Injection Molding Troubleshooting Guide - Westlake Chemical

1 CrackingCrazingBlack Specks or StreaksProblemDelaminationProblemGloss (Low)BlistersBlushBowingBubblesSource(s) Cause(s)MachineExcessive residence time in barrelHang-up of molten material in Injection barrel or runner systemContamination of Injection barrelDegradation due to malfunctioning heater bands or thermocouplesDefective nozzle shutoff mechanismInefficient Injection conditionsCracked Injection cylinder or pitted screwOil leaking into the Injection unitMoldSprue bushing nicked, rough, or not seatingBurned material caused by improper ventingContamination caused by grease or lubricantsMold too small for machine sizeMaterialContamination of raw materialWrong material used for particular moldOperatorInconsistent process cycleMachineInjection screw rotation (RPM)

2 Too highScrew back pressure too lowInjection speed too highCycle time too shortMoldMold temperature too lowImproper gate locationInsufficient ventingMaterialUse of regrind that is too coarseUse of highly volatile materialsExcessive moistureMachineInjection fill speed too fastMelt temperature too high or too lowInjection pressure too lowNozzle diameter too smallNozzle temperature too lowMachineClamp opens too quicklyEjector system not level or parallelCooling time too shortParts not packed properlyMoldTemperature too lowInconsistent mold temperatureImproper gate locationOperatorParts mishandled after ejectionMachineImproper Injection screw designCycle time too shortExcessive packingExcessive back pressure, screw RPM, or Injection speedNozzle too hotInjection pressure too lowMoldGate and/or runner restrictionsCondensationMaterialResin too coldExcessive moisture in resinResin is degradedMachineInjection temperature too highInjection pressure too lowInjection forward time too lowInsufficient material feedImproper Injection temperature profileExcessive Injection speedInsufficient back pressureMoldImproper ventingSection thickness too greatInjection Molding Troubleshooting GuideBrittlenessContaminationBubbles(con t.)

3 Source(s)Cause(s)Mold (cont.)Improper runners or gatesMold temperature too lowMaterialExcessive moistureOperatorInconsistent cycleMachineExcessive Injection speed or pressureExcessive back pressureScrew speed too highImproper compression ratio of screwFaulty temperature controllersNozzle too hotExcessive barrel temperaturesNozzle diameter too smallMoldImproper venting (size or lacation)Vents plugged or peened shutImproper gating (size or location)MaterialExcessive regrind useFlow too softExcessive lubricantOperatorInconsistent cyclesMachineBarrel temperature too lowBack pressure too lowScrew speed too lowImproper compression ratio of screwFaulty temperature controllersMaterialExcessive regrind useOperatorInconsistent cyclesMachineBarrel temperature too lowBack pressure too lowScrew speed too lowExcessive wear between barrel and screwMoldUneven packingDull finish on mold surfacePoor mold temperature controlMaterialExcessive moistureOperatorInconsistent cyclesMachineOil leaks and grease dripsMoldExcessive lubricationMaterialImproper regrind usageExcessive moistureOperatorPoor

4 HousekeepingMachineMolded in stressesCooling cycle too shortMoldExcessive lubricationInsufficient draft allowanceImproper injectionMaterialImproper regrind usageExcessive moistureOperatorInconsistent cyclesMachineMolded in stressesCycle time too shortInadequate Injection speed and/or timeInjection barrel temperature too highMoldExcessive gate sizeMold temperature too lowContaminated mold surfacesImproper ejectionMaterialContaminated materialExcessive moistureBurn MarksClear SpotsCloudy AppearanceDiscolorationFlashSource(s)Cau se(s)MachineInjection speed too lowInadequate Injection cushionInjection hold time too shortBarrel temperature too lowMoldMold temperature too lowSharp gate and runner cornersExcessive mold releaseMaterialContaminated regrindForeign materials and/or additivesExcessive moistureMachineExcessive shot size ratioExcessive residence timeBarrel temperature too highNozzle temperature too highExcessive cycle timeImproper screw designMoldMold temperature improperInefficient coolingInadequate ventingMaterialContaminated materialOperatorInconsistent cyclesMachineExcessive Injection pressureExcessive residence timeBarrel temperature too highExcessive

5 Cycle timeInadequate clamp pressureMoldImproper parting line sealInadequate mold supportsInadequate ventingSprue bushing too longImproper stackup dimensionsMaterialImproper flow rateExcessive mold lubricantOperatorImproper cyclingMachineInadequate Injection pressureInadequate residence timeBarrel temperature too lowNozzle temperature too lowOperatorInconsistent cyclesMachineInadequate Injection pressureInadequate residence timeBarrel temperature too lowNozzle temperature too lowExcessive feed cushionRam speed too slowNozzle bore too smallInadequate cycle timeMoldMold temperature too lowGates or runners too smallImproper gate locationInadequate ventingInadequate polishing of Molding surfacesContaminated Molding surfacesMaterialImproper flow rateInadequate lubricationMoisture in resinOperatorInconsistent cyclesFlow LinesProblem