Yarn Twist | Twist direction | Types of Twist | Twist Principle

Yarn Twist:
Twist is the spiral arrangement of the fibres around the axis of the yarn. The twist binds the fibres together and also contributes to the strength of the yarn. The amount of twist inserted in a yarn defines the appearance and the strength of the yarn. The number of twists is referred to as turns per inch. 
Yarn twist
There are different definitions given to twist of the yarn. Some of the definitions given are as follows:

Yarn twist is defined as the spiral deposition of the components of a twist is the measure of the spiral turns given to a yarn in order to hold the constituent fibres or threads together – Skinkle.


When a strand is twisted the component fibres tend to take on a spiral formation, the geometric perfection of which depends on their original formation – Morton.


Twist may be defined as the rotation about the yarn axis of any line drawn on the yarn which was originally, before twisting parallel to the yarn axis – Wool Res. Vol. 3.


Twist may also be defined as thread which is usually the result of relative rotation of the two ends.

Twist direction:
 

The direction of the twist at each stage of manufacture is indicated by the use of letters S or Z in accordance with the following convention:

A single yarn has S twist if, when it is held in the vertical position, the fibres inclined to the axis of the yarn conform in the direction of the slope to the central portion of the letter S. Similarly the yarn has Z twist if the fibres inclined to the axis of yarn conform in the direction of slope to the central portion of the letter Z.


The Amount of Twist: In B.S. 946: 1952 it is stated that the amount of twist in a thread at each stage of manufacture is denoted by a figure giving the number of turns of twist per unit length at that stage. It affects the characteristics and properties of a yarn including appearance, behaviour and durability.


The amount of twist is an important factor in finished consumer goods. It determines the appearance as well as the durability and serviceability of a fabric. Fine yarns require more twist than coarser yarns. Warp yarns, which are used for the length wise threads in a woven fabric, are given more twist than filling yarn which is used for cross wise threads. 

The amount of twist also depends upon the type of the fabric to be woven:
  1. Yarns intended for soft surfaced fabric are given slack twist. They are called as soft twisted yarns.
  2. Yarns intended for smooth surfaced fabrics are given optimum twists. Such twisted yarns contribute strength, smoothness and elasticity.
  3. Yarns intended for crepe fabrics are given maximum amount of twists.
Types of Twist
  • S-twist
  • Z-twist
Twist Principle
One end will be fixed and another end will be turned this is the twist principle.

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