moulding problem

8/8/2019 Moulding Problem

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2/52

MOULDING

PROBLEMS

MOULD

related

MACHINErelated

SINK MARKSSink Marks occurduring the coolingprocess if certainareas of the partare not cooledsufficiently causing

them to contract

Add more gas vents.

Increase sprue,

runner, or gate size.Decrease gate land

length.

Change location of

the gate

non uniformity of wallthickness.

Adjust feed.

Increase injection

pressure.Increase injection hold

time

Decrease melt

temperature

Decrease mouldtemperature.

Increase back

pressure.

Sink marks are small depressions on the moulding surface, caused by

material contraction during the cooling phase. They are usually found were

ribs, bosses etc. join a wall.


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Decrease amount of regrind use.

Decrease back pressure.

Confirm that the non-return valve being used is notleaking excessively.

Decrease melt temperature. Do this if the sink marks

are near the gate or thick walled areas.

Decrease mold temperature. Do this if the sink marksare near the gate or thick walled areas.

Decrease injection rate. Do this if the sink marks are

near the gate or thick walled areas.Dry material.

Increase injection pressure. Do this if the sink marksare away from the gate or in thin walled areas.

SINK MARKS


4/52

Increase injection speed. Do this if the sink marksare away from the gate or in thin walled areas.

Increase mold temperature. Do this if the sinkmarks are away from the gate or in thin walledareas.

Increase injection-hold.

Increase shot size and confirm that the a cushion isbeing maintained.

Increase size of sprue and/or runners and/orgates.

Relocate gates on or as near as possible to thicksections.

Increase cooling time.

If possible change the mold design to maintain aneven wall thickness throughout the part.

SINK MARKS


5/52

MOULDINGPROBLEMS

MOULDrelated

MACHINErelated

Jetting

Jetting is caused by

an undevelopedfrontal flow of meltin the cavity. Theuninterruptedplastic flows or"snakes" into thecavity and cools offenough so that itdoes not fusehomogeneouslywith the materialthat follows

Re-locate gate

position.

Increase sprue,runner, or gate size.

Decrease gate land

length.

Decrease injection

speed.

Increase/decreasemelt temperature.

Check nozzle

heating band.

Increase mould

temperature.Use larger opening

in nozzle

Jetting is caused during injection of the melt into the cavity. If the distance between the gate and

the opposite cavity wall or other obstacles is too long the melt develops a "sausage" like flow where

the outer layers cool off faster. The result is a "sausage" like pattern on the surface of the moulding.


6/52

Decrease injection speed.

C

hange the melt temperature, up or down.Use higher compression screw.

Increase the gate diameter.

Move the gate so that when the plastic first entersthe cavity it hits an obstruction such as a rib orwall.

Jetting


7/52

MOULDING

PROBLEMS

MOULD

related

MACHINErelated

Warpage

Warping, Part

Distortion isshows up as partsbeing bowed,warped, bent ortwisted beyond

the normalspecificationoutlined on thedrawing.

Change water

channels.

Ensure uniformmould temperature

Decrease mould

temperature.

Decrease stocktemperature.

Decrease back

pressure.

Increase cooling

time.Decrease injection

pressure.

Decrease injection

speed.

Warpage is caused by differential shrinkage due to different molecular orientation and / or varying

wall thicknesses in the product. It is therefore important to maintain a uniform mould temperatureand avoid Hot - or Cold - spots on the mould surface. In crystalline polymers the formation of

crystalline structures can also cause warpage.


8/52

Warpage

Adjust melt Temperature (increase to relieve molded-in stress,decrease to avoid over packing). stress, decrease to avoid overpacking). stress, decrease to avoid over packing).

Check gates for proper location and adequate size.

Check mold knockout mechanism for proper design andoperation.

Equalize/balance mold temperature of both halves.


Increase mold cooling time.

Relocate gates on or as near as possible to thick sections.

