Twist is the measure of the spiral turns given to yarn in order to hold the fibres or threads together. Twist is necessary to give a yarn coherence and strength. Twist is primarily instructed in to a staple yarn in order to hold the constituent fibres together, thus giving strength to the yarn. False twist is used in textured yarns. The effects of the twist are twofold: As the twist increases, the lateral force holding the fibres together is increased so that more of the fibres are contributed to the overall strength of the yarn. As the twist increases, the angle that the fibres make with the yarn axis increases, so preventing them from developing their maximum strength which occurs when they are oriented in the direction of the applied force. As a result, at certain point the yarn strength reaches a maximum value after which the strength is reduced as the twist is increased still further (Fig 1). The twist value required for the maximum strength of yarn is higher than the normal use since increased twist also has an effect on other important yarn properties. A small amount of twist is used in continuous filament yarn to keep the filaments together, but as twist is increased the yarn strength decreases below its maximum value. But because of the variability of the individual filament strengths, the initial effect of twist is to support the weaker filaments in the yarn (Fig 2). A filament yarn will be stronger than the equivalent staple fibre yarn as a comparatively large amount of twist is always needed in a staple yarn. Sometimes intermingling is used instead of twist.
2) Types of twists: 3) Twist effects on yarn and fabric properties: a) Handle: • As the twist level in a yarn is increased it becomes more compact because the fibres are held more tightly together, so giving a harder feel to the yarn. • Because of decrease in the yarn diameter, its covering power is reduced. • A fabric made from a high-twist yarn will therefore feel harder and will also be thinner. • A fabric produced from a low-twist yarn will have a soft handle but at the same time weaker yarn thus resulting in pilling and low abrasion resistance of fabric. b) Moisture absorption: • High twist holds the fibres tight thus restricting water to enter • Such a high twist yarn is used where a high degree of water repellency is required, e.g. in gabardine fabric. • Low twist yarn is used where absorbency is required. c) Wearing properties: • With an increase in twist level wearing properties (abrasion & pilling) are improved. • High level of twist helps to resist abrasion as the fibres can’t easily pulled out of the yarn. • The same effect also helps to prevent pilling (which result from the entanglement of protruding fibres) d) Aesthetic effects: • The level of twist in yarn alters its appearance both by changing the thickness and lightreflecting properties. • Diff. patterns can be produced in a fabric by using similar yarns but with different twist levels; a shadow stripe can be produced by weaving alternate bands of S & Z twist yarns. • Level of twist can also be used to enhance or subdue a twill effect: a Z-twill fabric produced by weaving Z-twist yarns will have enhanced Z-twill effect. Same is the case for S-twill. e) Faults: • Because of level of twist in a yarn can change its diameter and other properties such as absorption; same yarn can change the appearance of a fabric, so giving rise to complaints. Twist Applications: Georgette is made of highly twisted yarn (upto 1000 TPM) by weaving S and Z twisted yarns alternately both in warp and weft direction. email@example.com
Abu Bakkar Marwat (05-NTU-05)
Chifforn is made in the same way but yarn is more twisted (upto 2000 TPM) and finer than that used in georgette-Cupramonium rayon is used. Herringbone is made by using yarns of different types and levels of twists. Plus…….
4) Level of Twist:
Twist is usually expressed as the...