【英文标准名称】:StandardTestMethodforTwistinSingleSpunYarnsbytheUntwist-RetwistMethod
【原文标准名称】:退捻加捻法测定单细纱捻数的标准试验方法
【标准号】:ASTMD1422-1999(2008)
【标准状态】:现行
【国别】:美国
【发布日期】:1999
【实施或试行日期】:
【发布单位】:美国材料与试验协会(US-ASTM)
【起草单位】:D13.58
【标准类型】:(TestMethod)
【标准水平】:()
【中文主题词】:
【英文主题词】:spunyarn;twist;Twist--textiles
【摘要】:Thistestmethodisusedforacceptancetestinginthetradeforeconomicreasonseventhoughitislessaccuratethanthedirectmethod,TestMethodD1423.Iftherearedifferencesorpracticalsignificancebetweenreportedtestresultsfortwolaboratories(ormore),comparativetestsshouldbeperformedtodetermineiftheirisastatisticalbiasbetweenthem,usingcompetentstatisticalassistance.Asaminimum,thetestsamplesshouldbeusedthatareashomogeneousaspossible,thataredrawnfromthematerialfromwhichthedisparatetestresultsareobtained,andthatareassignedrandomlyinequalnumberstoeachlaboratoryfortesting.Othermaterialswithestablishedtestvaluesmaybeusedforthispurpose.Thetestresultsfromthetwolaboratoriesshouldbecomparedusingastatisticaltestforunpaireddata,ataprobabilitylevelchosenpriortothetestingseries.Ifabiasisfound,eitheritscausemustbefoundandcorrected,orfuturetestresultsmustbeadjustedinconsiderationoftheknownbias.Thex201C;settingx201D;oftwistinsomefiberscausesexcessivecontractionwhentheyarnisretwistedinthereversedirection.Therefore,thenumberofturnsrequiredtobringthespecimenbacktoitsoriginallengthmaybelessthanthenumberofturnsremovedinuntwisting.Thiseffectmaybepartiallyoffsetbytheuseofhigherpretensioningloads;butthisincreasesthedangerofstretchingtheyarn.Littleinformationisavailableonthecorrecttensionstouseforyarnsmadefromdifferentfibersorwithdifferentamountsoftwist.Inadditiontobeinglesstedious,thistestmethodrequiresfewerspecimensthanthedirect-countingmethodandtheresultsmaybesufficientlyaccurateforcertainpurposes.Thistestmethodcanbeusefulinthosecaseswherethemainobjectiveistomeasurevariationsfromanaveragevalue.Anotherpossibleapplicationiswherealargeamountoftwisttestingisrequiredonyarnsofsimilartypeandtwist.Inthiscasepreliminarytestscomparingthismethodandthedirectmethodcouldbeusedtodeterminethecorrectpretension.Twisthasimportanteffectsonthephysicalpropertiesofyarn.Low-twistyarnisloftyandisusuallypreferredforknittingbecauseofitssoftness,coveringpower,andwarmth.Increasingtheamountoftwistcausesanincreaseinyarnstrengthbyincreasingfibercohesion,butasthetwistangleincreasesbeyondanoptimumpoint,strengthdecreasesduetoalossineffectivefibercontribution.Maximumyarnstrengthisobtainedbyinsertingamediumamountoftwisttoobtainanoptimumbalancebetweenthesetwoopposingforces.Hightwistproducesyarnsofhighdensity(x201C;hardx201D;orx201C;wiryx201D;)andhighelongationandmayimprovetheabrasionandimpactresistanceoffabrics.Theoptimumtwistforeithermanufacturingefficiencyorphysicalpropertiesusuallyincreasesasstaplelengthdecreases.Thetwistinayarnbeforeitispackagedmaybedifferentfromthatoftheyarnafterithasbeenwithdrawnfromthepackagebecauseofchangesintensionandtheeffectofthemethodofwithdrawal.Iftheyarniswithdrawnover-end,aslightincreaseordecreaseintwistwilltakeplace,dependinguponthedirectionofthetwistintheyarn,thedirectionofwindingonthepackage,andthelengthoftheturn(orwrap)onthepackage.Note28212;Thedifferenceintwistbetweenunwindingfromthesideandover-endis1/x03C0;d,wheredisthediameterofthepackage.Thus,fora25-mm(1-in.)diameterpacka......