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CONCEPT OF SIMILAR CLOTH
Fibre or raw materials of the two cloths may be same but they can differ on other factors, such as:-
i) The yarn count may be different.
ii) The ratio of yarn count in warp and weft may differ.
iii) The warp ratio of yarn spacing may differ.
iv) The average of yarn spacing may differ.
v) The weave design may differ.
vi) The amount of twist in yarn may differ.
If there is similarity in COVER FACTOR of two cloths but they differ in such points as mentioned above then they are called similar cloth.
COVER FACTOR
Cover is the degree of evenness of thread spacing. Good cover gives the effect of a uniform plane surface & it can not be obtained with hard twisted yarn. In case of woven fabric cover factor is a number that indicates the extent to which the area of a fabric is covered by warp and weft threads. For any fabric by introducing suitable numerical constants its evaluation can be made in accordance with any system of counting. It is denoted by k.
Mathematically,
But 1/p = n, where n = threads/in., so
d / p= n/(28√N) ………………………………
(6)
GENERAL FORMULA FOR CALCULATING COVER FACTORS
Fibre or raw materials of the two cloths may be same but they can differ on other factors, such as:-
i) The yarn count may be different.
ii) The ratio of yarn count in warp and weft may differ.
iii) The warp ratio of yarn spacing may differ.
iv) The average of yarn spacing may differ.
v) The weave design may differ.
vi) The amount of twist in yarn may differ.
If there is similarity in COVER FACTOR of two cloths but they differ in such points as mentioned above then they are called similar cloth.
COVER FACTOR
Cover is the degree of evenness of thread spacing. Good cover gives the effect of a uniform plane surface & it can not be obtained with hard twisted yarn. In case of woven fabric cover factor is a number that indicates the extent to which the area of a fabric is covered by warp and weft threads. For any fabric by introducing suitable numerical constants its evaluation can be made in accordance with any system of counting. It is denoted by k.
Mathematically,
k = d / p;
where, d1 = Warp dia; d2 = Weft dia; P1
= Warp spacing; P2 = Weft spacing; k1 = Warp cover
factor, and k 2 = Weft cover factor.
So, k1 = d1/P1 &
k2 = d2/P2
Therefore, Fabric Cover Factor = k1 + k2.
The ratio of yarn diameter to
yarn spacing, d/p, is a measure of the relative closeness of the yarns in the
warp or weft of a woven fabric. This ratio also expresses the fraction of the
area of the cloth covered by the warp or weft yarns. We may therefore call it
the fractional cover, i.e.
Fractional cover = d / p.
Substituting Peirce’s estimate
of yarn diameter, d = 1/28 √N,
we have
d / p= [1/(28√N) x1/p]
Now d/p has a value of 1.0 when
the yarns are just touching. Peirce multiplied eq.(6) by 28 to eliminate the
numerical constant, 28, and defined the result as the ‘coverfactor’, K.
Cover Factor,
K = n /
√N ……………………………………………..(7)
Because we have multiplied by 28,
cover factor as defined in eq.(7) has a value of 28 when the yarns are just
touching. The relative yarn spacing corresponding to various cover factors are
shown below:
It is usual to calculate separate
cover factors for the warp and the weft. Using the suffices 1 and 2 for warp
and weft, we have
Warp Cover
Factor, K1 = n1 / √N1
and
Weft Cover
Factor, K2 = n2 / √N2.
The sum of the warp and weft
cover factors is known as cloth cover factor, Kc. It is customary and more informative, however,
to state the warp and weft cover factors separately. Just as twist factor
enables us to compare the relative hardness of twist in yarns of different
counts, so cover factor enables us to compare the relative closeness of
the yarns in different fabrics.
Math related to cover factor
Compare the relative closeness of
the warp yarns in the following two plain cloths; (a) 16s cotton; 50 ends/in;
and (b) 36s cotton; 84 ends/in.
We have the cover factor for
cloth (a), K1 = 50 / √16 = 12.5.
And for cloth (b) cover factor, K2
= 84 / √36 = 14.0
So the ends are more closely
spaced in cloth (b) than in cloth (a)
MATH:- Calculate the warp and
weft cover factors for the following fabric: 60 denier nylon x 48s worsted; 96
x 72.
60 denier = 5315/60 = 88.57s cotton
count.
So, K1
= 96 / √88.57 = 10.2
40s worsted = 48 x 560/840 = 32s cotton
count.
So, K2 = 72 / √32 = 12.7
GENERAL FORMULA FOR CALCULATING COVER FACTORS
Indirect systems direct systems.
K = cn/ √N K = cn √N
K = cn/ √N K = cn √N
Where N is the yarn number in the particular system.
System Value of c System Value of c
Cotton
1.0 Denier 0.01375
Worsted
1.228 Tex 0.04126
Linen lea 1.667 lb/spdl 0.2422
MATH: Calculate the cover factor
corresponding to 80 threads/in. of 100 denier.
From the table constant for the
denier system is 0.01375.
Therefore, K = 0.01375 x 80 x √100 = 11.0
MATH: How many threads/in. of 5 tex nylon are required to give the same cover factor as
90 threads/in. of 2/100s cotton?
Since the equivalent singles
count of 2 /100s is √50 s.
Therefore,
K = 90/ √50.
So, K = 12.7 = 0.04126 x n √5
Therefore
the number of threads required
n=12.7/0.04126 x √5 = 138
threads / in.
Thus required thread/in is 138 of
5 tex to give the same cover factor as 90 threads/in. of 2/100s cotton.
This problem can also be solved
with reference to the formula for calculating cover factor.
5 tex
= 590.5 / 5 = √118 s cotton count.
As before, K = 12.7
= n/ √118.
Therefore n = 12.7 x 118
= 138 as before.
Wish You Good Luck..................................
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