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”.“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”.
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.
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.
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