Try increasing or decreasing injection pressure


9/52

MOULDINGPROBLEMS

MOULDrelated

MACHINErelated

Weld burns Increase sprue,runner, or gate size.

Change location of

the gate.

Decrease injectionspeed.

Increase/decrease

melt temperature.Decrease injectionpressure.

Decrease screwspeed rpm.

Decrease backpressure.

Use larger opening innozzle.

Weld burns are caused by trapped air between two (or more) melt fronts during injection.

The temperature of the air increases under pressure and actually burns the polymer.


10/52

MOULDING

PROBLEMS

MOULD

related

MACHINErelated

Short mouldings Add more gasvents.

Increase sprue,runner, or gate size.

Decrease gate land

length.

Adjust feed.

Increase injection

pressure.Increase injectionspeed.

Increase stocktemperature.

Increase mouldtemperature.

Short mouldings indicate an under filling of the cavities. Short mouldings can

have several causes and are usually one of the easiest to solve moulding

problems

Short Shotsoccur when thepart does notcompletely fill.


11/52

Short Shot (Incomplete Filled Parts)

Increase back pressure.

Increase injection pressure.

Increase injection speed.

Increase melt temperature.

Increase mold temperature.

Increase nozzle temperature. Ensure that the manifold andnozzles have reached the set temperature.

Increase shot size and confirm cushion.

Make sure mold is vented correctly and vents are clear.

Confirm that the non-return valve used is not leakingexcessively.

Increase the switch over pressure, distance, or time (whichevermethod is being used) point from fill to hold so the fill stage isused longer.

Change part design. Thin areas of the mold may not fillcompletely, especially if there is a thick to thin transition, or

there is a long rib that cannot be vented very well. If the partdesign allows it, change in these areas can improve the situation.


12/52

MOULDING

PROBLEMS

MOULD

related

MACHINE

relatedColourstreaking

Discoloration is

similar to burnmarks or brownstreaks butgenerally not asdark or severe. Itmay cause the partto be a darker

shade than thevirgin pellets and isoften found nearestthe gate area,however it can alsoappear as darkstreaks throughout

the part.

Increase screw,

runner or gate size.


Increase/decreasestock temperature.

Increase mouldtemperature

Check material forcontamination.

Decrease gate land

length

Decrease screw speedrpm.

Decrease backpressure.

Check nozzle heating

band.

Colourstreaking in pigmented, compounded material can be an indication of:

a) excessive processing temperatures

b) exposure to high shear ratesc) material contamination


13/52

Check hopper and feed zone for contamination.


Decrease melt temperature.

Decrease nozzle temperature.

Move mold to smaller shot-size press.

Provide additional vents in mold.

Purge heating cylinder.

Shorten overall cycle.

Colourstreaking


14/52

MOULDINGPROBLEMS

MOULDrelated

MACHINErelated

Flash Re-match mould

parting line.

Decrease injectionpressure.

Increase clamppressure.


Decrease stock

temperature.Decrease mouldtemperature.

Flash is generally caused by overfilling of the mould cavity. Provided the moulding

machine is strong enough (in terms of clamping pressure) and the mould shut off faces

(parting line) are not damaged, flash can be corrected with one or more of the following

measures.

Excessive Flash is often

seen near sealing faces,out of vent grooves, ordown ejector pins. Itappears as thin orsometimes thicksections of plasticwhere it would not beon a normal part.


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Decrease cylinder temperature.

Decrease injection hold time.

Decrease injection pressure.


Decrease mold temperature.

Increase clamp pressure.

Check mold venting. Vents may have been ground too deep forthe material being used.

Check sealing surfaces to ensure that they seal off properly by"blueing" them in under clamp tonnage.

Check ejector pin bore diameter to pin diameter tolerances. Thetolerances may be too large allowing plastic to flash down theopening. The tolerances may be too large for the material being

used and can occur due to wear over time.

