Calculation and analysis of process parameters of spandex knitted fabrics

In the process of analyzing weft knitted fabrics Sometimes we encounter elastic fabrics, so we need to analyze and calculate the process parameters of elastic (spandex) fabrics.

In the production process of spandex knitted fabrics, spandex content is a key indicator for calculating fabric cost. Generally, the spandex content should be reduced as much as possible without affecting the weight, width and normal weaving of the finished product, so as to reduce costs.

1 Calculate the spandex content based on the width and weight of the finished fabric:

If the customer only provides Regarding the width (width, sealing degree, cloth sealing) and gram weight (weight per unit area) of the finished spandex fabric, it is necessary to select raw materials based on experience and calculate the spandex content. During the equipment debugging process, the amount of spandex must be reduced as much as possible while ensuring the normal operation of the machine.

For example: The customer requires that the width of the finished spandex jersey is 1600㎜ and the weight is 210g/m2. Then the calculation method is:

1. Calculate the fabric width:

(1) Select raw materials Line density:

According to our many years of practical production experience, 210g/m2 spandex jersey needs to be interwoven with 18tex (32s) cotton yarn and 3.33tex (30D) spandex bare yarn. The horizontal density is 41 eyes/25.4㎜, which can be achieved.

(2) Select equipment technical parameters:

According to the door width of 1600㎜ required by the customer, It is necessary to use a single-sided circular knitting machine with a barrel diameter of 762㎜ (30″), a machine number of 28 needles/25.4㎜ (28G), a total number of needles of 2962, and a pass number of 90F.

(3) Calculate door width (W):

W==Total number of needles÷Transverse density*2.54==2620÷41 *2.54==162.3㎝

2. Calculate spandex content:

(1) Coil length Calculation:

First of all, you need to calculate the coil length of the raw material (called “thread length” in the factory), which generally refers to the yarn length of 50 or 100 coils. According to many years According to the production experience, when the cotton yarn length in the finished spandex jersey is 14.5cm/50 needles, the feel, elasticity and style of the fabric are more suitable. In addition, the dyeing and setting shrinkage rate of cotton yarn is about 3% to 4%. .Based on the above data, the method to calculate the loop length of the blank spandex fabric is as follows:

L＝Lm*(1+B)＝14.5*(1＋3.5%)＝15㎝/50 stitches

In the formula: L——The length of the cotton yarn loop of woolen cloth, unit: cm/50 needles;

Lm—— The length of the cotton yarn loop of the finished fabric, unit: ㎝/50 needles;

B——The qualitative shrinkage rate of cotton yarn dyeing, unit: %.

According to the length of the cotton yarn loop of the blank fabric, the circular knitting machine has been debugged, but the yarn feeding tension needs to be controlled at 3 to 4g. The spandex yarn feeding tension is 5 to 7g, which is more suitable. After the circular knitting machine is debugged, cut the For a piece of cloth, measure the coil length of bare spandex yarn, assuming it is 8.4cm/100 needles. Then calculate the raw material ratio to get the content of spandex yarn.

W′=tex *L*10-5=18*30*10-5=0.0054g

In the formula: L——The length of the cotton yarn loop of the blank cloth, unit: cm/100 needles;

tex – linear density of cotton yarn, unit: tex;

W′ – weight of cotton yarn for 100 needles, Unit: g (gram).

W〞=tex*L′*10-5=3.33*8.4*10-5=0.00028 g

In the formula: Lˊ——The length of the spandex yarn coil, unit: ㎝/100 needles;

tex——The linear density of the spandex yarn, unit: Tex ;

W〞——The weight of 100-needle spandex yarn, unit: g (gram).

The spandex yarn content in spandex jersey is:

W〞0.00028

K==——————* 100% =——————* 100%=4.92%

W′+ W〞0.0054+0.00028

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In the formula: K – the spandex fiber content in the fabric, unit: %.

2 Calculate the spandex yarn content based on the sample:

Based on the sample provided by the customer (customer sample) For analysis, the sample is spandex jersey, the raw material is 16.7tex/144F (150D/144F) polyester DTY (low elastic yarn), the finished coil length is 31cm/100 stitches, the weight is 250g/m2, and the transverse density is 40 eyes/ 25.4㎜.

