Liquidinjectionmolding isanindustrialfabricationmethodthatmoldsstockmaterialsintoarangeofcomponentsandproducts.Itdiffersfromthestandardreactioninjectionmoldingprocessinthatitreliesonmechanicalmixingratherthanpressurizedimpingementmixing,anditfocusesspecificallyonliquidsiliconerubberandsimilarelastomericmaterials.Itiscapableofefficientlyproducingalargenumberofversatileitems,includingseals,o-rings,isolators,andelectroniccontacts. Alargepartofliquidinjectionmolding’sversatilityderivesfromthematerialpropertiesofliquidsiliconematerials.Thesesiliconesexhibitahighdegreeofheatandflameresistance,tensilestrength,andflexibility.Inaddition,siliconesprovidebeneficialformabilitycharacteristics,allowingforcoloringortransparencyinthefinishedproduct.Dependingontheirchemicalcomposition,thesematerialscanalsoserveasinsulatorsorconductors.Theliquidinjectionmoldingprocessusedtofabricateliquidsiliconeisapreciseanddistinctmethod,capableofproducinghighlyaccurateresults. TheLiquidInjectionMoldingProcess Liquidinjectionmolding focusesontheapportionedmixinganddispensingofplastic-basedmaterialsviaaseriesofplungers.Usually,oneplungercontainsthebaseformingplastic,whichcanbereinforcedwithadditivesandfibers,whiletheotherplungerholdsacatalystthatwillactivatethemixingreaction.Thecompoundedmaterialistheninjecteddirectlyintoasealedmold,andafterhardening,thenearlyfinishedcomponentisejectedfromthemoldingmachine. Siliconesandacrylicsarethematerialsmostcommonlyinvolvedinliquidinjectionmolding.Tohelppreventmachinehardwarefrombecomingcloggedwithliquidplastic,aspring-loadedpinnozzlecanbeusedfortheinjectionstage.Spring-loadingallowstheinjectionpressuretobehigherthanthatoftheextruderbarrel,thuskeepingthechannelunblocked.Computer-aideddesigntoolsarealsohelpfulformakingthemoldingprocessmoreefficient.Computerprogramscanrunsimulationstodeterminethemosteffectiveprocessingconditions,aswellasevaluateresultsandmonitorintegrateddevices.Thermalimagingtechnologyalsohaspotentialforidentifyingproductionerrors,suchasmoldingflawsordesigninconsistencies. LiquidInjectionMoldingMachines Astandardliquidinjectionmoldingmachinereliesonameteredpumpingdeviceandaninjectionunitwithadynamicorstaticmixerattached.Ideally,thesesystemsareintegratedinascompactandpreciseafashionaspossible,whileperipheralcomponentsareconfiguredtomeettheneedsofaparticularproject.Theessentialpartsofatypicalliquidinjectionmachineinclude: •Injectors: Theinjectiondevicepushesformingmaterial,suchasliquidsiliconerubber,intothepumpingsectionunderpressurizedforce.Theoperatorcanusuallyadjustthepressureandinjectionrate,whichvaryaccordingtoprojectparameters.•MeteringUnits: Themeteringunitpumpsthetwoliquidmaterialsincarefulproportions,releasingthemsimultaneouslyataconstantratio.•SupplyDrums: Thematerialsupplycontainers,orplungers,connecttothemachine’spumpingsystem.Besidesdrumsofthemixingmaterials,thereisoftenanadditionalcontainerforpigment.•Mixers: Afterpassingthroughthemeteringunit,theliquidformingmaterialsarecombinedusingastaticordynamicmixer.Thismixtureisthenpressurizedandforcedintothemold.•Nozzle: Thenozzlethatfeedstheliquidmixtureintothemoldoftencomesequippedwithanautomaticshut-offvalvethatpreventsthecompoundfromleakingorthemoldfromoverfilling.•MoldClamp: Themoldclampingdeviceistriggeredincoordinationwiththeinjector,pump,andsupplyunit.Itsecuresthemoldinplace,andopensitwhentheprocessiscomplete.
 MoldingConsiderations Therearenumerousconcernstakenintoaccountintheassemblyandoperationofliquidinjectionmoldingsystems.Preventingleaksisoneofthemajorissues,asliquidmoldingcompoundscanseepthroughgapsinthemachineandimpedeoperations.Forthisreason,sealsandsealantmaterialareimportantelementsinamoldingdevice,especiallyformovingorrotatingparts.Inorganicfiltersarefoundinsomemoldingcompounds,andbecausetheycancauseequipmenttodeteriorateatafasterrate,corrosionresistancetreatmentsorincreasedmaintenancemayberequiredtocompensateforwear.