Calculation and analysis of process parameters of Spandex Knitted Fabric

In the production process of Spandex Knitted fabric, spandex content is the key index to calculate the fabric cost. Generally, elastic fabrics are sometimes encountered in the analysis of weft knitted fabrics, so it is necessary to analyze and calculate the process parameters of elastic (spandex) fabrics. On the premise of not affecting the gram weight and door width of finished products and normal weaving, the spandex content should be reduced as much as possible, so as to reduce the cost.

Calculate the spandex content according to the door width and gram weight


If the customer only provides the width (width, sealing degree, 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 at the same time. In the process of equipment commissioning, the amount of spandex must be reduced as much as possible on the premise of ensuring the normal operation of the machine.
For example, the customer requires that the door width of the finished spandex sweat cloth is 1600mm and the gram weight is 210g / ㎡. Then the calculation method is as follows:

  1. Calculate fabric door width
    ① Selection of raw material linear density: according to your years of production experience, 210g / ㎡ spandex sweat cloth needs to be interwoven with 18tex (32S) cotton yarn and 33.3tex (30d) spandex bare silk, and the transverse density of the fabric is 41 eyes / 25.4mm.
    ② Selection of equipment technical parameters: according to the door width of 1600mm required by the customer, 762mm (30 ″) cylinder diameter needs to be selected, and the machine number is 28 stitches / 25.4
    ③ Calculated door width (W): w = total stitches ÷ transverse density * 2.54 = 2620 ÷ 41 * 2.54 = 162.3 cm
  2. Calculated spandex content:
    First, we need to calculate the coil length of raw materials (called “wire length” in the factory) )Generally, it refers to the yarn length of 50 or 100 coils. According to many years of production experience, when the cotton yarn in the finished spandex sweat cloth is 14.5cm/50 stitches, the handle, elasticity and style of the fabric are suitable. In addition, the dyeing and setting shrinkage rate of cotton yarn is about 3% ~ 4%. According to the above data, the coil length of blank spandex fabric is calculated as follows: l = LM * (1 + b) = 14.5 * (1 + 3.5%) = 15cm / 50 stitches
    Where: l — cotton yarn coil length of blank cloth, unit: cm / 50 stitches;
    LM — cotton yarn coil length of finished cloth, unit: cm / 50 stitches;
    B — qualitative shrinkage of cotton yarn dyeing, unit:%.
    According to the length of cotton yarn coil of rough cloth, the large round machine is debugged, but the yarn feeding tension needs to be controlled at 3 ~ 4G, and the spandex yarn feeding tension is 5 ~ 7g. After the big round machine is debugged, cut a piece of cloth and measure the coil length of the bare spandex wire, assuming that it is 8.4cm/100 stitches. Then calculate the proportion of raw materials to obtain the content of spandex fiber.
    W ′ = tex * L * 10-5 = 18 * 30 * 10-5 = 0.0054g, where: l — cotton yarn coil length of blank cloth, unit: cm / 100 stitches; Tex — linear density of cotton yarn, unit: tex; W ‘- weight of 100 needles of cotton yarn, unit: G (g).
    W “= tex * l ‘* 10-5 = 3.33 * 8.4 * 10-5 = 0.00028 g, where: l’ – length of spandex coil, unit: cm / 100 stitches; Tex — linear density of spandex filament, unit: tex; W “- weight of 100 stitches of spandex filament, unit: G (g).
    The content of spandex filament in spandex sweat cloth is: W “0.00028 k = * 100% = 4.92%
    W ′ + W ″ = 0.0054 + 0.00028, where: K — the content of spandex in the fabric, unit:%.
    Calculate the spandex content according to the sample
    Analyze the sample (customer sample) provided by the customer. The sample is spandex sweat cloth and the raw material is 167tex / 144f
    (150D / 144f) polyester DTY (low elastic yarn), the finished coil length is 31cm / 100 needles, the gram weight is 250G / ㎡, and the transverse density is 40 eyes / 25.4mm.
    According to experience, the single-sided large round machine with 762 mm (30 ″) barrel diameter, machine number of 28 needles / 25.4mm (28g), total number of needles of 2620 and number of channels of 90F is selected for production.
    Generally, 44.4tex (40d) bare spandex yarn is selected for the spandex fabric with a weight of 250G / m2, and the content of spandex yarn is ≤ 6%.
    The following is calculated according to the spandex content ≤ 6% and the dyeing shrinkage of polyester DTY is 7.25%.
  3. Door pair: door pair = total stitches ÷ transverse density * 2.54 = 2620 ÷ 42 * 2.54 = = 158.5cm
  4. Coil length of polyester DTY: La = LB * (1 + y) = 31 * (1 + 7.25%) = 33.25 cm / 100 needles, where: La – length of blank polyester coil, unit: cm / 100 needles; LB — length of blank polyester coil, unit: cm / 100 stitches; Y — qualitative shrinkage rate of polyester DTY dyeing, unit:%.
    Wa = tex * La * 10-5 = 16.7 * 333.25 * 10-5 = 0.00555 g, where: wa — weight of 100 needle polyester DTY, unit: G; Tex — linear density of polyester rty, unit: tex; La — coil length of rough polyester rty, unit: cm / 100 stitches.
    WB = wa ÷ (1-k) = 0.0555 ÷ (1-6%) = 0.00591 g, where: K – content of spandex filament in the fabric, unit:%; wa – weight of 100 needle polyester DTY, unit: G.
    L ˊ= (WB WA) * 10-5 / tex = (0.00591-0.00555) * 10-5 / 4.44 = 8.0 cm / 100 stitches
    Where: l ˊ—— Length of spandex coil, unit: cm / 100 stitches; Tex — linear density of spandex filament, unit: tex;

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