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中英文翻译注塑模.doc

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中英文翻译注塑模.doc

TheInjectionMolding1、TheinjectionmoldingInjectionmoldingisprincipallyusedfortheproductionofthethermoplasticparts,althoughsomeprogresshasbeenmadeindevelopingamethodforinjectionmoldingsomethermosettingmaterials.Theproblemofinjectionamethodplasticintoamoldcavityfromareservoirofmeltedmaterialhasbeenextremelydifficulttosolveforthermosettingplasticwhichcureandhardenundersuchconditionswithinafewminutes.Theprincipleofinjectionmoldingisquitesimilartothatofdiecasting.Theprocessconsistsoffeedingaplasticcompoundinpoweredorgranularformfromahopperthroughmeteringandmeltingstagesandtheninjectingitintoamold.Afterabriefcoolingperiod,themoldisopenedandthesolidifiedpartejected.Injectionmoldingmachineoperation.Theadvantageofinjectionmoldingare(ⅰ)ahighmoldingspeedadapterformassproductionispossible(ⅱ)thereisawidechoiceofthermoplasticmaterialsprovidingavarietyofusefulproperties(ⅲ)itispossibletomoldthreads,undercuts,sideholes,andlargethinsection.2、TheinjectionmoldingmachineSeveralmethodsareusedtoforceorinjectthemeltedplasticintothemold.Themostcommonlyusedsysteminthelargermachinesistheinlinereciprocatingscrew,asshowninFigure21.Thescrewactsasacombinationinjectionandplasticizingunit.Astheplasticisfedtotherotatingscrew,itpassesthroughthreezonesasshownfeed,compression,andmetering.Afterthefeedzone,thescrewflightdepthisgraduallyreduced,forcetheplastictocompress.Theworkisconvertedtoheatbyconductionfromthebarrelsurface.Asthechamberinfrontofthescrewbecomesfilled,itforcesthescrewback,trippingalimitswitchthatactivatesahydrauliccylinderthatforcesthescrewforwardandinjectsthefluidplasticintotheclosedmold.Anantiflowbackvalvepresentsplasticunderpressurefromescapingbackintothescrewflight.Theclampingforcethatamachineiscapableofexertingispartofthesizedesignationandismeasuredintons.Aruleofthumbcanbeusedtodeterminethetonnagerequiredforaparticularjob.Itisbasedontwotonsofclampforcepersquareinchofprojectedarea.Iftheflowpatternisdifficultandthepartsarethin,thismayhavetogotothreeorfourtons.Manyreciprocatingscrewmachinesarecapableofhandingthermosettingplasticmaterials.Previouslythesematerialswerehandledbycompressionortransfermolding.Thermosettingmaterialscureorpolymerizeinthemoldandareejectedhotintherangeof375°C~410°C.Thermosettingpartsmustbeallowedtocoolinthemoldinorderorremovethemwithoutdistortion.Thusthermosettingcyclescanbefaster.Ofcoursethemoldmustbeheatedratherthanchilled,aswiththermoplastics.3、BasicUnderfeedMouldAsimplemouldofthistypeisshowninFigure31,andthedescriptionofthedesignandtheopeningsequencefollows.Themouldconsistsofthreebasicparts,namelythemovinghalf,thefloatingcavityplateandthefeedplaterespectively.ThemovinghalfconsistsofThemovingmouldplateassembly,supportblock,backingplate,ejectorassemblyandthepinejectionsystem.Thusthemovinghalfinthisdesignisidenticalwiththemovinghalfofbasicmoulds.Thefloatingcavityplate,whichmaybeoftheintegerorinsertbolsterdesign,islocatedonsubstantialguidepillars(notshown)fittedinthefeedplate.Theseguidepillarsmustbeofsufficientlengthtosupportthefloatingcavityplateoveritsfullmovementandstillprojecttoperformthefunctionofalignmentbetweenthecavityandcorewhenthemouldisbeingclosed.Guidebushesarefittedintothemovingmouldplateandthefloatingcavityplaterespectively.Themaximummovementofthefloatingcavityplateiscontrolledbystoporsimilardevice.Themovingmouldplateissuitablyboredtoprovideaclearanceforthestopboltassembly.Thestopboltsmustbelongenoughtoprovidesufficientspacebetweenthefeedplateandthefloatingcavityplateforeasyremovalofthefeedsystem.Theminimumspaceprovideforshouldbe65mmjustsufficientforanoperatortoremovethefeedsystembyhandifnecessary.Thedesireoperatingsequenceisforthefirstdaylighttooccurbetweenthefloatingcavityplate.Thisensuresthesprueispulledfromthespruebushimmediatelythemouldisopened.Toachievethissequence,springsmaybeincorporatedbetweenthefeedplateandthefloatingcavityplate.Thespringsshouldbestrongenoughtogiveaninitialimpetustothefloatingcavityplatetoensureitmovesawaywiththemovinghalf.Itisnormalpracticetomountthespringsontheguidepillars(Figure32)andaccommodatetheminsuitablepocketinthecavityplate.Themajorpartofthefeedsystem(runnerandsprue)isaccommodatedinthefeedplatetofacilitateautomaticoperation,therunnershouldbeofatrapezoidalformsothatonceitispulledfromthefeedplateiscaneasilybeextracted.Notethatifaroundrunnerisused,halftherunnerisformedinthefloatingcavityplate,whereitwouldremain,andbepreventedfromfallingorbeingwipedclearwhenthemouldisopened.Nowthatwehaveconsideredthemouldassemblyinthesomedetail,welookatthecycleofoperationforthistypeofmould.Theimpressionsarefilledviathefeedsystem(Figure31(a))andafterasuitabledwellperiod,themachineplatenscommencetoopen.Aforceisimmediatelyexertedbythecompressionsprings,whichcausethefloatingcavityplatetomoveawaywiththemovinghalfaspreviouslydiscussed.Thesprueispulledfromthespruebushbythespruepuller.Afterthefloatingcavityplatehasmovedapredetermineddistance,itisarrestedbythestopbolts.Themovinghalfcontinuestomovebackandthemoldings,havingshrunkontothecores,arewithdrawnfromthecavities.Thepingatebreaksatitsjunctionwiththerunner(Figure31(b)).Thespruepuller,beingattachedtothemovinghalf,ispulledthroughthefloatingcavityplateandtherebyreleasethefeedsystemwhichisthenfreetofallbetweenthefloatingcavityplateandthefeedplate.Themovinghalfcontinuestomovebackuntiltheejectorsystemisoperatedandthemoldingsareejected(Figure31(c)).Whenthemouldisclosed,therespectiveplatesarereturnedtotheirmoldingpositionandthecycleisrepeated.4、FeedSystemItisnecessarytoprovideaflowwayintheinjectionmouldtoconnectthenozzle(oftheinjectionmachine)toeachimpression.Thisflowwayistermedthefeedsystem.Normallythefeedsystemcomprisesasprue,runnerandgate.Thesetermsapplyequallytotheflowwayitself,andtothemoldedmaterialwhichisremovefromtheflowwayitselfintheprocessofextractedthemolding.Atypicalfeedsystemforafourimpression,twoplatetypemouldisshowninFigure41.Itisseenthatthematerialpassesthroughthesprue,mainrunner,branchrunnerandgatebeforeenteringtheimpression.Asthetemperatureofmoltenplasticisloweredwhichgoingthroughthesprueandrunner,theviscositywillrisehowever,theviscosityisloweredbyshearheatgeneratedwhengoingthroughthegatetofillthecavity.Itisdesirabletokeepthedistancethatthematerialhastotraveldowntoaminimumtoreducepressureandheatlosses.Itisforthisreasonthatcarefulconsiderationmustbegiventotheimpressionlayoutgatesdesign.4.1.SprueAsprueisachannelthroughwhichtotransfermoltenplasticinjectedfromthenozzleoftheinjectorintothemold.Itisapartofspruebush,whichisaseparatepartfromthemold.4.2.RunnerArunnerisachannelthatguidesmoltenplasticintothecavityofamold.4.3.GateAgateisanentrancethroughwhichmoltenplasticentersthecavity.Thegatehasthefollowingfunctionrestrictstheflowandthedirectionofmoltenplasticsimplifiescuttingofarunnerandmoldingstosimplifyfinishingofpartsquicklycoolsandsolidifiestoavoidbackflowaftermoltenplastichasfilledupinthecavity.4.4.ColdslugwellThepurposeofthecoldslugwell,shownoppositethesprue,istheoreticallytoreceivethematerialthathaschilledatthefrontofnozzleduringthecoolingandejectionphase.Perhapsofgreaterimportanceisthefactthatitprovidespositionmeanswherebythespruebushforejectionpurposes.Thesprue,therunnerandthegatewillbediscardedafterapartiscomplete.However,therunnerandthegateareimportantitemsthataffectthequalityorthecostofparts.5、EjectionAmoldingisformedinmouldbyinjectingaplasticmelt,underpressure,intoanimpressionviaafeedsystem.Itmustthereforeberemovedmanually.Furthermore,allthermoplasticmaterialscontractastheysolidify,whichmeansthatthemoldingwillshrinkontothecorewhichformsit.Thisshrinkagemakesthemoldingdifficulttoremove.Facilitiesareprovidedontheinjectionmachineforautomaticactuationofanejectorsystem,andthisissituatedbehindthemovingplaten.Becauseofthis,themouldsejectorsystemwillbemosteffectivelyoperatedifplacedinthemovinghalfofthemould,i.e.thehalfattachedtothemovingplaten.Wehavestatedpreviouslythatweneedtoejectthemoldingfromthecoreanditthereforefollowsthatthecore,too,willmostsatisfactorilybelocatedinthemovinghalf.Theejectorsysteminamouldwillbediscussedunderthreeheadings,namely(ⅰ)theejectorgrid(ⅱ)theejectorplateassemblyand(ⅲ)themethodofejection.5.1、EjectorgridTheejectorgrid(Figure51)isthatpartofthemouldwhichsupportsthemouldplateandprovidesaspaceintowhichtheejectorplateassemblycanbefittedandoperated.Thegridnormallyconsistsofabackplateontowhichismountedanumberofconvenientlyshapedsupportblocks.Theejectorplateassemblyisthatpartofthemouldtowhichtheejectorelementisattached.Theassemblyiscontainedinapocket,formedbytheejectorgrid,directlybehindthemouldplate.Theassembly(Figure52)consistsofanejectorplate,aretainingplateandanejectorrod.Oneendofthislattermemberisthreadedanditisscrewedintotheejectorplate.Inthisparticulardesigntheejectorrodfunctionnotonlyasanactuatingmemberbutalsoasamethodofguidingtheassembly.Notethattheparallelportionoftheejectorrodpassesthroughanejectorrodbushfittedinthebackplateofthemould.5.2、EjectiontechniquesWhenamoldingcools,itcontractsbyanamountdependingonthematerialbeingprocessed.Foramoldingwhichhasnointernalform,forexample,asolidrectangularblock,themoldingwillshrinkawayfromthecavitywalls,therebypermittingasimpleejectiontechniquetobeadopted.However,whenthemoldinghasinternalform,themolding,asitcools,willshrinkontothecoreandsomepositivetypeofejectionisnecessary.Thedesignerhasseveralejectiontechniquesfromwhichtochoose,butingeneral,thechoicewillberestricteddependingupontheshapeofthemolding.Thebasicejectiontechniquesareasfollows(ⅰ)pinejection(ⅱ)sleeveejection(ⅲ)stripperplateejectionand(Ⅳ)airejection.Figure21aFigure21b

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