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With over 19 years of experience in the yarn and textile industry.

Advantages of Yarn Products

by:Chengyi     2021-04-09

The tensile strength of the yarn is called strength. It is expressed by the load of the broken yarn, and the length of the stretched yarn and wool yarn is called elongation.

The strength of the yarn is closely related to the fastness of the fabric and the production efficiency. Strength is the basis of the strength and elongation of the fabric. Therefore, the strength and elongation of the whole wool yarn and wool are important indicators of quality. Because the strength and elongation directly affect its quality, Appropriate strength and elongation are required. If the strength is too large, the wool yarn and woolen yarn will relax and the strength will decrease; if the strength is too low, the strength will increase and the wool yarn and woolen yarn will become stiff. The strength and elongation of the wool yarn and wool yarn are different with the raw materials used, the degree of processing, and the fiber arrangement. The quality of the raw materials is good, the fibers are arranged neatly, and the twisting is appropriate, the higher the strength of the wool yarn and the higher the stretch performance. .

Single yarn tensile performance test

1 Overview

The performance index of single yarn stretching is one of the main basis for assessing the grade of yarn. It is of great significance to yarn production, process formulation, process adjustment, weaving process and production efficiency. The main indicators for evaluating the tensile properties of yarns include average breaking strength, average breaking elongation, coefficient of variation of breaking strength, coefficient of variation of breaking elongation, average breaking time, etc. In addition, breaking power and breaking time are also required under certain special occasions. Detach strength, initial modulus and other indicators. The minimum strength and minimum elongation in the tensile properties can be used as reference indicators for the subsequent process (weaving).

2 Purpose and requirements

Through testing, master the measurement method of single yarn strength and elongation, understand the structure and working principle of single yarn strength meter, and learn to analyze various indexes of tensile performance.

3 Adopt the standard

⒊1 Standard adopted: GB/T 3916, ISO 2062 'Determination of breaking strength and elongation of single yarn of textile package yarn'

⒊2 Related standards: GB 6529 'Standard atmosphere for humidity control and testing of textiles', FZ/T 10014 'Cotton and chemical fiber blended yarn delivery acceptance sampling plan', FZ/T 10013.1 'Temperature and moisture regain and chemical fiber pure spinning , Correction method of breaking strength of blended products, correction method of breaking strength of natural yarn and dyeing processing line', GB/T 4743 'Determination of yarn linear density of textile package yarn, hank method'

4 Instruments and appliances

⒋1 YG061F Electronic Single Yarn Strength Tester (as shown in Figure 1)

⒋2 Sampling plate

5 principle

One end of the sample to be tested is clamped on the upper clamp of the CRE electronic single yarn strength tester, and the other end is clamped with the lower clamp after applying the pretension specified by the standard. At the same time, 100% of the gauge length (relative to the Tensile the specimen at a constant rate at the rate of the original length of the specimen until the specimen breaks. Because the gripper and the load cell are closely integrated, the load cell converts the force received on the upper gripper into a corresponding voltage signal, which is amplified by the amplifier circuit, and then performs A/D conversion, and finally the converted digital The signal is sent to the computer for processing. The instrument can record the breaking strength, breaking elongation and other technical indicators of each test. After the test, the data processing system will give the statistical values ??of all the technical indicators (see Figure 2 for the working principle of the instrument). After the instrument is connected to the computer, multiple test functions can be added, and the whole process of real-time display, diagram, and recording of stretching can be realized, which can realize long-term storage of data and graphics, which is more conducive to network management.

6 sampling

⒍1 Take one or more boxes to form a large sample according to Table 29-1 as a representative of the tested sample.

Table 29-1 Extraction regulations

Minimum number of boxes drawn at random

1

2

3

4

5

Number of boxes in the lot

≤3

4~10

11~30

31~75

≥76

6.2 If only the average value is needed, 10 rolls should be drawn as evenly as possible from each box of the large sample as laboratory sample rolls.

⒍3 Production is based on the requirements of product standards, using equidistant sampling; for trade inspection sampling, sampling is based on FZ/T 10014.

