What is Cloth Cover Factor?
Cover factor is nothing but the numerical value indicating the extent to which the area of a fabric is covered by component yarns. Fabric cover of fabric is denoted by k.
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| Cover Factor Formula |
There are two cover factors for woven fabric:
- Warp cover factor
- Weft cover factor
In cotton system cloth cover in particular direction (warp cover factor or weft cover factor) is calculated by taking the ration of threads per inch and square root of the yarn count (cotton count/English count).
What is concept of Similar Cloths?
Two fabrics may be manufactured using same raw material but they may differ in other parameters like:
- Yarn Count
- Twist in Yarn
- Thread Density (EPI, PPI)
- Weave etc.
When two fabric samples are having same cover factor but they differ in above mentioned points then they are called as similar cloths.
Factional Cover & Derivation of Cover Factor
Fractional cover may be defined as the fraction of the total fabric area that is ‘covered’ by the component yarns.
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| Factional Cover |
Relative closeness of yarns in a woven fabric depends on the ration of yarn diameter (d) & yarn spacing (s). This ratio of yarn diameter (d) to yarn spacing (s) is known as relative cover.
Relative Cover=d/s,
Percentage Cover= (d x 100)/s
In ideal model, ‘S’ will be equal to 1/n, where n is the number of threads per unit length.
The fractional cover could be expressed in terms of d and n, i.e.
Fractional cover = d ×n
With a woven fabric, two values of the fractional cover are necessary, one for warp and one for the weft.
When staple fibre and multifilament yarns are considered, yarns flatten in fabrics and assume non-circular cross-sections. One approach to this problem is to assume that the yarn cross section is still circular and derive a formula for yarn diameter.
Pierce has derived a formula for cotton spun yarn diameter as below:
Using this value of yarn diameter in fractional cover,
Total Cover Factor
Let us consider a simplified version of one-unit cell of a plain weave as shown in below figure.
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| Total Cover Factor |
The unit cell is rectangular ABCD.
The shaded area is the part of the total area covered by both yarns, and, because of this, it would not be strictly accurate to add the warp and weft cover values together and quotes as the total cover.
The shaded areas are each d1 × d2.
And the total area of the cell is S1 × S2
By definition,
Hence,
d1=C1XS1
d2=C2XS2
Now the area of the shaded portion is,
d1×d2=C1C2×S1S2
Expressed as a fraction of the total area S1S2,
The shaded area (d1×d2)becomes,
The term C1 C2 must be deducted from the sum of C1 and C2.
Hence,
Multiplying by 28
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