塑料注射成型设计外文文献翻译中英文翻译外文翻译Word格式.docx
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塑料注射成型设计外文文献翻译中英文翻译外文翻译Word格式.docx
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Atypicalinjectionmoldingcycleorsequenceconsistsoffivephases:
①Injectionormoldfilling
②Packingorcompression
③Holding
④Cooling
⑤Partejection
Fig.4.2.1Injectionmoldingprocess
Plasticgranulesarefedintothehopperandthroughanopeningintheinjectioncylinderwheretheyarecarriedforwardbytherotatingscrew.Therotationofthescrewforcesthegranulesunderhighpressureagainsttheheatedwallsofthecylindercausingthemtomelt.Asthepressurebuildsup,therotatingscrewisforcedbackwarduntilenoughplastichasaccumulatedtomaketheshot.heinjectionram(orscrew)forcesmoltenplasticfromthebarrel,throughthenozzle,sprueandrunnersystem,andfinallyintothemoldcavities.Duringinjectionthemoldcavityisfilledvolumetrically.Whentheplasticcontactsthecolcmoldsurfaces,itsolidifies(freezes)rapidlytoproducetheskinlayer.Sincethecoreremainsinthemoltenstate,plasticflowsthroughthecoretocompletemoldfilling.Typically,thecavity,isfilledto95%~98%duringinjection.Thenthemoldingprocessisswitchedovertothepackingphase
Evenasthecavityisfilled,themoltenplasticbeginstocool.Sincethecoolingplasticcontractsorshrinks,itgivesrisetodefectssuchassinkmarks,voids,anddimensionalinstabilities.③Tocompensateforshrinkage,additionplasticisforcedintothecavity.Oncethecavityispacked,pressureappliedtothemeltpreventsmoltenplasticinsidethecavityfrombackflowingoutthroughthegate.Thepressuremustbeapplieduntilthegatesolidifies.Theprocesscanbedividedintotwosteps(packingandholding)ormaybeencompassedinonestep(holdingorsecondstage).Duringpacking,meltforcedintothecavitybythepackingpressurecompensatesforshrinkage.Withholdingthepressuremerelypreventsbackflowofthepolymermelt.
Aftertheholdingstageiscompleted,thecoolingphasestarts.Duringcooling,thepartisheldinthemoldforspecifiedperiod.Thedurationofthecoolingphasedependsprimarilyonthematerialpropertiesandthepartthickness.Typically,theparttemperaturemustcoolbelowthematerial’sejectiontemperature.Whilecoolingthepart,themachineplasticatesmeltforthenextcycle.Thepolymerissubjectedtoshearingactionaswellastheconditionoftheenergyfromtheheaterbands.Oncetheshotismade,plasticationceases.Thisshouldoccurimmediatelybeforetheendofthecoolingphase.Thenthemoldopensandthepartisejected.
BlowMolding
Therapidgrowthintheuseofadvancedmaterialsinalargenumberof
highlydemandingautomotive,electronicandcunsumergoodsapplicationshaspromotedthedevelopmentof
newandmorecomplexmaterialformingprocesses.Inthelasttwentyyearsinjectionmoldingandblowmoldinghaveseen
arapidgrowthduetothedevelopmentof
newapplicationandpackagingindustries,.thissuccesscanbetracedtotheoptimizationofexistingprocessesandtothedevelopmentof
newprocessingtechniquesemployingnovelconcepts,injectionmolding
hasseentheintroductionof
techniquessuchasco-injection,gasassistedinjection
molding,lostcoremoldingandinjection/compression.
(a)Parisonextrusionstage(b)Clampingandblowingstage
Fig.4.2.2Extrusionblowmolding
Blowmoldinghasbeenabletodealwithmuchmorecomplex
partsthrough
thedevelopmentof3Dandsequential
blow
molding,complexmolds
for
deepdrawnpartsandcryogenicmoldcooling.Theintroductionofnewmaterials
hasalsomade
possibletheproductionofparts
having
multilayerstructure
Thecomplexityofthese
newmoldingtechniquescallsfor
amuchbetterunderstanding
ofthematerialbehavior
duringthebasicstagesoftheprocessanditsrelationtotheproperiesandperformanceofthefinalpart,whicharedirectlydependent
upon
dieandmolddesignsandonthe
operatingconditionsduringextrusion,
injection,inflationandcoolingin
themold.
