Method for detecting density of spandex yarn in removed yarn of knitted fabric

Abstract

The invention relates to a method for detecting the density of spandex yarns in removed yarns of a knitted fabric. The method comprises the following steps: preparing a spandex filament sample; taking a group of spandex filament samples, testing the recovery rate S of the spandex filament samples after boiling water treatment, and solving the average value S1 of the recovery rate; another group of spandex filament samples is taken, the total length L2 of the yarn is calculated, the total mass m of the yarn is weighed, and the original length L3 of the spandex filament samples is calculated through the shrinkage rate; and calculating the linear density T of the spandex filament sample according to a formula. According to the method, the spandex filaments are shrunk through boiling water treatment, the original length of the spandex filaments is calculated through the boiling water recovery rate, and therefore the density of the spandex filaments can be accurately reflected, the linear density deviation rate of all test data is controlled within 4%, that is, the accuracy of the test data reaches 96% or above and is completely within the standard error range; and the detection precision of the spandex linear density is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of spandex linear density detection, and particularly relates to a method for detecting the linear density of spandex in the yarn removed from knitted fabrics. Background Art

[0002] In the textile industry, due to its outstanding elasticity, spandex is widely used in the production of various fabrics. Spandex is rarely used alone and is mostly made into core-spun yarns by being incorporated in small amounts for use in fabrics. Core-spun yarns not only have excellent elasticity, can stretch greatly and quickly recover, are especially suitable for making high-elasticity clothing, but also only need to add 1%-10% of spandex to significantly improve the elasticity of the yarn, which can not only effectively control costs but also ensure that the fabric is lightweight. At the same time, the addition of spandex enhances the abrasion resistance and tear resistance of the yarn, greatly extending the service life of the fabric. Nowadays, spandex-containing fabrics have been widely used in performance-demanding clothing fabrics such as sportswear, underwear, socks, and medical fabrics, and can well meet the specific needs of different industries.

[0003] With the continuous improvement of consumers' performance requirements for fabrics such as lightweight, skin-friendly comfort, and soft texture, the proportion of low-denier spandex fabrics in synthetic fiber fabrics continues to increase. The market demand for high-elasticity, lightweight and comfortable fabrics is becoming increasingly strong, which makes manufacturers pay more and more attention to the accurate measurement of the linear density of spandex in fabrics. As a key component of core-spun yarns, the linear density of spandex directly determines the elasticity, feel of the yarn, and the quality performance of the final product. By precisely controlling the linear density of spandex, manufacturers can not only optimize the elasticity and durability of the yarn to ensure product quality, but also reasonably control costs.

[0004] The prior art usually uses the direct weighing method to detect the density of spandex yarn. Due to the high-elasticity characteristics of spandex, it is very easy to cause deviations in the test results, and the accuracy of linear density detection is relatively low. Therefore, there is an urgent need to develop an accurate and rapid method for detecting the linear density of spandex in the yarn removed from knitted fabrics, which is of extremely important practical significance for verifying whether the knitted fabrics are produced according to customer requirements and for the development of the textile industry. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above deficiencies and provide a method for detecting the linear density of spandex in the yarn removed from knitted fabrics. Through actual tests, it is verified that this method can accurately measure the linear density of spandex fibers in blended yarns, providing strong support for meeting customers' needs for spandex linear density testing and having good practicability.

[0006] The purpose of the present invention is achieved as follows: A method for detecting the linear density of spandex in the yarn removed from knitted fabrics, comprising the following steps: a. Preparation of spandex filament specimens: Select a fabric sample containing spandex filaments for conditioning. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament specimens. b. Take a group of spandex filament specimens with the number of specimens being M. Use a fiber cutter to cut the spandex filament specimens into a fixed length. Apply a pre-tension to the lower end of the spandex filament specimens to make each spandex filament specimen hang naturally. After waiting for several seconds, use a chemical fiber heat shrinkage tester to measure the length L0 before boiling water treatment. c. Conduct a heat shrinkage rate test on the spandex filament specimens in step b. Use a chemical fiber heat shrinkage tester to measure the length L1 of the spandex filament specimens after boiling water treatment. d. Calculate the recovery rate S of each spandex filament specimen after boiling water treatment and find the average recovery rate S1. e. Take another group of spandex filament specimens with the number of specimens being N. Apply a pre-tension to this group of spandex filament specimens to make each spandex filament specimen hang naturally. Use a steel ruler to measure and record the straightened length of each spandex filament specimen, calculate the total yarn length L2, and weigh the total yarn mass m. Calculate the original length L3 of the spandex filament specimens through the shrinkage rate. f. Calculate the linear density T of the spandex filament specimens according to the formula.

