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UNIT Ⅲ Fabric Design
11.1 Fabric Geometry
11.2 Fabric cover and cover factor
It is common to calculate warp cover and weft cover separately:
and the number of weft threads per unit length is determined as
The cover can be calculated in percentage:
In practice, we usually deal with yarn count or linear density. That is why it is advisable to introduce following terms and use them in calculations
(only for cotton yarn, the density of yarns in the fabric is 0.91 g/cm3)
Where T is the yarn linear density in g/km.
Developing the formula of fractional cover, we have:
Where S is the yarn spacing in mm; d, the yarn diameter in mm; P , the density of threads per 10 mm.
In the Tex system the product of threads per cm and the square root of linear density are called the cover factor
Note: there is a distinction between “cover factor” and “cover”. The former is a conventional measure of the closeness of setting of the threads running in one direction. The latter signifies the actual efficiency of the yarns in closing up the cloth. The cover of a cloth may be judged by the appearance of the cloth when held up against the light, and it depends not only on the number of threads per cm and their linear density but also on their regularity, hairiness, fiber composition, twist, and the cloth finishing processes.
Any irregularity in construction, as for example in the uniformity of the spacing of the threads, tends to reduce the lever of cover. “Cover factor” is calculated from only two of these quantities and, therefore, can’t provide a complete indication of “cover”.
Cover factor is, however, useful in making comparisons.
= 0.526 + 0.437-0.526 × 0.437 = 0.733
The spacing relationship of fabric parameters is called fabric geometry. See Fig. as following.
Knowing the fabric geometry, various problems can be solved and explained. Such as:
To build a geometry model:
Assume that the warp and weft threads have constant diameters. On the diagram in Fig. B ,C on the right, the plain weave fabric is shown.
1) Studying the plan of the fabric at A
characterized by the height or amplitude, hy, the length, and the angle of inclination to the central plane, ty
In this case the maximum theoretical density of warp threads
Calculate the warp and weft fractional covers, fabric cover, warp cover factor and weft cover factor.