Flash


16/52

MOULDING

PROBLEMS

MOULD

related

MACHINE

relatedSurface Finish (LowGloss). Gloss is the

appearance of thesurface of themolded part whenlight is reflected offof it. Molds that aretextured or resinsthat are filled have

an inherentlyreduced level ofgloss whencompared to highly

polished mold

Increase sprue,

runner, or gate size.

Polish surface of

the mould.

Pre-dry resin.

Check resin forcontamination.

Increase injectionpressure.

Increase mouldtemperature.

Decrease melt

temperature.

Poorsurface finish The quality of the surface finish of a moulding is determined by

several factors. Provided the cavity surface is in good condition, moisture, contamination

with a foreign polymer and of course processing condition determine the quality of the

reproduction of the cavity surface.


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Clean mold surface.

If the part design allows increase the polish of the molding surface.

Increase cylinder temperature. This applies to molds that have apolished surface.

Increase injection pressure. This applies to molds that have a polishedsurface.

Increase injection speed. This applies to molds that have a polishedsurface.

Increase mold temperature. This applies to molds that have a polishedsurface.

Decrease cylinder temperature. This applies to molds that have atextured surface.

Decrease injection pressure. This applies to molds that have a texturedsurface.

Decrease injection speed. This applies to molds that have a texturedsurface.

Decrease mold temperature. This applies to molds that have a texturedsurface.


Make sure venting is adequate.

Surface Finish


18/52

MOULDING

PROBLEMS

MOULD

related

MACHINErelated

VoidsVoids are hollows

created in thepart. They arenormally found inthick sectionedparts caused bymaterial being

pulled away fromthe hot centersection towardscold mold wallsleaving a void in

the center.

Increase venting

Use hot bush or hot

runnersystem

Increase filling stage

Injection pressure

Use cavity pressurecontrol

Increase mould

surface temperature

Enclosed cavitiesor holesin the bulkof the mouldings


19/52

Clean vents.


Decrease melt temperature.

Dry material.




Increase shot length.

Increase size of gate.

Increase size of sprue and/or runners and/or gates.

Voids


20/52

MOULDINGPROBLEMS MOULDrelated

MACHINE

related

WeldlinesWeld Lines arecreated when two

or more melt flowfronts meetpossibly causing acosmeticallyvisible line. It canalso create a

weakened area inthe finishedmolded partespecially withfilled resins.

If possible re-site gate

toshorten flow path

inside the mould and

obviate ''jetting'. Withthicksection moulding

increase gate size and

inject slowly

Improve venting

Increase injection

pressure

Increase melt

temperature (front zoneand nozzle)

Increase speedof

injection

Increase mould

temperature

Use hot sprue bush orhot runnersystem

Use high volume mould

temperature controller

Use mouldsurface

temperature control

Surface markswhere twoor more streamsof material meet


21/52


Increase injection speed.

Increase injection hold.



Make sure part contains no sharp variation in cross-sections.

Vent cavity in the weld area.

Weldlines


22/52

MOULDING

PROBLEMS

MOULD

related

MACHINE

relatedGate blush Increase sprue,

runner, or gate size

Pre-dry resin.

Minimise melt

decompression.Increase mouldtemperature



Increase/decreasemelt temperature.

Gate blushA Blush in the gate area can have several causes, the polymer might not be as dry as

required or the shear stress during the injection phase exceeds the permissible limit. Even sharp

edges or corners in the gate area can cause excessive shear stress. A common cause of gate

blush is also melt decompression as it allows a tiny amount of air to enter the melt stream


23/52

Gate Stringing, Drooling

DescriptionThe part does not break cleanly from the gate area.

Insufficient cooling time during the cycle.

Excessive heat in the gate area. Check thermocouplein the nozzle or decrease the temperature of the hotrunner manifold and nozzle.

Increase cooling at the gate area.Ensure that youhave controllable turbulent flow in the gate area.


24/52

MOULDING

PROBLEMS

MOULD

related

MACHINE

relatedSticking in

cavity

Part is getting

not pulling outof the cavityand in rarercircumstancescannot beejected off the

core.

