中英文翻译注塑模.doc

TheInjectionMolding1、TheinjectionmoldingInjectionmoldingisprincipallyusedfortheproductionofthethermoplasticparts,althoughsomeprogresshasbeenmadeindevelopingamethodforinjectionmoldingsomethermosettingmaterials.Theproblemofinjectionamethodplasticintoamoldcavityfromareservoirofmeltedmaterialhasbeenextremelydifficulttosolveforthermosettingplasticwhichcureandhardenundersuchconditionswithinafewminutes.Theprincipleofinjectionmoldingisquitesimilartothatofdie-casting.Theprocessconsistsoffeedingaplasticcompoundinpoweredorgranularformfromahopperthroughmeteringandmeltingstagesandtheninjectingitintoamold.Afterabriefcoolingperiod,themoldisopenedandthesolidifiedpartejected.Injection-moldingmachineoperation.Theadvantageofinjectionmoldingare：（）ahighmoldingspeedadapterformassproductionispossible；（）thereisawidechoiceofthermoplasticmaterialsprovidingavarietyofusefulproperties；（）itispossibletomoldthreads,undercuts,sideholes,andlargethinsection.2、Theinjection-moldingmachineSeveralmethodsareusedtoforceorinjectthemeltedplasticintothemold.Themostcommonlyusedsysteminthelargermachinesisthein-linereciprocatingscrew,asshowninFigure2-1.Thescrewactsasacombinationinjectionandplasticizingunit.Astheplasticisfedtotherotatingscrew,itpassesthroughthreezonesasshown：feed,compression,andmetering.Afterthefeedzone,thescrew-flightdepthisgraduallyreduced,forcetheplastictocompress.Theworkisconvertedtoheatbyconductionfromthebarrelsurface.Asthechamberinfrontofthescrewbecomesfilled,itforcesthescrewback,trippingalimitswitchthatactivatesahydrauliccylinderthatforcesthescrewforwardandinjectsthefluidplasticintotheclosedmold.Anantiflowbackvalvepresentsplasticunderpressurefromescapingbackintothescrewflight.Theclampingforcethatamachineiscapableofexertingispartofthesizedesignationandismeasuredintons.Arule-of-thumbcanbeusedtodeterminethetonnagerequiredforaparticularjob.Itisbasedontwotonsofclampforcepersquareinchofprojectedarea.Iftheflowpatternisdifficultandthepartsarethin,thismayhavetogotothreeorfourtons.Manyreciprocating-screwmachinesarecapableofhandingthermosettingplasticmaterials.Previouslythesematerialswerehandledbycompressionortransfermolding.Thermosettingmaterialscureorpolymerizeinthemoldandareejectedhotintherangeof375C410C.Thermosettingpartsmustbeallowedtocoolinthemoldinorderorremovethemwithoutdistortion.Thusthermosettingcyclescanbefaster.Ofcoursethemoldmustbeheatedratherthanchilled,aswiththermoplastics.3、BasicUnderfeedMouldAsimplemouldofthistypeisshowninFigure3-1,andthedescriptionofthedesignandtheopeningsequencefollows.Themouldconsistsofthreebasicparts,namely：themovinghalf,thefloatingcavityplateandthefeedplaterespectively.ThemovinghalfconsistsofThemovingmouldplateassembly,supportblock,backingplate,ejectorassemblyandthepinejectionsystem.Thusthemovinghalfinthisdesignisidenticalwiththemovinghalfofbasicmoulds.Thefloatingcavityplate,whichmaybeoftheintegerorinsert-bolsterdesign,islocatedonsubstantialguidepillars（notshown）fittedinthefeedplate.Theseguidepillarsmustbeofsufficientlengthtosupportthefloatingcavityplateoveritsfullmovementandstillprojecttoperformthefunctionofalignmentbetweenthecavityandcorewhenthemouldisbeingclosed.Guidebushesarefittedintothemovingmouldplateandthefloatingcavityplaterespectively.Themaximummovementofthefloatingcavityplateiscontrolledbystoporsimilardevice.Themovingmouldplateissuitablyboredtoprovideaclearanceforthestopboltassembly.Thestopboltsmustbelongenoughtoprovidesufficientspacebetweenthefeedplateandthefloatingcavityplateforeasyremovalofthefeedsystem.Theminimumspaceprovideforshouldbe65mmjustsufficientforanoperatortoremovethefeedsystembyhandifnecessary.Thedesireoperatingsequenceisforthefirstdaylighttooccurbetweenthefloatingcavityplate.Thisensuresthesprueispulledfromthespruebushimmediatelythemouldisopened.Toachievethissequence,springsmaybeincorporatedbetweenthefeedplateandthefloatingcavityplate.Thespringsshouldbestrongenoughtogiveaninitialimpetustothefloatingcavityplatetoensureitmovesawaywiththemovinghalf.Itisnormalpracticetomountthespringsontheguidepillars（Figure3-2）andaccommodatetheminsuitablepocketinthecavityplate.Themajorpartofthefeedsystem（runnerandsprue）isaccommodatedinthefeedplatetofacilitateautomaticoperation,therunnershouldbeofatrapezoidalformsothatonceitispulledfromthefeedplateiscaneasilybeextracted.Notethatifaroundrunnerisused,halftherunnerisformedinthefloatingcavityplate,whereitwouldremain,andbepreventedfromfallingorbeingwipedclearwhenthemouldisopened.Nowthatwehaveconsideredthemouldassemblyinthesomedetail,welookatthecycleofoperationforthistypeofmould.Theimpressionsarefilledviathefeedsystem（Figure3-1（a）andafterasuitabledwellperiod,themachineplatenscommencetoopen.Aforceisimmediatelyexertedbythecompressionsprings,whichcausethefloatingcavityplatetomoveawaywiththemovinghalfaspreviouslydiscussed.Thesprueispulledfromthespruebushbythespruepuller.Afterthefloatingcavityplatehasmovedapredetermineddistance,itisarrestedbythestopbolts.Themovinghalfcontinuestomovebackandthemoldings,havingshrunkontothecores,arewithdrawnfromthecavities.Thepingatebreaksatitsjunctionwiththerunner（Figure3-1（b）.Thespruepuller,beingattachedtothemovinghalf,ispulledthroughthefloatingcavityplateandtherebyreleasethefeedsystemwhichisthenfreetofallbetweenthefloatingcavityplateandthefeedplate.Themovinghalfcontinuestomovebackuntiltheejectorsystemisoperatedandthemoldingsareejected（Figure3-1（c）.Whenthemouldisclosed,therespectiveplatesarereturnedtotheirmoldingpositionandthecycleisrepeated.4、FeedSystemItisnecessarytoprovideaflow-wayintheinjectionmouldtoconnectthenozzle（oftheinjectionmachine）toeachimpression.Thisflow-wayistermedthefeedsystem.Normallythefeedsystemcomprisesasprue,runnerandgate.Thesetermsapplyequallytotheflow-wayitself,andtothemoldedmaterialwhichisremovefromtheflow-wayitselfintheprocessofextractedthemolding.Atypicalfeedsystemforafour-impression,twoplate-typemouldisshowninFigure4-1.Itisseenthatthematerialpassesthroughthesprue,mainrunner,branchrunnerandgatebeforeenteringtheimpression.Asthetemperatureofmoltenplasticisloweredwhichgoingthroughthesprueandrunner,theviscositywillrise；however,theviscosityisloweredbyshearheatgeneratedwhengoingthroughthegatetofillthecavity.Itisdesirabletokeepthedistancethatthematerialhastotraveldowntoaminimumtoreducepressureandheatlosses.Itisforthisreasonthatcarefulconsiderationmustbegiventotheimpressionlayoutgatesdesign.4.1.SprueAsprueisachannelthroughwhichtotransfermoltenplasticinjectedfromthenozzleoftheinjectorintothemold.Itisapartofspruebush,whichisaseparatepartfromthemold.4.2.RunnerArunnerisachannelthatguidesmoltenplasticintothecavityofamold.4.3.GateAgateisanentrancethroughwhichmoltenplasticentersthecavity.Thegatehasthefollowingfunction：restrictstheflowandthedirectionofmoltenplastic；simplifiescuttingofarunnerandmoldingstosimplifyfinishingofparts；quicklycoolsandsolidifiestoavoidbackflowaftermoltenplastichasfilledupinthecavity.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：（）theejectorgrid；（）theejectorplateassembly；and（）themethodofejection.5.1、EjectorgridTheejectorgrid（Figure5-1）isthatpartofthemouldwhichsupportsthemouldplateandprovidesaspaceintowhichtheejectorplateassemblycanbefittedandoperated.Thegridnormallyconsistsofabackplateontowhichismountedanumberofconvenientlyshaped“supportblocks”.Theejectorplateassemblyisthatpartofthemouldtowhichtheejectorelementisattached.Theassemblyiscontainedinapocket,formedbytheejectorgrid,directlybehindthemouldplate.Theassembly（Figure5-2）consistsofanejectorplate