/ 50 °C* cycle time. A moulding reaching 95 % ideal weight shrinks
MH 1 160-180 °C/ 180 °C* by 23 %. A moulding reaching 100 % ideal weight shrinks by
MH 2 180-205 °C/ 190 °C* 1.85 %. Slight, even shrinkage signifies consistent part size.
MH 3 185-205 °C/ 200 °C*
MH 4 195-215 °C/ 205 °C* Back pressure:
DH 190-215 °C/ 205 °C* 50-100 bar

* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1. Most favourable processing temperature around 210 °C.

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Injection speed: Machine shut-down:

Average injection speed. If injection is too slow or if mould or Switch off heating 5-10 minutes before production ends. Set
melt temperature is too low, pores tend to appear on the surface back pressure to “0” Purge cylinder. When changing to another
of the mouldings. material, e.g. PA or PC, PE should be run through in between,
as it has a broad processing latitude
Screw speed:
Max. equivalent to peripheral velocity of only approx. 0.7 m/sec. Cylinder equipment:
Advisable to set it so that plasticising finishes just before cooling
Standard screw
time expires. Average screw torque required.
Open nozzle
Recommended min. and max. metering stroke:
0.5-3.5 D metering stroke. Non-return valve
4 Residual melt cushion: 4
2-6 mm depending on metering stroke and screw diameter.
Pre-drying:
Not necessary. If material has become moist, dry for approx.
4 hours at 100 °C.
Re-processing:
100 % for straightforward applications. Up to 20 % regrind
possible for precision parts.
Shrinkage:
Approx. 2 % (1.8-3.0)
Final shrinkage only determined after 24 hours.
Gating:
Pin gate can be used for small parts with uniform wall thickness.
Select gate thickness to 50-60 % of the most concentrated wall
thickness on the moulding. It is helpful to inject against some
form of resistance in the mould cavity (core, wall), because of the
laminar flow. Processing with hot runner moulds is state of the
art.

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Polycarbonate, PC Melt temperature:

280-310 °C
Structure:
Amorphous Reduced cylinder temperature:
200 °C
Density:
1.2 g/cm3 Injection pressure:
Very high injection pressures are needed, as material does not
Thermal, optical, mechanical properties: flow well (1300-1800 bar).
Hard, stiff, impact resistant up to -100 °C, good heat resistance,
crystal clear, non-toxic, good pigmentability, low moisture ab- Follow-up pressure and follow-up pressure time:
sorption, weather resistant. Approx. 40-60 % of the required injection pressure. The lower
the follow-up pressure, the lower the stress in the mouldings.
4 Chemical properties:
Back pressure:
4
resistant to
oil, petrol, dilute acids, alcohol 100-150 bar

not resistant to Injection speed:

strong acids, alkaline solutions, benzene Dependent on flow length and wall thickness. Fast injection for
thin-walled parts. If good surface quality is required, use stepped
Material identification: (slow-fast) injection speed.
Does not burn easily, sample extinguishes away from source of
heat, burns bright yellow, is smoky, chars, blisters, has no typical Screw speed:
smell. Max. 0.6 m/sec peripheral velocity. Adjust plasticising time to suit
cooling time. High torque is required on the screw.
Cylinder temperature:
Flange 70- 90 °C / 80 °C* Recommended min. and max. metering stroke:
MH 1 230-270 °C / 250 °C* 0.5-3.5 D metering stroke can be utilised.
MH 2 260-310 °C / 270 °C* Residual melt cushion:
MH 3 280-310 °C / 290 °C* 2-6 mm depending on metering stroke and screw diameter.
MH 4 290-320 °C / 290 °C*
DH 300-320 °C / 290 °C* Pre-drying:
3 hours at 120 °C, Optimum mechanical properties if water
* These temperature profiles are valid for stroke utilisation of between 35 and
content is less than 0.02 %.
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1. Re-processing:
Up to 20 % regrind can be mixed with virgin material. Heat
resistance is also maintained if regrind quota is increased, but
the mechanical properties deteriorate.

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Shrinkage: Polymethyl methacrylate, PMMA

0.6-0.8 %
0.2-0.4 % glass fibre reinforced Structure:
Amorphous
Gating:
The diameter of the gate should correspond to at least 60-70 % Density:
of the most concentrated wall thickness on the moulding, but 1.18 g/cm3
1.2 mm is the smallest gate diameter (gate – angle of cone 3-5°, Thermal, optical, mechanical properties:
on a good surface 2°). Pin gate can be used for smaller compo- Hard, brittle, very strong, scratch-proof, crystal clear, good optical
nents with uniform wall thicknesses. quality, high gloss, extremely weather-resistant, good pigmentabi-
Machine shut-down: lity, non-toxic.
Where breaks in production occur during the night, empty the
4 cylinder and drop temperatures to approx. 200 °C. When clean-
Chemical properties: 4
resistant to
ing the cylinder it is useful to inject through with high-viscosity weak acids, weak alkaline solutions, fats and oils
PE. Draw the screw out of the heated barrel and remove residual
material from the screw using a wire brush. not resistant to
strong acids and alkaline solutions, chlorinated hydrocarbons,
Cylinder equipment: risk of stress cracking
Standard screw Material identification:
Non-return valve Highly flammable, burns brightly even when removed from
source of heat, crackling flame, rather smoky, sweet fruity smell.
Open nozzle
Cylinder temperature:
Flange 60- 80 °C / 70 °C*
MH 1 150-200 °C / 190 °C*
MH 2 180-220 °C / 210 °C*
MH 3 200-250 °C / 230 °C*
MH 4 200-250 °C / 230 °C*
DH 200-250 °C / 230 °C*
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.

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Melt temperature: Re-processing:

220-250 °C Possible with properly pre-dried and pigmented material. Crystal
clear regrind no longer produces parts with good optical quality.
Reduced cylinder temperature:
170 °C Shrinkage:
0.3-0.7 %
Injection pressure:
High pressures needed due to poor flow characteristics Gating:
(1000-1700 bar). Large gates required, as material does not flow easily. For lenses,
gate must be 0.5 mm smaller than wall thickness on the outer
Follow-up pressure and follow-up pressure time:
edge of the lenses. Smallest gate diameter – most concentrated
Very long and high follow-up pressure needed (2-3 min) for thick
wall thickness on moulding. To achieve good surface quality near
walled parts (lenses etc.). Follow-up pressure in general amounts
the gate it is important to avoid sharp edges between the gate
4 to 40-60 % of injection pressure.
and the moulding. Short, round or square gate cross-section
4
Back pressure: needed for good, long pressure transfer. Wide, thin gates are not
Relatively high back pressure required. 100-300 bar. Insufficient advisable.
back pressure causes gas bubbles in the moulding.
Machine shut-down:
Injection speed: No other material is required to follow up.
Dependent on wall thickness and flow length. For thick walled
Cylinder equipment:
articles initial injection should be extremely slow to achieve per-
fect frontal flow. Stepped injection speed (slow-fast) to obtain Standard screw; in some cases, special geometry
good surface quality near the gate.
Non-return valve
Screw speed:
Open nozzle
Plasticise as slowly as possible according to cooling time. Screw
requires high torque, max. 0.6 m/sec peripheral velocity.
Recommended min. and max. metering stroke:
0.5-3.5 D metering stroke can be utilised.
Residual melt cushion:
2-6 mm depending on metering stroke and screw diameter.
Pre-drying:
PMMA absorbs up to 1 % water. Pre-dry for 4 hours at approx.
80 °C.

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Polyphenylene ether, PPE Melt temperature:

270-290 °C
Structure:
Amorphous Reduced cylinder temperature:
200 °C
Density:
1.05-1.1 g/cm3 Injection pressure:
1000-1400 bar
Thermal, optical, mechanical properties:
Hard, stiff, good frictional and abrasion characteristics, good Follow-up pressure and follow-up pressure time:
heat resistance, low water absorption, good scratch resistance, 40-60 % of injection pressure
non-toxic. Back pressure:
30-100 bar
4 Chemical properties: 4
resistant to Injection speed:
acids, alkaline solutions, alcohol, fats, oils Mouldings with long flow paths require fast injection speed;
not resistant to in such instances, however, it is important to ensure adequate
benzene, chlorinated hydrocarbons mould venting.

