模具专业英语 教学课件 作者 王浩钢 14456第12章.ppt

《模具专业英语 教学课件 作者 王浩钢 14456第12章.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、Lesson12MouldcoolingOnefundamentalprincipleofinjectionmoldingisthathotmaterialentersthemould,whereitcoolsrapidlytoatemperatureatwhichitsolidifiessufficientlytoretaintheshapeoftheimpression.Thetemperatureofthemouldisthereforeimportantasitgovernsaportionoftheoverall

2、moldingcycle.Whilethemeltflowsmorefreelyinahotmould,agreatercoolingperiodisrequiredbeforethesolidifiedmoldingcanbeejected.Alternatively,whilethemeltsolidifiesquicklyinacoldmoulditmaynotreachtheextremitiesoftheimpression.Acompromisebetweenthetwoextremesmusttherefor

3、ebeacceptedtoobtaintheoptimummoldingcycle.Theoperatingtemperatureforaparticularmouldwilldependonanumberoffactorswhichincludethefollowing:typeandgradeofmaterialtobemolded;lengthofflowwithintheimpression;wallsectionofthemolding;lengthofthefeedsystem,etc.Itisoftenfou

4、ndadvantageoustouseaslightlyhighertemperaturethanisrequiredjusttofilltheimpression,asthistendstoimprovethesurfacefinishofthemoldingbyminimizingweldlines,flowmarksandotherblemishes①.Tomaintaintherequiredtemperaturedifferentialbetweenthemouldandplasticmaterial,water

5、(orotherfluid)iscirculatedthroughholesorchannelswithinthemould.Theseholesorchannelsaretermedflow-waysorwater-waysandthecompletesystemofflowwaysistermedthecircuit.Duringtheimpressionfillingstagethehottestmaterialwillbeinthevicinityoftheentrypoint,i.e.thegate,thecoo

6、lestmaterialwillbeatthepointfarthestfromtheentry.Thetemperatureofthecoolantfluid,however,increasesasitpassesthroughthemould.Thereforetoachieveanevencoolingrateoverthemoldingsurfaceitisnecessarytolocatetheincomingcoolantfluidadjacentto‘hot’moldingsurfacesandtolocat

7、ethechannelscontaining‘heated’coolantfluidadjacentto‘cool’moldingsurfaces②.However,aswillbeseenfromthefollowingdiscussion,itisnotalwayspracticabletoadopttheidealizedapproachandthedesignermustuseafairamountofcommonsensewhenlayingoutcoolantcircuitsifunnecessarilyexp

8、ensivemouldsaretobeavoided.Unitsforthecirculationofwater(andotherfluids)arecommerciallyavailable.Theseunitsaresimplyconnectedtothemouldviaflexiblehoses,