1、Designation: D 1422 99Standard Test Method forTwist in Single Spun Yarns by the Untwist-Retwist Method1This standard is issued under the fixed designation D 1422; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method2describes the determination of twist insingle spun yarns when only an approximation of the true twistis requ
3、ired.NOTE 1For a more accurate method see Test Method D 1423.1.2 This test method is applicable to spun single yarns incontinuous lengths, and also to spun yarns raveled fromfabrics, provided specimens at least 200 mm (8 in.) long can beobtained.1.3 The values stated in either inch-pound or SI units
4、 are tobe regarded separately as standard. Within the text, the SI unitsare shown in parentheses. The values stated in each system arenot exact equivalents; therefore each system shall be usedindependently of the other. Combining values from the twosystems may result in nonconformance within this te
5、st method.1.4 This test method has been found satisfactory for use indetermining twist in all single ring spun yarns and 100% cottonopen-end yarns. For all open-end spun yarns that are not 100 %cotton this test method has not been found to be satisfactory fordetermining twist but may be used to meas
6、ure deviation froman average value.1.5 This specification shows the values in both inch-poundunits and SI units. The “inch-pound” units is the technicallycorrect name for the customary units used in the United States.The “SI” units is the technically corrected name for the systemof metric units know
7、n as the International System of Units. Thevalues stated in either acceptable metric units or in other unitsshall be regarded separately as standard. The values expressedin each system may not be exact equivalents; therefore, eachsystem must be used independently of the other, withoutcombining in an
8、y way.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of this standard to establish appropriate safetyand health practices and determine the applicability of regu-latory limitations prior to use.2. Referenced Documents
9、2.1 ASTM Standards:D 123 Terminology Relating to Textiles3D 1059 Test Method for Yarn Number Based on Short-Length Specimens3D 1423 Test Method for Twist in Yarns by the Direct-Counting Method3D 2258 Practice for Sampling Yarn for Testing33. Terminology3.1 Definitions:3.1.1 direction of twist, nthe
10、right or left direction of thehelix formed in a twisted strand as indicated by superimposi-tion of the capital letter “S” or “Z.”3.1.1.1 DiscussionYarn has S twist if, when the yarn isheld in a vertical position, the visible spirals or helices aroundits central axis conform in direction of slope to
11、the centralportion of the letter“ S,” and Z twist if the visible spirals orhelices conform in direction of slope to the central portion ofthe letter “Z.” When two or more yarns, either single or plied,are twisted together, the letters “S” and “Z” are used in asimilar manner to indicate the direction
12、 of the last twistinserted.3.1.2 single yarn, nthe simplest strand of textile materialsuitable for operations such as weaving, knitting, etc.3.1.2.1 DiscussionA single yarn may be formed fromfibers with more or less twist; from filaments with or withouttwist; from narrow strips of materials such as
13、paper, cello-phane, or metal foil; or from monofilaments. A yarn which iseither twistless or can be rendered twistless in a singleuntwisting operation. When twist is present, it is usually all inthe same direction.3.1.3 spun yarn, nin a staple system, a continuous strandof fibers held together by so
14、me binding mechanism.3.1.3.1 DiscussionThe binding mechanism most com-monly used in spun yarns is twist. Other useful mechanismsthat are used are chemical additives, wrapping, entanglement,or some combination of these. Test Method D 1422 is appli-cable only to yarns which have twist.3.1.4 twist, nin
15、 textile strands, the helical or spiral con-figurations induced by turning a strand about its longitudinalaxis.1This test method is under the jurisdiction of ASTM Committee D13 on Textiles,and is the direct responsibility of Subcommittee D13.58 on Yarn Test Methods,General.Current edition approved N
16、ov. 10, 1999. Published January 2000. Originallypublished as D 1422 56 T. Last previous edition D 1422 92.2This test method is commonly designated by the less precise term“ Untwist-Twist Method.”3Annual Book of ASTM Standards, Vol 07.01.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 1
17、9428-2959, United States.3.1.4.1 DiscussionTwist is usually expressed as the num-ber of turns about the axis that are observed in a specifiedlength either metres (tpm) or inches (tpi).3.1.5 twist factor, TF, nthe product obtained when thetwist expressed in turns per centimetre is multiplied by thesq
