Cover Factor of Woven Fabric: Theory, Calculation and Example
B.Tech, Dept. of Textile Engineering
Giani Zail Singh Punjab Technical University Campus,
Bathinda, Punjab, India
Cover Factor of Woven Fabric:
The cover factor of woven fabric is defined as the extent of coverage of yarns in the fabric. The maximum cover can be a situation in which the yarns touch closely with the adjustment yarns without air spaces. The cover factor shows how much of the fabric in the direction of warp threads is filled in by the weft threads and vice versa.
Cover factor is a number that indicates the extent to which the area of a fabric is covered by one set of threads. For any woven fabric, there are two cover factors: a warp cover factor and a weft cover factor. Under the cotton system, the cover factor is the ratio of the number of threads per inch to the square root of the cotton yarn count.
Based on cover factors plain fabrics are classified into open set (with cover factors 10–22) and close set (with cover factors 22–35). Needless to mention here that yarn diameter or yarn count is an influencing factor for fractional cover (d/p) cover factor is used to compare relative closeness of different fabrics. Parameter like the type of weave cannot be ignored here as some type of weave like mock leno, matt weave where thread work in groups or threads in the group are drawn in one dent have to influence on the cover.
Best examples for cover factor can be observed from jute gunny bags (of course today PP is used in leno weave for vegetable onions packaging or transportation) as they are made faith different covers and for onion it is fully open, for cotton portation (earlier practice) moderately open, for rice package nearly close and for sugar complete close). But here a mention is made with respect to sweaters of wool. Even though woollen yarns are used, the fabrics are medium covered and warmthness is due to wool and the cover factor is the secondary factor for fabric weaving.
Formula and Calculation of Cover Factor:
Warp cover factor = EPI / V warp count
Weft cover factor = PPI / V weft count
Cloth cover factor = Warp cover factor + Weft cover factor – (Warp cover factor × Weft cover factor / 28)
The above figure shows projected views of two woven cloths of different construction. At A the warp and the weft threads cover the area of the cloth only partially, but at B the cloth area is covered completely with no spaces left between the adjacent warp yarns, and it will be seen that the relative closeness of yarns in a woven cloth is dependent upon the ratio of yarn diameter, d, to yarn spacing, p. This ratio known as relative cover can be defined as the proportion of a projected view of a given area of cloth which is covered by threads, and will have a scale from 0 to 1, although it may also be expressed as percentage cover with a scale from 0 to 100 per cent.
d/p = relative cover,
(d x 100)/p = percentage cover
It is preferable to express warp and weft relative cover separately, as the cumulative value of cloth cover does not indicate the comparative importance of each set of yarns which is essential for the determination of certain cloth characteristics.
From the relationship shown above it will be obvious that if d = p, the value of relative cover is one, and this is regarded as the theoretical maximum cover. In practice, however, this value can be exceeded considerably in any one direction, either through yarn distortion, or, by forcing the threads into different planes, especially if the relative cover of the opposite set of threads is reduced correspondingly.
The relative cover for one thread system can be calculated as follows by considering an area of 100 x 100mm:
Area per thread = 100 x d
Area covered by n threads of one system = n x 100 x d
Therefore, relative cover = (n x 100 x d)/(100 x 100) = (n x d)/100
The cloth represented at A is specified as follows: Warp — 25 tex cotton, 267 ends/100 mm; weft—36 tex cotton, 334 picks/100 mm. Find the relative warp and weft cover. (Subscript 1 refers to warp, subscript 2 to weft.)
Warp relative cover = (n1 x d1)/100
= (267 x √(25)/(26.7))/100
Weft relative cover = (n2 x d2)/100
= (334 x √(36)/(26.7))/100
Cover factor plays an important role in fabric texture and application of specific end use. For example, in the case of window curtains, openness is most important and hence open set constructions are preferred. This condition can be had either from coarse (window curtain) or fine and medium counts (some of the shirting construction with leno weave). Another interesting example is that of sail clothes made in 2/2 matt weave. It is well-known fact that matt weave give open constructions.
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- Thread Count and Thread Density of Different Types of Woven Fabric
- How to Determine Thread Count of Fabric by Beesley Balance
- Comparison of High Thread Count Cotton Fabrics for Comfort and Mechanical Properties
- Count Conversion System for Textile Yarns
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.