Polish the cavity and

core.

Check for the draft

Decrease injectionpressure.

Decrease injectionhold time.

Increase cycle time.Provide vacuumrelieve

Sticking in cavity


25/52

Check mold for undercuts and/or insufficient draft.

Decrease booster time.

Decrease cylinder and nozzle temperature.


Decrease injection-hold.

Decrease mold cavity temperature.

Increase clamp pressure.

Increase mold-close time.

Texturing on part is too deep. The parts may stick in the cavity ifa new texture or a retexturing has been performed on the cavity

half of the mold.

If possible add undercuts to the core to allow the part to pull outof the cavity.

Sticking in cavity


26/52

MOULDING

PROBLEMS

MOULD

related

MACHINE

relatedSprue stickingSprue Stickinggenerally occursin a cold runnermold when thesprue is staying inthe mold.

Polish sprue

bushing.

Polish surface ofthe mould.

Reseat nozzle(machine).

Decrease mouldtemperature.

Decrease injection

hold time. Increasecycle time.

Check nozzleheating band.

Check resin forcontamination.

Sprue sticking


27/52

Check mold for undercuts and/or insufficient draft.

Decrease booster time.



Decrease injection-hold.

Decrease mold close time.

Decrease nozzle temperature.

Increase core temperature.

Open the gates.

Ensure that the correct design of nozzle tip for thematerial is being used.

Sprue sticking


28/52

MOULDINGPROBLEMS

MOULDrelated

MACHINErelated

Poor

dimensional

stability

Change water

channels.

Increase/decreasestock temperature.

Increase injectionhold time.


Increase backpressure.

Increase/decreasemould temperature.

Poordimensional stability Is usually an indication of inconsistencies in themoulding process e.g. temperature, pressure, timing fluctuations.


29/52

Black Spots, Brown streaksDescriptionBlack spots and brown streaks appear as dark spots or streaks in the molded

part and are usually caused by thermal damage to the melt.Possible Solutions

Check the material for contamination.Decrease the melt temperature.Decrease the overall cycle time.Purge and/or clean the screw and barrel.D

ecrease the screw speed. High screw speeds may cause the materialto degrade.Material may have too much regrind content.

Material may be overdried.Decrease drying time/temperature. Refer todrying instructions provided by the material supplier.

Material may be prone to thermal degradation. It may be necessary touse a more thermally stable material.

Dead spots may be occurring, ensure that the alignment between themachine nozzle and mold sprue is correct.Residence time may be too long, or the shot size may be too small forthe machine. It may be necessary to move the mold to a machine withless injection capacity.


30/52

Blisters (Air Entrapment)DescriptionBlisters are hollows created on or in the molded part. In contrast tovoid (vacuum) this entrapped gas can also appear near the walls.

Possible Solutions

Decrease melt temperature.Decrease screw speed.

Dry material.

Increase back pressure.


Ensure regrind is not too coarse.

Provide additional mold vents.

Relocate gate.


31/52

Brittleness

DescriptionBrittleness is a condition where the part cracks or breaks at a muchlower stress level than would normally be expected based on thevirgin material properties.

Possible Solutions

Check for material contamination.Decrease amount of regrind use.



Decrease screw speed.


Dry material. Refer to the drying instructions provided by thematerial supplier.


32/52

Bubbles

DescriptionBubbles are similar to blisters in that there is airentrapped in the molded part.

Possible Solutions

Decrease injection speed.Decrease injection temperature.

Dry material further.


Increase number and/or size of vents.

Increase shot size.


33/52

Burn Marks, DieselingDescriptionBurn Marks or Dieseling show up on the finish molded parts as charred or

dark plastic caused by trapped gas and is usually accompanied by adistinctive burnt smell.Note: If this problem is allowed to continue without fixing the root cause itwill very quickly cause damage to the molding surface.

Possible SolutionsAlter gate position and/or increase gate size.Check for heater malfunction.

