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Failure Analysis of Polyoxymethylene Product Using Scanning Electron Microscope, Thermal and Processing Analysis (Majalah Polimer Indonesia - HPI) - Article Only

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  16 of175°Cand162-173°Crespectively.POMissemicrystallinepolymerwith75-85   degreeofcrystallinity.Asengineeringplastics,PolyOxyMethylene POM hastwotypes,homopolymerandcopolymerwhichdifferslightlyinitsmeltingpoint INTRODUCTION  ala unci Analisisretak,Polioksimetilen,Derajatkristalinitas,TermalANALISISRETAKPOLIOKSIMETILENMENGGUNAKAN SCANNINGELECTRONMICROSCOPE, ANALISISTERMALDANPROSES.Analisisretakdilakukanmenggunakan ScanningElectronMicroscope SEM dan DifferentialScanningCalorimetry DSC . PerbandingankarakteristikbahanantarasampelNGdanstandardilakukan.Analisis SEM menunjukkanbahwapermukaanretakanpadasampelNGcenderunglebihmudahpatahdibandingkanretakanpadasampelstandar.Retakandidugaberasaldari vicinitygatelocation. DerajatkristalinitaspatahanNGadalah59,6 lebihrendahdibandingkandengansampelstandard65,8 .Tidakadaperbedaanyangjauhantarasuhuleleh 164°C)dengansuhukristalisasi 1460C).Perubahandanjalurpatahandisekitar gatelocation berpotensimenyebabkanretakanselamaproses.Berdasarkanhasil SEM dan DSC, retakandidugaberasaldari setting prosesyangtidaktepatyangmenghasilkanderajatkristalinitasyangrendah danJrozen-instress. Bebanluaryangditerimajugamerupakansalahsatupenyebabterjadinyaretakan. ABSTRAK  eywords Failure,Polyoxymethylene,Crystallinitydegree,ThermalFAILUREANALYSISONPOLYOXYMETHYLENEPRODUCTUSINGSCANNINGELECTRONMICROSCOPE,THERMALANDPROCESSINGANALYSIS.FailureanalysisofPolyOxyMethylene POM)productwerecarriedoutusingScanningElectronMicroscope SEM),DifferentialScanningCalorymetry DSC)andparameterprocessrelatedfactors.ComparationofthefailuremodeandmaterialpropertiesbetweentheNGandProvensamplesweretaken.SEManalysisshowedthatfailuresurfacetenttohavemorebrittlefracturecomparedwiththeprovensamplefailure.Theoriginofcrackwaspredictedfromthevicinityofgatelocation.Degreeofcrystallinityoffailurepartwas59.6 ,whichwaslowerthantheprovenproducts 65.8 ).Melting Tm)and CrystallizationTemperature Tc)showednosignificantdifferences,164°Cand146°Cformeltingandcrystallizationtemperaturerespectively.Whiteningandmoldedstreamflowwereshownaroundthegatelocationwhichpotentiallycausedmoldedinstressandcrackpropagationduringapplicationinchemicalenvironment.Externalloadalsofoundinthevicinityofcrack.BasedontheSEM,DSCandprocessrelatedfactoranalysis,thefailureofproductwassupposedduetothecombinationofimpropersettingprocesswhichresultedinlowerdegreeofcrystallinityandfrozen-instressaroundthegateandexternalloadreceivedhavetriggeredthecrackonproduct. ABSTRACT Accepted: 13 December2013evised: 13 November2013eceived: 19 July2013 R Wijaya,A.Rifathinand   Afrinaldi CenterforPolymerTechnology STP -BPPTKawasanPuspiptek;Serpong 15314, TangerangSelatan FAILUREANALYSISONPOLYOXYMETHYLENEPRODUCTUSINGSCANNINGELECTRONMICROSCOPE,THERMALANDPROCESSINGANALYSIS Vol. 17, No.1,2014,hal:16-19ISSN:1410-7864 ajalakPolimerIndonesia  17 approximately10mg,placedintoaluminacrucible.ThealuminacruciblewasthenplacedinThermalGravimetryAnalysis(TGA)instrumentation.Thetestisconductedundertemperatureprogramasfollow:Firstlythesamplewasheatedupfromtemperatureof50to600   