[0007] Preferably, in steps b and e, according to the nominal linear density of the spandex filament specimens, look up Table 1 of the pre-tension selection table in Section 8.1 of FZ / T 50005-2013 "Test Method for Linear Density of Spandex Yarns" to determine the pre-tension of the spandex filament specimens.

[0008] Preferably, in step c, according to the nominal linear density of the spandex filament specimens, select the boiling water treatment duration to ensure sufficient shrinkage of the spandex.

[0009] Preferably, in step d, the calculation formula for the recovery rate S after boiling water treatment is as follows: .

[0010] Preferably, in step e, the calculation formula for the original length L3 of the spandex filament specimens is as follows: L3 = L2×(1 - S).

[0011] Preferably, in step f, the calculation formula for the linear density of the spandex filament specimens is: .

[0012] The beneficial effects of the present invention are: Optimize the detection method. Shrink the spandex filament by boiling water treatment, and calculate the original length of the spandex filament based on the boiling water recovery rate, so as to accurately reflect the linear density of the spandex filament. The linear density deviation rate of all test data is controlled within 4%, that is, the accuracy of the test data reaches more than 96%, which is completely within the standard error range, greatly improving the detection accuracy of the spandex linear density. Specific embodiments

[0013] The present invention relates to a method for detecting the linear density of spandex in the yarn removed from a knitted fabric, including the following steps: a. Preparation of spandex filament specimens: Select a fabric sample containing spandex filaments for conditioning, remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments therein to obtain spandex filament specimens; b. Take a group of spandex filament specimens, the number of spandex filament specimens is M, cut the spandex filament specimens into a fixed length with a fiber cutter, apply a pre-tension to the lower end of the spandex filament specimens, make each spandex filament specimen hang naturally, wait for 20 s, and measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0014] According to the nominal linear density of the spandex filament specimens, look up Table 1 of the pre-tension selection table in Clause 8.1 of FZ / T 50005-2013 "Test Method for Linear Density of Spandex Yarn" to determine the pre-tension of the spandex filament specimens. c. Conduct a heat shrinkage rate test on the spandex filament specimens in step b, and measure the length L1 after boiling water treatment of the spandex filament specimens with a chemical fiber heat shrinkage tester. According to the nominal linear density of the spandex filament specimens, select the boiling water treatment duration to ensure that the spandex is fully shrunk. The boiling water treatment duration selection table is as follows: Table 1 Boiling water treatment duration selection table

[0015] Due to the difference in linear density, the heat transfer rate of spandex filaments is also different. Generally, spandex filaments with a lower denier have finer fibers, relatively shorter molecular chains, and a higher degree of arrangement regularity. During the boiling water treatment process, the molecular chains of such filaments can move more smoothly, so the time required to return to the original length is shorter. On the contrary, spandex filaments with a larger denier have an increased fiber thickness, longer molecular chains, and more entanglements. In boiling water, it takes longer to promote the disentanglement of the molecular chains and return to the initial form. In view of this, in order to ensure the accuracy of the heat performance treatment of spandex filaments with different linear densities, it is necessary to adopt different boiling water treatment durations for spandex filaments with different linear densities.

[0016] The spandex filament specimens after boiling water treatment need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T 6529.