Based on experience, choose a 762㎜ (30″) barrel diameter, a gauge number of 28 needles/25.4㎜ (28G), a total number of needles of 2620, and a 90F path number. A circular knitting machine is used to produce the fabric.

Spandex fabrics with a weight of 250 g/m2 generally use 4.44tex (40D) spandex bare yarn, and its spandex yarn content is ≤6%.

The following calculations are based on the spandex content ≤ 6% and the dyeing shrinkage rate of polyester DTY 7.25%.

1. Door pair:

Door pair = total number of needles ÷ transverse density*2.54==2620÷42*2.54==158.5㎝

2. Coil length of polyester DTY:

La= Lb*(1+Y)=31*(1+7.25 %)=33.25㎝/100 stitches

In the formula: La——The length of the blank polyester coil, unit: ㎝/100 stitches;

Lb——Blank polyester coil length, unit: ㎝/100 stitches;

Y——Polyester DTY dyeing qualitative shrinkage rate, unit: %.

Wa=tex*La*10-5=16.7*333.25*10-5=0.00555 g

In the formula: Wa——100-needle polyester The weight of DTY, unit: g;

Tex – the linear density of polyester RTY, unit: tex;

La ——The coil length of raw polyester RTY, unit: ㎝/100 stitches.

Wb= Wa÷（1—K)=0.0555÷（1—6%)=0.00591 g

In the formula: K – the content of spandex filament in the fabric, unit: %;

Wa——The weight of 100-needle polyester DTY, unit: g.

Lˊ=(Wb—Wa)*10-5/tex=(0.00591—0.00555)*10-5/4.44

=8.0㎝/100 stitches

Where: Lˊ——Spandex yarn coil length, unit: ㎝/100 stitches;

tex——Linear density of spandex yarn, unit: tex;

3 Calculated based on the sample and fixed spandex yarn content:

Sometimes customers will require the spandex content in elastic fabrics, so we need to calculate based on this requirement.

If the customer requires small terry (two-thread sweatshirt, fish scale cloth), the weight is 250g/m2, the transverse density is 20 eyes/12.5㎜; the linear density of the raw material is: face yarn 18tex (32s) Polyester-cotton (65/35)

Blended yarn, loop length 30cm/100 needles; terry yarn 36.44tex (16s) Polyester-cotton (65/35)

Blended yarn, coil length 12cm/100 needles; spandex content 5%, width 165cm.

1. Selection of technical parameters of process equipment:

N=W*PA÷1.25= 165*20÷1.25=2640 pieces

In the formula: N——the total number of needles of the equipment, unit: pieces;

W ——Fabric width, unit: cm;

PA——Fabric transverse density. Unit: eye/25.4㎜.

According to the calculation results, the technical parameters of the process equipment that can be selected are: 762㎜

(30″) barrel diameter, machine The number is 28 needles/25.4㎜ (28G), the total number of needles is about 2640, and the yarn feed number is 90F single-sided circular knitting machine.

2. The coil length of the blank fabric:

The dyeing and setting shrinkage rate of polyester-cotton (65/35) blended yarn is generally about 6%, which can be calculated The loop length of the blank cloth.

Lˊ=LA*(1+Y)=30*(1+6%)=31.8㎝

In the formula: Lˊ——The length of the face yarn loop of the gray fabric, unit: ㎝/100 stitches;

LA——The length of the face yarn loop of the plain gray fabric, Unit: ㎝/100 needles;

Y——Dyeing and setting shrinkage rate of polyester-cotton (65/35) blended yarn, unit: %.

L″=LB*(1+Y)=12*(1+6%)=12.7㎝

Where: L″——blank Length of terry yarn loops of cloth, unit: ㎝/100 needles;

LB——Length of terry yarn loops of plain gray fabric, unit: ㎝/100 needles;

Y——Dyeing and setting shrinkage rate of polyester-cotton (65/35) blended yarn, unit: %.

WN =tex*Lˊ*10-5==18*31.8*10-5=0.0058g

In the formula: WN——The weight of the 100-needle face yarn, unit: g;

Tex – linear density of face yarn, unit: Tex;

WM=tex*L″*10- 5==36.44*12.7*10-5=0.0046g