Guidelines for the

Injection Molding of Sarlink

Contents
Introduction

Characteristics of the typical injection

molding equipment for Sarlink 3
Calculation of machine size 3

Processing conditions for optimal

injection molding of Sarlink 4
General principles 4
Drying Sarlink 4
Use of regrind 5
Coloring of Sarlink 5
Maintenance of the equipment 5

Machinery settings for the

injection molding of Sarlink 6
Temperature settings 6
(Hydraulic) pressure settings 6
Speed settings 6
Time settings 7
Cushion (buffer) 7
Special recommendations for the
injection molding of thick parts 7
Special recommendations for the
injection molding of thin parts 7

Mold design for Sarlink

injection molding parts 8
Mold balance 8
Sprue Runners 9
Gates 9
Ejectors 9
Venting 9
Mold material 10
Shrinkage 10

Multi-shot (2K) injection molding 11

Adhesion / connection 11
Molding conditions 11
Recycling 11
Hot runner technology 11

Appendix 1 12
Appendix 2 13
Appendix 3 14

1 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Introduction Special grades
In addition to standard types, a wide range of
Sarlink® thermoplastic vulcanizates (TPV) specialty grades are available, including:
are based on dynamically vulcanized EPDM • high flow: For thin long parts a special
rubber particles dispersed in a polypropylene high flow series is available. These grades
matrix. have an average spiral flow length of 30
% longer in comparison with standard
Because of this morphology, Sarlink Sarlink thermoplastic vulcanizates
thermoplastic vulcanizates combine the • UV stabilized grades
performance characteristics of widely used
thermoset rubbers, such as EPDM and Because of its combination of excellent
polychloroprene, with the ease of plastic finished part properties and easy processing,
processing. Sarlink thermoplastic vulcanizates have
found many applications in a wide range of
Sarlink offers a wide range of properties markets, including: automotive, building and
valuable to the end user. For instance: construction, electrical, mechanical rubber
• resistance to high temperature goods, medical and leisure.
• resistance to low temperature
• excellent flexural fatigue endurance Sarlink thermoplastic vulcanizates are widely
• high impact strength used in many injection molded parts such
• excellent resistance to chemicals and as seals, connectors, corner molds, (soft
solvents touch) grips, (car) mats, gaskets, O-rings,
• excellent resistance to weathering body plugs, bumpers, dampers, grommets,
• good electrical properties protectors, fittings, wheels and many other
• high tear strength applications in all market segments.
• low tension and compression set
• good resistance to oils (particularly harder This brochure is a guideline for the injection
grades) molding of Sarlink. Furthermore this brochure
contains information about multi-shot
Besides their superior performance injection molding, mold design and hot runner
characteristics, Sarlink thermoplastic systems. A checklist for trouble shooting is
vulcanizates, which are fully compounded, available on the last pages.
ready-to-use pellets, offer the following
processing advantages compared to thermoset ® Registered trademark of DSM
rubber:
• no compounding
• no vulcanization
• low capital investment
• easy processing on standard thermoplastic
equipment for extrusion, injection
molding and blow molding
• fast processing (short cycle times)
• thermal stability/wide processing
window
• low energy consumption
• recycling of scrap generated during
processing
• recycling of parts after service life
• excellent control of product quality and
dimensional tolerances
• in-line colorability
• easy weldability (profiles, sheeting...)
• material combinations by co-extrusion,
co-injection or multi-layer blow molding
to produce hard/soft articles, solid/
sponge profiles, et al.

