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Determination of twist in yarns method
2019/03/29
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This International Standard specifies a method for the determination of the direction of twist in yarns, the amount of twist, in terms of turns per unit length, and the Change in length on untwisting, by the direct counting method.
Normative references:
The following Standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All Standards are subject to revision, and Parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the Standards indicated below.
Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 2: 1973, Textiles - Designation of the direction of twist in yams and related products.
ISO 139: 1973, Textiles - Standard atmospheres for conditioning and testing.
ISOnR 8091:1983, Textiles - Twist factor related to the Tex System.
Definitions:
For the purposes of this International Standard, the following definitions apply.
1、twist: Number of turns about the axis of a yarn based on its nominal gauge length before untwisting.
Twist should preferably be expressed as turns per metre (turns/m), but it may be expressed as turns per centimetre (turnslcm).
2、gauge length: Distance between two effective clamping Points of the test specimen mounted in the testing equipment.
3、initial length: Length of a test specimen under a specified pretension at the beginning of a test.
4、Change in length on untwisting: Increase or decrease in initial length observed when the specimen is untwisted, expressed as the percentage extension, or contraction, based on the specimen initial length.
5、moisture equilibrium for testing: That state reached when the rate of increase in mass of a sample or specimen in a specified (test) atmosphere does not exceed that prescribed for the material being tested.
A textile material is in moisture equilibrium with the ambient atmosphere when it does not exchange water with this atmosphere; its mass then remains constant as lang as the experiment is carried out in an unchanged atmosphere. For test purposes, moisture equilibrium is reached by absorption, starting from a relatively low moisture content.
yarn package:
Length or lengths of yarn in a form suitable for use, handling, storing or shipping.
Packages may be comprised of unsupported yarn,such as balls, or supported yarn, such as skeins, cakes, bobbins, cops, cones, pirns, spools, tubes or beams.
twist factor:
Measure of the spiralling orientation of the fibres in a spun yarn or of the filaments in a filament yarn.
lt is related to the angle which fibres on the surface of the yarn make with the axis of the yarn and is a measure of the hardness of the resulting yarn due to twist.
Principle:
The twist in a known length of yarn is removed by rotating one end of the specimen with respect to the other until the components of the yarn being tested are parallel. The exact number of turns required to remove the twist is reported in terms of turns per unit length of yarn.
Apparatus:
Twist counter,
consisting of a pair of clamps,one of which is rotatable in either direction and positively connected to a revolution counter. The Position of one or both clamps shall be adjustable to permit testing yarn lengths from IO mm to 500 mm. There shall be no play in the clamp which might affect the gauge length.
consisting of a pair of clamps,one of which is rotatable in either direction and positively connected to a revolution counter. The Position of one or both clamps shall be adjustable to permit testing yarn lengths from IO mm to 500 mm. There shall be no play in the clamp which might affect the gauge length.
Means shall be provided for applying tension to the specimen and for rapidly determining the specimen length with an accuracy of + - 0,5 mm or + 2 %,whichever is smaller.
NOTE 2 The Iimit of 2 % is consistent with the highest accuracy required in counting the number of turns in the specimen.
The counting device shall be capable of recording the number of revolutions of the rotatable clamp.
If the contraction or extension of the untwisted specimen is to be measured, the movable but nonrotatable clamp shall be capable of travelling with essentially no friction.
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