[0017] d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and find the average recovery rate S1;

[0018] e. Take another group of spandex filament samples, with the number of spandex filament samples being N. Apply a pre-tension to this group of spandex filament samples to make each spandex filament sample hang naturally. Measure and record the straightening length of each spandex filament sample with a steel ruler, calculate the total yarn length L2, and weigh the total yarn mass m. Calculate the original length L3 of the spandex filament sample through the shrinkage rate, L3 = L2×(1 - S) f. Calculate the linear density T of the spandex filament sample according to the formula, and retain one decimal place for the result.

[0019]

[0020] In the formula: T—the linear density of the yarn (tex); m—the total mass of the yarn (g); L3—the original length of the yarn (m). Example 1

[0021] For the yarn removed from the knitted fabric with the spandex nominal of 10D, conduct the linear density detection, including the following steps: a. Preparation of spandex filament samples: Select the fabric sample containing spandex filaments for conditioning treatment. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain the spandex filament samples; b. Take a group of spandex filament samples, with the number of spandex filament samples being 20. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.02 cN to the lower end of the spandex filament samples to make each spandex filament sample hang naturally. Wait for 20 s, and measure the length L0 before boiling water treatment with a chemical fiber shrinkage tester.

[0022] c. Conduct the heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 20 minutes to ensure that the spandex is fully shrunk. The spandex filament samples after boiling water treatment need to be balanced under the standard atmospheric conditions specified in GB / T6529 for 2 h, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber shrinkage tester; d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 2.

[0023] Table 2 Test data record form of Example 1

[0024] The average recovery rate S1 = 12.6%; e. Take another group of spandex filament samples. The number of spandex filament samples is 40. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Use a steel ruler to measure and record the straightened length of each spandex filament sample, calculate the total yarn length L2 = 10.421 m, and weigh the total yarn mass m = 0.0100 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.421×(1 - 12.6%) ≈ 9.108 m.

[0025] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0100×1000 / 9.108 ≈ 1.1 tex (9.9 D) That is, the measured spandex linear density is 9.9 D. Example 2

[0026] For the yarn of a knitted fabric with a spandex nominal of 20 D, conduct a linear density test, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning treatment. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples. The number of spandex filament samples is 20. Use a fiber cutter to cut the spandex filament samples into a fixed length of 30 mm. Apply a pre-tension of 0.02 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and use a chemical fiber heat shrinkage tester to measure the length L0 before boiling water treatment.

[0027] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 25 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T6529. Use a chemical fiber heat shrinkage tester to measure the length L1 of the spandex filament samples after boiling water treatment. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 3.

[0028] Table 3 Test data record table of Example 2

[0029] The average recovery rate S1 = 10.4%; e. Take another set of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this set of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.433 m, and weigh the total yarn mass m = 0.0206 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.433×(1 - 10.4%) ≈ 9.348 m.

[0030] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0206×1000 / 9.348 ≈ 2.2 tex (19.8 D) That is, the measured spandex linear density is 19.8 D. Example 3

[0031] For the yarn of a knitted fabric with a spandex nominal of 30 D, conduct a linear density test, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a set of spandex filament samples, with 20 spandex filament samples. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.03 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure its length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0032] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 30 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T6529. Measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 4.

[0033] Table 4 Test data record table of Example 3

[0034] Find the average recovery rate S1 = 7.6%; e. Take another group of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.403 m, and weigh the total yarn mass m = 0.0327 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.403×(1 - 7.6%) ≈ 9.612 m.

[0035] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0327×1000 / 9.612 ≈ 3.4 tex (30.6 D) That is, the measured spandex linear density is 30.6 D. Example 4

[0036] Remove the yarn from the knitted fabric with a nominal spandex of 40 D for linear density detection, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples, with 20 spandex filament samples. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.04 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0037] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 35 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T6529, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 5.

[0038] Table 5 Test data record table of Example 4

[0039] Calculate the average recovery rate S1 = 6.4%; e. Take another group of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.384 m, and weigh the total yarn mass m = 0.0447 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.384×(1 - 6.4%) ≈ 9.719 m.