2 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Characteristics of In cases where a computer flow simulation
is not used, the value can be calculated as
the Typical Injection follows:
• evaluate the total projected surface area of
Molding Equipment the part
• multiply this value by the number of
for Sarlink cavities. Include cold runners if present
• multiply by the average cavity pressure:
Sarlink can be easily processed on standard - 50 N/mm2 for thicker parts (above 1.5
polyolefin thermoplastic injection molding mm)
equipment without further modification. - 40 N/mm2 for thinner parts (1.5 mm or
less)
To obtain the optimum injection molding
performance, or if dedicated equipment for An estimation for minimal required clamping
processing Sarlink has to be purchased, it is force can be made by using the following
recommended to take following items into formula:
consideration:
• conventional thermoplastic injection Fc = Pc (Ac x n + Ar)
molding equipment
• clamping force: 0.5 to 0.9 Mton/cm2 Fc = clamping force (N)
of projected shot area, including gates, Pc = average cavity pressure (N/mm2)
runners, etc Ac = projected surface area
• screw: of the product (mm2)
- general purpose polyolefin type Ar = projected surface area
- L/D ratio 20:1 to 25:1 of the runner system (mm2)
- compression ratio of at least 2.5:1 n = number of cavities.
- compression ratio of 3:1 is optimum, 2.5:1
is minimum 3 barrel capacity: ideally An inaccurate clamping force can lead to
between 2 and 4 weight shots serious production problems. In particular,
• temperature control capable of if the clamping force is too low the part will
maintenance 280 °C. (Digital PID show flash.
controllers are recommended)
• injection nozzle: standard type. A hole Evaluation of the barrel size
diameter: 1.5 to 6 mm depending on shot Barrel size is also best derived from flow
size used is typical simulation programs. In cases where a
• in some cases the use of a shut off nozzle computer flow simulation is not used the value
will improve the surface appearance can be calculated as follows:
at the gate • calculate the total shot weight including
• fume ventilation at the nozzle. all cavities and runners
• the barrel size should be 2 to 4 times the
shot weight
Calculation of machine size
If the barrel capacity is too small or too large,
How to calculate the minimal machine size for constancy problems in processing will occur.
a given part is shown below:
When choosing equipment for Sarlink, it
Calculation of the minimal required should be remembered that large injection
clamping force molding machines tend to have less precision
The most accurate calculation of clamp than smaller ones.
tonnage required is derived using injection
molding flow simulation programs.
These programs calculate press tonnage
requirements directly from the filling analysis
based on the pressure required to fill the
cavity.

3 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Processing &IG 4HE


3PIRALFLOW MM
INFLUENCEOFTHE
Conditions for MELTTEMPERATURE
 ONTHESPIRALFLOW
Optimal Injection ę# LENGTH
OF3ARLINK
ATACONSTANT
Molding of Sarlink  INJECTIONTIME
OFS

ę#

General principles

• The viscosity of Sarlink thermoplastic 

vulcanizates is more sensitive to shear
than to heat. Figures 1 and 2 show these
influences. 
• Optimum moldings are usually obtained ! ! ! $
with a relatively high injection speed. (ARDNESS SHORE
• The material melt temperature has
influence on cycle time, surface
appearance and weld-line strength.
 &IG 4HE
3PIRALFLOW MM

INFLUENCEOFTHE
* Spiral thickness 1.6 mm, width 10 mm. INJECTIONTIMEON
 THESPIRALFLOW
S LENGTH
OF3ARLINK
Drying Sarlink ATACONSTANT
 TEMPERATUREOF
ę#
Sarlink should be processed with a moistures
content of less than .06%. Although Sarlink

is dried prior to packaging, it can pick up some S
moisture during storage, especially when
packaged in gaylords. 

Recommended drying conditions:

• dry minimal 3-4 hours at 80 °C (or 3 hours 
at 70 °C for softer grades) in a desiccant ! ! ! $
dryer with a dew point of -40°C. (ARDNESS SHORE

Recommended storage conditions

The storage conditions for Sarlink are
important because of the fact that Sarlink
granules will pick up moisture to a slight
degree.

Suggested storage conditions for Sarlink are:

• store Sarlink bags closed and undamaged
in a non-humid environment
• open bags just before use 3 close the bags
securely when the whole content has not
been used completely
• bring cold granules to ambient
temperature in the processing room while
keeping the bags closed.