Material identification: Screw speed:

Does not ignite easily, flame extinguishes away from source, does Average screw speeds. Max. peripheral velocity 0.6 m/sec.
not drip, smoky, luminous flame, pungent smell. PPE is not trans- Recommended min. and max. metering stroke:
parent. 0.5-3.5 D metering stroke can be utilised,
Cylinder temperature: Residual melt cushion:
Flange 40- 60 °C / 50 °C* 3-6 mm depending on metering stroke and screw diameter.
MH 1 240-280 °C / 250 °C*
MH 2 280-300 °C / 280 °C* Pre-drying:
MH 3 280-300 °C / 280 °C* 2 hours at 110 °C
MH 4 280-300 °C / 280 °C* Re-processing:
DH 280-300 °C / 280 °C* Can be reprocessed as regrind providing the material has not
* These temperature profiles are valid for stroke utilisation of between 35 and been charred.
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1

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Shrinkage: Acrylonitrile-butadiene styrene + polycarbonate, ABS + PC

0.8-1.5 %
Structure:
Gating: Amorphous
Pin/tunnel gate for small mouldings, otherwise sprue gate or
diaphragm gate, hot runner. Density:
1.15 g/cm3
Machine shut-down:
Switch off heating; where screw back pressure is low, dose Thermal, optical, mechanical properties:
several times and purge cylinder. Impact resistant, high gloss, light-resistant, electroplatable,
heat-resistant, good fracture resistance.
Cylinder equipment:
Chemical properties:
Standard screw
4 resistant to 4
Non-return valve limited hydrolysis resistance

Open nozzle not resistant to

ketone, ester, chlorinated hydrocarbon
Cylinder temperature:
Flange 50- 70 °C / 70 °C*
MH 1 230-250 °C / 250 °C*
MH 2 250-260 °C / 260 °C*
MH 3 250-270 °C / 265 °C*
MH 4 250-270 °C / 265 °C*
DH 250-270 °C / 270 °C*
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1

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Melt temperature: Shrinkage:

260-270 °C Shrinkage is almost identical in all axes and amounts to 0.5-
0.7 %; 0.2-0.4% on glass reinforced types.
Reduced cylinder temperature:
200 °C Gating:
Any recognised type of gate can be used. When injecting via
Injection pressure:
hot runner, temperature in the hot runner must be accurately
800-1500 bar
controlled.
Follow-up pressure and follow-up pressure time:
Machine shut-down:
Approx. 40-50% of the required injection pressure in order to
Switch off heating. Purge cylinder.
avoid sink marks appearing. Follow-up pressure must be set as
low as possible to produce low-stress mouldings. Cylinder equipment:
4 Back pressure: Standard screw up to 50 mm diameter. Where larger screw
4
diameters are concerned, use screw with lower compression
Only around 50-100 bar in order to avoid frictional heat.
and shorter metering section.
Injection speed:
Non-return valve
Average injection speed (up to 60 mm/sec) to keep frictional heat
down. Partially stepped – slow-fast. Open nozzle
Screw speed:
Max. screw speed corresponding to approx. 0.4 m/sec peripheral
velocity.
Recommended min. and max. metering stroke:
1.0-3.0 D metering stroke because the melt is susceptible to
overheating or because of excessive melt dwell time in the plas-
ticising cylinder. Dwell time for the melt in the cylinder should
not exceed 6 min.
Residual melt cushion:
2-5 mm depending on screw diameter and metering stroke.
Pre-drying:
4 hours at 80 °C.
Re-processing:
Up to 20 % regrind can be added, provided it has been properly
pre-dried and is not charred. It is better to use regrind for parts
where strength requirements are not so stringent.

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Polybutylene terephthalate, PBT Melt temperature:

250-260 °C narrow processing range below 240 °C danger of
Structure: freezing, above 270 °C material becomes charred.
Partially crystalline
Reduced cylinder temperature:
Density: 210 °C
1.30 g/cm3
Injection pressure:
Thermal, optical, mechanical properties: Injection pressure of 1000-1400 bar can result. Follow-up
Good heat resistance, good stiffness and hardness, low water pressure should amount to 50-60 % of the resulting injection
absorption, good resistance to stress cracking, excellent frictional pressure.
characteristics and abrasion resistance, good dimensional stability,
non-toxic. Back pressure:
4 Only approx. 50-100 bar in order to avoid frictional heat. 4
Chemical properties:
resistant to Injection speed:
oils, fats, alcohol, ether, petrol, weak acids, weak alkaline Fast injection speeds are required because of melt setting speed
solutions and the rate of crystallisation. Cooling or setting of the melt
during injection must be avoided. Ensure mould is well vented,
not resistant to otherwise there will be signs of charring at the end of the flow
benzene, alkalis, strong acids, strong alkaline solutions, ketone path as a result of compressed air.
Material identification: Screw speed:
Material does not ignite easily, extinguishes when removed from Max. screw speed corresponding to approx. 0.7 m/sec peripheral
flame, luminous flame, yellowy-orange, smoky, slightly sweet velocity.
aromatic smell. Recommended min. and max. metering stroke:
Cylinder temperature: 0.5-3.5 D metering stroke because melt is susceptible to over-
Flange 50- 70 °C / 70 °C* heating or because of excessive melt dwell time in the plastici-
MH 1 230-250 °C / 240 °C* sing cylinder. Dwell time for the melt in the cylinder should not
MH 2 240-260 °C / 250 °C* exceed 5 min.
MH 3 250-260 °C / 260 °C* Residual melt cushion:
MH 4 250-260 °C / 260 °C* 2-5 mm depending on metering stroke and screw diameter.
DH 250-260 °C / 260 °C*
Pre-drying:
* These temperature profiles are valid for stroke utilisation of between 35 and
4 hours at 120 °C.
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.

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Re-processing: Polyethylene terephthalate, PET

Up to 10 % regrind can be added for material types containing
flame retardants, providing the material has not been charred Structure:
and has been properly pre-dried. Up to 20 % for material types Partially crystalline
without flame retardants. Density:
Shrinkage: 1.35 g/cm3
Very dependent on mould temperature. The higher the mould Thermal, optical, mechanical properties:
temperature, the greater the shrinkage – 1.4-2.0 %. 0.4-0.6 % Good impact strength, extreme hardness and stiffness (slightly
for 30 % GF. more so than PBT), good dimensional stability, low water absorp-
Gating: tion, only slight internal stresses, good flowability.
Do not use concentric sprue or pin gate with glass fibre reinfor-
4 ced materials. Injection point should be selected so that the cavity
Chemical properties: 4
resistant to
is filled evenly. When gating via hot runner, temperature must be oils, tats, alcohol, ether, petrol, weak acids, weak alkaline
accurately controlled in the hot runner. solutions
Machine shut-down: not resistant to
Switch off heating. Empty cylinder. During breaks in production benzene, alkalis, strong acids, strong alkaline solutions, ketone
and before restarting the machine, squirt the melt out until it is
free from bubbles. Material identification:
The material is difficult to ignite, extinguishes away from flame,
Cylinder equipment: luminous flame, yellowy-orange, smoky, slightly sweet aromatic
Standard screw smell.

Non-return valve Cylinder temperature:

Flange 50- 70 °C / 70 °C*
Open nozzle MH 1 240-260 °C / 250 °C*
MH 2 240-260 °C / 250 °C*
MH 3 250-290 °C / 270 °C*
MH 4 250-290 °C / 270 °C*
DH 250-290 °C / 270 °C*
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.

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Melt temperature: Pre-drying:

270-280 °C 4 hours at 140 °C
Reduced cylinder temperature: Re-processing:
220 °C Max. 20 % regrind can be added providing it has not been
charred and has been properly pre-dried. Not possible to achieve
Injection pressure:
the same tensile, flexural and impact strength as when virgin
For thin-walled articles, injection pressure up to 1600 bar can
material is used.
result.
Shrinkage:
Follow-up pressure and follow-up pressure time:
Approx. 50-70 % of the required injection pressure in order to Varies greatly depending on material type, wall thickness, mould
avoid sink marks. Set follow-up pressure time only for as long temperature, follow-up pressure and follow-up pressure time
4 as is necessary. With amorphous materials in particular, excessive 1.2-2.0 %, or 0.4-0.6 % with 30 % GF. 4
follow-up pressure times cause increased stress, which reduces
Gating:
the impact strength of the mouldings.
Any well-known type of gate can be used. When injecting via
Back pressure: hot runner, temperature in the hot runner must be accurately
Only around 50-100 bar in order to avoid frictional heat. controlled.
Injection speed: Machine shut-down:
Fast injection speeds are required because of melt setting speed Switch off heating. Empty cylinder. When changing to another
and the rate of crystallisation. Cooling or setting of the melt thermoplastic material it is advisable to flush through with PE
during injection must be avoided. Ensure mould is well vented, or PP beforehand.
otherwise there will be signs of charring at the end of the flow
Cylinder equipment:
path as a result of compressed air.
Standard screw
Screw speed:
Max. screw speed corresponding to approx. 0.7 m/sec peripheral Non-return valve
velocity.
Recommended mm. and max. metering stroke:
0.5-3.5 D metering stroke because melt is susceptible to over-
heating or because of excessive melt dwell time in the plasti-
cising cylinder. Dwell time for the melt in the cylinder should
not exceed 5 min.
Residual melt cushion:
2-5 mm depending on metering stroke and screw diameter.

