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【英文标准名称】:Drysealpipethreads(inch)
【原文标准名称】:干封管螺纹(英制)
【标准号】:ASMEB1.20.3-1976
【标准状态】:现行
【国别】:美国
【发布日期】:1976-11-18
【实施或试行日期】:
【发布单位】:美国机械工程师协会(US-ASME)
【起草单位】:ASME
【标准类型】:()
【标准水平】:()
【中文主题词】:尺寸;规范;管;螺纹;管螺纹;名称与符号
【英文主题词】:Designations;Dimensions;Pipethreads;Pipes;Specification;Threads
【摘要】:DrysealpipethreadsarebasedontheUSA(American)pipethread,however,theydifferfromtheUSA(American)pipethreadinthattheyaredesignedtosealpressuretightjointswithoutthenecessityofusingsealingcompounds.Toaccomplishthissomemodificationofthreadformandgreateraccuracyinmanufactureisrequired.Therootsofboththeexternalandinternalthreadsaretruncatedslightlymorethanthecrests,Le.rootshavewiderflatsthancrests,sothatmetal-to-metalcontactoccursatthecrestsandrootscoincidentwithorpriortoflankcontact,seeFigure1.Thusasthethreadsareassembledbywrenching,therootsofthethreadscrushthesharpercrestsofthematingthreads.Thissealingactionatboththemajorandminordiameterstendstopreventspiralleakageandmakesthejointspressuretightwithoutthenecessityofusingsealingcompounds,providedthatthematingthreadsareinaccordancewithstandardspecificationsandtolerancesandarenotdamagedbygallinginassembly.Thecontrolofcrestandroottruncationissimplifiedbytheuseofproperlydesignedthreadingtools.Also,itisdesirablethatbothexternalandinternalthreadshavefullthreadheightfortheLIlength.However,wherenotfunctionallyobjectionable,theuseofacompatiblelubricantorsealantmaybeusedtominimizethepossibilityofgalling.ThisisdesirableinassemblingDrysealpipethreadsinrefrigerationandothersystemstoeffectapressuretightseal.1.1.1InordertoobtainapressuretightsealusingDrysealpipethreadswithoutasealer,itisnecessarytoholdcrestandroottruncationofbothinternalandexternalthreadswithinthelimitsspecified.Unlessthisisdonebyuseofthreadingtoolswiththecrestandroottruncationcontrolledsoastoassurerepro-ductionontheproductthreads,itisnecessarytouseasystemofmeasuringorasystemofgagingandmeasuringtodetermineconformance.1.1.2Evenwithouttruncationgages,thestandardpracticeofusingtwoseparatethreadgagesforDrysealpipethreads,eachwithadifferenceintruncation,lengthofengagementandpointofengagement,providesamoredetailedcheckofangle,leadandtaperdeviationsthanisrequiredfornon-drysealtaperpipethreads.1.I.3Onemethodofcheckingcresttruncationisbyusing6stepplaingages.Itshouldberecognizedthatthismethodmaygivemisleadingresultsinthatthecresttruncationoftheproductthreadsisalwaysless(flatnarrower)thanthatindicatedbythepositionofthegages,thedegreeofinconsistencydependingontheangle,leadandtaperdeviationspresentintheproductthread.1.1.4Anothermethodemploysbothcrestandroottruncationcheckgages.Therootcheckgageismadewithathreadformhavinganincludedangleof50degreesandwithasmallergagecrestflatthantherootflattobechecked.Themajordiameterofthisgageiscontrolledinrelationto6gagingstepsinasimilarmannertotheplain6stepcrestcheckgage.Likethecrestcheckgage,theresultsmaybesomewhatmisleadingexceptthatinthecaseoftherootcheckgage,theroottruncationoftheproductthreadisalwaysmore(flatwider)thanisindicatedbythepositionofthegages.1.1.5Unlesslead,angleandtaperofproductthreadsareveiywellcontrolled,useof6stepcrestandrootcheckgageswillresultinproductthreadswithnarrowercrestflatsandwiderrootflatsthanenvisionedbythedrysealtolerances.Useofsuchagagingsystemcouldresultinrejectionofthreadswhichwouldactuallyconformtothedrysealtolerancesspecified.Theonlycompletelyreliablerefereemethodfordeterminingwhethercrestandroottruncationhasbeenheldwithintoleranceisdirectmeasurementoftheexternalthreadflatsandmeasurementoftheseflatsonacastorsectionoftheinternalthread.
【中国标准分类号】:J04
【国际标准分类号】:21_040_20
【页数】:30P.;A4
【正文语种】:英语