What is Twist?
Twist is defined as the spiral turns given to yarn to hold the fibers or yarns together. Twist gives coherence and strength to yarn.
Twist Direction:
There are two possibilities of twist directions, left and right. The fiber windings can also have two directions. Twist direction is indicated as Z- or S-twist depending on the transverse orientation of the fibers, i.e., the orientation relative to the diagonals of the letters Z and S. Z-twist is normally used in short staple spinning, though in some cases yarns with S-twist are also produced.
S-Twist: A single yarn is said to be “S” twist when it is held in the vertical position, the fibers inclined to the yarn axis conform in direction of slope to the central position of the letter S.
Z-Twist: A single yarn is said to be “Z” twist when it is held in the vertical position, the fibers inclined to the yarn axis conform in direction of slope to the central position of the letter Z.
Classification of Twist Amount:
Zero Twist: In this case yarn is given “0” TPI (Twist per Inch). This only exist in raw reeled silk yarn (filament) where silk gum can hold the filaments together.
Very Low Twist: In this case yarn is given 3-5 TPI (1-2 Twist per Centimeter).
Napping Twist: In this case yarn has 6-8 TPI, Napping twist in spun yarns produces lofty yarns.
Medium Twist: In this case yarn has 20-25 TPI (8-10 Twist per Centimeter), this twist is used in most of the spun yarns.
Voile Twist (Hard Twist): In this case yarn has 30-40 TPI (12-17 Twist per Centimeter).
Crepe Twist: In this case yarn has 40-75 TPI (17-30 Twist per Centimeter). This the highest twist of all.
Twist Effects on Yarn and Fabric Properties:
Handle:
With increase in yarn twist level, feel become more harder which is due to the compactness of yarn.
With increase in twist yarn diameter decreases and its covering power is reduced.
Fabric made of high twist yarn will be harder and thinner.
Fabric made of low twist yarn will have soft feel and at the same time it results in pilling and low abrasion resistance of fabric.
Moisture absorption:
Fabric made of high twist yarns results low moisture absorption.
Fabric made of low twist yarns results high moisture absorption.
Wearing Properties:
Fabric made of high twist yarns results in high wearing properties i.e., abrasion & pilling. As the twist increases fibers bond tightly and it can’t be pulled easily out of the yarn. Which also helps to prevent pilling.
Aesthetic effects:
The level of twist in yarn alters its appearance both by changing the thickness and light reflection property.
Different patterns can be produced in a fabric by using similar yarns but with different twist levels, a shadow stripe can be produced in weaving by using alternate S&Z twisted yarns.
Level of twist can also be used to enhance or subdue a twill effect: a S-twist fabric produced by weaving S-twist yarns will enhance S-twist effect. Similarly in case of Z-twill.
Faults:
Level of twist can change yarn diameter and some other properties like absorption, same yarn can change the appearance of a fabric, which may lead to some complications.
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