18、uare root of the yarn number expressed in tex:Twist factor TF!5tpcm 3 =T (1)where:T = yarn number expressed in tex.3.1.5.1 DiscussionTwist multiplier and twist factor are ameasure of the “twist hardness” of yarn because they areapproximately proportional to the tangent of the angle betweenfibers on
19、the outer yarn surface and the axis of the yarn; thelarger this angle, the harder the twist. Furthermore, this angleis a function of both the twist content (turns per unit length)and the number of fibers per yarn cross section (yarn number).Hence, twist content alone cannot provide a measure of thet
20、wist hardness of a yarn. Twist multiplier and twist factor areproportional to each other and differ only in the units used.The two are related by Eq 2 and Eq 3:TF 5 k 3 TM (2)k 5 277.29/=L (3)where:L = length in yards of the hank used to define the indirectyarn number of the type,N = hanks/lb. In pa
21、rticular for cotton count,k = 9.567 so that Eq 2 becomes Eq 4:TF 5 9.567 3 TM (4)3.1.6 twist multiplier, TM, nthe quotient of the twistexpressed in turns per inch and the square root of the yarnnumber in an indirect system.Twist multiplier TM!5tpi/ =N (5)where:N = yarn number in an indirect system,
22、the cotton systemunless otherwise specified.3.1.7 yarn, na generic term for a continuous strand oftextile fibers, filaments, or material in a form suitable forknitting, weaving, or otherwise intertwining to form a textilefabric.3.2 For definitions of other textile terms used in this testmethod, refe
23、r to Terminology D 123.4. Summary of Test Method4.1 A specimen is untwisted and then retwisted in theopposite direction until it contracts to its original length. It isassumed that the same amount of twist has been inserted as wasoriginally present. Twist, as turns per unit length, is calculatedas h
24、alf the number of turns registered on the counter divided bythe specimen length.5. Significance and Use5.1 This test method is used for acceptance testing in thetrade for economic reasons even though it is less accurate thanthe direct method, Test Method D 1423.5.1.1 If there are differences or prac
25、tical significance be-tween reported test results for two laboratories (or more),comparative tests should be performed to determine if their isa statistical bias between them, using competent statisticalassistance. As a minimum, the test samples should be used thatare as homogeneous as possible, tha
26、t are drawn from thematerial from which the disparate test results are obtained, andthat are assigned randomly in equal numbers to each laboratoryfor testing. Other materials with established test values may beused for this purpose. The test results from the two laboratoriesshould be compared using
27、a statistical test for unpaired data, ata probability level chosen prior to the testing series. If a bias isfound, either its cause must be found and corrected, or futuretest results must be adjusted in consideration of the knownbias.5.2 The “setting” of twist in some fibers causes excessivecontract
28、ion when the yarn is retwisted in the reverse direction.Therefore, the number of turns required to bring the specimenback to its original length may be less than the number of turnsremoved in untwisting. This effect may be partially offset bythe use of higher pretensioning loads; but this increases
29、thedanger of stretching the yarn. Little information is available onthe correct tensions to use for yarns made from different fibersor with different amounts of twist.5.3 In addition to being less tedious, this test methodrequires fewer specimens than the direct-counting method andthe results may be
30、 sufficiently accurate for certain purposes.This test method can be useful in those cases where the mainobjective is to measure variations from an average value.Another possible application is where a large amount of twisttesting is required on yarns of similar type and twist. In thiscase preliminar
31、y tests comparing this method and the directmethod could be used to determine the correct pretension.5.4 Twist has important effects on the physical properties ofyarn. Low-twist yarn is lofty and is usually preferred forknitting because of its softness, covering power, and warmth.Increasing the amou
32、nt of twist causes an increase in yarnstrength by increasing fiber cohesion, but as the twist angleincreases beyond an optimum point, strength decreases due toa loss in effective fiber contribution. Maximum yarn strength isobtained by inserting a medium amount of twist to obtain anoptimum balance be
33、tween these two opposing forces. Hightwist produces yarns of high density (“hard” or “wiry”) andhigh elongation and may improve the abrasion and impactresistance of fabrics.5.5 The optimum twist for either manufacturing efficiencyor physical properties usually increases as staple length de-creases.5
34、.6 The twist in a yarn before it is packaged may bedifferent from that of the yarn after it has been withdrawn fromthe package because of changes in tension and the effect of themethod of withdrawal. If the yarn is withdrawn over-end, aslight increase or decrease in twist will take place, dependingu