undernitrogengas.Thetemperaturewasheldat600   for5minutesnitrogengasenvirontment.Thetemperaturewasthencontinuingheatedupuntil900   underoxygengas.Therateofheatingwas10   perminute,andthenitrogen/oxygengasflowratewas50mLperminute.AftermeasurementwascompletelyfinishedtheTGA-thermogramswereanalyzed.DSC821-MettlerToledowasusedtomeasurethethermalpropertiesofthesamplessuchasmeltingpoint,glasstransitiontemperature,thermalhistory,degreeandthegrowth ofcrystallinity.ThetestwasconductedaccordingtoASTMD3418-2003.Samplewascutandweighedapproximately20mg,placedintoAlcrucible.TheAl-crublewasthenplacedinDSCsamplechamber.Thetestisconductedundernitrogengasenvironmentwithtemperatureprogramof heating-cooling-heating asfollow:thetemperatureprogramwasstartedfrom30to200 C,thencooleddownto-100°Candfinallyheatedupto200°C.Therateofheatingwas10  c perminute,andthenitrogengasflowratewas50mLperminute.AfterthetestwascompletelyfinishedtheDSC-thermogramswereanalyzed. Figure 2.FTIRtestresultsofNGandprovensamples   ._ ThefailurePOMproductwasreceivedasfailured-partappliedinmotorcycle.Toidentifythemainmaterial,possibledegradationandsemiquantitativelyanalysisthematerialcomposition,weusedFT-IR-BrukerTensor27,ATRmethod.PlacedthesampleonATRcrystal.Touchedthesamplesurfaceperfectlyonthecrystallbysettingdownthestainlesssteeltip.SamplesanalysiswerecarriedoutbyOPUSsoftware(Figure2).Tomeasurethematerialcomposition.ThetestwascarriedoutinaccordancetoASTM1131-1998.Samplewascutandweighed EXPERIMENTALMETHOD Figure 1.Frozen-inorientation(top)andpotentialshrinkageneartothegate(bottom)   dgep le \\~I   >: ~I : _____ POMaregenerallyprocessedininjectionmoldingwithspecialrunnersystem.HotrunnertypesarecommonlyappliedinPOM.Wrongselectionofrunnertypecouldresultinlossofpressureduringprocess.Toovercomethepressurereduction,operatorsusuallyincreasethetemperature.Unfortunatelythiscouldseverethematerialtodegradation.Themeltenteringthecavitywillformorientationduringfillingphase.Andmeltadjacenttothemoldwillfreeze:firstandleadtohighinterfacialshearstressbetweenthemeltandthesolidlayer.Thisfrozen-inorientationwillcontinuetodevelopduringholdingpressureinordertocompensateforvolumeshrinkage,particularlynearthegateregionofthepart(Figure1).However,fastcycletimeduringproductionisrequired.Thoseprocessparametersinfluentthemicrostructureofpartwhichalsoaffectthepropertiesandperformances.Inthispaper,weanalyzedtheeffectofsettingprocesstothermalpropertiesascontributionofpotentialcausesoffailurebyobservingthecrackpatternonthefailedsurface. FailureAnalysisonPolyOxyMethyleneProductUsingScanningElectronMicroscope,ThermalandProcessingAnalysis R.Wijaya)  Figure 4.DSCtestresultsofNG(a)andproven(b)samplesoncoolingphaseafterfirstheating  --- ; ::; ; ;; j   ________. ._H.__, _ __...,_.___.___,_.._ .. ~:I  to~,(;~.  ....~   ,. .~--....-......----- :;-;.;~= ~-·-=· ·~-- u=·~= :=  ;~~.:;;::~:.;\.~-~-::::;i: ~;~~_,.:.. _-6 .'Ii \,)U~.ll :<;;:.~ \ \. : ; ~   \  \ :  (a)   . _----,._-------, : ___._ .1 Figure 3.DSCtestresultsofNG(a)andproven (b)samplesonheatingphase   .ã. _--------- ..   ..._. ,,';j : ~ : ..:...: _-;=-~--._---...~--.-.-~.