7 samples

⒎1 The minimum number of samples to be tested is: 50 short fiber yarns and 20 other types of yarns; or determine the number according to product standards. The samples shall be collected evenly from 10 packages.

⒎2 On the premise that the yarn does not cause damage, use the sampling pan to take the sample.

8 Environment and correction

The test should be carried out under the standard atmosphere required by the GB 6529 standard, and the measured strength under non-standard atmospheric conditions should be corrected in accordance with FZ/T 10013.1 (see appendix). The arbitration test adopts the secondary standard atmosphere.

9 Procedures and operations

⒐1 Warm up the instrument: Turn on the power 10 minutes before the test to warm up the instrument, and the display will show the test parameters at the same time.

⒐2 Determine the pretension: (0.5±0.10) cN/tex for the humidity-conditioning sample and (0.25±0.05) cN/tex for the wet sample. The pre-tension requirement of textured yarn can eliminate the crimp of the yarn without making it elongate. If there is no other agreement, the following pre-tension is recommended for textured yarn (except for carpet yarn with a linear density of more than 50tex).

Table 29-2 Pre-tension calculation of textured yarn (according to nominal linear density)

Polyester and polyamide yarn

Acetic acid, triacetate and viscose yarn

Double shrinkage and air-jet bulked yarn

(2.0±0.2)cN/tex

(1.0±0.1)cN/tex

(0.5±0.05)cN/tex

9.3 Setting parameters

⒐3.1 Gap: set according to the test needs, generally 500mm, 250mm for samples with large elongation.

⒐3.2 Stretching speed: Set according to the test needs. Generally, 500mm/min is used for 500mm gauge, and 250mm/min for 250mm gauge, which allows faster speeds.

⒐3.3 Input other parameters: such as times, yarn number, etc.

⒐3.4 Choose the method needed for testing: such as constant speed tensile test, timed tensile test, elastic recovery rate test, etc.

⒐4 Press the 'Test' button to enter the test state.

⒐5 The bobbin is placed on the bobbin holder, and the yarn is drawn into the upper and lower clamp jaws through the yarn guide, and then the upper clamp is clamped.

⒐6 Apply pre-tension on the pre-tensioner according to 9.2 (the pre-tensioner is adjusted before the test and used for standby).

⒐7 Clamp the lower gripper, press the 'stretch' switch, the lower gripper will go down, and the gripper will return automatically after the yarn breaks. During the test, check that the sample slip between the jaws should not exceed 2mm. If slipping occurs multiple times, the holder or jaw liner must be replaced. Discard the test data when slippage occurs, and discard the test data where the yarn breaking point is within 5mm from the jaw or clamp.

⒐8 Repeat 9.5~9.7, change yarn and tube, continue stretching, until the stretching reaches the set number of times, the test ends.

⒐9 Print out statistical data. After the test is completed, turn off the power supply.

Note: When the instrument needs to be calibrated, the following calibration procedure can be performed: After warming up for 30 minutes, press the 'Zero' button in the reset state of the instrument, put a 1000cN weight on the upper holder, and press 'Full Scale' after the data display is stable. 'Key, then press the 'verify' key, and finally press the 'reset' key to exit.

10 Results and calculations

⒑1 Breaking strength

(29-1)

In the formula:-the average value of breaking strength, cN;

-Each breaking strength value, cN;

-Number of stretches.

Note: 1. If it is not under standard temperature and humidity conditions, the measured results should be corrected in accordance with the appendix. Refer to FZ/T10013.1 for other materials.

⒉ Breaking strength refers to the ratio of yarn breaking strength to its linear density, usually expressed in cN/tex.

⒑2 Elongation at break:

(29-2)

In the formula:-average elongation at break, %;

-Elongation at break, %;

-Number of stretches.

⒑3 The formula of standard deviation and coefficient of variation of breaking strength and breaking elongation:

(29-3)

(29-4)

In the formula: - standard deviation;

--Data value measured each time;

--The average value of the test data;

--The number of test pieces, at least 50 pieces;

-Coefficient of variation, %.

