Yarn product twist

The twist of a yarn refers to the number of twists per unit length. The twist has twist direction, there are 'S' twist and 'Z' twist. The twist generally refers to the number of twists/m. The counts of the wool yarn and the yarn are different, and the twists are different. In order to facilitate the comparison of the twists of the different yarns and yarns, they are commonly used.' The concept of 'twist coefficient'. The choice of 'twist coefficient' is generally that pure wool is larger than blended yarn, blended yarn is larger than chemical fiber yarn, short wool content is higher than short wool content, and yarn count is finer than thick yarn.

Yarn twist test

1 Overview

Short fibers need to be twisted in order to be spun into yarns, and filaments need to be twisted in order to facilitate processing or improve tightness. The twist has a direct impact on the structure of the yarn, the physical properties, the style of the fabric and the wearability of the finished garment. It is an assessment The main basis of product grade. The testing methods of yarn twist are: direct counting method, untwisting and twisting method. Among them, untwisting and twisting methods are divided into: untwisting and twisting A method, untwisting and twisting B method, and three-time untwisting and twisting method. The direct counting method is suitable for short fiber single yarns, twisted multifilaments, strands, and cables; the untwisting and twisting method is suitable for single yarns of cotton, wool, silk, hemp and their blended fibers.

2 Purpose and requirements

Through the yarn twist test, understand the basic structure and working principle of the yarn twist meter, master the operation method and sampling requirements of the instrument, and understand the meaning of various indicators.

3 Adopt standards

⒊1 Adopting standards: GB/T 2543.1, ISO 2061 'Determination of textile yarn twist Part 1: Direct counting method', GB/T 2543.2, ISO/DIS 17202 'Determination of textile yarn twist Part 2: Untwisting Twist Method', GB/T 14345 'Test Method for Twist of Synthetic Fiber Filament'.

⒊2 Relevant standards: FZ/T 10001 'Determination of Airflow Yarn Twist, Untwisting and Twisting Method' and other method standards and the product standards covered by it, GB 6529 'Standard atmosphere for humidity control and testing of textiles', related foreign ASTM D 1422 , D 1423, AS 2001.1.2.14, BS 2085, JIS L 1095, CAN/CGSB-4.2N0.8, BISFA and other standards. 4 Instruments and utensils

⒋1 Y331LN yarn twist tester (as shown in Figure 1).

⒋2 Analysis needle.

5 Principle

⒌1 Direct counting method refers to the method of clamping the two ends of a certain length of sample under the specified tension, rotating one end of the sample, and reducing the twist of the sample until the number of twists is measured when the constituent units of the sample are parallel. The number of twists removed is the number of twists of the yarn sample of that length.

⒌2 The untwisting and twisting method is an indirect method for measuring twist. The untwisting and twisting method A is to clamp the two ends of the tested sample yarn with a known length under a certain tension. After untwisting and reverse twisting, the sample returns to the original length. 50% of the number of turns is the number of twists of the yarn under the length; the untwisting and twisting method B is based on the first sample tested according to the method A, and the second sample is measured according to the first sample 1/4 of the twist number is untwisted, and then twisted to the initial length to avoid measurement errors caused by pre-tension and accidental drafting. The triple untwisting and twisting method is generally applicable to air-jet spinning products. The block diagram of the detection principle is shown in Figure 2.

6 sampling

Samples shall be taken according to the relevant provisions of the product standard or agreement, and those not specified in the product standard or agreement shall be taken according to the provisions of Table 1.

Table 1 Sampling of batch samples

The number of boxes loaded in a batch or at a time

≤3

4~10

11~30

31~74

≥75

Minimum number of boxes drawn at random

1

2

3

4

5

7 Environment and correction

Changes in relative humidity will cause changes in the length of certain material samples, which will have an indirect effect on twist. Therefore, the atmosphere for humidity control and testing should meet the requirements of GB 6529.

8 samples

⒏1 The sample should be taken out from the end or side of the package with the minimum traction force that can be actually achieved. In order to avoid bad yarn sections, the beginning and the end of the package are a few meters long each.

⒏2 If more than 1 sample is sampled from the same package, there must be at least 1m between each sample. If more than 2 samples are sampled from the same package, sampling should be done in groups. There should be no more than 5 samples, with a few meters between each group.

9 Procedures and operations

⒐1 Direct counting method (take strand as an example)

⒐1.1 Turn on the power switch, the display will show information and parameters.