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Cellulose acetate, CA Melt temperature:

200-210 °C
Structure: Colour change in the melt indicates that melt temperature is too
Amorphous high. If melt temperature is too low, surface gloss and transpa-
Density: rency deteriorate.
1.2-1.3 g/cm3 Reduced cylinder temperature:
Thermal, optical, mechanical properties: 160 °C
Tough, resistant to boiling water, difficult to break, good scratch Injection pressure:
resistance and self-polishing effect, low electrical charging, non- 800-1200 bar
toxic, good surface gloss. The strength of this material makes it
suitable for embedding metal parts (e.g. screw drivers). Follow-up pressure and follow-up pressure time:
4 40-70 % of the injection pressure. Not too high if internal stress 4
Chemical properties: is to be avoided. Relatively long follow-up pressure for thick wall-
resistant to ed parts.
oils, fats, benzene, petrol
Back pressure:
not resistant to 50-100 bar
vinegar, acids, alkaline solutions
Injection speed:
Material identification: Fast injection speed for thin walled parts. Inject slowly for thick
Does not ignite easily, extinguishes away from flame, smoky walled parts.
with greenish yellow flame, smells of burnt paper and vinegar.
Screw speed:
Cylinder temperature: Average screw speed, corresponding to max. 0.6 m/sec starting
Flange 30- 40 °C / 40 °C* speed.
MH 1 140-160 °C / 150 °C*
MH 2 160-185 °C / 170 °C* Recommended min. and max. metering stroke:
MH 3 170-200 °C / 180 °C* 1.0-3.5 D metering stroke can be utilised.
MH 4 170-200 °C / 180 °C* Residual melt cushion:
DH 170-200 °C / 180 °C* 3-8 mm depending on metering stroke and screw diameter.
* These temperature profiles are valid for stroke utilisation of between 35 and
Pre-drying:
65 % and for parts with a flow length/wall thickness ratio of between 50:1
and 100:1.
3 hours at 70 °C.

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Re-processing: Polyvinyl chloride PVC (rigid)

Up to 20 % regrind can be added, providing it has not been
charred and is properly pre-dried. Structure:
Amorphous
Shrinkage:
0.4-0.7 % Density:
0.4 % in direction of flow 1.35 g/cm3
0.6-0.7 % across the direction of flow Thermal, optical, mechanical properties:
Gating: Stiff, hard, transparent to opaque, good bonding properties,
Pin/tunnel gate. Avoid jetting by spring-actuated auxiliary core, certain formulations non-toxic.
otherwise surface defects will occur near the gate. Chemical properties:
4 Machine shut-down: resistant to 4
Switch off heating. Plasticise several times without back pressure acids, alkaline solutions, oils, fats, petrol
and squirt melt out. not resistant to
Cylinder equipment: benzene, ketone, ester, stain removers

Standard geometry, in some cases special geometry Material identification:

Does not ignite easily, smoky, burns green, sputters, smells of
Non return valve hydrochloric acid, self-extinguishing.
Open nozzle Cylinder temperature:
Flange 30- 50 °C / 50°C*
MH 1 140-160 °C / 150°C*
MH 2 165-180 °C / 170°C*
MH 3 180-210 °C / 190°C*
MH 4 180-210 °C / 200°C*
DH 180-210 °C / 200°C*
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a tow length/wall thickness ratio of between 50:1
and 100:1.

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Melt temperature: Re-processing:

210-220 °C Can be reused providing material has not been charred.
Reduced cylinder temperature: Shrinkage:
120 °C 0.5-0.7 %
Injection pressure: Gating:
800-1600 bar Sprue, film and diaphragm gates advisable. The gate must be
radiused towards the moulding. Pin gate possible for small parts.
Follow-up pressure and follow-up pressure time:
Do not set too high. 40-60 % of injection pressure to suit the Machine shut-down:
moulding and the gate. Switch off heating. Plasticise without back pressure, let the melt
stand for 2-3 minutes and then squirt it out slowly. Repeat the
Back pressure:
4 It is very important with PVC to select the right setting, because
process until cylinder temperature has fallen to 160 °C, then 4
empty the cylinder.
the material is heat-sensitive. Heat from the friction of the screw,
when properly directed, is better than heat from the cylinder Cylinder equipment:
heater bands. Back pressure up to 300 bar is possible.
Screw geometry for rigid PVC
Injection speed:
Flighted or unflighted screw tip
Do not set too high. Make sure that the material is not subject
to shearing. For this reason, stepped injection is advisable. Open nozzle
Screw speed:
Set as low as possible, corresponding to max. speed 0.2 m/sec
peripheral velocity. With long cooling times and despite slow
screw speed, delayed plasticising can be used to ensure that
metering finishes just before cooling time expires. High, even
torque is required.
Recommended min. and max. metering stroke:
1.0-3.5 D metering stroke can be utilised.
Residual melt cushion:
1-5 mm depending on metering stroke and screw diameter.
Keep cushion small and make sure axial screw clearance is
minimal.
Pre-drying:
1 hour at 70 °C (only necessary if material has not been stored
properly).

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Polyvinyl chloride PVC (flexible) Melt temperature:

200-220 °C
Structure:
Amorphous Reduced cylinder temperature:
120 °C
Density:
1.1-1.4 g/cm3 Injection pressure:
800-1200 bar
Thermal, optical, mechanical properties:
The material is flexible, rubbery-elastic, non-toxic. Follow-up pressure and follow-up pressure time:
30-50 % of the necessary injection pressure.
Chemical properties:
resistant to Back pressure:
50-100 bar
4 acids, alkaline solutions, detergents oils, fats 4
not resistant to Injection speed:
petrol, ester, chlorinated hydrocarbons Do not inject too fast if good surface quality is required
(stepped injection, perhaps).
Material identification:
Does not ignite easily, smoky, burns green, sputters, smells Screw speed:
of hydrochloric acid with plasticiser. Set average screw speed; max. equal to 0.5 m/sec peripheral
velocity.
Cylinder temperature:
Flange 30- 50 °C / 50 °C* Recommended min. and max. metering stroke:
MH 1 140-160 °C / 150 °C* 1.0-3.5 D metering stroke can be utilised.
MH 2 150-180 °C / 165 °C* Residual melt cushion:
MH 3 160-220 °C / 180 °C* 2-6 mm depending on metering stroke and screw diameter.
MH 4 160-220 °C / 190 °C*
DH 160-220 °C / 200 °C* Pre-drying:
1 hour at 70 °C (only f material has not been properly stored).
* These temperature profiles are valid for stroke utilisation of between 35 and
65 % and for parts with a flow length/wall thickness ratio of between 50:1 Re-processing:
and 100:1. Can be reused providing material has not been charred.

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Concise material science Notes

Shrinkage:
1-2.5%
Gating;
The gate must be radiused towards the moulding. Pin gate
possible for small parts.
Machine shut-down:
Switch off heating. Plasticise several times without back pressure,
and squirt melt out.
Cylinder equipment:
Standard screw
4 4
Open nozzle
Non-return valve

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4.2 Distinguishing characteristics of plastics

Material PE PP PS SAN ABS POM PMMA PA

Distinguishing characteristics
Appearance transparent/opaque X X X X X X X
crystal clear X X X
Fracture no fracture X X
stress-whitening / tough X X X
brittle fracture X X X
Float test floats X X
sinks X X X X X X
4 Burn test highly flammable X X X X X X X X 4
slow to ignite
self-extinguishing
continues to burn X X X X X X X X
smoky X X X
not smoky X X X X X
drips X X X X
does not drip
Flame luminous yellow X X X X
bright with blue core X X
bluish X X
greenish/yellow
Smell during burn test waxy/paraffin X X
burnt bone X
slightly sweet X X X
tar-like X
pungent/formaldhyde X
like fish X
like paper and vinegar
like styrene X X X
fruity X
like hydrochloric acid
not typical
Finger nail scratch test scratch-proof X X X X X X X
not scratch-proof X

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Material PC CA PPE PET PBT ABS/PC PVC PVC

Distinguishing characteristics rigid flexible
Appearance transparent/opaque X X X X X X X
crystal clear X X X X
Fracture no fracture X X X
stress-whitening / tough X X X X X
brittle fracture
Float test floats
sinks X X X X X X X X
4 Burn test highly flammable 4
slow to ignite X X X X X X X X
self-extinguishing X X X X
continues to burn X X
smoky X X X X X X
not smoky
drips X X X
does not drip X X X
Flame luminous yellow X X X X
bright with blue core
bluish
greenish/yellow X X X
Smell during burn test waxy/paraffin
burnt bone X
slightly sweet X X X X
tar-like X
pungent/formaldhyde
like fish
like paper and vinegar X
like styrene X X
fruity
like hydrochloric acid X X
not typical X
Finger nail scratch test scratch-proof X X X X X X X
not scratch-proof X

78 79
 4

80
Material Cylinder temperature Melt Reduced

4.3
Flange MH1 MH2 MH3 MH4 DH temp. °C temp.
Polyethylene PE-LD 30-50 140-200 160-230 200-260 200-260 200-260 200-250 220
Polyethylene PE-HD 30-50 160-250 200-300 220-300 220-300 220-300 220-280 220
Polypropylene PP 30-50 160-250 200-300 220-300 220-300 220-300 220-280 220
Polystyrene PS 30-50 160-220 180-240 210-260 220-280 220-280 220-280 220
Acrylonit. -butad. styrene ABS 40-60 160-180 180-230 210-260 220-260 220-260 220-250 200
Styrene-acrylonit. copol. SAN 30-50 160-180 180-230 210-260 220-260 220-260 220-250 200
Polyvinyl chloride PVC rigid 30-50 140-160 165-180 180-210 180-210 180-210 210-220 120
Polyvinyl chloride PVC flexible 30-50 140-160 150-180 160-220 160-220 160-220 200-220 120

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Poymethylmethacrylate PMMA 60-80 150-180 180-220 200-250 200-250 200-250 220-250 170
Polyoxymethylene POM 40-50 150-180 180-205 195-215 195-215 190-210 205-215 150
Polycarbonate PC 70-90 230-270 280-310 280-310 290-320 290-320 280-310 200

and demoulding temperatures

Polyamide 6 PA 6 60-90 230-240 230-240 240-250 240-250 230-240 240-250 220
Polyamide 66 PA 66 60-90 260-280 260-280 280-290 280-290 280-290 270-280 250
30.03.2005

