NPT和NPTF螺纹的区别.doc

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1、NPT和NPTF螺纹的区别NPTVs.NPTFTaperPipeThreadsThetwomostcommontaperpipethreadsusedintheUnitedStatesareNPTandNPTF.Applicationsrangefromelectricalconduitsandhandrailingstohigh-pressurepipelinesthatcarrygasorcausticfluids.NPTthreadsareformechanicalorlow-pressureairorfluidapplicationsandrequiretheuse

2、ofsealingcompoundslikeTeflontape,toprovidetheseal.Whentheapplicationismorecritical,andthesealingcompoundmayfailduetohighheatorpressure,NPTFDrysealthreadsareused.Thismechanicalsealisproducedbythematingandslightcrushingofthethreadswhenawrenchisappliedtotightenthefittings.NPT和NPTF螺纹是两种美国最常用的锥

3、管螺纹。应用范围从电线管道和扶手到运送煤气或腐蚀性液体的高压管线。NPT用于机械的或者低压的气体和液体，要求使用密封剂来保证密封。当密封要求严格时，密封剂可能由于高温高压会失效，这时可以采用NPTF干密封螺纹。当用扳手上紧配件时，这种机械密封会在螺纹配合和轻微的变形来生成密封效果。Visually,boththreadsappeartobeidentical.Bothhavea¾”taperoveronefootoflength.Bothhavethesamepitchdiameteratthetopoftheholeofinternalthreadsorendofthep

4、ipeonexternalthreads,andbothhavethesamethreadlengthsordepths.However,thereisasubtledifferenceinthethreadformthatdifferentiatesthetwo.Themajorandminordiametersofboththreadsdifferslightly.WithNPTthreads,afterawrenchisapplied,slightspacesatthemajorandminordiametersmayexistthatwouldallowtheass

5、emblytoleakandthereforeasealingcompoundisusedtofillanygaps.Ontheotherhand,NPTFthreadsaredesignedtoensurethatsufficientcrushingoftheentirethreadformwilltakeplacetoproduceamechanicalseal.这两种螺纹在目测时是相同的。两种在一英尺的长度上都有3/4的锥度。在内螺纹的孔的顶端或者外螺纹的管的端部拥有相同的中径，而且拥有相同的螺纹长度和深度。尽管如此，在螺纹牙型上还是有细微的差别。两螺纹的大直径和小直

6、径上有细微的差别。对于NPT螺纹，使用扳手上紧后，在大直径和小直径上可能允许装配后漏气，因此会使用密封剂来填充所有的间隙。另一方面，NPTF螺纹的设计用于保证在整个牙形上产生足够的变形以生成这种机械密封。HowdoesthedifferenceinthreadformseffectthetoolingusedtoproduceNPTandNPTFthreads?TapsareavailableforbothNPTandNPTFthreadshavingtheappropriateformtoproduceeachtypeofthread.SinceNPTthreadedpa

7、rtsrequiresealingcompounds,itisacceptabletouseanNPTFtapforNPTapplications.However,NPTtapscannotbeusedforNPTFapplications,asitwilllikelyproduceathreadthatwillleak.Thesameistrueofexternalthreads.Inmostcasesthetapdrillisthesameforbothforms.牙型的不同如何影响使用的工具来生产NPT和NP