How to Prevent Mold Inaccuracies 　

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).