Cellulose acetate butyrate CAB 30-40 140-160 160-170 170-190 170-190 160-190 190-200 160

Concise material science

Cellulose acetate CA 30-40 140-160 160-185 170-200 170-200 170-200 200-210 160
Cellulose propionate CP 30-40 160-190 190-230 190-240 190-240 190-240 220-240 160
Polyphenylene ether PPE 40-60 240-260 260-300 280-300 280-300 280-300 270-290 200

Processing temperatures, drying, cavity-wall,

Acrylon.-but.-styr.+ polyc. ABS/PC 50-70 230-250 250-260 250-270 250-270 250-270 260-270 200
10:46 Uhr

Polybutylene terephthalate PBT 50-70 230-250 240-260 250-260 250-260 250-260 250-260 210
Polyethylene terephthalate PET 50-70 240-260 240-260 250-290 250-290 250-290 270-280 220
Seite 80

Material Pre-drying Cavity wall Mean demoulding

°C hrs temperature °C temperature °C
Polyethylene PE-LD *80 1 20-60 70
Polyethylene PE-HD *80 1 20-60 70

unsatisfactory.
Polypropylene PP *90 1 20-60 70
Polystyrene PS *80 1 15-50 70
Acrylonit. -butad. styrene ABS 80 3 40-60 70
Styrene-acrylonit. copol. SAN 80 3 40-60 70
Polyvinyl chloride PVC rigid *70 1 30-60 70
Polyvinyl chloride PVC flexible *70 1 30-50 70
Poymethylmethacrylate PMMA 80 3 40-70 80
Polyoxymethylene POM *100 3 60-110 105
Polycarbonate PC 120 3 80-110 110
Polyamide 6 PA 6 80 4 60-90 100
Polyamide 66 PA 66 80 4 60-90 100
Cellulose acetate butyrate CAB 70 3 40-80 80
Concise material science

Cellulose acetate CA 70 3 40-80 80

* Material only needs to be pre-dried if storage conditions are

Cellulose propionate CP 70 3 40-80 80
Polyphenylene ether PPE 110 2 80-120 80
Acrylon.-but.-styr.+ polycarb. ABS/PC 100 4 70-90 80
Polybutylene terephthalate PBT 120 4 60-80 90
Polyethylene terephthalate PET 120 4 120-140 110

81
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Process optimisation at the Process optimisation at the

injection moulding machine injection moulding machine

Principles: 5.1 Correlation between quality characteristics and

process parameters displayed as a cavity pressure
1. When optimising process parameters, it is important to change
profile
no more than one parameter at a time until the effect of the
parameter on the quality of the moulding is clearly under-
stood. There are often obvious changes which can be made Injection phase Compression Follow-up pressure phase
phase
where parameter influence becomes immediately apparent.
2. Optimisation should always begin with the quality of the moul- Pressure

ding in mind. The fundamental links between quality characte-

ristics and setting parameters are sufficiently well known (see
diagram on next page). It is important to make a firm assess-
ment of quality characteristics and their limits. Then the stabi-
lity and quality of the process should be optimised on the
basis of parameter and flow distribution. Only when this has
been done can cycle time be optimised.
5 3. There is a screen page for process optimisation on the NC4 Time
5
control system which combines all significant parameters. All Surface contour definition weight, dimensional deviations
essential optimisation steps can be made on this page. Also (roughness, gloss, colour) flash formation, shrinkage, warpage
Quality
warpage, orientation in skin, weight, voids, sink marks characteristics
displayed on this same page are all the relevant ACTUAL val- crystallinity dimensional internal orientation
deviations
ues. An integrated data acquisition system is also available to
Injection speed change-over point follow-up pressure
enable the operator to optimise hydraulic pressure and cavity temperature cylinder follow-up pressure time
Machine
pressure profiles in those phases where they have a significant mould temperature temperature cylinder temperature parameters
mould mould temperature
and decisive effect on quality. temperature

Injection time max. hydraulic integral cavity pressure

Important parameters for process optimisation are discussed integral injection pressure or cavity pressure melt temperature Monitoring
as follows: melt temperature mould temperature parameters
mould temperature

1. Plasticising cylinder- and melt temperature

2. Cavity wall temperature
3. Injection speed
4. Change-over point
5. Follow-up pressure time
6. Follow-up pressure level
7. Cooling time
8. Screw speed
9. Back pressure
10. Decompression (screw retraction)
11. Monitoring parameters

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Re. 1 Plasticising cylinder- and melt temperature Re 2: Cavity wall temperature

The pre-set cylinder temperatures, together with the friction Although the importance of the cavity wall temperature is well-
induced by the screw speed, ensure there is sufficient heat known, moulders frequently fail to pay sufficient attention to it in
to melt the plastic material (plasticisation). practice. Especially in the case of partially crystalline engineering
thermoplastics, such as POM, PBT, PA and PET, the mould surface
Setting recommendations can be found in the setting data
temperature is crucial because it not only influences the cooling-
for the individual materials (see Chapter 4 of this booklet).
down time or cycle time, but also affects the crystallinity of the
Valid for all materials:
structure, the surface finish as well as the weight and dimen-
Melt temperature too high: sional accuracy of the moulded parts. Therefore, the range of va-
riation in cavity wall temperature when producing technical pre-
thermal degradation cision parts in small moulds should not exceed 1 to 2 °C or, in
differences in colour/colour change large moulds, 4 to 5 °C.

increased shrinkage/dimensional variations Setting recommendations for mould temperatures can be found
in Chapter 4.4 of this booklet.
prolonged cooling time
5 In principle: 5
inferior mechanical properties
A higher cavity wall temperature ensures:
Melt temperature too low:
less after-shrinkage
inhomogeneous melt
less orientation, fewer internal stresses, less warpage
increased stresses in the moulded part
lower pressure requirement
higher pressure requirement during injection
improved crystallinity
flow lines and weld lines clearly visible
Mould temperature too high:
Normally, cylinder temperatures are set with a rising profile
(exception: PA). The first two heating zones (MH1 and MH2) longer cooling time (2 %/1 °C)
should be set at the lower limit when there is minimal stroke
dimensions undersized
utilisation, and at the upper limit for substantial stroke
utilisation. Mould temperature too low:
matt surface
ripple effect
flow lines/weld lines clearly visible
increased stresses in moulded part

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A high performance temperature control unit can be used to main- Injection speed too high:
tain a constant cavity wall temperature. Cavity wall temperature
flash formation
is one of the most important setting parameters which needs to
be kept within very tight tolerances. For parts with stringent re- surface defects near the gate
quirements (e.g. technical parts), if is advisable to use integrated
charring at end of flow path (Diesel effect)
temperature control units, whose setting values can be stored
and also monitored by the Operator panel. high clamp force requirement

Re 3. The injection speed Injection speed too low:

The injection phase is the time it takes for the melt to pass from
ripple effect
the machine nozzle to the far end of the moulded part and to fill
out the cavity completely. part not completely filled
The injection phase is a critical sub-process in as much as it has warpage
a major influence on the properties of the moulded parts. It is in
weld lines visible
the injection phase that quality parameters, such as surface finish,
5 appearance, warpage, orientation in the skin layer, and crystalli- Monitoring pressure must be set to maximum first of all to opti- 5
nity can be controlled. In the injection phase, it is possible to in- mise injection speed. If the injection pressure limit should be
fluence, for instance, the location of weld lines, their visibility, the reached, however, this will be indicated, on the one hand, on
direction of streaks, or differences in gloss on the surface of the the data acquisition screen and, on the other hand, by the fact
part. By varying such machine parameters as cylinder temperatu- that when changes are made to injection speed (set values) the
re, cavity wall temperature or injection speed, the moulder is able actual injection time remains unaltered.
to influence orientation, strength, impact toughness, surface pro-
perties, visibility of weld lines and, to a lesser extent, also the Re 4. Change-over point
dimensions and weight of the moulded part. Accurate and reproducible change-over from the injection phase
to the follow-up pressure phase plays a critical part in the manu-
Injection speed influences the rate of melt dispersion in the mould. facture of technical injection-moulded products. In the speed-
In principle, it should be set as fast as possible. controlled injection phase, the plastic melt is introduced into the
Where there are changes in wall thickness it may be necessary cavity until its volume is completely filled. In the subsequent pres-
to set stepped profiles. A rising and falling profile may need to sure-controlled follow-up pressure phase, packing is applied to
be set at the start and at the end of the filling phase, respectively. compensate for the shrinkage caused by thermal contraction of
the melt.
Ideally, the change-over is timed to take place exactly when vo-
lumetric filling of the cavity has been completed. The change-
over may be effected as a function of distance, time, hydraulic
pressure, and cavity pressure.

