THEINJECTIONMOLDING1、THEINJECTIONMOLDINGINJECTIONMOLDINGISPRINCIPALLYUSEDFORTHEPRODUCTIONOFTHETHERMOPLASTICPARTS,ALTHOUGHSOMEPROGRESSHASBEENMADEINDEVELOPINGAMETHODFORINJECTIONMOLDINGSOMETHERMOSETTINGMATERIALSTHEPROBLEMOFINJECTIONAMETHODPLASTICINTOAMOLDCAVITYFROMARESERVOIROFMELTEDMATERIALHASBEENEXTREMELYDIFFICULTTOSOLVEFORTHERMOSETTINGPLASTICWHICHCUREANDHARDENUNDERSUCHCONDITIONSWITHINAFEWMINUTESTHEPRINCIPLEOFINJECTIONMOLDINGISQUITESIMILARTOTHATOFDIECASTINGTHEPROCESSCONSISTSOFFEEDINGAPLASTICCOMPOUNDINPOWEREDORGRANULARFORMFROMAHOPPERTHROUGHMETERINGANDMELTINGSTAGESANDTHENINJECTINGITINTOAMOLDAFTERABRIEFCOOLINGPERIOD,THEMOLDISOPENEDANDTHESOLIDIFIEDPARTEJECTEDINJECTIONMOLDINGMACHINEOPERATIONTHEADVANTAGEOFINJECTIONMOLDINGARE（）AHIGHMOLDINGSPEEDADAPTERFORMASSPRODUCTIONISPOSSIBLE；（）THEREISAWIDECHOICEOFTHERMOPLASTICMATERIALSPROVIDINGAVARIETYOFUSEFULPROPERTIES；（）ITISPOSSIBLETOMOLDTHREADS,UNDERCUTS,SIDEHOLES,ANDLARGETHINSECTION2、THEINJECTIONMOLDINGMACHINESEVERALMETHODSAREUSEDTOFORCEORINJECTTHEMELTEDPLASTICINTOTHEMOLDTHEMOSTCOMMONLYUSEDSYSTEMINTHELARGERMACHINESISTHEINLINERECIPROCATINGSCREW,ASSHOWNINFIGURE21THESCREWACTSASACOMBINATIONINJECTIONANDPLASTICIZINGUNITASTHEPLASTICISFEDTOTHEROTATINGSCREW,ITPASSESTHROUGHTHREEZONESASSHOWNFEED,COMPRESSION,ANDMETERINGAFTERTHEFEEDZONE,THESCREWFLIGHTDEPTHISGRADUALLYREDUCED,FORCETHEPLASTICTOCOMPRESSTHEWORKISCONVERTEDTOHEATBYCONDUCTIONFROMTHEBARRELSURFACEASTHECHAMBERINFRONTOFTHESCREWBECOMESFILLED,ITFORCESTHESCREWBACK,TRIPPINGALIMITSWITCHTHATACTIVATESAHYDRAULICCYLINDERTHATFORCESTHESCREWFORWARDANDINJECTSTHEFLUIDPLASTICINTOTHECLOSEDMOLDANANTIFLOWBACKVALVEPRESENTSPLASTICUNDERPRESSUREFROMESCAPINGBACKINTOTHESCREWFLIGHTTHECLAMPINGFORCETHATAMACHINEISCAPABLEOFEXERTINGISPARTOFTHESIZEDESIGNATIONANDISMEASUREDINTONSARULEOFTHUMBCANBEUSEDTODETERMINETHETONNAGEREQUIREDFORAPARTICULARJOBITISBASEDONTWOTONSOFCLAMPFORCEPERSQUAREINCHOFPROJECTEDAREAIFTHEFLOWPATTERNISDIFFICULTANDTHEPARTSARETHIN,THISMAYHAVETOGOTOTHREEORFOURTONSMANYRECIPROCATINGSCREWMACHINESARECAPABLEOFHANDINGTHERMOSETTINGPLASTICMATERIALSPREVIOUSLYTHESEMATERIALSWEREHANDLEDBYCOMPRESSIONORTRANSFERMOLDINGTHERMOSETTINGMATERIALSCUREORPOLYMERIZEINTHEMOLDANDAREEJECTEDHOTINTHERANGEOF375C410CTHERMOSETTINGPARTSMUSTBEALLOWEDTOCOOLINTHEMOLDINORDERORREMOVETHEMWITHOUTDISTORTIONTHUSTHERMOSETTINGCYCLESCANBEFASTEROFCOURSETHEMOLDMUSTBEHEATEDRATHERTHANCHILLED,ASWITHTHERMOPLASTICS3、BASICUNDERFEEDMOULDASIMPLEMOULDOFTHISTYPEISSHOWNINFIGURE31,ANDTHEDESCRIPTIONOFTHEDESIGNANDTHEOPENINGSEQUENCEFOLLOWSTHEMOULDCONSISTSOFTHREEBASICPARTS,NAMELYTHEMOVINGHALF,THEFLOATINGCAVITYPLATEANDTHEFEEDPLATERESPECTIVELYTHEMOVINGHALFCONSISTSOFTHEMOVINGMOULDPLATEASSEMBLY,SUPPORTBLOCK,BACKINGPLATE,EJECTORASSEMBLYANDTHEPINEJECTIONSYSTEMTHUSTHEMOVINGHALFINTHISDESIGNISIDENTICALWITHTHEMOVINGHALFOFBASICMOULDSTHEFLOATINGCAVITYPLATE,WHICHMAYBEOFTHEINTEGERORINSERTBOLSTERDESIGN,ISLOCATEDONSUBSTANTIALGUIDEPILLARS（NOTSHOWN）FITTEDINTHEFEEDPLATETHESEGUIDEPILLARSMUSTBEOFSUFFICIENTLENGTHTOSUPPORTTHEFLOATINGCAVITYPLATEOVERITSFULLMOVEMENTANDSTILLPROJECTTOPERFORMTHEFUNCTIONOFALIGNMENTBETWEENTHECAVITYANDCOREWHENTHEMOULDISBEINGCLOSEDGUIDEBUSHESAREFITTEDINTOTHEMOVINGMOULDPLATEANDTHEFLOATINGCAVITYPLATERESPECTIVELYTHEMAXIMUMMOVEMENTOFTHEFLOATINGCAVITYPLATEISCONTROLLEDBYSTOPORSIMILARDEVICETHEMOVINGMOULDPLATEISSUITABLYBOREDTOPROVIDEACLEARANCEFORTHESTOPBOLTASSEMBLYTHESTOPBOLTSMUSTBELONGENOUGHTOPROVIDESUFFICIENTSPACEBETWEENTHEFEEDPLATEANDTHEFLOATINGCAVITYPLATEFOREASYREMOVALOFTHEFEEDSYSTEMTHEMINIMUMSPACEPROVIDEFORSHOULDBE65MMJUSTSUFFICIENTFORANOPERATORTOREMOVETHEFEEDSYSTEMBYHANDIFNECESSARYTHEDESIREOPERATINGSEQUENCEISFORTHEFIRSTDAYLIGHTTOOCCURBETWEENTHEFLOATINGCAVITYPLATETHISENSURESTHESPRUEISPULLEDFROMTHESPRUEBUSHIMMEDIATELYTHEMOULDISOPENEDTOACHIEVETHISSEQUENCE,SPRINGSMAYBEINCORPORATEDBETWEENTHEFEEDPLATEANDTHEFLOATINGCAVITYPLATETHESPRINGSSHOULDBESTRONGENOUGHTOGIVEANINITIALIMPETUSTOTHEFLOATINGCAVITYPLATETOENSUREITMOVESAWAYWITHTHEMOVINGHALFITISNORMALPRACTICETOMOUNTTHESPRINGSONTHEGUIDEPILLARS（FIGURE32）ANDACCOMMODATETHEMINSUITABLEPOCKETINTHECAVITYPLATETHEMAJORPARTOFTHEFEEDSYSTEM（RUNNERANDSPRUE）ISACCOMMODATEDINTHEFEEDPLATETOFACILITATEAUTOMATICOPERATION,THERUNNERSHOULDBEOFATRAPEZOIDALFORMSOTHATONCEITISPULLEDFROMTHEFEEDPLATEISCANEASILYBEEXTRACTEDNOTETHATIFAROUNDRUNNERISUSED,HALFTHERUNNERISFORMEDINTHEFLOATINGCAVITYPLATE,WHEREITWOULDREMAIN,ANDBEPREVENTEDFROMFALLINGORBEINGWIPEDCLEARWHENTHEMOULDISOPENEDNOWTHATWEHAVECONSIDEREDTHEMOULDASSEMBLYINTHESOMEDETAIL,WELOOKATTHECYCLEOFOPERATIONFORTHISTYPEOFMOULDTHEIMPRESSIONSAREFILLEDVIATHEFEEDSYSTEM（FIGURE31（A）ANDAFTERASUITABLEDWELLPERIOD,THEMACHINEPLATENSCOMMENCETOOPENAFORCEISIMMEDIATELYEXERTEDBYTHECOMPRESSIONSPRINGS,WHICHCAUSETHEFLOATINGCAVITYPLATETOMOVEAWAYWITHTHEMOVINGHALFASPREVIOUSLYDISCUSSEDTHESPRUEISPULLEDFROMTHESPRUEBUSHBYTHESPRUEPULLERAFTERTHEFLOATINGCAVITYPLATEHASMOVEDAPREDETERMINEDDISTANCE,ITISARRESTEDBYTHESTOPBOLTSTHEMOVINGHALFCONTINUESTOMOVEBACKANDTHEMOLDINGS,HAVINGSHRUNKONTOTHECORES,AREWITHDRAWNFROMTHECAVITIESTHEPINGATEBREAKSATITSJUNCTIONWITHTHERUNNER（FIGURE31（B）THESPRUEPULLER,BEINGATTACHEDTOTHEMOVINGHALF,ISPULLEDTHROUGHTHEFLOATINGCAVITYPLATEANDTHEREBYRELEASETHEFEEDSYSTEMWHICHISTHENFREETOFALLBETWEENTHEFLOATINGCAVITYPLATEANDTHEFEEDPLATETHEMOVINGHALFCONTINUESTOMOVEBACKUNTILTHEEJECTORSYSTEMISOPERATEDANDTHEMOLDINGSAREEJECTED（FIGURE31（C）WHENTHEMOULDISCLOSED,THERESPECTIVEPLATESARERETURNEDTOTHEIRMOLDINGPOSITIONANDTHECYCLEISREPEATED4、FEEDSYSTEMITISNECESSARYTOPROVIDEAFLOWWAYINTHEINJECTIONMOULDTOCONNECTTHENOZZLE（OFTHEINJECTIONMACHINE）TOEACHIMPRESSIONTHISFLOWWAYISTERMEDTHEFEEDSYSTEMNORMALLYTHEFEEDSYSTEMCOMPRISESASPRUE,RUNNERANDGATETHESETERMSAPPLYEQUALLYTOTHEFLOWWAYITSELF,ANDTOTHEMOLDEDMATERIALWHICHISREMOVEFROMTHEFLOWWAYITSELFINTHEPROCESSOFEXTRACTEDTHEMOLDINGATYPICALFEEDSYSTEMFORAFOURIMPRESSION,TWOPLATETYPEMOULDISSHOWNINFIGURE41ITISSEENTHATTHEMATERIALPASSESTHROUGHTHESPRUE,MAINRUNNER,BRANCHRUNNERANDGATEBEFOREENTERINGTHEIMPRESSIONASTHETEMPERATUREOFMOLTENPLASTICISLOWEREDWHICHGOINGTHROUGHTHESPRUEANDRUNNER,THEVISCOSITYWILLRISEHOWEVER,THEVISCOSITYISLOWEREDBYSHEARHEATGENERATEDWHENGOINGTHROUGHTHEGATETOFILLTHECAVITYITISDESIRABLETOKEEPTHEDISTANCETHATTHEMATERIALHASTOTRAVELDOWNTOAMINIMUMTOREDUCEPRESSUREANDHEATLOSSESITISFORTHISREASONTHATCAREFULCONSIDERATIONMUSTBEGIVENTOTHEIMPRESSIONLAYOUTGATESDESIGN41SPRUEASPRUEISACHANNELTHROUGHWHICHTOTRANSFERMOLTENPLASTICINJECTEDFROMTHENOZZLEOFTHEINJECTORINTOTHEMOLDITISAPARTOFSPRUEBUSH,WHICHISASEPARATEPARTFROMTHEMOLD42RUNNERARUNNERISACHANNELTHATGUIDESMOLTENPLASTICINTOTHECAVITYOFAMOLD43GATEAGATEISANENTRANCETHROUGHWHICHMOLTENPLASTICENTERSTHECAVITYTHEGATEHASTHEFOLLOWINGFUNCTIONRESTRICTSTHEFLOWANDTHEDIRECTIONOFMOLTENPLASTIC；SIMPLIFIESCUTTINGOFARUNNERANDMOLDINGSTOSIMPLIFYFINISHINGOFPARTS；QUICKLYCOOLSANDSOLIDIFIESTOAVOIDBACKFLOWAFTERMOLTENPLASTICHASFILLEDUPINTHECAVITY44COLDSLUGWELLTHEPURPOSEOFTHECOLDSLUGWELL,SHOWNOPPOSITETHESPRUE,ISTHEORETICALLYTORECEIVETHEMATERIALTHATHASCHILLEDATTHEFRONTOFNOZZLEDURINGTHECOOLINGANDEJECTIONPHASEPERHAPSOFGREATERIMPORTANCEISTHEFACTTHATITPROVIDESPOSITIONMEANSWHEREBYTHESPRUEBUSHFOREJECTIONPURPOSESTHESPRUE,THERUNNERANDTHEGATEWILLBEDISCARDEDAFTERAPARTISCOMPLETEHOWEVER,THERUNNERANDTHEGATEAREIMPORTANTITEMSTHATAFFECTTHEQUALITYORTHECOSTOFPARTS5、EJECTIONAMOLDINGISFORMEDINMOULDBYINJECTINGAPLASTICMELT,UNDERPRESSURE,INTOANIMPRESSIONVIAAFEEDSYSTEMITMUSTTHEREFOREBEREMOVEDMANUALLYFURTHERMORE,ALLTHERMOPLASTICMATERIALSCONTRACTASTHEYSOLIDIFY,WHICHMEANSTHATTHEMOLDINGWILLSHRINKONTOTHECOREWHICHFORMSITTHISSHRINKAGEMAKESTHEMOLDINGDIFFICULTTOREMOVEFACILITIESAREPROVIDEDONTHEINJECTIONMACHINEFORAUTOMATICACTUATIONOFANEJECTORSYSTEM,ANDTHISISSITUATEDBEHINDTHEMOVINGPLATENBECAUSEOFTHIS,THEMOULDSEJECTORSYSTEMWILLBEMOSTEFFECTIVELYOPERATEDIFPLACEDINTHEMOVINGHALFOFTHEMOULD,IETHEHALFATTACHEDTOTHEMOVINGPLATENWEHAVESTATEDPREVIOUSLYTHATWENEEDTOEJECTTHEMOLDINGFROMTHECOREANDITTHEREFOREFOLLOWSTHATTHECORE,TOO,WILLMOSTSATISFACTORILYBELOCATEDINTHEMOVINGHALFTHEEJECTORSYSTEMINAMOULDWILLBEDISCUSSEDUNDERTHREEHEADINGS,NAMELY（）THEEJECTORGRID（）THEEJECTORPLATEASSEMBLYAND（）THEMETHODOFEJECTION51、EJECTORGRIDTHEEJECTORGRID（FIGURE51）ISTHATPARTOFTHEMOULDWHICHSUPPORTSTHEMOULDPLATEANDPROVIDESASPACEINTOWHICHTHEEJECTORPLATEASSEMBLYCANBEFITTEDANDOPERATEDTHEGRIDNORMALLYCONSISTSOFABACKPLATEONTOWHICHISMOUNTEDANUMBEROFCONVENIENTLYSHAPED“SUPPORTBLOCKS”THEEJECTORPLATEASSEMBLYISTHATPARTOFTHEMOULDTOWHICHTHEEJECTORELEMENTISATTACHEDTHEASSEMBLYISCONTAINEDINAPOCKET,FORMEDBYTHEEJECTORGRID,DIRECTLYBEHINDTHEMOULDPLATETHEASSEMBLY（FIGURE52）CONSISTSOFANEJECTORPLATE,ARETAININGPLATEANDANEJECTORRODONEENDOFTHISLATTERMEMBERISTHREADEDANDITISSCREWEDINTOTHEEJECTORPLATEINTHISPARTICULARDESIGNTHEEJECTORRODFUNCTIONNOTONLYASANACTUATINGMEMBERBUTALSOASAMETHODOFGUIDINGTHEASSEMBLYNOTETHATTHEPARALLELPORTIONOFTHEEJECTORRODPASSESTHROUGHANEJECTORRODBUSHFITTEDINTHEBACKPLATEOFTHEMOULD52、EJECTIONTECHNIQUESWHENAMOLDINGCOOLS,ITCONTRACTSBYANAMOUNTDEPENDINGONTHEMATERIALBEINGPROCESSEDFORAMOLDINGWHICHHASNOINTERNALFORM,FOREXAMPLE,ASOLIDRECTANGULARBLOCK,THEMOLDINGWILLSHRINKAWAYFROMTHECAVITYWALLS,THEREBYPERMITTINGASIMPLEEJECTIONTECHNIQUETOBEADOPTEDHOWEVER,WHENTHEMOLDINGHASINTERNALFORM,THEMOLDING,ASITCOOLS,WILLSHRINKONTOTHECOREANDSOMEPOSITIVETYPEOFEJECTIONISNECESSARYTHEDESIGNERHASSEVERALEJECTIONTECHNIQUESFROMWHICHTOCHOOSE，BUTINGENERAL,THECHOICEWILLBERESTRICTEDDEPENDINGUPONTHESHAPEOFTHEMOLDINGTHEBASICEJECTIONTECHNIQUESAREASFOLLOWS（）PINEJECTION（）SLEEVEEJECTION（）STRIPPERPLATEEJECTIONAND（）AIREJECTIONFIGURE21AFIGURE21BFIGURE31FIGURE32FIGURE41AFIGURE41BFIGURE51FIGURE52注塑模1、注塑模盡管成型某些熱固性材料的方法取得了一定的進步，但注塑模主要（還是）用來生產(chǎn)熱塑性塑件。（這主要是因為）熱固性塑料熔體在很短的時間內(nèi)就固化和硬化，在從料斗想模具型腔注入熱固性塑料熔體的過程中，也會出現(xiàn)這種情況，這個問題一直非常難解決，注塑成型原理和鑄造十分相似。注塑成型的工藝包括首先把料斗中的粉狀或粒狀的塑料混合物依次輸送發(fā)哦計量區(qū)和溶化區(qū)，然后再注射到模具的型腔中，經(jīng)過短時冷卻后，開模，推出成型塑件，注塑機分為手動、半自動及全自動操作。