4 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Use of regrind Coloring of Sarlink Maintenance of the equipment

Sarlink has excellent melt stability. All scrap Natural color Sarlink can be colored by Purging of equipment before processing
generated during processing can be recycled addition of a suitable color masterbatch. Sarlink
provided it is kept clean. Polypropylene based masterbatches offer To avoid contamination, the equipment
the best compatibility with Sarlink, but may should be cleaned before processing
As an example, figure 3 shows that there is slightly increase the hardness. Low density Sarlink. Polyethylene or polypropylene of
very little variation in physical properties of polyethylene based master batches are also low melt index is recommended. Purge
Sarlink after reprocessing the same material suitable. at a temperature of 200 °C. This cleaning
10 times. operation is particularly important if the
In very critical cases pre-compounded Sarlink equipment has been used previously for PVC
As shown in figure 3, the viscosity of Sarlink based color masterbatches can be used. or POM/acetals.
slightly decreases after reprocessing. For this
reason, it is recommended during production Recommended level of color masterbatch in Equipment shut down and cleaning
to blend a constant level of less than 20% Sarlink is 1 to 5 % by weight to minimize the At the end of the production, run the
regrind within the virgin material in order to impact on Sarlink properties. hopper and screw empty of Sarlink. Purge
keep processing conditions constant. Addition the barrel thoroughly with polypropylene
of regrind has no negative influence on the During injection molding the dispersion of the or polyethylene if change over to another
surface quality. color masterbatch can be improved if needed, material is anticipated. The use of high
by: viscosity polyolefins will speed up the purging
As mentioned in the paragraph on drying, it is • increasing the back pressure. Beware that process.
recommended to dry recycled material before this will increase melt temperature and Perform a general clean up of the hopper and
reuse. may increase the cycle time. any pneumatic conveying lines to remove
• decrease the screw speed eventual Sarlink fines. Clean the mold and
• in critical cases, use mixing elements on protect the mold for corrosion.
the screw or a static mixer in the nozzle.

 &IG 2EGRIND

#HANGEINPROPERTY 

STABILITYOF
3ARLINK











4ENSILE %LONGATION  (ARDNESS 6ISCOSITY
STRENGTH MODULUS
VIRGIN REGRIND REGRIND

5 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Machinery Settings &IG %XAMPLE
OFģTIGERSTRIPESĤ
INJECTION
for the Injection DIRECTION

Molding of Sarlink

Temperature settings

Typical temperature settings for the injection

molding of Sarlink are shown in table 1.

0ROCESSINGTEMPERATURESę#
2EAR  
-IDDLE  
&RONT  

4ABLE 4YPICALAVERAGE TEMPERATURE (Hydraulic) pressure settings • A high holding pressure will improve the
SETTINGSFORTHEPROCESSINGOF3ARLINK adhesion in weld lines and the adhesion to
THERMOPLASTICVULCANISATES Back pressure inserts or other materials in a multi-shot
Typical back pressures for Sarlink are process.
Material melt temperature 5 to 20 bar. • Low holding pressure may lead to sink
The material melt temperature for Sarlink marks and will increase shrinkage.
thermoplastic vulcanizates typically ranges • Low back pressure will result • Longer holding times tend to lower
from 193 °C to 232 °C. in plasticizing problems and an shrinkage.
inhomogeneous melt. • Excessively high holding pressures can
High melt temperatures give: • Higher back pressures will improve the lead to deformations.
• better surface appearance dispersion of color master-batches or • Adjust holding pressures to eliminate
• better adhesion in weld lines other added additives. It also will improve flash.
• better adhesion to inserts 3 reduce internal the melt homogeneity. The plasticizing
stress time will be longer.
• increased flow length (see figure 1) Speed settings
• decreased anisotropy Injection pressure
• longer cooling times. The injection pressure should be high enough Injection speed
to achieve the desired injection speed. A A high injection speed will improve the flow
For standard Sarlink grades, it is in general not typical injection pressure for Sarlink is from 60 length.
necessary to have a melt temperature above to 120 bar.
250 °C. High injection speeds will reduce also the
• Higher injection pressures will improve visibility of the so called ’tiger stripes’ (see
Mold temperatures the weld line strength. figure 4).
The chosen mold temperature is a balance • Too high injection pressures may lead to
between part quality and productivity. A flashing. Screw speed
typical mold temperature for the injection A screw speed of 50 to 100 rpm is typically
molding of Sarlink is 26 °C to 62 °C. Holding pressure used.
A typical holding pressure for Sarlink is 50 to
Higher mold temperatures are advisable 70 % of the injection pressure. A lower screw speed will improve dispersion
when: of additives like color masterbatch and will
• parts have a long flow path and/or thin help to maintain low melt temperatures when
wall sections molding thick parts.
• a minimum of warpage is required 3 a
good surface appearance is required.