[0040] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0447×1000 / 9.719 ≈ 4.6 tex (41.4 D) That is, the measured spandex linear density is 41.4 D. Example 5

[0041] For the yarn of a knitted fabric with a spandex nominal of 50 D, conduct a linear density test, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples, with 20 spandex filament samples. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.04 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0042] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 40 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T6529, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 6.

[0043] Table 6 Test data record table of Example 5

[0044] Find the average recovery rate S1 = 5.5%; e. Take another group of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.412 m, and weigh the total yarn mass m = 0.0561 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.412×(1 - 5.5%) ≈ 9.839 m.

[0045] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0561×1000 / 9.839 ≈ 5.7 tex (51.3 D) That is, the measured spandex linear density is 51.3 D. Example 6

[0046] For the yarn of a knitted fabric with a spandex nominal of 60 D, remove the yarn for linear density detection, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples, with 20 spandex filament samples. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.07 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure its length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0047] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 45 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T6529, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 7.

[0048] Table 7 Test data record table of Example 6

[0049] Find the average recovery rate S1 = 4.8%; e. Take another group of spandex filament samples. The number of spandex filament samples is 40. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.378 m, and weigh the total yarn mass m = 0.0672 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.378×(1 - 4.8%) ≈ 9.881 m.

[0050] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0672×1000 / 9.881 ≈ 6.8 tex (61.2 D) That is, the measured spandex linear density is 61.2 D. Example 7

[0051] Dismantle the yarn from the knitted fabric with a nominal spandex of 70 D for linear density detection, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Dismantle the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples. The number of spandex filament samples is 20. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.07 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0052] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 50 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T 6529, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 8.

[0053] Table 8 Test data record table of Example 7

[0054] Find the average recovery rate S1 = 4.2%; e. Take another group of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.422 m, and weigh the total yarn mass m = 0.0799 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.422×(1 - 4.2%) ≈ 9.988 m.

[0055] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0799×1000 / 9.988 ≈ 8.0 tex (72.0 D) That is, the measured spandex linear density is 72.0 D. Example 8

[0056] For the yarn of a knitted fabric with a spandex nominal of 80 D, conduct a linear density test, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples, with 20 spandex filament samples. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.07 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0057] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 55 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T 6529, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 9.

[0058] Table 9 Test data record table of Example 8

[0059] Find the average recovery rate S1 = 3.7%; e. Take another group of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.426 m, and weigh the total yarn mass m = 0.0904 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.426×(1 - 3.7%) ≈ 10.044 m.

[0060] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0904×1000 / 10.044 ≈ 9.0 tex (81.0 D) That is, the measured spandex linear density is 81.0 D. Example 9

[0061] Dismantle the yarn from the knitted fabric with the spandex labeled 90 D for linear density detection, including the following steps: a. Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for conditioning. Dismantle the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament samples. b. Take a group of spandex filament samples, with 20 spandex filament samples. Cut the spandex filament samples into a fixed length of 30 mm with a fiber cutter. Apply a pre-tension of 0.07 cN to the lower end of the spandex filament samples so that each spandex filament sample hangs naturally. Wait for 20 s and measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester.

[0062] c. Conduct a heat shrinkage rate test on the spandex filament samples in step b. Put 20 spandex filaments into a water bath at 100 °C and boil for 60 minutes to ensure full shrinkage of the spandex. After boiling water treatment, the spandex filament samples need to be balanced for 2 h under the standard atmospheric conditions specified in GB / T 6529, and measure the length L1 of the spandex filament samples after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament sample after boiling water treatment, and record L0, L1, and S in Table 10.

[0063] Table 10 Test data record table of Example 9

[0064] Calculate the average recovery rate S1 = 3.3%; e. Take another group of spandex filament samples, with 40 spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.418 m, and weigh the total yarn mass m = 0.1038 g. Calculate the original length L3 of the spandex filament sample through the shrinkage rate. L3 = 10.418×(1 - 3.3%) ≈ 10.074 m.