Decrease booster time.Decrease injection pressure.Decrease injection speed.Decrease melt and/or mold temperature.

Improve mold cavity venting. Vents may become smaller over time dueto wear and they will need to be brought back to their original depth.

Reduce clamp force to improve venting. Vents may become smaller

because they are being crushed by the clamping force. If it is possible toreduce the clamping force without causing flash then this should be done.Note: This is always good practice to minimize wear on the mold andmachine. Improve venting at the burn location. Burn marks often occuron deep ribs that have no venting. If possible it may be helpful to put anejector pin or sleeve at the burnt area to allow the trapped gas to escapeto atmosphere.


34/52

Cracking, Crazing

DescriptionCracking or Crazing is caused by high internal molded in stress or byan external force imposed upon the part. They can also be caused byan incompatible external chemical being applied to the finished partsThe cracks often don't appear until days or weeks after the partshave been molded.

Possible SolutionsDecrease injection pressure.Dry material.Increase cylinder temperature.Increase mold temperature.

Increase nozzle temperature.Modify injection speed.

If the material is partially crystalline then it may help to reducethe mold and/or melt temperature.If the material is amorphous then it may help to increase themold and/or melt temperature.


35/52

DelaminationDescriptionDelamination occurs when single surface layers start flaking off themolded part.

Possible SolutionsAdjust injection speed.

Check for material contamination. Incompatible resins orcolorants may have been accidently mixed causing this conditionto be seen.Dry material.Increase melt temperature.

Increase mold temperature.Insufficient Blending. Check melt homogeneity and plasticizingperformance.


36/52

DiscolorationDescriptionDiscoloration is similar to burn marks or brown streaks but generallynot as dark or severe. It may cause the part to be a darker shadethan the virgin pellets and is often found nearest the gate area,however it can also appear asdark streaks throughout the part.

Possible Solutions

Check hopper and feed zone for contamination.Decrease back pressure.Decrease melt temperature.Decrease nozzle temperature.Move mold to smaller shot-size press.Provide additional vents in mold.

Purge heating cylinder.Shorten overall cycle.


37/52

Flow, Halo, Blush MarksDescriptionFlow, Halo, Blush Marks are marks seen on the part due to flow of themolten plastic across the molding surface.

Possible Solutions

Decrease injection speed.Increase cold slug area in size or number.Increase injection pressure.Increase melt temperature.Increase mold temperature.

Increase nozzle temperature.Increase size of sprue/runner/gate.


38/52

Gate Stringing, Drooling

DescriptionThe part does not break cleanly from the gate area.

Possible Solutions

Insufficient cooling time during the cycle.Excessive heat in the gate area. Check thermocouplein the nozzle or decrease the temperature of the hotrunner manifold and nozzle.Increase cooling at the gate area.Ensure that youhave controllable turbulent flow in the gate area.


39/52

Material Leakage

DescriptionMaterial Leakage is usually caused by material forces overcoming thestructural strength of the mold.

NOTE:One sign that indicates that material has leaked is that themanifold reaches processing temperature very slowly.

Possible SolutionsManifold locator is oversize.

Processing temperature may be too low causing increasedpressure in the manifold.

Manifold locator may be hobbed into the mold. Decrease theforce applied to the nozzle pad by the machine then repair thedamaged area, then check and if necessary replace the locator.

Insufficient number of mold assembly screws. Ensure that thequantity, type of screw, and the location of the screws correspond

to the general assembly drawing.Nozzle may have overheated causing damage to the seal orgate. Check/replace the thermocouple in the nozzle, then checkand if necessary repair the nozzle well area.Manifold may have overheated. Check and replace if necessarythe following components; nozzle well area, thermocouple, valvedisks, sprue disks, or pressure disks.


40/52

Oversized Part

DescriptionPart is too large when compared to the drawingspecifications.

Possible SolutionsDecrease booster time.

Decrease cylinder temperature.Decrease holding pressure.Decrease injection pressure.Decrease injection speed.Decrease overall cycle time.

