ByAllanFish)
Bykeepingcompressedairdry,moldmakerscanpreventdamagetocriticalequipment.
Theprocessofproducingmoldsgenerateslargevolumesoffinechipsofmetalthat,
iftheyarentpromptlyremoved,willlodgeinprecisionequipmentandmakeitimpossibletomeetclosetolerancesrequired.
Toolsusedinmachiningcentersandengraverstotypicallyproducemolds,
areautomaticallymovedintoandoutofthemachinespindlesduringeachmachiningcycle,
asrequiredtoperformspecificoperations.Eachtimeatoolchangeoccurs,
boththeoldandnewtoolsareexposedtochipsandotherparticlesfromthecuttingbed.
Ifanyoftheseparticlesweretosticktotheshank,thetoolwouldnotruntruewheninsertedintothespindle.
Thismightmakeitimpossibleforthemachinetomeetthelevelofprecisionrequiredinproducingmolds.
AirProblems
Topreventthisfromhappening,boththespindleandtoolareblastedwithcompressedaireachtimeatoolischanged.Insomecases,
thespindleandtoolarecleanedautomaticallybythecompressedairserviceinst
alledinthemachinewhileothermachinesspindlesarecleanedmanually.
Theprobleminmanyplantsisthattheairusedtocleanthespindlescontainswaterthatcollectsinthecompresse
dairlineswheneverhumidityishigh.Inthehotsummermonths,
theairlinecanlookjustlikeagardenhose.Theresultisthatwaterissprayedintothespindlealongwiththeair,
causingrustthatcreatesthesameaccuracyproblemsasthechipsthattheairwasdesignedtoremove.
Sometimesspindlesneedtoberebuiltorscrapped,
andinothercasesexpensiverepairstothemachinetoolmayberequired.
Thepresenceofwaterinairlinescancauseothermaintenanceproblemsaswell.
Mostplantsuseairmotorsinawiderangeoftoolssuchaspneumaticdrills.
Ifwatercontaminatesthecompressedairservice,thesemotorsmayrusttothepointthattheystopfunctioningafterjustafewweeksofservice.
Rebuildingthemotorstypicallytakesaboutfivehoursandcostsabout$500inparts.
Prevention
Thereareanumberofpotentialsolutionstothisproblem.Refrigerateddryersarerelativelyinexpensivetopurchase,
butconsumeaconsiderableamountofelectricityandalsorequireregularmaintenanceforthemotorsandothermovingparts.
Ontheotherhand,compressedairdryersbasedonthemembraneseparationprinciplecostslightlymorefromaninitialpurchasestandpoint,
buthavenomovingpartsanddonotrequireanymaintenanceexceptforchangingthefiltereveryyear.
Dryersthatusethemembraneseparationprincipleworklikethis:
First,thecompressedairpassesthroughhighefficiencycoalescingfilters.
Thesefiltersremoveoilandwaterdropletsandparticulatecontamination.
Then,theairmovesintothedehydrationmembranes,whichconsistofbundlesofhollowmembranefibers,
eachpermeableonlytowatervapor.
Asthecompressedairpassesthroughthecenterofthesefibers,watervaporpermeatesthewallsofthefiber,anddryairexitsfromtheotherend.
Asmallportionofthedryairisredirectedalongthelengthofthemembranefibertocarryawaythemoisture-ladenairthatsurroundsit.
Theremainderofthedryairispipedtotheapplication.
Thesedryersaredesignedtooperatecontinuously24/7.Anelectricalsupplyisnotrequiredtousethesedryers.
Theonlymaintenancerequiredischangingtheprofiteercartridgeamaximumofonceayear.
Thetimerequiredtochangetheprofiteercartridgeisapproximatelyfiveminutes.
Forthesereasons,mostmoldmakerscalculationsshowthatmembraneseparationcostsconsiderablylessoverthelongrun.
(selecedfromMoldmakingTechnologyMagazine).