High mold temperatures will, of course,

increase cooling times.

6 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Time settings Poppet valves are used in the mold cavity to Special recommendations for the
control the air ejection. injection molding of thin parts
The major components of the cycle time are: • Use high melt temperatures (200 °C
Not included here is the time for manual or minimum).
Mold filling time robotic part removal. • Use fast injection speed.
This time is a function of the volume of the • Use a high mold temperature (50 to 70
part, the material grade, location and number °C).
of gates, and the injection pressure. A typical Cushion (buffer) • Avoid overpacking. Fill the part up to 98
injection time for Sarlink is 0.5 to 2 s. % using first stage injection and keep the
A cushion of material should remain in the holding pressure 1 to 3 s at 50 to 70 % of
Holding time barrel, in front of the screw, after the injection the injection pressure.
This time should be as low as possible. Thick is completed and the mold is filled. The roles
parts require longer holding times (5 to 10 of this cushion are:
s). For thin parts shorter holding times are • to ensure that there is enough material left 3UMMARIZEDRECOMMENDED
possible (1 to 3 s). for packing the mold PROCEDUREFORMOULDFILLING
• to prevent metal to metal contact during ī &ILLTHEMOULDQUICKLYINTOS
Cooling time the injection cycle 3 to minimize wear on UPTOUSINGFIRSTSTAGE
The cooling time depends on: the nozzle, screw and barrel. INJECTION
• the wall thickness of the part ī +EEPTHEHOLDINGPRESSUREDURING
• the melt temperature of the material Special recommendations for the TOSATTOOFTHE
• the hardness of the particular Sarlink injection molding of thick parts INJECTIONPRESSURE
grade The following factors will reduce cycle times
• the complexity of the part. for thick parts: A summary of recommended settings for
• reduce barrel temperatures optimal injection molding of standard Sarlink
Ejection/part removal time • reduce screw speed to a minimum in order parts is shown in appendix 3.
The ejection time is dependent on the to reduce melt temperatures
hardness of the grade, the complexity of the • use a cold mold, chilled if possible
part and the ejector design. Softer parts need • use a moderate injection speed to reduce
slower ejection. Blade ejectors, which have shear heating during filling of the mold.
a larger ejecting surface, can reduce the time
before ejection. Air assisted part ejection These recommendations can have negative
is often used to eject parts with undercuts. effects on the surface appearance.

7 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

 Example 1 system is properly flow balanced in order to
Mold Design for 16 cavity mold compensate for the difference in part weight
Figure 5 shows a correct design, in which all and cavity size.
Sarlink Injection cavities are at equal distance from the sprue. In
this design, all cavities will fill in the same time Figure 7 shows the correct mold design. The
Molded Parts and with the same pressure. runners going to the smaller cavities are
In contrast, figure 6 exhibits an inadequate longer and/or thinner, so that these smaller
mold design, in which some cavities are closer cavities fill in the same time and under the
Mold balance to the sprue. These cavities will be filled first same pressure as the bigger ones.
and may be over-packed. On the contrary,
It is important to have a well balanced mold, cavities further away from the sprue may not Figure 8 shows an inadequate design. In this
in which all cavities are filled in the same time fill or fill incompletely. Such a mold design design, the runner system is symmetrical;
and under the same pressure. If a mold is not should be avoided for Sarlink. therefore the smaller cavities will fill much
correctly balanced, warpage and distortion more quickly and will be overpacked, while
will occur, and a part of the production will Example 2 the bigger cavities may not fill completely.
have to be recycled. Shown are two sets of 4 cavity mold with unequal parts (family
examples of good and bad mold designs are mold) Mold filling computer simulations can be
explained. It is possible to produce parts of different used to determine the proper runner and gate
sizes in one mold, provided the runner dimensions.

&IG CAVITY &IG CAVITY

MOULDBALANCED MOULDUNBALANCED
ģ(ĤCORRECT RUNNERINADEQUATE
DESIGN DESIGN

&IG "ALANCED &IG 5NBALANCED

FAMILYMOULD MULTICAVITYMOULD
#ORRECTDESIGN )NCORRECTDESIGN

8 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Sprue Gates

The sprue should be as short as possible. Hot Type The optimal filling of the part is besides
sprue bushings are often used to reduce cycle Cylindrical or trapezoidal gate sections are depending on the number and size of the
time and eliminate sprue sticking for softer preferred. gates, influenced by the material type, gate
grades. thickness, melt temperature injection speed
It is advisable to adapt the type of gate to and spiral flow length (see figure 1 and 2).
Tapered sprue extractors with 5 degrees taper the part, e.g.:
or more are preferred. The sprue base should • circular parts should have, if possible, Tips for gate design
be equal to the runner diameter. ’Z’ puller or a centered gate • For complex parts, the use of a prototype
conical designs are preferred. • submarine or tunnel gates are tool is recommended.
recommended for small parts • It is advisable to start with small diameter
Recommended are short sprue bushings. A gates, which can be easily increased
cold slug catcher should be located at the end Various types of gates are shown in figure 9. if necessary.
of the sprue.
Size
The gate size should be as small as possible, Ejectors
Runners typically 1mm in diameter.
• For a part weight less than 10 g, choose Softer grades of Sarlink require more
Type a gate diameter of 0.6-1.0 mm or less. ejectors than harder ones. Sarlink parts with
Full round runners or trapezoidal shapes • The gate diameter should be small in small undercuts can be easily demolded. A
are preferred, half round runners should order to generate shear at the entrance conjunction of ejectors pins and air ejection
be avoided. of the cavity. will facilitate demolding.
• Too large or too small gates could lead
Size to un-aesthetic traces on the part. Type
The size of the runners should be as short • The gate land length (“the tip”) should Prefer large ejectors to avoid piercing for
as feasible. They should be big enough to be kept to a minimum; maximum half soft grades. Blade ejectors can be used. Air
minimize the pressure drop in the melt before of the gate diameter. assisted ejectors are useful for parts with large
it enters the mold cavity. undercuts.
• The primary runner diameter should Number of gates
be equal to the sprue base. For small parts one gate is sufficient. Location
• The secondary runners should have For larger parts two or more gates are The ejectors should be spread evenly around
a smaller diameter. recommended. Round parts may require in order to balance the ejection and to avoid
more gates to maintain concentricity. distortion of the part.
Cold slug catchers should be placed at the
extremity of each runner.
Venting

&IG %XAMPLES Sarlink molds must be vented in order to allow

OFDIFFERENTGATE for the escape of the air present in the mold
DESIGNS when the molten material fills runners and
cavities.

Inadequate venting can lead to incomplete

parts, burn marks, flash, poor surface
appearance or weak welding lines. On the
contrary, well vented tools will allow faster
cycles.

3UBMARINEGATE 0INGATE &ILMGATE

9 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

 &IG %XAMPLE
Vents should be located on the mold parting
OFVENTING
line, in the area(s) furthest from the gate(s)
and at the weld lines. Their depth should not
exceed 0.025 millimeter for the part which is
in contact with the cavity. This will prevent the
4YPICALVENTMM 0ART
formation of flash and the escape of Sarlink
material through the vent. At a short distance
from the cavity (10-15 mm), the depth of the
vent can be increased to 0.15 mm or larger to
facilitate the escape of the air (see figure 10).

As previously mentioned, large runners 4YPICALVENTMM

should also be vented. Besides the venting of
the cavity, it may also be helpful to add venting
on the ejector pins, as depicted in figure 11.

Mold Surface
&IG %XAMPLE
OFEJECTORPIN
Avoid all polished surfaces. It is preferred to VENTING
have a medium EDM finish. Vapor honing or
0ART
bead blasting is also recommended.

