â–¶ Calculation and analysis of process parameters of spandex knitted fabrics

Calculation and Analysis of Process Parameters of Spandex Knitted Fabric

During the analysis of weft knitted fabrics, sometimes elastic fabrics are encountered, which requires analysis and calculation of the process parameters of elastic (spandex) fabrics.

In the production process of spandex knitted fabrics, spandex content is a key indicator for calculating fabric costs. Generally, under the premise of not affecting the weight of the finished product and the width of the door and the normal weaving, the content of the spandex should be reduced as much as possible to achieve the purpose of reducing the cost.

1 Calculate the spandex content according to the finished door width and weight of the fabric:

If the customer only provides the width (width, seal, cloth seal) and gram weight (weight per unit area) of the finished spandex fabric, it is necessary to select the raw materials according to experience and calculate the spandex content. In the process of equipment commissioning, 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 1600mm and the gram is 210g/m2. Then the calculation method is:

1. Calculate the fabric width:

(1) Select the material line density:

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

(2) Select equipment technical parameters:

According to the customer's request for the width of 1600mm, it is necessary to use 762mm (30′′) cylinder diameter, the machine number is 28 needles/25.4mm (28G), the total number of needles is 2962, and the single-sided circular machine with 90F roads is produced.

(3) Calculate the width (W):

W==total number of stitches÷lateral density*2.54==2620÷41*2.54==162.3cm

2. Calculate the spandex content:

(1) Calculation of coil length:

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

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

Where: L - the length of the cotton yarn loop of the woolen cloth, unit: cm / 50 needles;

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

B——Qualitative retraction rate of cotton yarn dyeing, unit: %.

According to the length of the cotton yarn of the blank fabric, the large circular machine is debugged, but it is necessary to control the yarn tension to 3 to 4 g and the spandex yarn tension to be 5 to 7 g. After the large circular machine is commissioned, cut a piece of cloth and measure the coil length of the spandex bare wire, assuming 8.4 cm/100 stitches. Then, the raw material ratio is calculated to obtain the content of the spandex.

W'=tex*L*10-5=18*30*10-5=0.0054g

Where: L——the length of the cotton yarn loop of the rough cloth, unit: cm/100 needles;

Tex - the linear density of cotton yarn, in units of tex;

W'——100 needle cotton yarn weight, unit: g (gram).

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

Where: Lˊ——the length of the spandex filament coil, unit: cm/100 needles;

Tex - the linear density of spandex, in tex;

W〞——100-pin spandex weight, unit: g (g).

The spandex content in spandex jersey is:

W〞0.00028

K==——————* 100% =——————* 100%=4.92%

W'+ W〞0.0054+0.00028

In the formula: K - the content of spandex in the fabric, unit: %.

2 Calculate the spandex content based on the sample:

According to the sample (customer sample) provided by the customer, the sample is spandex jersey, the raw material is 16.7tex/144F (150D/144F) polyester DTY (low elastic wire), the finished coil length is 31cm/100 needle, the weight is 250 g/m2, lateral density 40 eyes/25.4 mm.

According to experience, the 762mm (30′′) cylinder diameter is selected, the machine number is 28 needles/25.4mm (28G), the total number of needles is 2620, and the single-sided circular machine with 90F roads is produced.

The spandex fabric with a weight of 250 g/m2 is generally made of 4.44 tex (40D) spandex bare wire, and its spandex content is ≤6%.

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

1. Door pair:

Door pair = total number of stitches ÷ lateral density *2.54==2620÷42*2.54==158.5cm

2. Coil length of polyester DTY:

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

Where: La - length of the polyester polyester coil, unit: cm / 100 needles;

Lb——the length of the blank polyester coil, unit: cm/100 needles;

Y——Qualitative retraction rate of polyester DTY dyeing, unit: %.

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

Where: Wa - the weight of 100 needle polyester DTY, unit: g;

Tex - linear density of polyester RTY, in units of Tex;

La - coil length of the blank polyester RTY, unit: cm / 100 needles.

Wb= Wa÷(1—K)=0.0555÷(1—6%)=0.00591 g

Where: K - the content of spandex in the fabric, unit: %;

Wa - Weight of 100-pin polyester DTY, unit: g.

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

=8.0cm/100 pin

Where: Lˊ——the length of the spandex filament coil, unit: cm/100 needles;

Tex - the linear density of spandex, in tex;

3 Calculate according to the sample and the fixed spandex content:

Sometimes customers will ask for the spandex content in the stretch fabric so that we need to calculate it with this requirement.

If the customer requires small terry (two-line sweater, fish scale cloth) weight 250 g / m2, horizontal density is 20 eyes / 12.5mm; raw material line density: face yarn 18tex (32s) polyester cotton (65 / 35)

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

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

1. Selection of technical parameters of process equipment:

N=W*PA÷1.25=165*20÷1.25=2640 pieces

Where: N - the total number of needles in the device, the unit: a piece;

W——fabric door width, unit: cm;

PA - the lateral density of the fabric. Unit: Eye / 25.4mm.

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

(30′′) The diameter of the cylinder is 28 needles / 25.4 mm (28G). The total number of needles is 2,640 pieces, and the single-face circular machine with 90F yarn feeding is produced.

2, the length of the coil of the rough cloth :

The dyeing and setting shrinkage rate of polyester/cotton (65/35) blended yarn is generally about 6%, so that the coil length of the blank fabric can be calculated.

LËŠ=LA*(1+Y)=30*(1+6%)=31.8cm

Where: Lˊ——the length of the face yarn of the rough cloth, unit: cm/100 needles;

LA——the length of the face yarn of the light grey cloth, unit: cm/100 needles;

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

L′′=LB*(1+Y)=12*(1+6%)=12.7cm

Where: L" - the loop length of the loop yarn of the rough cloth, unit: cm / 100 needles;

LB - the loop length of the loop yarn of the light grey fabric, unit: cm / 100 needles;

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

WN=tex*LËŠ*10-5==18*31.8*10-5=0.0058g

Where: WN - the weight of the 100-pin face yarn, unit: g;

Tex - the linear density of the face yarn, in units of Tex;

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

Where: WM - the weight of 100 needle loop yarn, unit: g;

Tex - the linear density of the loop yarn, in units of Tex;

WK=(WN+ WM)/(1—G)—WN—WM=(0.0058+0.0046)/(1-5%)—0.0058—0.0046=0.00055g

Where: WK - the weight of 100 needle spandex, unit: g;

G——the content of spandex, unit: special %;

Then we calculate the coil length of the spandex:

GA= WK÷Tex*105=0.00055÷4.44*105=12.36cm/100 needle

In the formula: WA——the length of the coil of spandex yarn, unit: cm/100 needle

Tex - the linear density of spandex, in tex.