35、pon the direction of the twist in the yarn, the direction ofwinding on the package, and the length of the turn (or wrap) onthe package.NOTE 2The difference in twist between unwinding from the side andD 14222over-end is 1/pd, where d is the diameter of the package.4Thus, for a25-mm (1-in.) diameter p
36、ackage, the difference would be about 13 tpm orabout one third tpi.5.7 When a yarn is taken from a more complex yarnstructure or from a fabric, the resultant twist should beconsidered only an approximation of the original value becauseof alterations that may have occurred as a result of the effectso
37、f unwinding, handling, and mechanical strains met in process-ing.6. Apparatus6.1 Twist Tester, consisting of a pair of clamps, one of whichis rotatable in either direction and positively connected to arevolution counter. The tester may be hand- or power-driven.The position of one clamp (or both clam
38、ps) shall be adjustableto accommodate specimens having the length prescribed in10.2. The tester shall be provided with a variable tensioningdevice so constructed that a specific force may be applied to thespecimen at the beginning and end of the test and removedcompletely during the intervening untw
39、isting and twistingoperations.6.2 Dissecting needle or stylus.6.3 Metal ruler to verify gage length (accurate to 2 mm or0.1 in.).7. Sampling7.1 Lot SampleSelect one or more shipping units taken atrandom to represent an acceptance sampling lot and used as asource of laboratory samples.7.2 Laboratory
40、SampleFor packaged yarns, take a mini-mum of five packages for the laboratory sample unlessotherwise agreed upon between purchaser and seller. For yarnsfrom woven or knitted fabrics, the sample must be largeenough to furnish specimens of the length and number speci-fied in 7.3.3.7.3 Selection of Spe
41、cimens:7.3.1 As nearly as possible take an equal number of speci-mens from each package or unit of the laboratory sample. Takethe specimens from each package in a random manner tominimize the effect of cyclic variations introduced duringmanufacturing processes. When preparing specimens, condi-tionin
42、g them, or inserting them in the tester, take care to avoidany change in twist.7.3.2 For packaged yarns, remove and discard the first 25 m(25 yd) of yarn. Using a minimum of tension, take specimensat random intervals greater than1m(1yd)along the yarn.Withdraw the yarn from the package in the directi
43、on of normaluse, either from the side or over-end, if known. If the directionis not known, withdraw the yarn from the side (Note 2). Whenmore than five specimens are taken from an individual pack-age, take groups of five or less at intervals of several yards. Donot cut the specimen free from the pac
44、kage or from the yarn tobe discarded until after the yarn is secured in the clamps of thetwist tester. When possible, take the specimen from near thecenter of the traverse and not at the traverse reversals.7.3.3 For woven fabric, take warp specimens from separateends, since each represents a separat
45、e package. Because thefabric may have been woven on any of a variety of loomswhich are random quilling, sequential quilling or shuttleless,take filling specimens at random through the whole laboratorysample to obtain as representative data as possible. If a stripabout2m(2yd)long is used as a source
46、of specimens.7.3.4 For weft-knit fabric known to be multi-feed, takespecimens from successive courses in one portion of laboratorysample. For weft-knit fabric known to be single-feed or forwhich the type of feed is not known, take specimens at randomfrom the whole sample.7.3.5 For warp-knit fabrics,
47、 cut a walewise strip from whichspecimens can be raveled for testing as needed (Note 3). Cutstrips from which the test specimens can be raveled for testingas needed (Note 4). Cut these strips to provide yarn specimensat least 75 mm (3 in.) longer than the specimen length and tocontain more than the
48、required number of specimens for test. Ifseveral strips are cut, divide the number of specimens amongthe strips as nearly equally as possible. Use care to avoid lossof twist prior to testing.NOTE 3In order to minimize changes in twist, specimens should notbe unraveled from the strips until they are
49、to be placed in the twist tester.7.4 Number of Specimens:7.4.1 Spun Yarn SinglesTake 25 specimens from eachlaboratory sampling unit of spun yarn singles.8. Conditioning8.1 Conditioning is not required for this test method.9. Procedure9.1 To Determine Twist:9.1.1 Check the twist tester to be sure that the longitudinalplay and radial play of the clamp assemblies are small enoughto secure the required precision.9.1.2 Determine the twist with the precision stated in thefollowing table:Turns of Twist in Test Specimen(tpm or tpi) 3 Length (metres or inches)Precision, inre