It
is
inthese
areas
that
thecomputer
simulation
fotthe
coupled
phenomentof
fluid
flowandheattransferhasproventobeaveryvaluabletoolfortheequipmentmanufacturer,molddesignerandprocessengineer!
Blowmoldingprocess
Blowmoldingcanbecarriedreciprocatingscrewinjectionmachine.Abouteitheronanextruderorasectionofmoltenpolymertubing(parsion)isextrudedintoanopenmold.Bymeansofcompressedairorsteamtheplasticisthenblownintotheconfigurationofthemold.Thistechniqueiswidelyusedforthemanufactureofbottlesandsimilararticles.Inthecaseoflargearticles,suchasliterbeveragebottles,theparisonmaypreviouslyhavebeeninjectionmoldedandorientedtoprovideadditionalstrengthtothefinalblownpiece.
Intheextrusionblowmoldingprocess(Fig.4.2.2),therawmaterialisfedtoaplasticatingextruderingranularorpelletform.Theplasticismeltedbyheatwhichistransferredthroughthebarrelbytheshearingmotionoftheextruderscrew.Thehelicalflightsofthescrewchangeconfigurationalongitslengthfrominputtooutput(solidsconveying,meltingandmeteringsections)toassureauniformlyhomogeneousmeltatthescrewtip.
Incontinuousextrusionblowmolding,thescrewfeedsthemeltdirectlyintothehead-dieassembly.Themeitflowsaroundthemandrelandintoanannulardieoftheconvergentordivergenttype.Ahollowtubeor“parison”isextrudedcontinuouslvandcutatpresettimeintervalsfortransferintotheblowmold.
Inthecaseofintermittentextrusionblowmolding,theextruderfeedsthematerialtoanaccumulator/headdevice.Oncethedesiredvolumehasaccumulatedaramorplungerpushesthematerialrapidlythroughthehead-dieassembly.Themoldclampmechanismdoesnotneedtotransfertoablowingstation.Thenextparisonisonlyextrudedafterthepartisblown,cooledandremovedfromthemold.
Onceaparisonofthedesiredlengthhasbeenformed,themoldisclosedandtheparisonisinflatedbyinternalairintroducedthroughthedie-headassembly.Themoldwallsarevented,andavacuummaybeapplied.Themoltenpolymeristhusforcedtoconformtotheshapeofthemoldcavity.ThearticleiSthencooled,solidifiedandejectedfromthemold.
Inbothmethodstheannulardiemaybedesignedtoincorporateahydraulicmechanismtovaryorprogramtheannulargapsize.Inthisway,theextrusionprocesscanbeprogrammedtoimpartaspecificwallthicknessdistributionorcontrolledweighttotheparison.
Injection/stretchblowmolding(Fig.4.2.3)isatwo—stageprocess.Inthefirststage,thematerialisinjectionmoldedaroundacorerodtoformapreform.Inthesecondstage,thepreformisthenstretchedthroughtheactionofastretchrod,inflatedandcooledinmuchthesamemannerasintheextrusionblowmoldingprocess.Theresultisalighterproductbiaxiallyorientedintheaxialandradialdirections.Biaxialorientationprovidesincreasedtensilestrength(topload),lessgas,liquidandodourpermeationduetoanincreasedmolecularalignmentandimproveddropimpact,clarityandlightweightingofthecontainer.Injection/stretchblowmoldingalsoproducesscrap—free,close-tolerance,completelyfinishedbottlesorcontainersthatrequirenosecondaryoperations.Preformdesignanditsrelationshiptothefinalcontainerpropertiesremainoneofthemostcriticalaspectsoftheprocess.Thepartthicknessdistributionhastobemappedontothepreformandthroughtheknowledgeofthematerialproperties(degreeofcrystallinityandshrinkageaftermolding;
stretchingcharacteristicsandtheirtemperaturedependenceamongothers)thepreform
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