Increase gate size and/or change gate location.Increase mold temperature.


41/52

Part Sticking

DescriptionPart is getting not pulling out of the cavity and in rarer circumstances

cannot be ejected off the core.Possible Solutions

Check mold for undercuts and/or insufficient draft.Decrease booster time.Decrease cylinder and nozzle temperature.Decrease injection pressure.

Decrease injection-hold.Decrease mold cavity temperature.Increase clamp pressure.Increase mold-close time.Texturing on part is too deep. The parts may stick in the cavity if

a new texture or a retexturing has been performed on the cavityhalf of the mold.If possible add undercuts to the core to allow the part to pull outof the cavity.


42/52

Short Shot (Incomplete Filled Parts)

DescriptionShort Shots occur when the part does not completely fill.

PossibleS

olutionsIncrease back pressure.Increase injection pressure.Increase injection speed.Increase melt temperature.Increase mold temperature.

Increase nozzle temperature. Ensure that the manifold andnozzles have reached the set temperature.Increase shot size and confirm cushion.Make sure mold is vented correctly and vents are clear.

Confirm that the non-return valve used is not leakingexcessively.

Increase the switch over pressure, distance, or time (whichevermethod is being used) point from fill to hold so the fill stage isused longer.Change part design. Thin areas of the mold may not fillcompletely, especially if there is a thick to thin transition, orthere is a long rib that cannot be vented very well. If the partdesign allows it, change in these areas can improve the situation.


43/52

Splay Marks, Silver Streaks

DescriptionSplay Marks, Silver Streaks are usually caused by water vapor

blisters at the flow front burst and freeze on the wall of the moldingsurface.

Possible SolutionsCheck for contamination.Decrease melt temperature.Decrease nozzle temperature.

Dry resin pellets before use. As per the manufacturersrecommendations.

Incorrect storage of pellets. Moisture on the pellets could betransferred into the melt, especially if the resin is not normallypre-dried.

Raise mold temperature. This will prevent condensation on themold walls from being carried into the melt.

Ensure the mold is not leaking water onto the cores or cavities.Again this will prevent condensation on the mold walls from beingcarried into the melt.

Relocate gates on or as near as possible to thick sections.Shorten overall cycle.


44/52

Undersized Part

Description

Part is too small when compared to the drawingspecifications.

Possible SolutionsDecrease mold temperature.Increase booster time.Increase cylinder temperature.Increase hold-time.Increase holding pressure.Increase injection pressure.

Increase injection speed.Inspect mold for surface defects.


45/52

Weld Lines

DescriptionWeld Lines are created when two or more melt flow frontsmeet possibly causing a cosmetically visible line. It canalso create a weakened area in the finished molded partespecially with filled resins.

Possible SolutionsIncrease injection pressure.Increase injection speed.Increase injection hold.Increase melt temperature.Increase mold temperature.

Make sure part contains no sharp variation in cross-sections.Vent cavity in the weld area.


46/52

SINK MARKS Filled polymer can reduce sink mark

POOR MECHANICALSTRENGTH

Consider high molecular weight

polymers.

Consider filled polymers. Pre heatpolymer in dehumidifier if required

for polymer as recommended for

polymer.

DIMENSIONALVARIATION

Check shrinkage characteristics ofmaterial.

DEGRADATIONOFMELT

Check thermal stability of polymer aswell as pigments and other additives

if any used with material.

