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A measure of twist

February 21,2023

Twist: The number of twists within a specified length of nylon dty yarn before it is untwisted, usually expressed as number of twists per British hour (TPI) or TPM per meter (TPM).

The commonly used twist testing methods include direct counting method and untwist twist method. The test of staple fiber and strand wire generally adopts the direct counting method, and the fine nylon dty yarn adopts the untwisting twisting method, in addition to the second and third untwisting twisting method, sliding method and so on.

1.direct counting method

Under a certain tension, clamp two ends of nylon dty yarn of known length, one end is fixed, and the other end is rotated around the axis in the direction of untwisting until the single nylon dty yarn in the strand or the single fiber in the single nylon dty yarn and the single fiber in the complex nylon dty yarn are completely parallel. The number of receding twists is the number of twists within the length of the sample of the nylon dty yarn.

2. back twist twist method

Under a certain tension, clamp two ends of a known length of nylon dty yarn, one end is fixed, and the other end is rotated axially in the direction of untwisting. Measure the number of twists that return to the starting length after untwisting and reverse twisting. The number of twists is twice the number of twists in the length of the nylon dty yarn sample.

Twist influences the strength, rigidity, elasticity, and shrinkage of nylon dty yarns. As the nylon dty yarn's twist increases, its strength increases, but the twist cannot exceed a certain value, otherwise its strength will decrease. This value is called the critical twist of the nylon dty yarn. The critical twist varies from nylon dty yarn to nylon dty yarn. Generally, under the premise of meeting the strength requirements, the smaller the twist of nylon dty yarn, the better, because the increase of twist will make the nylon dty yarn feel hard, elasticity decreases, shrinkage increases, which is also the reason why filament nylon dty yarn generally does not twist or add less twist.

In addition, twist has an effect on the volume weight and diameter of the polyester dty yarn,  and twisting increases the tightness of the polyester dty yarn.  Within a certain range, the volume weight of the polyester dty yarn increases with the increase of twist, and the diameter of the polyester dty yarn decreases with the increase of twist, so that the covering and comfort of the fabric change.

The twist of the polyester dty yarn should be selected according to the use of the fabric.
The warp needs to have a higher strength, the twist should be larger;

Weft polyester dty yarn and knitting polyester dty yarn should be soft, twist should be small;
The twist of polyester dty yarn used for knitting and pile fabric should be small to facilitate pile;

Thin and cool crepe fabric, required to have smooth, straight, cool characteristics, polyester dty yarn twist should be larger.

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