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In general, change-over should occur when approx. 90-95 % of Re 5. Follow-up pressure time
cavity volume is filled. With thin-walled articles it may be neces- The injection phase, during which the volumes of the cavities are
sary to fill up to 98 % of cavity volume before switching over to completely filled, is followed by the follow-up pressure phase. It
follow-up pressure. compensates volume contraction of the material as it cools down
by continued delivery of melt into the cavity. The follow-up pres-
Change-over too soon: sure should act until the gate seal point is reached,after which no
change-over mark more melt can enter or flow out of the mould.

moulding not completely filed As long as there is no freezing of the plastic in the area of the
gating system, the cavity pressure may still be influenced by var-
sink marks ying the hydraulic pressure. Upon reaching the gate seal point,
dimensions undersized the pressure variation in the mould is determined only by the
cooling characteristics of the material.
weld line marks
As explained earlier in Chapt. 5.1, the follow-up pressure phase
Change-over too late: has the greatest influence on such quality criteria as weight, di-
5 flash formation
mensions, shrinkage, warpage, voids, sink marks and orientation. 5
increased clamp force requirement Follow-up pressure time too long:

dimensions oversized increased stresses in the moulded part

demoulding problems increased energy consumption

increased stresses in the moulded part Follow-up pressure time too short:

Initially, an early change over point should be selected. Gradually, sink marks, voids
this should be set later (mould fill study) until volumetric filling
variations in component weight
is almost achieved. This also provides a valuable insight into the
flow front profile in the mould and into the development of flow dimensions undersized
lines and weld line marks.
fluctuations in melt cushion
In the case of multiple-cavity moulds, the form fill study will show
To establish optimum follow-up pressure time, continue to raise
the degree of filling in the individual cavities. The variation in fill
the setting until no further weight increase can be detected in
should not exceed 5-10 %, depending on moulded part require-
the moulded parts without sprues.
ments.

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Weight (g) Optimum follow-up Re. 7 Cooling time

pressure time Cooling time serves as the final cooling period for the moulding
in the cavity until sufficient dimensional stability is reached to
allow demoulding. The criteria here are the dimensions and the
warpage on the moulding.

Cooling time too long:

increased cycle time

Cooling time too short:

0 2 4 6 8 10 12 14 16 18 Follow-up pressure time (s) warpage

Determining optimum follow-up pressure time by checking weight ejector imprints

increased after-shrinkage
Re. 6 Follow-up pressure level
5 Follow-up pressure is the pressure that is active during follow-up
See also Chapter 5.2 – Calculation of cooling time. 5
pressure time and which is intended to avoid the development Re. 8 Screw speed
of sink marks. In most cases, the follow-up pressure amounts to
30-60 % of the required injection pressure. Screw speed is responsible for plasticising i.e. for the thermal,
mechanical and homogenous preparation of the raw material.
Follow-up pressure too high:
The upper limit for the screw speed setting is the maximum per-
flash formation missible peripheral velocity of the screw for the particular type
of material. The resulting metering time, however, should not be
increased clamp force requirement
much shorter than the cooling time in order to plasticise as
increased stresses in the moulded part smoothly as possible.
dimensions oversized Screw speed too low:
demoulding problems fluctuations in cycle time (in case t met > T cool )
ejector imprints
Screw speed too high:
Follow-up pressure too low: thermal and mechanical degradation of the material
sink marks, voids large difference in melt temperature over the screw stroke
dimensions undersized increased screw wear and wear on the non-return valve
greater volume shrinkage
increased fluctuations in weight

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Process optimisation at the Process optimisation at the

injection moulding machine injection moulding machine

Re. 9 Back pressure a) Injection monitoring (injection pressure limitation)

Back pressure is the prevailing pressure in front of the screw During the filling phase there is a build-up of pressure dependent
against which the screw must operate during plasticising. on the set injection speed which corresponds to the flow resist-
ance of the met. Under normal circumstances this pressure pro-
Back pressure too high: file is reproducible. Only if faults occur during the process or if
material degradation due to excessive friction one of the parameters fluctuates can this pressure rise involun-
tarily.
low plasticising capacity, long metering time
For this reason, injection pressure limitation is set approx. 10-
Back pressure too low: 15 % above the maximum filling pressure. If this is exceeded an
error message is given and the machine stops without any dam-
non-homogeneity of the melt (mechanical, thermal
age occurring to the mould or hot runner.
fluctuations)
unmelted material pellets
air streaks
5 5
Re. 10 Decompression (screw retraction)
Decompression assists in decreasing the melt pressure in the
space in front of the screw following plasticising. It should be
around 4 % of the shot volume but may amount to as much
as 10 % of the screw diameter. For more accurate details see
Chapter 4.1 “Processing guidelines for the most important
plastics”.

Decompression too high:

air streaks around the gate

Decompression too low: b) Injection monitoring

During the mould filling phase the actual injection time is de-
material escapes from the nozzle or the hot runner pendent on the injection speed. Obvious deviations from this
time indicate an error in the process. The injection time limit
Re. 11 Monitoring parameters
should also be set approx. 10-15 % above the actual injection
Monitoring parameters are only set when all the important para-
time.
meters have been optimised and the necessary quality is being
consistently achieved within the tolerance limits.

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Process optimisation at the Process optimisation at the

injection moulding machine injection moulding machine

5.2 Cooling time Control equations:

Cooling time is calculated using the following formula: PC: t c = 2,17 x s2

PA 6, PBT, PE-LD: t c = 2,64 x s2
ABS, PS, SAN, PA 66: t c = 2,82 x s2
PE-HD, PMMA: t c = 3,00 x s2
PP: t c = 3,67 x s2
POM: t c = 4,18 x s2
Where cooling time
s = Wall thickness [mm]
wall thickness
t c = Cooling [secs]
thermal diffusivity
The curves for the different groups of plastics are given in the
5 melt temperature following table. These curves are also shown on the two sub- 5
mean demoulding temperature sequent diagrams, where s = 1 to 2.5 mm and s = 2.5 to 4 mm.

average cavity wall temperature (average

Wall thickness s = 2 mm s = 4 mm
value derived from minimum and maximum
cavity wall temperature over the course of Change in cavity wall
an injection moulding cycle) temperature by [°C] +10 +5 -5 -10 +10 +5 -5 -10

For an initial estimate of cooling time with the aid of a diagram, Change in cooling time
the cooling time equations can be grouped according to the dif- by [secs] +5 +2 -1,2 -2 +20 +7,5 -5 -9
ferent plastics. These groups are determined by taking as a basis
the average temperatures for melt, cavity wall and demoulding. Influence of cavity wall temperature on cooling time with
(Compare with Chapter 4.1 “Processing guidelines for plastics”). wall thicknesses of 2 and 4 mm

Changes in melt temperature have no appreciable effect with

wall thicknesses up to 4 mm (< 1 sec).
Changes in cavity wall temperature, on the other hand, must
be taken into consideration.

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Process optimisation at the Process optimisation at the

injection moulding machine injection moulding machine

5.2 Cooling time as a function of wall thickness 5.2 Cooling time as a function of wall thickness
(1 to 2.5 mm) (2.5 to 4 mm)

5 5

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The correct evaluation and selection The correct evaluation and selection
of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

Ever shorter machine cycles, the growing complexity of products At this point, of course, there is still no indication of which para-
and increasingly stiff competition all call for economic injection meters are required for controlling the quality of the mouldings.
moulding production. Quality assurance and the ability to reduce
scrap to a minimum are becoming increasingly important.
Only those processors who can accurately predict the output of
perfect mouldings will have costs under control, be able to meet
delivery deadlines and be acknowledged as reliable partners.
When it comes to quality control, the control and analysis featu-
res on modern injection moulding machines are highly efficient.
The operator can have complete control over the production pro-
cess, carry out long-term statistical evaluations or anticipate trends.
Of course, to make best use of these resources the setter needs
to know which machine and process parameters influence the
quality of a moulding – and, most importantly, to what extent.
Practice shows, however, that the significance of these parame-
ters varies from application to application and is determined by
the demands of the particular moulding.
6 6
The following report and data tables are the result of extensive
long-term testing and the evaluation of a large number of indi-
vidual cases. They assist in the selection and evaluation of the
correct parameters and in defining the required tolerances for
quality control on the machine.
The table opposite (Fig. 6.1) shows the 5 most significant quality
characteristics and their relative importance for the production of
different product groups. For technical precision parts, dimensio-
nal stability is clearly of greatest importance, while for optical
parts, for example, surface quality and melt homogeneity are cru-
cial factors.
Of course, there are still a good many other quality characteristics
– the “inherent properties”, for example, like molecular weight,
orientation on the skin and the core, dispersion of fillers and rein-
forcing materials etc. These selected criteria, however, represent
essential performance properties which can also be subjected to Fig. 6.1
direct and mainly non-destructive testing.

