ARTICLES ON TEXTILE FIBER, YARN, FABRIC, DYEING AND GARMENTS PRODUCTION: March 2013

Thursday, March 14, 2013

Crimp based on warp and weft yarn on fabric

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CRIMP
When warp and weft yarns are interlaced in a fabric they follow a WAVE or CORRUGATED configuration, the plane of the weave being substantially perpendicular to that of the fabric. This WAVINESS OF YARN is called CRIMP of yarn and is expressed quantitatively either as a fraction, c or as a percentage, c per cent:

c = (Ly - Lf)/Lf; and, c per cent = (Ly – Lf) x 100/Lf

Where Ly = the un crimped length of the yarn, and, Lf = its extent in the fabric.

The expression c = (Ly – Lf) / Lf may be written as:

c = Ly / (Lf - 1), from which

(1 + c) = Ly / Lf;

where (1 + c) is called the crimp ratio. It is useful in fabric calculations.

MATH: Calculate the length of warp required to weave 160 yds. of cloth if the warp crimp is 12 percent.

We know,
Lf = 160 yd. and c1 percent = 12; so c1 = 0.12, where c1 is fractional warp crimp, and

Ly = Lf (1 + c) = 160 x 1.12 = 179.2 yd.

So, to prepare 160 yds of fabric 179.2 yds of warp is required.

MATH: What length of cloth can be woven from 800 yds of warp if the crimp is 8 percent?

We know
Ly = 800 Yd., and c1 percent = 8, so c1 = 0.08; where c1 is fractional warp crimp, and

Lf =Ly/(1+c) = 800/1.08 = 740.8 yds.

So, 800 yds. of warp will weave 740.8 yd of cloth.

When the shuttle inserts the weft in the open shed, the weft is un crimped, and each pick has a length Ly, which is equal to the width occupied by the warp in the reed. This is called the reed width. When it is beaten up by the reed and incorporated into the cloth at the cloth fell, the weft attempts to crimp under the scissors-like pressure exerted by the warp threads. At this stage, it is prevented from crimping freely by the temples, whose function is to hold out the cloth near the fell to reed width, so as to prevent excessive abrasion of the warp threads near each selvedge by the reed. As the cloth moves forward towards the breast beam, it leaves the temples and is free to contract to a length Lf, called loom-state width. The weft is now crimped. We have three variables, i) reed width, ii) the width of the loom-state cloth, and iii) the weft crimp in the loom-state cloth. If we know two of these variables, the third can be calculated as illustrated by the following examples.

MATH: Calculate the reed width required to give a cloth with a loom-state width of 38”, if the weft crimp in the loom-state cloth is known to be 6 percent.

We know
Lf = 38”, and c2 percent = 6; so c2 = 0.06, where c2 weft crimp, and

Ly = Lf (1 + c) = 38 x 1.06 = 40.28”

which is the required reed width.

MATH: Calculate the loom-state cloth width if the reed width is 60”, and the weft crimp is known to be 9 percent.

We know

Ly = 60” and c2 percent = 9; so c2 = 0.09, where c2 is weft crimp, and

Lf = Ly/ (1+c) = 60/1.09 = 55.05”

which is loom-state cloth width.

MATH: Calculate the weft crimp in the loom-state cloth if the reed width is 44” and the loom-state cloth width is 40”.

We know

Ly = 44”, and Lf = 40”.

Therefore (1+c) = Ly/Lf = 44/40 = 1.10, so c2 = 0.10 and c2 percent = 10

which is the weft crimp.

In any of the above examples we could substitute the width of the finished cloth for that of the loom-state cloth, provided that we also substitute the weft crimp in the finished cloth for that of the in the loom-state cloth. The calculation would be valid, if no unrecoverable shrinkage had occurred during finishing, but not, for example for a milled woolen cloth.

EFFECT OF CRIMP OF YARN ON FABRIC PROPERTIES
a) RESISTANCE TO ABRASION: With the increase of crimp %, the abrasion resistance will also increase
b) SHRINKAGE: With the increase of crimp %, shrinkage of fabric will decrease.
c) FABRIC BEHAVIOUR DURING TENSILETESTING: With the increase of crimp%, breaking load of fabric will also increase.
d) FABRIC COSTING: With the increase of crimp%, fabric costing will also increase. Because crimp decrease the length of yarn as a result more yarn will be needed for fabric manufacture in case of more crimp on yarn.
e) FAULTS IN FABRIC: If there is variation of crimp in the threads then the following faults may be found in fabric; A) Reduction in strength may occur, and B) Stripes will be seen in yarn dyed cotton fabric.
f) FABRIC DESIGN: To achieve satisfactory appearance and required shape in finished fabric control of crimp in warp and weft yarn is necessary..
g) FABRIC STIFFNESS: If crimp is increased then stiffness of fabric will decrease.
h) ABSORBENCY: With the increase of crimp % absorbency of the fabric will increase.
i) DIMENSIONAL STABILITY: Dimensional stability will decrease with the increase of crimp%.
j) FABRIC HANDLE: If crimp is increased then the fabric will be soft in handle.
k) DYE TAKE-UP: With the increase of crimp the take-up percentage of dye-uptake will also increase.