Mold material

In appendix 2 the recommended types of %JECTOR

pre-hardened steels and fully hardened steels
are listed.
4YPICALVENTMM

Aluminum or pre-hardened steel tooling

can be used for prototyping and for short
production runs.

Shrinkage

Shrinkage is a critical item to control the For shrinkage data on a specific Sarlink grade, Summary
dimensions of the finished part. It is also a contact your Account Manager. Reduce shrinkage by:
particularly complex parameter, as it can be • increasing the injection speed
influenced by many interrelated factors, such Influence of processing conditions on • increasing the holding pressure
as: shrinkage • reducing the mold temperature
• the machinery Some of the variables which influence • increasing the mold cooling time.
• the mold design shrinkage may be very difficult to change
• the part geometry and the (machinery, part geometry, Sarlink grade, Increase shrinkage by reversing the above
direction of flow etc.). Processing conditions, such as holding mentioned actions.
• the Sarlink grade used pressure, have an influence on shrinkage but
• the processing conditions can be varied.
• the injection molding system • Holding pressure: higher and longer
(e.g. hot runners) holding pressures will result in less
shrinkage.
Influence of part geometry and direction of • Mold temperature: higher mold
flow on shrinkage temperature creates higher shrinkage.
The geometry of the part, and its thickness, • Melt temperature: the melt temperature
play an important role to determine the of Sarlink does not have a big influence on
shrinkage. Generally, in the case of Sarlink, shrinkage.
the shrinkage is higher in the flow direction • Injection speed
than perpendicular to the flow direction.

10 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Multi-Shot (2K) Due to the fact that Sarlink is based on Hot runner technology
polypropylene and EPDM rubber, the
Injection Molding adhesion between Sarlink and polypropylene Sarlink can be injection molded using hot
is excellent. Normally the hardest material is runner technology. This technology reduces
injected first followed by the softer material. scrap generated during processing by
Multi-shot injection molding or also called eliminating cold runners.
2K injection molding is the technology where If the materials are not compatible it is
two or more different materials are injected possible to create a connection via mechanical In addition to the general information
sequentially or together at the same time in a interlocking design. provided previously, the following specific
special mold. In this process it is necessary to recommendations will help obtaining optimal
create a separate cavity space for each material results when molding Sarlink with hot
in a single mold. This is accomplished by: Molding conditions runners:
• translation of the entire mold • internal heated runner systems are not
• rotation of the entire mold Elevated mold and melt temperatures aid recommended
• a replacement of a part of the mold by in the adhesion of Sarlink to the substrate • small runner channels are used to keep
translation or rotation. material. the shear rate high throughout the runner
system
For multi-shot injection molding the injection • each runner should be equipped with an
molding machine must be equipped with a Recycling individual temperature control, located as
separate barrel for each material. These barrels close as possible to the gate
can be standing parallel or perpendicular Multi-shot products of Sarlink and • runner should be as short as possible to
depending on the layout of the machine. polypropylene can be recycled easily. reduce the residence time
Recycled material which is a mixture of • gates should be smaller than the gates for
Sarlink and polypropylene is compatible cold runner molds
Adhesion with polypropylene and/or Sarlink. The • balanced runners are strongly
composition of the multi-shot part will recommended.
Important factors for a good connection are: influence the properties of polypropylene or
• the compatibility of the materials Sarlink.
• the design of the product
• molding conditions.

11 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Appendix 1

Recommended Mold Materials

Steel types moulds
3TEELTYPESMOULDS !PREHARDENED !PREHARDENED !THROUGH !VERSATILETHROUGH
.) #R -OSTEEL STAINLESSHOLDER HARDENINGSTAINLESS HARDENING#R
SUPPLIEDAT STEELWITHEXCELLENT STEELWITHGOOD MOULDANDDIESTEEL
"RINELLWITH MACHINEBILITYHIGH CORROSION WITHGOODWEAR
EXCELLENTPOLISHING TENSILESTRENGTH RESISTANCEANDVERY RESISTANCEAND
ANDPHOTO ETCHING ENDGOODCORROSION GOODPOLISHABILITY POLISHABILITY
PROPERTIES3UITABLE RESISTANCE
FORAWIDERANGEOF
INJECTIONMOULDS
BLOWMOULDS
EXTRUSIONDIES
0ROPERTIES  ) )) ))) )6
.) #R 8#R-O 8#R 8#R-
.ORMALHARDNESS      
7EARRESISTANCE
4OUGHNESS
#OMPRESSIVESTRENGTH
#ORROSIONRESISTANCE
-ACHINING
0OLISHABILITY
7ELDABILITY
.ITRIDING
0HOTO ETCHABILITY

