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《机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 9.ppt》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。
1、Lesson9InjectionMoldingTextInjectionmoldingisessentiallythesameprocessashot-chamberdiecasting.Thepelletsorgranulesarefedintoaheatedcylinder,wheretheyaremelted.Themeltisthenforcedintoasplit-diechamber(Fig.9.1a),eitherbyahydraulicplungerorbytherotatingscrewsystemofanextruder.Newerequipmentisofther
2、eciprocatingscrewtype(Fig.9.1b).Asthepressurebuildsupatthedieentrance,therotatingscrewbeginstomovebackwardunderpressuretoapredetermineddistance,thuscontrollingthevolumeofmaterialtobeinjected.Thescrewstopsrotatingandispushedforwardhydraulically,forcingthemoltenplasticintothediecavity.Fig.9.1Injec
3、tionmoldingwith（a）plungerand（b）reciprocatingrotatingscrew.Telephonereceivers,plumbingfittings,toolhandles,andhousingsaremadebyinjectionmolding.Typicalinjection-moldedproductsarecups,containers,housings,toolhandles,knobs,electricalandcommunicationcomponents(suchastelephonereceivers),toys,andplumb
4、ingfittings.Althoughforthermoplasticsthediesarerelativelycool,thermosetsaremoldedinheateddieswherepolymerizationandcross-linkingtakeplace.Ineithercase,afterthepartissufficientlycooled(forthermoplastics)orsetorcured(forthermosets),thediesareopenedandthepartisejected.Thediesarethenclosedandtheproc
5、essisrepeatedautomatically.Elastomersalsoareinjectionmoldedbytheseprocesses.Becausethematerialismoltenwheninjectedintothemold,complexshapesandgooddimensionalaccuracycanbeachieved,asindiecasting.Dieswithmovingandunscrewingmandrelsarenotunusual,andallowthemoldingofpartswithmultiplecavitiesandinter
6、nalandexternalthreads.Injectionmoldingisahigh-rateproductionprocess,withgooddimensionalcontrol.Typicalcycletimesrangefrom5to60seconds,butcanbeseveralminutesforthermosettingmaterials.Thedies,generallymadeoftoolsteelsorberylliumcopper,mayhavemultiplecavitiessothatmorethanonepartcanbemadeinonecycle
7、.Properdiedesignandcontrolofmaterialflowinthediecavitiesareimportantfactorsinthequalityoftheproduct.Otherfactorsaffectingqualityareinjectionpressure,temperature,andconditionoftheresin.Injection-moldedpartsaregenerallymoldedt
