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附录附录1AnexperimentalstudyofthewaterassistedinjectionmoldingofglassfiberfilledpolybutyleneterephthalatePBTcompositesAbstractThepurposeofthisreportwastoexperimentallystudythewaterassistedinjectionmoldingprocessofpolybutyleneterephthalatePBTcomposites.Experimentswerecarriedoutonan80toninjectionmoldingmachineequippedwithalabscalewaterinjectionsystem,whichincludedawaterpump,apressureaccumulator,awaterinjectionpin,awatertankequippedwithatemperatureregulator,andacontrolcircuit.ThematerialsincludedvirginPBTanda15glassfiberfilledPBTcomposite,andaplatecavitywitharibacrosscenterwasused.Variousprocessingvariableswereexaminedintermsoftheirinfluenceonthelengthofwaterpenetrationinmoldedparts,andmechanicalpropertytestswereperformedontheseparts.XraydiffractionXRDwasalsousedtoidentifythematerialandstructuralparameters.Finally,acomparisonwasmadebetweenwaterassistedandgasassistedinjectionmoldedparts.Itwasfoundthatthemeltfillpressure,melttemperature,andshortshotsizewerethedominantparametersaffectingwaterpenetrationbehavior.Materialatthemoldsideexhibitedahigherdegreeofcrystallinitythanthatatthewaterside.Partsmoldedbygasalsoshowedahigherdegreeofcrystallinitythanthosemoldedbywater.Furthermore,theglassfibersnearthesurfaceofmoldedpartswerefoundtobeorientedmostlyintheflowdirection,butorientedsubstantiallymoreperpendiculartotheflowdirectionwithincreasingdistancefromtheskinsurface.KeywordsWaterassistedinjectionmoldingGlassfiberreinforcedpolybutyleneterephthalatePBTcompositesProcessingparametersB.MechanicalpropertiesCrystallinityA.Polymermatrixcomposites1.IntroductionWaterassistedinjectionmoldingtechnology1hasproveditselfabreakthroughinthemanufactureofplasticpartsduetoitslightweight,fastercycletime,andrelativelylowerresincostperpart.Inthewaterassistedinjectionmoldingprocess,themoldcavityispartiallyfilledwiththepolymermeltfollowedbytheinjectionofwaterintothecoreofthepolymermelt.AschematicdiagramofthewaterassistedinjectionmoldingprocessisillustratedinFig.1.Waterassistedinjectionmoldingcanproducepartsincorporatingboththickandthinsectionswithlessshrinkageandwarpageandwithabettersurfacefinish,butwithashortercycletime.Thewaterassistedinjectionmoldingprocesscanalsoenablegreaterfreedomofdesign,materialsavings,weightreduction,andcostsavingsintermsoftoolingandpresscapacityrequirements2–4.Typicalapplicationsincluderodsandtubes,andlargesheetlikestructuralpartswithabuiltinwaterchannelnetwork.Ontheotherhand,despitetheadvantagesassociatedwiththeprocess,themoldingwindowandprocesscontrolaremorecriticalanddifficultsinceadditionalprocessingparametersareinvolved.Watermayalsocorrodethesteelmold,andsomematerialsincludingthermoplasticcompositesaredifficulttomoldsuccessfully.Theremovalofwateraftermoldingisalsoachallengeforthisnoveltechnology.Table1liststheadvantagesandlimitationsofwaterassistedinjectionmoldingtechnology.Fig.1.Schematicdiagramofwaterassistedinjectionmoldingprocess.Waterassistedinjectionmoldinghasadvantagesoveritsbetterknowncompetitorprocess,gasassistedinjectionmolding5,becauseitincorporatesashortercycletimetosuccessfullymoldapartduetothehighercoolingcapacityofwaterduringthemoldingprocess.Theincompressibility,lowcost,andeaseofrecyclingthewatermakesitanidealmediumfortheprocess.Sincewaterdoesnotdissolveanddiffuseintothepolymermeltsduringthemoldingprocess,theinternalfoamingphenomenon6thatusuallyoccursingasassistedinjectionmoldedpartscanbeeliminated.Inaddition,waterassistedinjectionmoldingprovidesabettercapabilityofmoldinglargerpartswithasmallresidualwallthickness.Table2listsacomparisonofwaterandgasassistedinjectionmolding.Withincreasingdemandsformaterialswithimprovedperformance,whichmaybecharacterizedbythecriteriaoflowerweight,higherstrength,andafasterandcheaperproductioncycletime,theengineeringofplasticsisaprocessthatcannotbeignored.Theseplasticsincludethermoplasticandthermosetpolymers.Ingeneral,thermoplasticpolymershaveanadvantageoverthermosetpolymersinpopularmaterialsinstructuralapplications.PolybutyleneterephthalatePBTisoneofthemostfrequentlyusedengineeringthermoplasticmaterials,whichisformedbypolymerizing1.4butyleneglycolandDMTtogether.Fiberreinforcedcompositematerialshavebeenadaptedtoimprovethemechanicalpropertiesofneatplasticmaterials.Today,shortglassfiberreinforcedPBTiswidelyusedinelectronic,communicationandautomobileapplications.Therefore,theinvestigationoftheprocessingoffiberreinforcedPBTisbecomingincreasinglyimportant7–10.ThisreportwasmadetoexperimentallystudythewaterassistedinjectionmoldingprocessofpolybutyleneterephthalatePBTmaterials.Experimentswerecarriedoutonan80toninjectionmoldingmachineequippedwithalabscalewaterinjectionsystem,whichincludedawaterpump,apressureaccumulator,awaterinjectionpin,awatertankequippedwithatemperatureregulator,andacontrolcircuit.ThematerialsincludedavirginPBTanda15glassfiberfilledPBTcomposite,andaplatecavitywitharibacrosscenterwasused.Variousprocessingvariableswereexaminedintermsoftheirinfluenceonthelengthofwaterpenetrationinmoldedparts,whichincludedmelttemperature,moldtemperature,meltfillingspeed,shortshotsize,waterpressure,watertemperature,waterholdandwaterinjectiondelaytime.Mechanicalpropertytestswerealsoperformedonthesemoldedparts,andXRDwasusedtoidentifythematerialandstructuralparameters.Finally,acomparisonwasmadebetweenwaterassistedandgasassistedinjectionmoldedparts.Table1AdvantagesanddisadvantagesofwaterassistedinjectionmoldingAdvantagesDisadvantages1.Shortcycletime1.Corrosionofthesteelmoldduetowater2.Lowassistingmediumcostwaterismuchcheaperandcanbeeasilyrecycled2.Largerorificesfortheinjectionpinrequiredeasiertogetstuckbythepolymermelt3.Nointernalfoamingphenomenoninmoldedparts3.Somematerialsaremoredifficulttomoldespeciallyamorphousthermoplastics4.Removalofwateraftermoldingisrequired2.Experimentalprocedure2.1.MaterialsThematerialsusedincludedavirginPBTGrade1111FB,NanYaPlastic,Taiwananda15glassfiberfilledPBTcompositeGrade1210G3,NanYaPlastic,Taiwan.Table3liststhecharacteristicsofthecompositematerials.2.2.WaterinjectionunitAlabscalewaterinjectionunit,whichincludedawaterpump,apressureaccumulator,awaterinjectionpin,awatertankequippedwithatemperatureregulator,andacontrolcircuit,wasusedforallexperiments3.Anorificetypewaterinjectionpinwithtwoorifices0.3mmindiameteronthesideswasusedtomoldtheparts.Duringtheexperiments,thecontrolcircuitofthewaterinjectionunitreceivedasignalfromthemoldingmachineandcontrolledthetimeandpressureoftheinjectedwater.Beforeinjectionintothemoldcavity,thewaterwasstoredinatankwithatemperatureregulatorfor30mintosustainanisothermalwatertemperature.2.3.MoldingmachineandmoldsWaterassistedinjectionmoldingexperimentswereconductedonan80tonconventionalinjectionmoldingmachinewithahighestinjectionrateof109cm3/s.Aplatecavitywithatrapezoidalwaterchannelacrossthecenterwasusedinthisstudy.Fig.2showsthedimensionsofthecavity.Thetemperatureofthemoldwasregulatedbyawatercirculatingmoldtemperaturecontrolunit.Variousprocessingvariableswereexaminedintermsoftheirinfluenceonthelengthofwaterpenetrationinwaterchannelsofmoldedpartsmelttemperature,moldtemperature,meltfillpressure,watertemperatureandpressure,waterinjectiondelaytimeandholdtime,andshortshotsizeofthepolymermelt.Table4liststheseprocessingvariablesaswellasthevaluesusedintheexperiments.2.4.GasinjectionunitInordertomakeacomparisonofwaterandgasassistedinjectionmoldedparts,acommerciallyavailablegasinjectionunitGasInjectionPPC1000wasusedforthegasassistedinjectionmoldingexperiments.DetailsofthegasinjectionunitsetupcanbefoundintheRefs.11–15.TheprocessingconditionsusedforgasassistedinjectionmoldingwerethesameasthatofwaterassistedinjectionmoldingtermsinboldinTable4,withtheexceptionofgastemperaturewhichwassetat25C.2.5.XRDInordertoanalyzethecrystalstructurewithinthewaterassistedinjectionmoldedparts,wideangleXraydiffractionXRDwith2DdetectoranalysesintransmissionmodewereperformedwithCuKaradiationat40kVand40mA.Morespecifically,themeasurementswereperformedonthemoldsideandwatersidelayersofthewaterassistedinjectionmoldedparts,withthe2hanglerangingfrom7to40.Thesamplesrequiredfortheseanalysesweretakenfromthecenterportionofthesemoldedparts.ToobtainthedesiredthicknessfortheXRDsamples,theexcesswasremovedbypolishingtheTable3Characteristicsoftheglass–fiberreinforcedPBTcompositePropertyASTMPBT15G.F.PBTYieldstrengthkg/cm2D6386001000Bendingstresskg/cm2D5709001500HardnessRscaleD785119120HeatdistortiontemperatureC18.6kg/cm2D64860200MeltflowindexMFID123840251238ImpactstrengthKgcm/cmD25655MeltingtemperatureCDSC224224samplesonarotatingwheelonarotatingwheel,firstwithwetsiliconcarbidepapers,thenwith300gradesiliconcarbidepaper,followedby600and1200gradepaperforabettersurfacesmoothness.2.6.MechanicalpropertiesTensilestrengthandbendingstrengthweremeasuredonatensiletester.Tensile
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