⒐1.2 Speed ??adjustment: In the reset state, press the 'speed' button, the motor drives the right gripper to rotate, the display shows the speed per minute, adjust the speed control button I to rotate at a speed of (1000±200)r/min , Press the 'reset' button to return to the reset state.

⒐1.3 Parameter setting

⒐1.3.1 Set the test interval (after setting, check whether it matches the actual test length)

⒐1.3.1.1 Short fiber single yarn gauge setting

The test gauge should be as long as possible, but should be less than the average length of short fibers in the yarn. Usually, the test gauge is shown in Table 2.

Table 2 Test Gauge of Short Fiber Single Yarn

Test distance (mm)

10 or 25

25 or 50

25 or 50

100 and 250

Material category

Cotton yarn

Combed yarn

Carded yarn

Bast fiber

9.1.3.1.2 Multifilament, strand and cable spacing

When the nominal twist ≥ 1250 twists/m, the gauge is (250 ± 0.5) mm; when the nominal twist is less than 1250 twists/m, the gauge is (500 ± 0.5) mm.

⒐1.3.2 Set the preset number of twists: The number of twists can be set based on the designed twist.

⒐1.3.3 Enter the number of tests, linear density, and test method (direct counting method: F0) according to the test needs.

⒐1.4 Enter the test

⒐1.4.1 Press the test key to enter the test, and press (0.5±0.1) cN/tex to add a tension weight on the tension mechanism of the instrument.

⒐1.4.2 Yarn threading operation: discard a few meters of yarn at the beginning of the sample, press the jaws on the left gripper, and clamp the sample from the left without causing the sample to be stretched and untwisted unexpectedly. The jaws of the holder pass through, lead to the right holder, clamp the left holder, press the right holder jaws to make the yarn enter the positioning groove, and pull the yarn to make the pointer on the left holder match Extend the zero position of the ruler until the zero indicator lights up, then lock the right gripper jaws to clamp the yarn, and finally guide the yarn to the yarn cutter, and gently pull the yarn to cut off the excess yarn.

⒐1.4.3 Press the 'Start' button, the right gripper rotates to start untwisting, and automatically stops when the preset number of twists is reached. Observe the untwisting situation of the sample. If the untwisting is not completed, press '+' or '-' again Key (if the speed is too fast, use the speed control knob Ⅱ to adjust the speed) jog, or rotate the right holder by hand (insert the analysis needle into the sample at the left holder, and move the needle to the right holder) Until completely untwisted. At this time, the display shows the number of twists. After pressing the 'Process' button, the number of completions, twists and twist coefficients will be displayed. Repeat 9.1.4.2~9.1.4.3 for the next test until the end, and press the print button to print the statistical results.

⒐2 Untwisting and twisting method (take single yarn as an example)

⒐2.1 Turn on the power switch, the display will show information and parameters.

⒐2.2 Speed ??adjustment is the same as 9.1.2.

⒐2.3 Preliminary program--determine the limit position of allowable elongation

Set the gauge length (500±1)mm, adjust the pre-tension weight according to the requirement of (0.5±0.1)cN/tex, the tension acts on the specimen clamped by the clamps at both ends, and adjust the specimen length at the same time, Make the pointer point at the zero position. Then the right gripper rotates at a speed of 800r/min or slower to start untwisting until the fibers in the yarn have obvious slippage. At this time, read the elongation value at the moment of breaking. If the yarn is not broken, you should Read the maximum elongation value before re-twisting in the reverse direction, and the result is accurate to 1mm. After performing 5 tests in the above manner, calculate the average value, and finally take 1/4 of the average value as the limit position of allowable elongation.

⒐2.4 Determine the pre-tension

⒐2.4.1 The pre-tension of worsted yarn is determined by the twist coefficient (as shown in Table 3); the pre-tension of other yarns is (0.5±0.1) cN/tex. Under certain circumstances, if the measured twist ratio is If the twist applied by the spinning machine is high or low, it is recommended to do more preliminary tests.

Table 3 The relationship between worsted yarn twist coefficient and pre-tension

Twist coefficient

<80

80~150

>150

Pre-tension (cN/tex)

0.1±0.02

0.25±0.05

0.5±0.05

9.2.4.2 The pretension of synthetic fiber filaments is shown in Table 4.

Table 4 Pre-tension of synthetic filament

Filament varieties

Traction wire

Textured wire

High elastic textured yarn

Pre-tension (cN/tex)

0.050±0.005

0.10±0.01

0.20±0.02

9.2.5 Parameter setting

⒐2.5.1 Set the gauge length to (500±1)mm, and check whether it matches the actual test length.