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of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

Fig. 6.2 shows important process parameters and their relation Fig. 6.3 illustrates the connection between quality characteristics
to the various quality characteristics. The correlation between and process parameters with the aid of the (integral) cavity pres-
machine or setting parameters and the characteristics of the sure profile. It shows clearly how the majority of quality characte-
mouldings is sometimes very complex. In almost all instances, ristics are influenced during the follow-up pressure phase. Con-
there are several setting parameters relating to a single quality sequently, the cavity pressure profile must fall within specified
characteristic, which is why more than one parameter needs tolerance limits during this phase. The diagram also shows those
to be controlled. setting and monitoring parameters relevant to quality. The cavity
pressure profile, mould temperature and melt temperature are
the most significant and informative factors here.
In 50 % of all cases cavity pressure monitoring proves very useful
from a processing point of view, but it is only realistic in 3 % of
these, since the cost in terms of machine, mould and personnel
is relatively high. Cavity pressure monitoring is applied to around
20 % of mouldings, predominantly technical precision and func-
tional components, optical products and automotive parts.
The use of cavity pressure enables the setting parameters for the
machine and peripheral equipment to be largely indirectly moni-
tored, because the smallest changes or disruptions – to mould or
6 melt temperature, to the function of the non-return valve, to the 6
change-over point to follow-up pressure or to the batch of mate-
rial – all have an effect on cavity pressure. Very often it is possible
to monitor several settings via one single parameter and also to
document them in accordance with DIN ISO 9000.
The time profile for cavity pressure can be divided into three phases.
These are the injection, compression and follow-up pressure
phases.
In the injection phase, cavity pressure is determined mainly by
flow resistance, viscosity of the moulding compound and injec-
tion speed, During the compression phase the melt is compres-
sed up to the so-called change-over point, which then initiates
the follow-up pressure phase. In this latter phase, the pressure
rises in the mould initially, because the mould is now completely
tilled.

Fig. 6.2

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The correct evaluation and selection The correct evaluation and selection
of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

As the melt cools down, so the pressure falls slowly. In conjunc- Fig. 6.4 shows a characteristic profile of hydraulic and cavity pres-
tion with the cooling process, this phase is decisive in terms of sure. If, for example, the hydraulic pressure (upper curve) rises
shrinkage and internal orientation, and also for crystallisation in during the injection phase as a result of a lower mould tempera-
partially crystalline materials. ture (caused by increased flow resistance during injection), then
cavity pressure falls – (with hydraulic pressure remaining constant
Injection phase Compression Follow-up pressure phase during the follow-up pressure phase) – due to the reduced pres-
phase
sure transfer performance of the low-viscosity melt. The result is
Pressure
a lower integral cavity pressure. If it were only the hydraulic pres-
sure being monitored, no indication would be given as to the qua-
lity of the mouldings. The rise in hydraulic pressure during the in-
jection phase would indeed be noticeable, but the effects of this
increase once change-over has occurred could not be monitored,
since hydraulic pressure during this phase is regulated at a con-
stant level. By selecting integral cavity pressure with suitable inte-
gral limits, however, the quality-related phases can be accurately
monitored.
Time
The most important factors for technical precision parts are dimen-
contour definition
Surface
(roughness, gloss, colour)
weight, dimensional deviations
sional stability, melt homogeneity and low warpage, which means
flash formation, shrinkage, warpage
Quality
6 warpage, orientation in skin,
crystallinity
weight,
dimensional
voids, sink marks
internal orientation
characteristics that the parameters for monitoring must be selected from relevant 6
deviations phases in the process. Dimensional stability and warpage are main-
Injection speed change-over point follow-up pressure ly influenced during the follow-up pressure phase, which is why
temperature cylinder follow-up pressure time
temperature
Machine integral cavity pressure is particularly suitable.
mould temperature cylinder temperature parameters
mould mould temperature
temperature Changes in melt homogeneity occur during the metering phase
Injection time max. hydraulic integral cavity pressure due to fluctuations in screw speed and/or back pressure, and these
integral injection pressure or cavity pressure melt temperature
melt temperature mould temperature
Monitoring
parameters
can be diagnosed by monitoring the above-mentioned parame-
mould temperature ters. Where particularly sensitive materials are concerned, the me-
tering operation can also be monitored via the screw load.
Fig. 6.3
Pressure transducers have been used in the mould for more than
20 years and at the moment are probably the simplest form of
total control, without directly including the characteristics of the
moulded part. Care should be taken to ensure that the cavity
pressure sensor is located at a quality-determining point – as close
to the sprue as possible – approx. 30-40 % of the way along the
flow path. A pressure sensor can also be integrated in the hydrau-
lic circuit (in or on the hydraulic injection cylinder).

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The correct evaluation and selection The correct evaluation and selection
of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

Selection criteria
On the assumption that the machine has been optimally set prior
to the start of the production cycle, the following selection crite-
ria have emerged in the course of daily practice for the 8 most
significant process parameters which need to be kept constant.
In general, cycle time says little about component quality, apart
from when processing thermally sensitive materials in semi-auto-
matic operation.
Consistent injection time is important for short injection times
and for parts with stringent surface requirements.
Ideally, a constant metering time should be observed, particu-
larly when processing (plasticising) material blends (LDPE-HDPE),
blends for automotive parts and regrind. It is also important
where irregularities occur during plasticising as a result of the
material (PA-PMMA), and when colouring using pigment paste
or masterbatch.
A decreasing melt cushion when processing with filled materials
6 indicates wear on the non-return valve. Fluctuations are often a 6
sign of inhomogeneous melt. Where there is only very slight fluc-
tuation in the melt cushion and the non-return valve is function-
ing correctly, the dimensions of the moulded part will then remain
constant. For products with relatively dense wall thicknesses re-
quiring a correspondingly long, high and uniform follow-up pres-
sure profile, integral cavity pressure is the first choice.
Maximum cavity pressure is informative for products with small
wall thicknesses and a short follow-up pressure time or high in-
jection pressure.
Melt temperature is important for thermally sensitive materials.
This is equally so for materials with a narrow processing range or
for materials whose properties change at the slightest variation in
temperature.
Finally, accurate mould temperatures are required, particularly
when processing any of the engineering materials (PC, PA, POM,
PMMA ...), for example, for the production of optical lenses in
Fig. 6.4 PMMA or gear wheels in POM.

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The correct evaluation and selection The correct evaluation and selection
of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

In order to be able to put these findings to practical use, it is nec-

achievable on
the products
fluctuations

0.05-0.15

0.05-0.10

0.10-0.20

0.10-0.20

0.20-0.30

0.50-1.00

0.20-0.30

0.20-0.40

0.20-0.40

0.20-0.40

0.20-0.40

0.30-0.50

0.20-0.40

0.30-0.60
essary first of all to evaluate the relative importance of the indivi-

Weight
dual process parameters for the different product groups and to

[%]
establish the tolerances.

PP, ABS, Blends

POM, PA, PBT

PS, SAN, CAB

PS, SAN, ABS
Fig. 6.5 summarises the selection criteria and also evaluates the

PA, PC, PBT

materials

PE, PP, PS

PE, PP, PS

PE, PP, PS
extent of the influence of the individual process parameters on the

PP, ABS
Typical

PMMA

PMMA

PS, PA

PE, PP
quality of the various product groups. The quality characteristic

PVC
here is the percentage weight fluctuation which can be achieved
Gear wheels, program control cylinders (thick-walled)
on the mouldings. The data shown is a recommendation as to
the level of quality to which the mouldings in the different pro-
Plugs, multi-point connectors (thin-walled)

Cartons, containers, aerosol caps, buckets

Radiator grills, instrument panels, bumpers

very important

Music and video cassettes, CD packaging

less important

Disposable razors, slide frames, cable ties

duct groups can be manufactured.

Pipe joints, fittings, housing components

important

General purpose functional parts

“1” denotes a parameter with the largest influence on quality,

Bottle crates, shipping containers

Housings, covers, storage cases
while “8” denotes minimum influence. These should not, how-
High-speed precision parts

Disposable syringes, pipettes

Technical packaging parts

Technical functional parts

Rulers, set squares, stencils

Technical precision parts

ever, be seen as absolute values for comparison between the var-

Rear light fittings, mirrors

ious product groups, but as being based on a specific characte-

Container systems

Stacking boxes, cars

Automotive parts
Packaging parts

ristic value for each product group.

Rigid PVC parts

Office supplies
Medical parts
Optical parts

Optical parts

Fig. 6.6 goes one step further by showing the permissible percent-
Products

6 age deviations (+/- tolerances) for each of the parameters. The 6

Lenses

Toys
variation in values is as a result of varying processing conditions
for the respective products. For example, the mould temperature Cycle time
8

8
for technical functional parts is around 80 °C, while for high speed
Injection
precision parts it is only 25 °C. Thus, when converted to absolute
2

4
time
values, the permissible deviations are almost identical. Dosing
5

time 2
The percentage values also utilise the evaluation capacity of mod- Melt
6

ern injection moulding machines. Modern control systems such cushion

as NC4, enable deviations to be represented in percentages (see Integr. cavity
7

pressure
Fig. 6.10). The recommended values can be directly compared
Max. cavity
with the current Actual values. If the deviations fall within the
1

pressure
tolerance limits, the component quality is acceptable. Melt
3

temperature
Mould
4

temperature

Fig. 6.5

106 107
 6
Weight
Products very important Typical

time
time

108
Melt
Melt
fluctuations

Mould
materials

Dosing
achievable on

cushion

pressure
pressure
Injection
important

Fig. 6.6
the products

Cycle time

Max. cavity

temperature
temperature
Integr. cavity
less important [%]

3% 3% 3% 6% 2% 2% 2% 2% Technical precision parts PA, PC, PBT 0.05-0.15

Plugs, multi-point connectors (thin-walled)
3% 3% 3% 6% 3% 3% 2% 3% Technical functional parts POM, PA, PBT 0.05-0.10
Gear wheels, program control cylinders (thick-walled)
3% 3% 3% 6% 3% 3% 3% 3% Optical parts PMMA 0.10-0.20
Lenses
3% 3% 3% 6% 3% 3% 2% 3% Optical parts PMMA 0.10-0.20
Rear light fittings, mirrors
10% 3% 4% 6% 3% 4% 6% 4% High-speed precision parts PS, PA 0.20-0.30
Disposable razors, slide frames, cable ties

Spritzg. k+b Innenseiten gb.

10% 3% 4% 6% 4% 4% 6% 4% Packaging parts PE, PP, PS 0.50-1.00
Cartons, containers, aerosol caps, buckets
10% 3% 4% 6% 4% 4% 6% 4% Medical parts PE, PP, PS 0.20-0.30
Disposable syringes, pipettes
6% 3% 3% 6% 4% 3% 2% 2% Automotive parts PP, ABS, Blends 0.20-0.40
Radiator grills, instrument panels, bumpers
10% 3% 3% 6% 3% 4% 6% 3% Technical packaging parts PS, SAN, ABS 0.20-0.40
Music and video cassettes, CD packaging
30.03.2005

10% 4% 4% 10% 4% 6% 3% 4% Office supplies PS, SAN, CAB 0.20-0.40

Rulers, set squares, stencils
10% 4% 4% 10% 4% 6% 3% 4% General purpose functional parts PP, ABS 0,20-0.40
Housings, covers, storage cases
6% 3% 4% 6% 4% 6% 2% 4% Rigid PVC parts PVC 0.30-0.50
Pipe joints, fittings, housing components

assurance in injection moulding

6% 3% 4% 6% 4% 3% 3% 2% Container systems PE, PP 0.20-0.40
10:46 Uhr

Bottle crates, shipping containers

of process parameters for quality
10% 6% 6% 10% 6% 6% 6% 4% Toys PE, PP, PS 0.30-0.60
Stacking boxes, cars
The correct evaluation and selection
Seite 108

Fig. 6.7
parameters to adhere to specific tolerances (Fig. 6.7).
assurance in injection moulding
of process parameters for quality

previously mentioned parameters – and even if, in general, 3-5

Even if the quality depends essentially on the constancy of the 8

of these would suffice – it is still necessary for the less important

109
The correct evaluation and selection

6
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The correct evaluation and selection The correct evaluation and selection
of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

Quality control on the machine Fig. 6.9 shows the maximum injection pressure in an unstable pro-
When activating quality control it is important to establish wheth- cess and how metering time fluctuations depend on and influen-
er the process is normally distributed i.e. without influences in- ce the residual melt cushion. In a stable process, the statistical
herent in the system. Quality control is only possible with normal evaluation reveals only minor fluctuations for all relevant process
distribution. A mean value and independent upper and lower to- parameters.
lerance limits are then specified for the quality-determining pro-
With the aid of just two statistics pages, the machine setter can
cess parameters.
easily monitor process constancy. “Process Statistics 1” indicates
Fig. 6.8 shows a screen page from the new NC4 control system the Actual values for the last 16 cycles. The penultimate line also
of the Demag machine range. Using this page the machine setter shows the mean value, and the last line the range of measured
can select from a total of 25 available parameters those which values. The control system provides not only tabular displays, but
are most important for a particular moulding. The Process Statis- also a wide range of control features in graph form.
tics page can display up to 20 parameters, and the selected para-
meters can then be controlled either continuously (CPC) or statis-
tically (SPC).

6 6

Fig. 6.9

Fig. 6.8

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The correct evaluation and selection The correct evaluation and selection
of process parameters for quality of process parameters for quality
assurance in injection moulding assurance in injection moulding

At the touch of a key the system not only provides graphic eva- Fig. 6.11 looks at tolerance settings for the selected process pa-
luation, but also percentage deviation from the mean value, and rameters, (parameters selected are indicated by a black square in
the statistical distribution – (black bars to the right of the screen) the column headed “permissible deviation”). In addition to the
– over the last 100 cycles for each selected process parameter upper and lower tolerances, the permissible number of deviations
(injection time, metering time, hydraulic pressure, melt cushion, per 1000 parts is also indicated. If a variable exceeds its set tole-
cycle time ...). A thermal printer integrated in the operator termi- rances, by using selected parameters reject indication can be given
nal is also available as optional equipment for printing out all and this is then shown in the deviation counter.
screen pages. It enables the relevant quality data and proof of
In such cases, providing tolerance deviation is switched on, moul-
quality to be documented directly at the machine.
dings can be automatically sorted by means of mechanical qua-
lity flaps or a robot fitted with a reject signal. Only the most ad-
vanced machine control systems can offer such a comprehensive
range of possibilities for keeping processing parameters constant
over long periods of production. Such systems can indicate the
effects of any emerging influences by deviations in the process
parameters and enable statistical evaluation. This represents the
first step towards our aim of “Total Quality Control”.

6 6

Fig. 6.10

Fig. 6.11

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Notes Recognition and elimination of

surface defects in the injection
moulding process

Injection moulding is an extremely complex process, in which the

quality of the moulded parts is determined by a variety of factors,
which differ from one application to the next.
Flaws in quality can be caused by machine or processing param-
eters being wrongly set and by incorrect mould or moulded part
design.
The causes of potential faults, unfortunately, are as diverse as the
injection moulding process itself. Starting with visual defects such
as streaks, sink marks or gloss variation, through to inadequate
mechanical properties – entrapped air, voids or unmelted material
in the moulding, for example - and ending with all manner of
dimensional deviations (see table on page 116).
This poses the question of what practical steps can be taken to
eliminate the wide variety of faults.
In order to narrow down the causes, the fault must be located
and accurately defined i.e. what it looks like, where, when and
how often it occurs. To do this you need to be familiar with the
6 machines and process parameters listed in the tables on pages
116-119 and be able to make a careful evaluation of their poten-
tial influence.
This will enable you to see at what stage in the injection moul- 7
ding process a fault can occur. The cause of surface defects, for
instance, is to be found predominantly in the plasticising and in-
jection phase. Dimensional deviations and inadequate mechanical
properties, on the other hand, occur mainly during plasticising
and injection and in the follow-up pressure phase.
The design of the mould and moulded part also has a consider-
able effect on all types of fault, with clamp force, mould opening
and demoulding playing a secondary role.

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Recognition and elimination of Recognition and elimination of

surface defects in the injection surface defects in the injection
moulding process moulding process

Cause of defect

Process phase Mould

Follow-up pressure

Temperature
Open mould

Demoulding
Plasticising

Injection

Stability

Venting
Cooling

Gating
Surface, mechanical and dimensional defects
in injection-moulded parts

Flaws in appearance
Charred streaks X X X
Coloured streaks X X
Glass fibre streaks X X
Sink marks X X
Gloss, variations in gloss X X X X X
Unmelted material pellets in the moulding X X X
Weld line, flow lines X X X X
Jetting X X X
Diesel effect, charring X X
Visible ejector imprints X X X
Ripple effect X X
7 Dark spots X 7
Matt spots near the gate X X X
Delamination of surface layer X
Cold slug, cold flow marks X X X
Gray/black clouds X
Dimensional deviations
Mouldings not completely filled X X X X X
Moulding overpacked (flash formation) X X X X
Deformation on demoulding X X X X X
Component warpage X X X X X X X
Dimensional variations on the moulding X X X X X
Inadequate mechanical properties
Stress cracking on the moulding, stress whitening X X X
Entrapped air, blistering X X X
Voids X X
Thermal degradation of melt X X
Unmelted material pellets in the moulding X

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Recognition and elimination of Recognition and elimination of

surface defects in the injection surface defects in the injection
moulding process moulding process

Follow-up pressure time

Stepped injection speed
Cavity wall temperature

Change-over injection
to follow-up pressure

Follow-up pressure
Melt temperature

Injection speed

Back pressure

Locking force
Screw speed

Venting

Gating
Surface, mechanical and dimensional defects
in injection-moulded parts

Flaws in appearance
Charred streaks
1
2
4 3
Coloured streaks
2 1
Glass fibre streaks 3 4
2 1
Glasfaserschlieren 3 2 1
Sink marks
4
3 1 2 5
Gloss, variations in gloss 3 4 6 1 2 5
Unmelted material pellets in the moulding 3
2 1
Weld line, flow lines 3 2 1 4 5 6
Jetting 2 4
1 3 5
Diesel effect, charring
3
1
4 2
Visible ejector imprints 3
1
2
Ripple effect 2 3 1 5 4 6
7 Dark spots
1 7
Matt spots near the gate 2 4
1 3 5
Delamination of surface layer 4 3
1
2
Cold slug, cold flow marks 1 2
4 3
Gray/black clouds
2
3 1
Dimensional deviations
Mouldings not completely filled 4 5 1 3 2 7 6
Moulding overpacked (flash formation)
4
5 2
3
4 1
Deformation on demoulding 3
1
2
Component warpage 4 3 2
1 5
Dimensional variations on the moulding 1 2 3 4
Inadequate mechanical properties
Stress cracking on the moulding, stress whitening 4 3
1
2
Entrapped air, blistering
1
2
Voids
4 3
6 1 2 5
Thermal degradation of melt
1
2 3
Unmelted material pellets in the moulding 3
2 1

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Examples of clamp force Examples of clamp force

calculation calculation

Basics 8.1 Clamping force calculation for general injection-

The clamping force is the sum of the forces to which the tiebars moulded parts
are subjected to, in tension upon complete clamp close but be-
fore the start of injection. The mould-opening force results from In order to determine the clamping force required, it is necessary
the maximum cavity pressure and the projected area of the moul- to find the projected area of the moulded part, which is the moul-
ding. ded part area in the opening direction (Fig. 8.1).

