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外文翻译--注塑模.doc

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外文翻译--注塑模.doc

英文原文TheInjectionMolding1.TheinjectionmoldingInjectionmoldingisprincipallyusedfortheproductionofthethermoplasticparts,althoughsomeprogresshasbeenmadeindevelopingamethodforinjectionmoldingsomethermosettingmaterials.Theproblemofinjectionamethodplasticintoamoldcavityfromareservoirinjectionmoldingisquitesimilartothatofdiecasting.Theprocessconsistsoffeedingaplasticcompoundinpoweredorgranularformfromahopperthroughmeteringandmeltingstagesandtheninjectionitintoamold.Afterabriefcoolingperiod,themoldisopenedandthesolidifiedpartejected.Injectionmoldingmachineoperation.Theadvantageofinjectionmoldingareiahighmoldingspeedadapterformassproductionispossibleiithereisawidechoiceofthermoplasticmaterialsprovidingavarietyofusefulpropertiesiiiitispossibletomoldthreads,undercuts,sideholes,andlargethinsection.2.TheinjectionmoldingmachineSeveralmethodsareusedtoforceorinjectionthemeltedplasticintothemold.Themostcommonlyusedsystemintheinlinereciprocatingscrew,asshowninFigure21.Thescrewactsasacombinationinjectionandplasticizingunit.Astheplasticisfedtorotatingscrew,itpassesthroughthreezonesasshownfeed,compression,andmetering.Afterthefeedzone,thescrewflightdepthisgraduallyreduced.forcetheplastictocompress.Theworkisconvertedtoheatbyconductionfromthebarrelsurface.Asthechamberinfrontofthescrewbecomesfilled,itforcesthescrewback,trippingalimitswitchthatactivatesahydrauliccylinderthatforcesthescrewforwardandinjectsthefluidplasticintotheclosedmold.Anantiflowbackvavlepresentsplasticunderpressurefromescapingbackintothescrewflight.Theclampingforcethatamachineiscapableofexertingispartofthesizedesignationandismeasuredintons.Aruleofthumbcanbeusedtodeterminethetonnagerequiredforaparticularjob.Itisbasedontwotonsofclampforcepersquareinchofprojectedarea.Iftheflowpatternisdifficultandthepartsarethin,thismayhavetogotothreeorfourtons.Manyreciprocatingscrewmachinesarecapableofhandingthermosettingplasticmaterials.Previouslythesematerialswerehandledbycompressiongortransfermolding.Thermosettingmaterialscureorpolymerizeinthemoldandareejectedhotintherangeof375℃410℃.Thermosettingpartsmustbeallowedtocoolinthemoldinorderorremovethemwithoutdistortion.Thusthermosettingcyclescanbefaster.Ofcoursethemoldmustbeheatedratherthanchilled,aswiththermoplastics.3.BasicUnderfeedMouldThedescriptionofthedesignandtheopeningsequencefollows.Themouldconsistsofthreebasicparts,namelythemovinghalf,thefloatingcavityplateandthefeedplaterespectively.ThemovinghalfconsistsofThemovingmouldplateassembly,supportblock,backingplate,ejectorassemblyandthepinejectiongsystem.Thusthemovinghalfinthisdesignisidenticalwiththemovinghalfofbasicmoulds.Thefloatingcavityplate,whichmaybetheintegerorinsertbolsterdesign,islocatedonsubstantialguidepillarsnotshownfittedinthefeedplate.Theseguidepillarsmustbeofsufficientlengthtosupportthefloatingcavityplateoveritsfullmovementandstillprojecttoperformthefunctionofalignmentbetweenthecavityandcorewhenthemouldisbeingclosed.Guidebushesarefittedintothemovingmouldplateandthefloatingcavityplaterespectively.Themaximummovementofthefloatingcavityplateiscontrolledbystoporsimilardevice.Themovingmouldplateissuitablyboredtoprovidesufficientaclearanceforthestopboltassembly.Thestopboltsmustbelongenoughtoprovidesufficientspacebetweenthefeedplateandthefloatingcavityplateforeasyremovalofthefeedsystem.Theminimumspaceprovideforshouldbe65mmjustsufficientforanoperatortoremovethefeedsystembyhandifnecessary.Thedesireoperatingsequenceisforthefirstdaylighttooccurbetweenthefloatingcavityplate.Thisensuresthesprueispulledfromthespruebushimmediatelythemouldisopened.Toachievethissequence,springsmaybeincorporatedbetweenthefeedplateandthefloatingcavityplate.Thespringsshouldbeenoughtogiveaninitialimpetustothefloatingcavityplatetoensureitmovesawaywiththemovinghalf.Itisnormalpracticetomountthespringsontheguidepillarsandaccommodatetheminsuitablepocketinthecavityplate.Themajorpartofthefeedsystemrunnerandsprueisaccmmodatedinthefeedplatetofacilitateautomaticoperation,therunnershouldbeofatrapezoidalformsothatonceitispulledfromthefeedplateiscaneasilybeextracted.Notethatifaroundrunnerisused,halftherunnerisformedinthefloatingcavityplate,whereitwouldremain,andbepreventedfromfallingorbeingwipedclearwhenthemouldisopened.Nowthatwehaveconsideredthemouldassemblyinthesomedetail,welookatthecycleofoperationforthistypeofmould.Theimpressionsarefilledviathefeedsystemandafterasuitabledwellperiod,themachineplatenscommencetoopen.Aforceisimmediatelyexertedbythecompressionsprings,whichcausethefloatingcavityplatetomoveawaywiththemovinghalfaspreviouslydiscussed.Thesprueispulledfromthespruebushbythespruepuller.Afterthefloatingcavityplatehasmovedapredetermineddistance,itisarrestedbythestopbolts.Themovinghalfcontinuedtomovebackandthemoldings,havingshrunkontothecores,arewithdrawnfromthecavitities.Thepingatebreaksatitsjunctionwiththerunner.Thespruepuller,beingattachedtothemovinghalf,ispulledthroughthefloatingcavityplateandtherebyreleasethefeedsystemwhichthenfreetofallbetweenthefloatingcavityplateandthemoldingsareejected.Whenthemouldisclosed,therespectiveplatesarereturnedtotheirmoldingpositionandthecycleisrepeated.4.FeedSystemItisnecessarytoprovideaflowwayintheinjectionmouldtoconnectthenozzleoftheinjectionmachinetoeachimpression.Thisflowwayistermedthefeedsystem.Normallythefeedsystemcomprisesasprue,runnerandgate.Thesetermsapplyequallytotheflowwayitself,andtothemoldedmaterialwhichisremovefromtheflowwayitselfintheprocessofextractedmolding.Atypicalfeedsystemforafourimpression,twoplatetypemould.Itisseenthatthematerialpassesthroughthesprue,mainrunner,branchrunnerandgatebeforeenteringtheimpression.Asthetemperatureofmoltenplasticisloweredwhichgoingthroughthesprueandrunner,theviscositywillrisehowever,theviscosityisloweredbysheargeneratedwhengoingthroughthegatetofillthecavity.Tiisdesirabletokeepthedistancethatthematerialhastotraveldowntoaminimumtoreducepressureandheatlosses.Itisforthereasonthatcarefulconsiderationmustbegiventotheimpressionlayoutgatesdesign.4.1SprueAsprueisachannelthroughwhichtotransfermoltenplasticinjectedfromthenozzleoftheinjectorintothemold.Itisapartofspruebush,whichisaseparatepartfromthemold.4.2RunnerArunnerisachannelthatguidesmoltenplasticintothecavityofamold.4.3GateAgateisanentrancethroughwhichmoltenplasticentersthecavity.Thegatehasthefollowingfunctionrestrictstheflowandthedirectionofmoltenplasticsimplifiescuttingofarunnerandmoldingstosimplifyfinishingofpartsquicklycoolsandsolidifiestoavoidbackflowaftermoltenplastichasfilledupinthecavity.4.4ColdslugwellThepurposeofthecoldslugwell,shownoppositethesprue,istheoreticallytoreceivethematerialthathaschilledatthefrontofnozzleduringthecoolingandejectionphase.Perhapsofgreaterimportanceisthefactthatitprovidespositionmeanswherebythespruebushforejectionpurposes.Thesprue,therunnerandthegatewillbediscardedafterapartiscomplete.However,therunnerandthegateareimportantitemsthataffectthequalityorthecostofparts.5.EjectionAmoldingisformedinmouldbyinjectingaplasticmelt,underpressure,intoanimpressionviaafeedsystem.Itmustthereforeberemovedmanually.Furthermore,allthermoplasticmaterialscontractastheysolidify,whichmeansthatthemoldingwillshrinkontothecorewhichformsit.Thisshrinkagemakesthemoldingdifficulttoremove.Facilitiesareprovidedontheinjectionmachineforautomaticactuationofanejectorsystem,andthisissituatedbehindthemovingplaten.Becauseofthis.Themouldsejectorsystemwillbemosteffectivelyoperatedifplacedinthemorninghalfofthemould,i.e.Thehalfattachedtothemovingplaten.Wehavestatedpreviouslythatweneedtoejectthe,molding,fromthescoreanditthereforefollowsthatthecore,too,willmostsatisfactorilybelocatedinthemovinghalf.Theejectorsysteminamouldwillbediscussedunderthreeheadings,namelyitheejectorgirdiitheejectorplateassemblyandiiithemethodofejection.5.1EjectorgirdTheejectorgirdisthatpartofthemouldwhichsupportsthemouldplateandprovidesaspaceintowhichtheejectorplateassemblycanbefittedandoperated.Thegirdnormallyconsistsofabackplateontowhichismountedanumberofconvenientlyshapedsupportblocks.Theejectorplateassemblyisthatpartofthemouldtowhichtheejectorelementisattached.Theassemblyconsistsofanejectorplate,aretainingplateandanejectorrod.Oneendofthislettermemberisthreadedanditisscrewedintotheejectorplate.Inthisparticulardesigntheejectorrodfunctionnotonlyasanactuaingmemberbutalsoasamethodguidingtheassembly.Notethattheparallelportionoftheejectorrodpassesthroughanejectorrodbushfittedinthebackplateofthemould.5.2EjectiontechniquesWhenamoldingcools,itcontactsbyanamountdependingonthematerialbeingprocessed.Foramoldingwhichhasnointernalform,forexample,asolidrectangularblock,themoldingwillshrinkawayfromthecavitywalls,therebypermittingasimpleejectiontechniquetobeadopted.However,whenthemoldinghasinternalform,themolding,asitcools,willshrinkontothecoreandsomepositivetypeofejectionandsomepositivetypeofejectionisnecessary.Thedesignerhasseveralejectiontechniquesformwhichtochoose,butingeneral,thechoicewillberestricteddependingupontheshapeofthemolding.ThebasicejectiontechniquesareasfollowsipinejectioniisleeveejectioniiistripperplateejectionandIVairejection.

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