In the production process of spandex knitted fabrics, spandex content is a key indicator for calculating fabric cost. Generally, during the analysis of weft knitted fabrics, sometimes elastic fabrics are encountered, so it is necessary to analyze and calculate the process parameters of elastic (spandex) fabrics. On the premise of not affecting the weight, width and normal weaving of the finished product, the spandex content should be reduced as much as possible to achieve the purpose of reducing costs.
Calculate spandex content based on door width and weight
If the customer only provides 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 fabric is 1600mm and the weight is 210g/㎡. Then the calculation method is as follows:
1. Calculate the fabric width
①Select the linear density of raw materials: According to our many years of practical production experience, 210g/㎡ spandex jersey needs to be interwoven with 18tex (32s) cotton yarn and 33.3tex (30D) spandex bare yarn, and the transverse density of the fabric is 41 eyes/25.4mm. reached.
②Select equipment technical parameters: According to the door width required by the customer: 1600mm, you need to select 762mm (30″) barrel diameter, and the machine number is 28 needles/25.4
③Calculate door width (W): W=total number of needles÷transverse density*2.54=2620÷41*2.54=162.3 cm
2. Calculate spandex content:
First, 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. Based on years of production experience, when the cotton yarn length in the finished spandex jersey is 14.5cm/50 needles, the fabric’s feel, elasticity and style 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%）＝15cm/50 needles
In the formula: L – the length of the cotton yarn loop of the blank fabric, unit: cm/50 needles;
Lm – the length of the cotton yarn loop of the finished fabric, unit: cm/50 needles;
B——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 was debugged, but the yarn feeding tension needs to be controlled at 3 to 4g, and the spandex yarn feeding tension is 5 to 7g, which is more suitable. After debugging the circular knitting machine, cut a piece of cloth and measure the coil length of the bare spandex wire, assuming it is 8.4cm/100 stitches. Then calculate the raw material ratio to get the content of spandex filament.
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——The linear density of the cotton yarn, unit : Tex; W′——weight of cotton yarn with 100 needles, unit: g (gram).
W〞=tex*L′ *10-5=3.33*8.4*10-5=0.00028 g In the formula: L＇——Spandex yarn coil length unit: cm/100 needles; tex——Linear density of spandex yarn, unit :Tex; W〞——The weight of spandex yarn with 100 needles, unit: g (gram).
The spandex yarn content in spandex jersey is: W〞0.00028 K= * 100%=4.92%
W′+ W〞=0.0054+0.00028 Where: K——The content of spandex filament in the fabric, unit: %.
Calculate the spandex content based on the sample
Analyze the sample (customer sample) provided by the customer. The sample is spandex jersey and the raw material is 167tex/144F.
(150D/144F) polyester DTY (low stretch yarn), the finished coil length is 31cm/100 stitches, the weight is 250g/㎡, and the transverse density is 40 mesh/25.4mm.
Based on experience, a single-sided circular knitting machine with a barrel diameter of 762 mm (30″), a machine number of 28 needles/25.4mm (28G), a total number of needles of 2620, and a pass number of 90F is selected for production.
Spandex fabrics with a weight of 250 g/㎡ generally use 44.4tex (40D) spandex bare yarn, with a spandex content of ≤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 == 158.5cm
2. Coil length of polyester DTY: La= Lb*(1+Y)=31*(1+7.25%)=33.25 cm/100 needles: La——Blank polyester coil length, unit: cm/100 needles; Lb——Blank polyester coil length, unit: cm/100 needles; 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——The weight of 100-needle polyester DTY, unit: g; Tex——The linear density of polyester RTY, unit: Tex Si; La – the coil length of the blank polyester RTY, unit: cm/100 needles.
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 cm/100 needles
In the formula: Lˊ – the length of the spandex yarn coil, unit: cm/100 needles; tex – the linear density of the spandex yarn, unit: tex;
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