Lesson5Three-plateInjectionMoldThree-plateinjectionmoldsareinjectionmoldspossessingtwopartinglines,havingbeendesignedasdegatingmolds.Thismeansthatthesprueisseparatedfromthepartsinthemold.Attheconclusionofinjectionthemoldopensatthefirstpartingline,whichcontainsthesprueandrunnerandseparatedthelineopened,gatefromthepart.Onlywhenthesecondpartinglineopened,thepartwouldbereleased.thereareseveralpossibilitiesforachievingthis.InFig.2-5,withshortstrokedistancesofpushplate1,compressionspring3orspringwasherscanbeinsertedbetweenplate1,whichpushplate1forward.thestop2limitsthestroke.Theretentionsystemofplate4showninFig.2-6isoftenemployed.Dowel1isprovidedwithanannulargroove3intowhichtheballcatch2ispushed.Anottooheavyplatecanbecarriedalongbytheresultantadhesiveeffect.Theplate4tobemovedinFig.2-7isconnectedtotheejectorplatesbyejectorrods,whichinturnarefixedintheirbasicpositionbystrongspring3.Plate4iscarriedalonguntiltheejectorplatesarestoppedbyrunningagainsttheejectorbarofthemachine.Thenonlythecompletemoldbodykeepsmovingonintheusualmanner.Caremustbetakenwiththisdesignthattheejectorbar1isslightlydelayed.Theymustnotberigidlyconnectedtotheejectorplate;otherwisetherewouldbeatendencyforthepartstobepushedbackintothecavitiesinlate4.Withthisdesignthestrokeofplate4canbearbitrary.Moreover,whentheejectorrods2arehardenedandguidedinbushes,theseejectorrodscantakeoverthefunctionoftheguidepinsfittedonthefixedmoldhalf,sothatthespacebetweenplate4and5isnotclutteredupwithprotrudingrodsorsprings.Thiscanbeofadvantageifarathercomplicatedrunnersystemhastobedesigned.Fig.2-8showsamechanicaltypeofplatemovement.Althoughmoreelaborate,itisneverthelessthesafestway,particularlyiflarge,heavyplateshavetobemoved.Thelatch6,whichhooksoverplate3,movesthelatteralong.Themovementiscontinueduntilthepin5inthehookisliftedbytheriseintheguidestrip4whichitruns.Thepinhastoescapeupward,therebyreleasingthehookfromtheplate5.Theplatenowpushesupagainstastop,whichinthiscasehasbeenfittedtotheundersideoftheguidestripat1,andthemoldca