NPT & NPTF 区别

NPT&NPTF区别NPT：美制一般用途圆锥管螺纹（密封）NPTF：美制干密封圆锥管螺纹NPT=NationalPipeThreadNPTF=NationalPipeThreadFine使用时前者可以在螺纹副内填加密封介质，而后者则完全依靠螺纹自身形成密封，螺纹间无任何密封介质。所以前者属于经济型螺纹，产品设计中常用，而干密封管螺纹则 规定 关于下班后关闭电源的规定党章中关于入党时间的规定公务员考核规定下载规定办法文件下载宁波关于闷顶的规定 了较为严格的公差，属精密型螺纹，仅用在特殊场合。它们两者的牙型角、斜度等指标都是相同的，关键是牙顶和牙底的削平高度不一样（螺纹牙高不一样。NPT可能有过盈也可能有间隙，但NPTF没有间隙；NPT内外螺纹均为圆锥，而NPTF外螺纹是圆锥，内螺纹则有圆锥、圆柱两种；NPT有右旋也有左旋，NPTF只有右旋一种旋向。）NPTvsNPTFTHREADDESIGNTherequirementsforNPT(NationalPipeThread)arespelledoutinANSIB1.20.1TherequirementsforNPTF(NationalPipeThreadFuel)arespelledoutinANSIB1.20.3BothNPTandNPTFhavethesamethreads-per-inch,pitchdiameters,andtaper-per-inch.Thedifferencescomeinthemajorandminordiameters,therootandcrestofthethreads.TheNPTFthreadcrestsfallwithintheparametersoftheNPTrequirements,buthaveasmallerrangethantheNPT.TheNPTFthreadrootsaredifferentthantheNPTthreadroots.NPTFthreadrootsaredesignedtointerferewiththecrestofthematingthreadwiththeintentionofcreatingamechanicalsealthroughthreadformdeformationatassembly.NPTFthreadshavetwoclassesidentified:Class1andClass2.NPTthreadrootsaredesignedtoallowclearancewiththematingthreadcrestsonassembly.NPTVs.NPTFTaperPipeThreadsThetwomostcommontaperpipethreadsusedintheUnitedStatesareNPTandNPTF.Applicationsrangefromelectricalconduitsandhandrailingstohigh-pressurepipelinesthatcarrygasorcausticfluids.NPTthreadsareformechanicalorlow-pressureairorfluidapplicationsandrequiretheuseofsealingcompoundslikeTeflontape,toprovidetheseal.Whentheapplicationismorecritical,andthesealingcompoundmayfailduetohighheatorpressure,NPTFDrysealthreadsareused.Thismechanicalsealisproducedbythematingandslightcrushingofthethreadswhenawrenchisappliedtotightenthefittings.Visually,boththreadsappeartobeidentical.Bothhavea¾”taperoveronefootoflength.Bothhavethesamepitchdiameteratthetopoftheholeofinternalthreadsorendofthepipeonexternalthreads,andbothhavethesamethreadlengthsordepths.However,thereisasubtledifferenceinthethreadformthatdifferentiatesthetwo.Themajorandminordiametersofboththreadsdifferslightly.WithNPTthreads,afterawrenchisapplied,slightspacesatthemajorandminordiametersmayexistthatwouldallowtheassemblytoleakandthereforeasealingcompoundisusedtofillanygaps.Ontheotherhand,NPTFthreadsaredesignedtoensurethatsufficientcrushingoftheentirethreadformwilltakeplacetoproduceamechanicalseal.HowdoesthedifferenceinthreadformseffectthetoolingusedtoproduceNPTandNPTFthreads?TapsareavailableforbothNPTandNPTFthreadshavingtheappropriateformtoproduceeachtypeofthread.SinceNPTthreadedpartsrequiresealingcompounds,itisacceptabletouseanNPTFtapforNPTapplications.However,NPTtapscannotbeusedforNPTFapplications,asitwilllikelyproduceathreadthatwillleak.Thesameistrueofexternalthreads.Inmostcasesthetapdrillisthesameforbothforms.Themostsignificantdifferenceinthetwothreadsistheinspectionrequired.SincesealingcompoundswillbeusedforNPTthreads,onlyasingleplugwithastep,knownasanL1plug(internalthread)orasinglethinL1ring(external)arerequiredtochecksize.However,sincethetaperandthepositionofmajorandminordiametersaresocriticaltothesealingofNPTFthreads,theadditionalthreadsintheassemblyknownasL2andL3,andthemajorandminordiametersareinspectedwitheitherspecialplugorringgages.