Wish You Good Luck..................................
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Cover Factor of Fibre, Yarn and Fabric

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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,

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]

But 1/p = n, where n = threads/in., so

d / p= n/(28√N) ……………………………… (6)

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

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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Friday, March 1, 2013

SEWING THREAD

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Sewing threads have to make with the properties by which it can be possible to sewn garments smoothly. It has to be designed for smooth & efficient stitching. It should contain the properties for these it will not break in the time of sewing & after complete the sewing as well as up to buyer use. The composition & the construction have to manufacture as required for the efficient smooth stitching to the proper selection of fabric, based on the seam type.

CONSTRUCTION OF THREAD

Sewing threads are made of cotton, linen, silk, rayon, or polyester or blends thereof. The properties of the fiber determine its use and application. For example, cotton is the most widely used because of its high versatility and low cost; rayon, which is much weaker, is used primarily for fancy stitch work; polyester is used where strength and water repellency are more important.

All sewing threads are made of ply yarns. The single yarns, which may be spun, filament, or multi-component are highly twisted (plied) to form a firmer and more uniform thread than ordinary yarn. Sewing thread may be given special finishes, such as mercerizing, glace or water repellency or swelling to serve particular uses.

THREAD SIZES

The size of spun thread had been expressed in terms of its diameter: the higher the number the finer the thread. At one time, thread had been made only from three-ply spun yarns. Therefore, a spun yarn thread of 50 three ply (50/3) had a ticket number of 50, a thread of 60 three ply (60/3) had a ticket number of 60, and so forth.. Subsequently, the number of plies in sewing thread was extended to, two, three, four and six ply. A ticket number of 50 could therefore indicate a 50 two ply (50/2), a 50 three ply (50/3), a 50 four ply (50/4), or a 50 six ply (50/6); but the thickness of the thread in each case was the same, while each ply was thinner. The greater number of ply yarns implied greater thread strength. The size of mercerized cotton sewing thread were identified by letter as well as number. The range was found from F (coarsest) to A (medium) and then from 0 to 00000 (finest).

Identification of thread size, called ticket number, is undergoing a transition. Different kinds of yarns had different numbering designations. The Thread Institute adopted a standardized ticket numbering system based on the tex system of numbering yarn.

The tex system is intended to give an orderliness by providing one ticket numbering system based upon metric system which is now universally accepted. Since tex is the weight in grams of a 1000-meter length and is a direct numbering system, the greater the weight the thicker the thread and therefore higher the number. Ticket numbers are based on actual tex size of the thread in the griege state, i.e. twisted, braided, or extruded before any dyeing, special processing, or finishing. The purpose of the stipulation is intended to obviate the alteration of the thread’s apparent size by any finish.

STANDARD SEWING THREAD TEX TICKET NUMBER

1 10      35    105    300
2    12    40    120    350
3    14      45    135      380
4    16    50    150    400
5    18    60    180    450
6    21      70    210    500
7    24    80    240    Above 500, in
8    27      90    270   increment of 100
9    30

One important caution should be noted when using the tex ticket numbers. When selecting proper thread size, threads of the same fiber and type must be compared. Since the tex ticket numbering system is based on weight and since different kinds of fibers and/or types have different weights and moisture, the same tex number of threads of different fibers or types will not necessarily be of the same thickness and may therefore not be interchangeable.

THREAD SELECTION

Selection of the appropriate kind and size of sewing thread is important. The thread should be as fine as possible, consistent with the nature of the fabric and the strength requirements of the stitching. Finer threads could be less obvious, they become hidden below the surface of the cloth, and they are less subject to abrasion than heavier threads. Also, finer threads require finer needles which cause less fabric distortion than heavier needles. Threads composed of the same kind of fibre as that of the fabric is also important because of such factors as general appearance, color fastness, finish retention, elasticity and strength.

Wish You Good Luck..................................
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