.ORMS
$).    
53!!)3) 0 &  (
$ELIVERY(" ^   

!NALYSIS
#    
#R    

1) The properties of steel grades have

been rated from 1-10, where 10 is the
highest rating. Such comparisons must be
considered as approximate, but can be a
useful guide te steel selection.
2) Special process required.
3) Rockwell C (Brinell).
4) Tested in delivery condition.

Source properties: Steels for Moulds, Uddeholm

12 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Appendix 2

Summary of Recommended Settings for

Optimal Injection Molding of Standard
Sarlink Parts

4EMPERATURESETTINGSę# 
2EARBARREL  
-IDDLEBARREL  
&RONTBARREL  
.OZZLE  

-ELT  

-OULD  

(YDRAULIC PRESSURESETTINGS
ī)NJECTIONPRESSURE  BAR
ī(OLDINGPRESSURE  OFINJECTIONPRESSURE
ī"ACKPRESSURE  BAR

3PEEDSETTINGS
ī)NJECTIONSPEED OFMAXIMUM
ī3CREWSPEED  RPM

4IMESETTINGS
ī)NJECTIONTIME  S
ī(OLDINGTIME  S
ī#OOLINGTIME !SSHORTASPOSSIBLE4HEPARTSHOULD
BEREMOVABLEWITHOUTDEFORMATIONOR
PIERCINGOFTHEEJECTORS

4YPICALMELTTEMPERATURESFOR3ARLINKINAMULTI SHOTPROCESS

-ATERIAL -ATERIAL 4MELT 4MELT 4MOULD

ę# ę# ę#
POLYPROPYLENE 3ARLINK      
POLYAMIDE 3ARLINK      

13 | Guidelines for the Injection Molding of Sarlink www.sarlink.com

Appendix 3

Troubleshooting Table for the Injection

Molding of Sarlink

0ROBLEM #AUSE 3OLUTIONCORRECTIVEACTION

3HORTSHOT )NSUFFICIENTFILLINGOFTHE )NCREASESHOTSIZENORMALLYFILLTOOFTOTALVOLUME

MOULD )NCREASEINJECTIONSPEEDPRESSURE
$ECREASEHOPPER SIDETEMPERATURETOIMPROVEPLASTICIZING
#HECKOPERATIONOFSPARERING
)NCREASEBACKPRESSURE
#HECKVENTING
#HECKMOULDTEMPERATURE
#HECKHOT RUNNERTEMPERATURECONTROLLERS
#HECKBALANCEOFFLOWFORHOT RUNNERGATESYSTEMS
%NLARGESMALLPASSAGESINTHEMOULD

-OULDFUNCTIONINGPROBLEMS #HECKWORKINGOFMOVABLEPARTSINTHEMOULDESPECIALLY

FORMULTI SHOTINJECTIONMOULDING

3INKMARKS )NSUFFICIENTFILLINGOFTHE )NCREASESHOTSIZENORMALLYFILLTOOFTOTALVOLUME

MOULDMOULDIS )NCREASEINJECTIONSPEED
UNDERPACKED )NCREASEHOLDINGPRESSUREANDORHOLDINGTIME
)NCREASEBARRELANDNOZZLETEMPERATURE
)NCREASEBACKPRESSURE
)NCREASEGATESIZEANDORHEATERS
)NCREASECHECKTHEVENTING

7ELDLINES 4OOLOWMATERIAL )NCREASEMELTTEMPERATURE

3TRENGTHANDVISIBILITY TEMPERATURE )NCREASEMOULDTEMPERATURE
)NCREASEBACKPRESSURE
)NCREASEINJECTIONSPEEDPRESSURE
)NCREASEHOLDINGPRESSURE