-.-.-------. -. --.-----.--.. ~ ._..._( - ã _ .. - , :. :-< ,~,-, 18 DegreeofcrystalinityoftheNGsample showalittlebitlower(Figure3),whilecrystalization rateishigherandthecrystaldistribution(which indicatesthesizeofcrystaline)islowerthanthe provenone.(Figure4)Figure5showscrackthatoccurednearto thegate.Smoothlbrittlepatternofcrackfoundon thecracksurfaceofNGsample.Ontheotherhand, thefracturepatternofprovensampleshowedmore ductile(seeFigure6).Cracksupposedinitiallyoccuredfromthe outertotheinnersurfacesandwascausedbythe extemalload.Thiswasshownwithwhiteningcircle likedefectonoutersurface(seeFigure4). Lowerdegreeofcrystallinitywhichisfound ontheNGsampleisusuallyrelatedtohighthe TestMethodsProvensampleNGsample FTIR,polymertypePolyoxymethylene Polyoxymethylene TGA,   polymer10099.99 DSCHeatingphase Meltingpoint(OC) 164.51164.06 DeltaH (Jig) 156.1098149.6349 Crystallinity ( ) 65.859.6 Coolingphase TempofCrytalline145.80146.45   Crystallinerate0.310.29 (min)Crystallinedistr0.38 0.32(min) Table 1.ComparativetestresultsofNGandproven samples. .NosignificancedifferencesonspectraofNGandprovensamples.BothshowthePOMmaterialaccordingtoOPUSsoftwareanalysis.Nodegradationisindicatedbothsamples.Table1showstheresultsofFT-IR,TGAandDSC. RESULTSANDDISCUSSION ScanningElectronMicroscopyJEOLJSM-6510LAwasappliedtoobservethefracturesurfaceinordertoseethecrackinitiationand propagation. In ordertoanalyzetherootcausesoffailure, thecomparativemethodbetweenthefailureandthenewprovenproductarecarriedoutonthetestresults. VoL 17, No.1 2014 hal: 16-19 ISSN:1410 7864 ajalahPolimerIndonesia    REFERENCES [1].DuPont,2008,ProblemswithHotRunners.[2].DuPont,DuPont™Delrin®acetalresinMoldingGuide:TechnicalInformation.[3].ARCHODOULAKIVM,LUFTLS,KOCHT,SEIDLERS,Propertychangesinpolyoxymethylene POM resultingfromprocessing,ageingandrecycling,PolDegradStab,92 2007 2181-2189[4].MALLOYRA.,PlasticPartDesignforInjectionMolding:   Introduction,HanserGardnerPublicationsInc. 1994 TheauthorsaregratefultoTheCenterforPolymerTechnologyforsupportingthisproject. ACKNOWLEDGMENTS Extemalloadonthesurfaceofhighlyfrozeninstresspartduetoimpropersettingprocesstendtoformbrittleonthesurfaceandlayerbetweenthesurface.Theinnercorepartresultedincrackbeginningfromtheoutersurfacepartandpropagatetowardtheentirepartofthickness CONCLUSION Figure 7.Delaminationformonthefracturesurface,supposedduetolayerformationbetweentheskinandthecore. Figure 6.Differentpatternsurfacefracture Provensample N sample Figure 5.Crackaroundthegate bottom and top ofNGsample. coolingrate.Thesettingprocessalsotendtoincreasethefrozen-instressorientationonthesurfaceneartothegate seeFigure2 .Thissupposedcausetwolayersformation,surfacepartwithhighlyfrozen-instressorientation  smooth brittlesurface-patterncrack ;delaminationformedandductilefracturemodeintheinnercorepart.Thisisinaccordancetotheinformationreceivedaboutthecyclingtimereductionduringproduction Figure7 .Frozen-instressinmicrostructureandtheexternalloadappliedfromoutersurfacehasresultedininitialcrackandpropagatetoentirethicknessproduct. FailureAnalysisonPolyOxyMethyleneProductUsingScanningElectronMicroscope,ThermalandProcessingAnalysis R.Wijaya)

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