DIFFICULTY IN FILLING Consider polymer of higher MFI

MATERIAL RELATED PROBLEMS

PROBLEMS IN PERFORMANCE OF PLASTIC PARTS


47/52

The predominantly material

causesinvolvedin failure were:

The predominating process faults

were:

Environmental Stress Cracking, Excessive moulded-in stresses,

Cyclic Fatigue, Voiding,

Notch Sensitivity, Poorweldlines,

ChemicalAttackand; Stress

Cracking,

Adverse Orientation,

UV Degradation,Material contamination,

Thermal Degradation, Longer Residence time in the machine,

Creep, Wrong materialselection or poor partdesign,

Buckling, Wrong materialselection or poor partdesign

PROBLEMS IN PERFORMANCE OFPLASTIC PARTS

ANALYSIS OF PLASTIC PART FAILURES

High failure cause to low failure cause- in descending order


48/52

MATERIAL MOULD MACHINE

Characteristics ofPolymer

Design factors in Partand; Mould

Specification to meet the

requirement of Part and;

Mould

Molecularweight, Gate location, size and type, Maximum shot capacityof plasticating

unit,

MFI, Sprue / runnersize balanced type, Residence time,

pvT characteristics, Air vent, Maximum injection rate,

Response toshear rate (Shear

thinning) andlimitation,

Wall thickness uniform and capable

of promoting balancing of melt flow,

Numberofstroke controlledsteps for

filling phase,

Heat andThermalstability, Balancing of flow in un-symmetricpart geometry,

Maximum injection pressure,

Shrinkage behaviour, Mould release Numberof time controlledsteps for

pressure phase,

Maximum flow ratio, Plasticating rate,

Hygroscopic or not. Clamp force

FACTORS INFLUENCING QUALITY OFMOULDING


49/52

Fault Probable Cause Suggested Remedy

Silverstreaking Mixture of coarse and

fine granulesNon uniform plastictemperatureExceeding plasticizingcapacityAir tapped between thegranules at the hopperendIntermitent flow in thecavityInjection speed too fastMould temperature toolowInjection pressure toohighMoisture and volatilesin the materialMaterial too hotContamination of

foreign materialGates and runners toosmallExcessive condensate /lubricants on the mouldmaterialAdjust injection rate

Use uniform granulationReduce temperature of nozzle

Preheat material

Reduce rear cylinder temperatureand use uniform granulation

Balance gate position , relocategates,

Vent Mould, reduce injectionpressure, reduce cylindertemperature

Increase mould temperatureReduce injection pressure

Preheat the material adequately,use a hopper dryer

Decrease the mould cycle time,decrease the cylinder temperature

Check the moulding powder for

contamination ,check the feedsystem, purge the cylinder ,

Check the regrind content and

quality.Increase the size of the runnerand the gates.

Wipe the mould , use lesser

quantity of lubricants, change thelubricant and try

Increase or decrease the injectionrate.


50/52

Blackstreaks

Frictional heatcaused bymovement of coldgranules past one

anotherAir trapping in themould

Plunger off-centercausing frictionburning of materialContamination

Use external indication,increase rear cylindertemperature , vent mould

properly, relocate gates.Reduce injectionpressure.Relocate plungerPurge the cylinder

Short


51/52

Shortshots Cold material

Cold mouldInsufficientpressureInsufficient feedPoor venting

Insufficientplunger forwardtimeInsufficientinjection speedImproperbalance of plasticflow in multiplecavity moulds.InsufficientfeedingMelt flowrestrictedBack pressure incavityUnbalancedrunner designCold slugclogging gates,

runners andsprue.Un uniformmouldtemperatureUn uniform meltcushionMachinecapacity not

enough

Increase plastictemperature

Increase mouldtemperature

Increase pressure andtemperatureIncrease feedIncrease number and size

of ventsIncrease plunger forwardtime.Increase injection speed

Correct unbalancedcoixlition

Check the material in thehopper, check the feedthroat for resinagglomerates, machinecapacity not enough

Increase the gate, runner,and sprue size, use thenozzle with a higherdiameter hole, try with ahigher MFI material, checkthe nozzle for blocks.Provide adequate venting,reduce the clamping force.Balance the runner design ,cavity locationIncrease the size of cold

slug well, provide cold wellfor sub runners.

Rearrange the cooling lineof mould to provide auniform coolingMaintain a uniform meltcushion, check the backflow valve and, repair ifneededUse a bigger machine.


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moulding problem

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