)NSUFFICIENTVENTING #HECKVENTINGCLEANANDORINCREASESIZE

-OULDDESIGNPROBLEM )NCREASEVENTSIZE
)NCREASERUNNERSIZE

3ILVERSTREAKSONPART -OISTUREINMATERIALIS $RYMATERIAL

TOOHIGH #HECKTHEVENTINGOFTHEMOULD

4OOCOLDMOULDMOISTURE )NCREASETHEMOULDTEMPERATURE
CONDENSING 7AITFORCONSTANTPRODUCTION

#OLOURDEGRADATION -ATERIALORCOLOUR $ECREASETEMPERATUREPROFILE

CONCENTRATEDEGRADATION 2EDUCEINJECTIONSPEEDPRESSURE
2EDUCEBACKPRESSURE
#HANGETOHIGHERTEMPERATURESTABLECOLOURCONCENTRATE

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 0ROBLEM #AUSE 3OLUTIONCORRECTIVEACTION

6OIDSANDBUBBLES -OISTUREINMATERIALIS $RYMATERIAL

TOOHIGH )NCREASEBACKPRESSURE
)NCREASEINJECTIONSPEEDPRESSURE
)NCREASEMOULDTEMPERATURE

0ARTSTICKSINTHE )NSUFFICIENTCOOLINGOFTHE 2EDUCEINJECTIONPRESSURE

MOULDCAVITYORIN PART $ECREASEHOLDINGPRESSURE
SPRUE
)NCORRECTMOULDFILLING !DDDECOMPRESSION

)NCREASEMOULDFILLINGVOLUME
)NCREASEINJECTIONSPEED
)NCREASEMELTTEMPERATURE
)NCREASEBACKPRESSURE

)NCORRECTFUNCTIONINGOFTHE #HECKANDORCLEANTHEVENTINGOFTHEMOULD
MOULD #LEANMOULDANDCAVITY
#HECKHEATINGOFHOTRUNNERCAVITIES

0OORSURFACE )NCORRECTMOULDDESIGN )NCREASEGATESIZEREDUCESHEAR

APPEARANCE $ECREASETHESURFACESMOOTHNESSADDAGRAIN

0ROBLEMWITHADDITIVES 3TOPWITHUSINGMOULDLUBRICANTS
"ASISOFCOLOUR56 MASTERBATCHISNOTCORRECT

4OOHIGHMOISTURECONTENT $RYMATERIAL

$ISTORTEDPARTS )MPROPERREMOVALOPERATION $ECREASEEJECTIONTIME

#HANGETOLARGEREJECTIONPINS
%JECTONSTRONGESTAREAOFTHEPART
)NCREASECOOLINGTIME
2EDUCEMELTANDORMOULDTEMPERATURE

3TRESSESAREMOULDEDINTO )NCREASEMELTTEMPERATURE
THEPART 2EDUCEFILLINGTIMEPRESSURE
2EDUCEHOLDINGPRESSURE

!DHESIONPROBLEMSINA 4EMPERATURESARETOOLOW )NCREASEĤCONTACTTEMPERATUREĤ MELTTEMPERATUREOFMATERIALS

MULTI SHOTPROCESS 3TARTWITHINCREASINGTHETEMPERATUREOFTHEFIRSTINJECTEDMATERIAL
2EDUCESWITCHTIMEBETWEENTWOMATERIALS
)NCREASEHOLDINGTIMEPRESSUREOFSECONDMATERIAL

-ATERIALSARENOTCOMPATIBLE #HECKIFTHEMATERIALISCOMPATIBLEWITHTHE3ARLINKGRADEINUSE

.EGATIVEINFLUENCEOFADDING 4OOMUCHADDINGOFANINCOMPATIBLEINGREDIENTTOTHE3ARLINK
OFADDITIVE GRADEUSEDCANLEADTOADHESIONPROBLEMS

15 | Guidelines for the Injection Molding of Sarlink www.sarlink.com