⒐2.5.2 Input the test times, linear density, test method (untwisting and twisting A method: F1; untwisting and twisting B method: F2) and twist direction according to the test needs.

⒐2.5.3 Determine the elongation limit according to 9.2.3, and apply yarn tension weight according to 9.2.4.

⒐2.6 Yarn threading operation: same as 9.1.4.2.

⒐2.7 Start testing

⒐2.7.1 Method A-One-shot method

Press the 'Start' button, the right gripper rotates to start untwisting, and after untwisting stops, reverse twisting until the pointer of the left gripper returns to the zero position, the instrument stops automatically, the zero indicator lights up, and the instrument displays the number of completions, Number of twists/m, number of twists/10cm, twist coefficient. Repeat the above operation until the set number of times is reached. Press the 'Print' button to print the statistical value.

⒐2.7.2 Method B-Quadratic Method

Take 1/4 of the designed twist of the sample, or 1/4 of the number of twists measured by Method A as the basis to set the number of twists. Do not reset the counter to zero after executing all the procedures in Method A. Take the second sample and fix it between the grippers according to the above requirements, press the 'start' button, the right gripper rotates to start untwisting, when the number of twists set above is retracted, the motor reverses twisting When the zero indicator light is on, the motor automatically stops, and displays the number of completions, the number of twists/m, the number of twists/10cm, and the twist coefficient. Repeat the above double sample operation until the set number of times is reached to complete the test. Press the 'Print' button to print the statistical value.

⒐3 Three times untwisting and twisting method

Parameter setting and operation are the same as method A. (Difference: setting method F3, untwist and twist a yarn three times).

10 Result calculation

⒑1 Calculation formula of sample twist:

(27-1)

In the formula:-sample twist, twist/m;

-The initial length of the sample, mm;

-The number of twists of the sample.

⒑2 The formula for calculating the average twist of the sample:

(27-2)

In the formula:-the average twist of the sample;

-The sum of twists of all samples;

-Number of samples.

⒑3 Twist coefficient calculation formula:

(27-3)

In the formula:-twist coefficient;

-Twist, twist/m;

-Yarn linear density, tex.

11 Test report

⒒1 Record: Test parameters such as instrument model, gauge length, temperature, relative humidity, linear density, etc., sample name, quantity, specification, twist direction, twist coefficient and other list printing.

Figure 27-2 Twisting direction of yarn

11.2 Results: average twist/m, average twist coefficient/m, average twist coefficient/cm, average twist below average/m, average twist coefficient below average/m, times below average, mean square deviation, average unevenness , Coefficient of Variation (CV%), etc. 12 Related knowledge

⒓1 Determine the twist direction of the sample according to the following description: first make the yarn drape, and then determine the inclination direction of the suspended part of the fiber. The middle section of the letter 'S' is the same as the S twist, and the middle section of the letter 'Z' is the Z Twist (shown in Figure 3). 12.2 Fabric sampling

⒓2.1 Warp samples of woven fabrics should be taken from different yarns, because different yarns represent different packages. Weft yarn samples should be randomly obtained from the entire laboratory sample to obtain as representative data as possible; if the sample is obtained from a strip sample with a length of 2m, it can usually be considered to be taken from a different weft yarn tube.

⒓2.2 Multi-feed type weft-knitted fabrics, samples are obtained from the continuous courses of some laboratory samples; single-channel weft-knitted fabrics or those with unknown feeding type are randomly selected from all samples.

⒓2.2 For warp knitted fabrics, in most cases it is impossible to remove the required length of the sample, and the untwisting and twisting method is generally not applicable.

⒓3 The twist coefficient can compare the twisting degree of the same variety of different thickness yarns, that is, the same variety of yarns with the same twist coefficient but different linear densities have the same twist angle. There are three types of special twist coefficient, metric twist coefficient and inch twist coefficient. Their calculation formula is as follows:

Special twisting coefficient (27-4)

Metric twist factor (27-5)

British twist coefficient (27-6)

The three can be converted to each other under the same conditions of the publicly set moisture regain:

(27-7)

(27-8)

(27-9)

Among the above formulas:-various twist coefficients;

- Yarn characteristics;

--Various counts;

--Various twists.