注塑模具有以下優(yōu)點（）較高的成型速度使大批量生產(chǎn)成為可能；（）為成型具有不同使用性能的熱塑性材料提供了較寬的選擇；（）可以成型帶有螺紋的塑件、側向凹陷的塑件、帶有側孔的塑件以及較大的薄壁件。2、注塑機熔融塑料進入模具中通常有幾種方式。在大型注塑機上常帶采用螺桿式的注入方式，如圖21所示。螺桿同時具有注射和塑化的功能。樹脂原料進入旋轉(zhuǎn)的螺桿時，要經(jīng)過圖示的三個區(qū)域喂入?yún)^(qū)、壓實區(qū)和計量區(qū)。經(jīng)過喂入?yún)^(qū)后，為壓實樹脂原料，螺桿螺旋部分的深度逐漸降低，同時傳遞樹脂原料間因剪切作用而產(chǎn)生的熱量，使原料呈半流動狀態(tài)。在計量區(qū)，螺缸表面的加熱裝置對熔體進一步加熱。當熔體充滿螺桿前部區(qū)域時，螺桿在熔體壓力的作用下后退，觸動限位開關使液壓缸工作，在液壓力的作用下推動螺桿向前運動，將熔融塑料注射到閉合的模具型腔中。防倒流閥能夠阻止受壓熔體倒流進螺桿的螺旋區(qū)。注塑機的鎖模系統(tǒng)做提供的鎖模力由（塑件在分型面的投影）尺寸決定，鎖模力以噸位單位。通?？拷?jīng)驗來決定塑件所需要的鎖模力總噸數(shù)，一般在塑件投影面積上每平方英寸需要作用兩噸鎖模力。如果熔體流動困難或塑件較薄，鎖模力應提高到三到四噸。許多往復螺桿式注塑機能生產(chǎn)熱固性塑料。以前，熱固性塑料由擠出模具或傳遞模具生產(chǎn)。熱固性塑料熔體在模具內(nèi)固化或發(fā)生聚合反應，并在溫度357410范圍內(nèi)推出。熱塑性塑料熔體必須在模具內(nèi)冷卻成型，以保證推出時不發(fā)生變形，這種熱固性循環(huán)速度很快。當然，生產(chǎn)熱塑性塑料時，模具必須被加熱，而不是冷卻。3、模具基本結構這種簡單的模具結構如圖31所示，模具設計和開模順序?qū)⒃谝韵碌钠姓撌?。模具由三個基本部分組成，分別是動模部分、浮動型腔板和定模板。動模部分包括動模板組件、支撐塊、支撐板，推出機構和頂桿推出系統(tǒng)。這樣設計的動模部分與最基本的模具結構中的動模部分相同。浮動型腔板通過導柱（圖中沒有示出）固定在定模板上，設計形式可以是整體式，也可以是鑲拼式。導柱必須有足夠的長度，（以便磨具工作時）支撐浮動型腔板完成開合動作，并在模具合模時完成對型腔和型芯的找正作用。導套分別安裝在動模板和浮動型腔板上。浮動型腔板的最大運動距離由限位釘或類似裝置控制。在動模板的適當位置鉆孔，以便安裝限位釘。限位釘必須有足夠的長度為定模板和浮動型腔板之間提供足夠的空間，從而使?jié)沧⑾到y(tǒng)的凝料順利脫落。如果必須使用手動方式取出凝料，開模時取出凝料所需的最小距離應為65MM。模具的開模順序是浮動型腔板和定模板先分開。確保模具打開時澆注系統(tǒng)凝料立即從澆口套脫出。為實現(xiàn)這樣的順序，定模板和浮動型腔板之間裝有彈簧。彈簧的彈力必須足夠大，確保在初始推力的作用下浮動型腔板跟隨動模部分一起運動。彈簧套在導柱上，一同裝在浮動型腔板上相應的彈簧座處（見圖52），這種形式在彈簧裝配中十分常見。澆注系統(tǒng)的主要部分（分流道和主流道）開設在定模板上，為便于自動操作，分流道應采用梯形截面，以便于脫出澆注系統(tǒng)凝料。注意，如果采用圓形分流道，分流道的一半開設在浮動型腔板上，開模時，分流道可能留在浮動型腔板，將阻礙凝料的脫落或去除。我們已經(jīng)詳細討論模具裝配，再看這類模具的生產(chǎn)循環(huán)過程。熔體經(jīng)過澆注系統(tǒng)充滿型腔后（見圖31（A），經(jīng)過適當?shù)谋哼^程，注塑機帶動模具開模。壓縮彈簧的彈力立即釋放出來，推動浮動型腔板和動模部分一起移動，如同前面論述的一樣。主流道凝料被拉料桿從澆口套中拉出。浮動型腔板移動預定距離后，被限位釘限位。動模部分繼續(xù)后移，塑件由于收縮作用包緊在型芯上從型腔中脫出（跟隨動模一同移動）。點澆口在結合處拉斷，與分流道脫離（見圖31（B）。安裝在動模部分的拉料桿脫離浮動型腔板，澆注系統(tǒng)凝料由此脫下，然后在浮動型腔板和定模板之間自由落下。動模部分繼續(xù)后退，直到推出機構開始運動，推出塑件（見圖31（C）。和模時，模具的各模板回到成型位置，重復下一個注塑循環(huán)。4、澆注系統(tǒng)在注塑模中，連接（注塑機）噴嘴和各個型腔的流動通道是十分必要的，這種進料通道稱為澆注系統(tǒng)。通常，澆注系統(tǒng)由主流道、分流道和澆口組成。這些術語應用在相應的進料通道本身，以