The clamping force should be set at least 10 % higher than ne-

cessary. It is practical to determine the clamping force either on
the basis of mould breathing or on the moulded part geometry
and the cavity pressure.
Determining the clamping force on the basis of mould breathing
is rather complex and is not proposed to be discussed here. Using
the alternative approach, the clamping force is calculated from
the following formula:

pwi x Aproj
Fz =
100
where
Fz = clamping (locking) force [kN]
pwi = mean cavity pressure [bar] Fig. 8.1: Examples for calculating the projected area
of moulded parts
Aproj = projected area of moulded part [cm2]

In addition, it is necessary to estimate the expected mean cavity

8 pressure for the moulded part. The examples in Fig. 8.2 provide 8
some guidance. The values in the examples have been determin-
ed in injection-moulding tests. When performing the calculation,
the procedure is to select pressure values for an example whose
geometry and material properties come closest to the moulded
part to be calculated.

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 8
Product category Article Material Injection Follow-up Injection Follow-up Cavity

122
time pressure pressure pressure pressure
time
s s bar bar bar
General injection mouldings Tote box PS 3.0 6.0 1000 450 280-350
Container PP 2.5 5.5 1250 550 350-400
Quality requirements Vacuum cleaner body ABS 2.5 7.0 980 550 350-400
Dim. and shape deviations modest Machine housing PA 2.5 7.0 1000 550 350-400

for various articles

Microstructure modest Coffee machine housing PP 2.0 6.0 1100 550 350-400
Surface finish medium TV housing PS 3.5 6.0 1200 600 350-400
Computer housing ABS 3.5 6.0 1300 600 350-400
Disposable/reusable funct. parts 3.5” diskette ABS 0.22 0.9 1700 600 380-420

calculation
Quality requirements CD cover PS 0.4 1.0 1550 650 400-450
Dim. and shape deviations high Video-cassette PS 0.9 3.5 1300 500 280-350
Microstructure medium Slide frame PS 0.25 0.7 1600 600 400-450

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Surface finish high Razor handle PS 0.5 1.5 1450 600 400-450
Music cassette PS 0.45 2.2 1300 600 350-400
Technical functional parts Fascia for CD-player ABS 1.5 5.0 800 650 450-500
Quality requirements Mobile phone housing ABS/PC 0.2 1.5 1600 850 650-700
Dim. and shape deviations medium Camcorder housing PC 1.2 2.5 1400 850 550-600
Microstructure medium Video-recorder chassis PS 2.3 5.0 1100 650 400-450
Surface finish high Hub cab PA 6-GF 2.0 5.0 1000 650 400-450
30.03.2005

Large automotive parts Connector PBTP 0.5 1.5 1200 600 750-800

Examples of clamp force

Gear POM 2.0 8.0 880 1000 750-800
Quality requirements Camera housing PC-GF 0.7 6.0 1300 700 500-550
Dim. and shape deviations high Brake cylinder POM 1.8 10.0 900 900 700-750
Microstructure high Program drum POM 2.2 7.0 750 900 700-750
Surface finish medium Connector plug PA 66-GF 1.5 5.0 800 700 500-550

Fig. 8.2: Injection, follow-up and cavity pressures required

Ball bearing cage PA 66 0.8 3.5 950 600 450-500
10:46 Uhr
Seite 122

Large automotive parts Center console PP 3.0 6.0 1300 550 350-400
Quality requirements Bumper PP 4.0 6.0 1200 500 350-400
Dim. and shape deviations modest Instrument panel PP 3.0 6.0 1200 550 350-400
Microstructure medium Door lining PP 2.5 5.0 1150 500 350-400
Surface finish medium Wheel casing PP 2.5 4.5 1450 550 350-400
Disposable functional parts Screw over PP 0.8 2.5 1200 500 330-380
Quality requirements Screw closure PE 1.3 3.5 950 500 350-400
Dim. and shape deviations medium Screw cap PE 1.2 2.5 1500 800 550-600

is then calculated.
Microstructure medium Hinged lid PE 0.7 1.5 1200 500 350-400
Surface finish medium Sput PE 0.8 1.6 1300 500 350-400
Reusable functional parts Mixing bowl PP 1.5 3.0 900 500 300-350
Quality requirements Strainer PP 1.3 3.0 1050 550 300-350
Dim. and shape deviations modest DIN A4 pad PS 1.8 2.2 1100 550 300-350
calculation

Microstructure modest Desk set SAN 1.9 2.2 1000 600 350-400
Surface finish medium Coffee filter SAN 1.4 3.5 950 600 350-400
Disposable functional parts Cylinder PP 0.5 1.8 1300 600 350-400
Quality requirements Piston PP 1.1 4.0 850 500 400-450
Dim. and shape deviations high Pipette PP 0.6 0.8 1400 600 400-450
Microstructure medium Test tube PS 0.6 1.0 1200 550 400-450
Surface finish medium Petri dish PS 0.3 1.3 1200 550 400-450
Throwaway/returnable containers Drinking cup PS 0.2 0.7 1300 650 550-600
Quality requirements Yoghurt container PP 0.15 0.4 1500 700 550-600
Dim. and shape deviations medium Planting pot PP 0.11 0.4 1600 700 600-700
Examples of clamp force

Microstructure medium Ice cream container PP 0.2 0.5 1600 800 550-600
Surface finish medium Pail PP 0.46 0.6 1800 800 450-500
Optical parts Taillight PMMA 1.4 9.0 1300 850 600-650

Using the above mentioned formula, the clamping force

Quality requirements Optical lens PMMA 18.0 55.0 800 800 600-650
Dim. and shape deviations high Prism PMMA 15.0 50.0 850 800 600-650
Microstructure medium Diffuser PC 4.0 9.0 1500 850 600-650
Surface finish high Spectracle lens PMMA 4.0 12.0 950 800 600-650

123
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Examples of clamp force Examples of clamp force

calculation calculation

8.2 Clamping force calculation for thin-walled

injection-moulded parts
The term “thin-walled” generally means injection-moulded parts
whose flow-distance/wall-thickness ratio is at least 200:1. In the
case of such parts, there is a substantial pressure building up
from the machine nozzle through the hot runner manifold, the
hot runner nozzle, and in the cavity through to the end of the
flow path (Fig. 8.3).

Fig. 8.4: Pressure drop along flow path (empirical values)

The pressure drop along long and thin flow paths reduces the av-
erage cavity pressure, consequently, the opening force and, as a
result, clamping force requirements. For such thin-walled parts
with long flow lengths, it is possible on the strength of empirical
values to define a so-called “effective pressure location” the pres-
Fig. 8.3: Pressure drop along flow path in the injection phase sure of which can be used as an average value for the cavity pres-
(example: beaker made of PS, wall thickness: 0.55 mm) sure and, consequently, for the clamping force calculation. In a
plane moulded part, this effective pressure location is at half the
In order to ensure neat duplication of the cavity contours at the
flow length (Fig. 8.5). In cup-shaped moulded parts with long
end of the flow path, a packing pressure of at least 300 bar should
8 be effective there during filling. This makes it necessary to use a
flow paths, the effective pressure location in the light of experi- 8
ence is at approximately 1/7 of the flow path, which means it is
correspondingly higher pressure for injection. A general rule is:
still in the bottom of the container.
The thinner the wall thicknesses, the greater the pressure drop.
From the pressure drop between the gate and the end of the
The thicker the wall sections, the lesser the pressure drop.
flow path, it is possible to estimate the cavity pressure at the
The tougher the material, the greater the flow resistance and effective pressure location (Fig. 8.6).
the pressure loss. The more viscous the material, the lower the
flow resistance and the pressure drop.
The longer the flow distance, the greater the pressure drop.
The influence of flow path length, wall thickness, and material on
the pressure required is illustrated in Fig. 8.4.

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Examples of clamp force Examples of clamp force

calculation calculation

red taking into consideration the MFI value (Fig. 8.7a: MFI = 15,
Fig. 8.7b: MFI = 35, Fig. 8.7c: MFI = 45).

Fig. 8.5: Effective pressure location in a beaker and a plate

Fig. 8.7 a: Cavity pressure required as a function of flow-length/
wall-thickness ratio and viscosity of the material (MFI = 15).

8 8

Fig. 8.6: Pressure drop along the flow path and pressure at the
effective pressure location on a beaker and a plate
As already mentioned, the material properties, such as viscosity,
influence mould filling and the pressure required for it. Fig. 8.7 Fig. 8.7 b: Cavity pressure required as a function of flow-length/
provides some guidance in establishing the cavity pressure requi- wall-thickness ratio and viscosity of the material (MFI = 35).

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INJECTION MOULDING
Pocketbook
INJECTION MOULDING – Pocketbook

Demag Plastics Group

Demag Ergotech GmbH

Altdorfer Str. 15
D-90571 Schwaig
Tel. +49 911/50 61-0
Fax +49 911/50 61-265
E-Mail: info-dpde@dpg.com
www.dpg.com