Fabric Parameters

Woven fabric parameters

There are four basic parameters that are essential for every woven fabric.

1. Ends per Inch and Picks per inch (EPI and PPI).
2. Yarn count
3. Crimp
4. Weave or Fabric Structure or Design

1. Ends per Inch or Picks per Inch

It is a measure of thread density. The normal method used to determine thread density is to use a pick glass.

2. Yarn count

EPI and PPI affects the compactness of the fabric. It is also known as thread count or cloth count. Thread counts range from as low as 20 threads per inch as used in tobacco cloth to as high as 350 threads per inch, found in type writer ribbon fabrics. Normally EPI and PPI of a fabric are described as EPI×PPI. Thus a fabric of 74×66 means 74 EPI×66 PPI.

Balanced constriction

A fabric is said to be well balanced if the number of warp yarns and weft yarns per inch are almost equal.

3.Crimp

Crimp refers to the amount of bending that is done by thread as it interlaces with the threads that are lying in the opposite direction of the fabric. Crimp is defined as the ratio of difference of length of yarn (Ly) taken from length of fabric (Lf) to the length of fabric (Lf).

Crimp = (Ly-Lf)/Lf

Often it is more convenient and preferable to use percentage values. Thus we can define crimp percentage as:

Crimp% = (Ly-Lf)/Lf

A crimp will normally give values ranging from 0.01 to 0.14 ie. (1% to 14%).

Crimp is related to many aspects of the fabric. It affects the cover, thickness, softness and hand of the fabric. When it is not balanced it also affects the wear behaviour and balance of the fabric, because the exposed portions tend to wear at a more rapid rate than the fabric. The crimp balance is affected by the tensions in the fabric during and after weaving. If the weft is kept at low tension while the tension in warp directions is high, then there will be considerable crimp in the weft and very little in the warp.

4. Weave

It refers to the arrangement of warp and weft in the fabric.

OTHER FABRIC PROPERTIES

1. Fabric weight (W)

It is the weight of the yarn per square meter in the woven fabric, which is the sum of the weight of the warp (W1) and weight of the weft (W2).

Weight of the warp is calculated as (per square m):

W1= [n1 x 100 (1+c1%)/100] x [N1/1000] g

Where
n1 = Ends per cm
N1 = Warp count in Tex

C1% = Warp crimp percentage.

Similarly weight of the weft is calculated as (per square m)

W2= [n2 x 100 (1+c2%)/100] x [N2/1000] g

Total weight per square meter = W1+W2

weight/piece = (W1+W2) × piece length × piece width in gram.

Example

A fabric 120m long, 1.3 m wide and having 30 ends per cm of 12 tex warp and 24 picks per cm of 15 tex weft. The warp and weft crimp percentages are five percent and eight percent respectively. We describe these fabric particulars as
30×24; 12 tex × 15 tex; 5%×8%

Warp weight per square m = [30 x 100 x (1+5)/100] x [12/1000] = 37.8 gms

Weft weight/square m = [24 x 100 x (1+8)/100] x [15/1000] = 38.8 gms

Piece weight

= total weight per m × piece length × piece width
= 76.68 × 120× 1.3
= 11962.08 gm or 11.96 kg.

2. Cover factor

(K) it is defined as the area covered by the yarn when compared with the total area covered by the fabric.
The warp cover factor can be found by using the formula.
k1= n1 x sqrt(N1)/10
Where
n1 = Ends/cm
N1 = Count of warp in tex

Similarly the weft cover factor can be found by the formula

k2 = n2 x sqrt(N2) /10

So the total cover factor is
K = K1 + K2

Thus with fabric (30×24; 12 tex×15 tex) the values are

k1= (30 x sqrt12)/10 = 10.39

k2 = (24 x sqrt15)/10 = 9.30

K = K1+K2 = 10.39+9.30 = 19.69

3. Fabric Thickness

For a wide range of fabric, this parameter is not important, but it becomes critical for fabrics that are to be used as belts and felts.