Types of Yarn twist | different types of yarn twist | S twist | Z twist

Types of Yarn twist different types of yarn twist S twist Z twist“S” TWIST: A single yarn has “S” twist if when it is held in the vertical direction, the fibers inclined to theconform in direction of slope of the contact portion of the letter “S”.

axis of the yarn

“Z” TWIST. A single has “Z” twist if when it is held in the vertical direction, the fibers inclined to the yarn axis conform in the direction of the slope to the central portion of the letter “Z”.

DIRECTION OF TWIST:

In the designation of yarns, it is essential to specify the direction of twist. Besides its importance in simplifying the trade, it is of great technical importance in designing fabrics. For example, in a twill fabric, the direction of twist in the yarn is of particular importance in determining the predominance of twill effect. For a  right-handed twill, the best contrasting effect will be obtained when a yarn with Z twist is used; on the other-hand a left-handed twist will produce a fabric having flat appearance.

The direction of twist in a yarn is designated in two ways:-

1)      RIGHT-HANDED TWIST. S twist or clock-wise  and

2)      LEFT-HANDED Twist. Z twist or anticlockwise

Single yarns are generally Z twisted in anticlockwise directions, whereas the S or right-handed twist is very common in ply yarns.

Single warp yarns are generally given Z twist, and the weft or filling yarns S twist. When the warp and weft yarns are interwoven, they generally lie at an angle approximately 90  at the intersection, as shown in Fig. 5.4 (of Goswami). It is clear from figure 5.4a and 5.4b that there is no possibility of the warp and weft yarns bedding  or nesting into each other. However, of the two sets of yarns (warp and weft) have similar twist, that is both Z or both S the fibers at the point of yarn contact be more or less parallel and will induce nesting of yarns into each other resulting the production of thinner and firmer in hand than when nesting is prevented. The relative direction of twist has very important implications in determining the distinctness of the diagonal lines in a twill fabric. There are three major considerations that has to be taken into account in selecting the direction of twist. They are:-

1)      THE TWIST DIRECTION IN RELATION TO THE TWILL HAND. The diagonal twill effect will be predominant if the yarn twist (warp or weft) opposes the twill direction.

2)      THE RELATIVE DIRECTION OF TWIST IN THE WARP AND WEFT. The use of warp and filling yarns with the direction of fibers opposing each other will result in a distinct twill effect. In other words, both sets of yarn should have the same twist direction.

3)      NESTING OR BEDDING OF YARNS. If nesting is prevented by  using warp and filling yarns twisted in opposite directions, the yarn floats become prominent, thus emphasizing the twill line.

 

DETERMINATION OF TWIST:

There are generally two methods used by the industry for determining the twist in single yarns. These are 1) direct counting method, and 2) Indirect untwist-twist method.     

In the direct counting method, twist can be determined either by I) direct directly counting the number of turns in a unit length under a magnifying glass or by ii) the parallel fiber method in which the specimen is untwisted to zero twist until all the fibers are parallel.

The indirect untwist-twist method is much simpler and easier to perform. It is based on the assumption that when the twist in one direction is removed and retwisted by an equal number of turns in the opposite direction, the initial conditions of length and tension will be achieved. Thus average turn per unit length is obtained.