11 test report

⒒1 Record: Instrument test parameters, including test date, instrument model, sample name, specifications, temperature, humidity, etc.

⒒2 Results: breaking strength, breaking strength, breaking elongation, breaking strength and coefficient of variation of breaking elongation, etc.

12 related knowledge

⒓1 Comparison of instruments with different tensile testing mechanisms

⒓1.1 Standards and instruments: The GB/T 3916 method standard is equivalent to the ISO 2062 standard, which is applicable to the various product standards it covers. The standard stipulates that the CRE (constant velocity extension) type strength tester is used. The CRL (constant load) and CRT type (constant velocity traction) instruments specified in the old standard are only used as transitions and can be adopted according to the agreement. The GB/T 3916 standard adopts constant-speed stretching, which discards the old-standard timed stretching. There are three different detection mechanisms, and the measured results are quite different. For example, the widely used CRT instrument in the past adopts timed stretching, and the instrument inevitably has mechanical friction and the 'inverted scale' negative error of the self-stop mechanism. In addition, The uncertainty error caused by the inertia of the force measuring mechanism and the operator's human error cannot often be ignored.

⒓1.2 Advantages of CRE type single yarn strength tester: CRE (constant velocity elongation) type strength tester mostly adopts non-electrical measuring technology, the mechanical friction and inertial influence of the load cell are almost negligible, and the operator's human error There are also fewer factors, so the measured results are more accurate. In addition, the electrical measurement system can generally be connected to a computer, so the work efficiency is high, especially the powerful data analysis and storage function, which is completely unmatched by the CRT mechanical strength tester.

⒓2 The effect of tensile speed on breaking strength: When the yarn sample is drawn at a relatively low speed, because the cohesive force between the fibers increases at a relatively small rate, some of the fibers in the sample are pulled out to cause the sample to break; When the yarn sample is stretched at a relatively high speed, the cohesive force between the fibers increases rapidly, and the proportion of fiber breakage in the sample increases under the action of the force, so the breaking strength of the sample increases. In addition, the force required for fiber extraction and breakage during the yarn drawing process is also related to the twist coefficient of the sample.

⒓3 The CRE single yarn strength tester is divided into semi-automatic and fully automatic: the semi-automatic instrument abandons the complicated automatic tube changing and yarn threading auxiliary system, simplifies the instrument structure and control circuit, reduces the cost, and increases the reliability. During the working process of the instrument, the procedures such as tube changing and yarn threading can be carried out at the same time by means of man and machine crossing, thereby improving the working efficiency of the instrument; its disadvantage is that the operator is more labor-intensive. Fully automatic instruments have a high degree of automation. Although the labor intensity of the operators is small, the reliability is slightly worse than that of the semi-automatic instruments, and the price is more expensive.

⒓4 The basic requirements of the instrument for the detection of different test materials: the instrument must first meet the strength requirements for sample fracture. For specimens with larger elongation, the test gauge length should be reduced. For samples with relatively small elongation, the instrument force measurement system should have a sufficient sampling rate. For instruments whose sampling rate cannot meet the requirements, sometimes it can be compensated by reducing the stretching speed.

⒓5 The requirements of the instrument holder for the detection of different test materials: the yarn spun from short fiber has no special requirements for the holder; the holder of the chemical fiber filament sample should be made of a soft cushion lining with suitable hardness, and Continuously pressurize during the stretching process to make it clamped; specimens with relatively high fracture strength should be clamped in a roundabout or bolted manner, and the specimens are hugged in the grooves drawn by the clamp. In short, it is necessary to ensure that the sample neither slips off nor breaks near the jaws.

⒓6 Some manufacturers developed a portable electronic single yarn strength tester in 2013, which can be used to test the joint strength of the air twister on site. With the continuous emergence of new materials, the requirements for testing technology are getting higher and higher, and the intervention of computer technology has made the instrument more and more accurate and more powerful, and most of the desired functions are relatively easy to implement.
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