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Spandex is the abbreviation of polyurethane fiber, which is a kind of elastic fiber. Spandex is generally composed of multiple filaments, generally 10d / fiber. At present, there are 15d / fiber, even 20d / fiber. The fewer the number of theoretical fibers is, the better the evenness of the fiber is. The less the chance of overlapping morphology is, the DMAC solution produced by dry spinning is harmful to human liver. Generally, the content of 10d / fiber is controlled by 0.5mg/kg, and that of 15d / fiber is 0.7mg/kg, exceeding the standard. In the production of spandex, special attention should be paid to the coiling tension, number of tubes, breaking strength, breaking elongation, formability, oil adhesion, elastic recovery rate, etc. these problems directly affect the knitting, especially in the production of single-sided knitting fabric.

Calculation and analysis of technological parameters of Spandex Knitted Fabric

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

Calculation of spandex content based on door width and weight

If customers only provide the width (width, sealing degree, cloth sealing) and weight (weight per unit area) of finished spandex fabric, they need to select raw materials according to experience and calculate the content of spandex at the same time. In the process of equipment debugging, 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 jersey is 1600mm, and the weight is 210g / ㎡. Then the calculation method is as follows:

1 calculate fabric door width

① selection of raw material line density: according to many years of practical production experience, 210g / ㎡ spandex sweat fabric needs to be interwoven with 18tex (32S) cotton yarn and 33.3tex (30d) spandex naked yarn, and the transverse density of the fabric is 41 eyes / 25.4mm, which can be achieved.

② select the technical parameters of the equipment: according to the door width of 1600mm required by the customer, 762mm (30 ″) cylinder diameter shall be selected, and the machine number is 28 stitches / 25.4

③ calculated door width (W): w = total number of stitches ÷ transverse density * 2.54 = 2620 ÷ 41 * 2.54 = 162.3cm

2. Calculate spandex content:

First of all, we need to calculate the coil length of raw materials (called "thread length" in the factory), which generally refers to the yarn length of 50 or 100 coils. According to many years of production experience, when the length of cotton yarn in the finished spandex jersey is 14.5cm/50 stitches, the handle, elasticity and style of the fabric are suitable. In addition, the shrinkage rate of cotton yarn is about 3% - 4%. According to the above data, the coil length of the blank spandex fabric is calculated as follows:

l = LM * (1 + b) = 14.5 * (13.5%) = 15cm / 50 stitches

Where: l -- length of cotton yarn coil of rough cloth, unit: cm / 50 stitches;

LM -- length of cotton yarn coil of finished cloth, unit: cm / 50 stitches;

B -- cotton yarn dyeing qualitative shrinkage, unit:%.

According to the length of the cotton yarn coil of the rough cloth, the large round machine has been debugged, but the feeding tension should be controlled at 3-4g, and the feeding tension of spandex should be 5-7g. After the big round machine is debugged, cut a piece of cloth, and measure the coil length of spandex naked wire, assuming it is 8.4cm/100 stitches. Then the ratio of raw materials is calculated to get the content of spandex.

W ′ = tex * L * 10-5 = 18 * 30 * 10-5 = 0.0054g, where: L - length of cotton yarn coil of rough cloth, unit: cm / 100 stitches; tex - linear density of cotton yarn, unit: tex; w ′ - weight of cotton yarn of 100 stitches, unit: G (G).

W ＂ = tex * l ′ * 10-5 = 3.33 * 8.4 * 10-5 = 0.00028g, where: l '- spandex coil length unit: cm / 100 stitches; tex - density of spandex yarn unit: tex; w ＂ - weight of 100 stitches spandex yarn unit: G (g).

The content of spandex in spandex jersey is: W "0.00028 k = * 100% = 4.92%

Where w ′ w ＂ = 0.0054 0.00028, K is the content of spandex in the fabric, unit:%.

Calculation of spandex content based on samples

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 elastic yarn), the length of the finished coil is 31cm / 100 stitches, the weight is 250G / m2, and the transverse density is 40 eyes / 25.4mm.

According to experience, 762 mm (30 ″) cylinder diameter, 28 stitches / 25.4mm (28g), 2620 stitches in total and 90F single-sided circular machine are selected for production.

For spandex fabric with a weight of 250G / m2, 44.4tex (40d) spandex naked silk is generally selected, and its spandex content is ≤ 6%.

The following is calculated according to the content of spandex ≤ 6% and the dyeing shrinkage rate of polyester DTY is 7.25%.

1. Door pair: door pair = total number of stitches ÷ transverse density * 2.54 = 2620 ÷ 42 * 2.54 = = 158.5cm

2. Coil length of polyester DTY: La = LB * (1 y) = 31 * (17.25%) = 33.25 cm / 100 needle type: La - coil length of roughcast polyester, unit: cm / 100 needle; LB - coil length of roughcast polyester, unit: cm / 100 needle; 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 needle.

WB = wa ÷ (1-k) = 0.0555 ÷ (1-6%) = 0.00591 g, where: K - content of spandex in 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 needle; tex - linear density of spandex, unit: tex;