[0065] f. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.1038×1000 / 10.074 ≈ 10.3 tex (92.7 D) That is, the measured spandex linear density is 92.7 D.

[0066] According to the nominal linear density and the measured linear density of the spandex filament sample, calculate the linear density deviation rate of Examples 1 - 9. The linear density deviation rate = (measured linear density - nominal linear density) / nominal linear density × 100%. The linear density deviation rates of Examples 1 - 9 are -1.0%, -1.0%, 2.0%, 3.5%, 2.6%, 2.0%, 2.9%, 1.3%, 3.0% respectively.

[0067] Compare the conventional direct weighing method with the detection method proposed in the present invention to provide Comparative Examples 1 - 4.

[0068] Comparative Example 1: Carry out the linear density detection of the yarn removed from the knitted fabric with a nominal spandex of 10 D by the direct weighing method. The steps are as follows: Preparation of spandex filament samples: Select a fabric sample containing spandex filaments for moisture conditioning. Remove 40 yarns from the fabric sample, untwist the yarns and extract the spandex filaments inside to obtain spandex filament samples. Apply a pre-tension to this group of spandex filament samples so that each spandex filament sample hangs naturally. Measure and record the straightened length of each spandex filament sample with a steel ruler. Calculate the total yarn length L2 = 10.263 m, and weigh the total yarn mass m = 0.0123 g. Calculate the linear density T of the spandex filament sample according to the formula and convert the linear density unit. T = 0.0123×1000 / 10.263 ≈ 1.2 tex (10.8 D) That is, the measured spandex linear density is 10.8 D. Its linear density deviation rate is 8.0%.

[0069] Comparative Example 2: Carry out the linear density detection of the yarn removed from the knitted fabric with a nominal spandex of 20 D by the direct weighing method. The steps are as follows: Preparation of spandex filament specimens: Select a fabric sample containing spandex filaments for conditioning. Remove 40 yarns from the fabric sample, untwist the yarns and extract the spandex filaments inside to obtain spandex filament specimens; Apply a pre-tension to this group of spandex filament specimens, let each spandex filament specimen hang naturally, measure and record the straightening length of each spandex filament specimen with a steel ruler, calculate the total yarn length L2 = 10.342 m, and weigh the total yarn mass m = 0.0248 g. Calculate the linear density T of the spandex filament specimens according to the formula and convert the linear density unit. T = 0.0248×1000 / 10.342≈2.4 tex (21.6 D) That is, the measured spandex linear density is 21.6 D. Its linear density deviation rate is 8.0%.

[0070] Comparative Example 3: For the knitted fabric with a spandex nominal of 30 D, remove the yarns and conduct a linear density test by the direct weighing method. The steps are as follows: Preparation of spandex filament specimens: Select a fabric sample containing spandex filaments for conditioning. Remove 40 yarns from the fabric sample, untwist the yarns and extract the spandex filaments inside to obtain spandex filament specimens; Apply a pre-tension to this group of spandex filament specimens, let each spandex filament specimen hang naturally, measure and record the straightening length of each spandex filament specimen with a steel ruler, calculate the total yarn length L2 = 10.597 m, and weigh the total yarn mass m = 0.0381 g. Calculate the linear density T of the spandex filament specimens according to the formula and convert the linear density unit. T = 0.0381×1000 / 10.597≈3.6 tex (32.4 D) That is, the measured spandex linear density is 32.4 D. Its linear density deviation rate is 8.0%.

[0071] Comparative Example 4: For the knitted fabric with a spandex nominal of 40 D, remove the yarns and conduct a linear density test by the direct weighing method. The steps are as follows: Preparation of spandex filament specimens: Select a fabric sample containing spandex filaments for conditioning. Remove 40 yarns from the fabric sample, untwist the yarns and extract the spandex filaments inside to obtain spandex filament specimens; Apply a pre-tension to this group of spandex filament specimens, let each spandex filament specimen hang naturally, measure and record the straightening length of each spandex filament specimen with a steel ruler, calculate the total yarn length L2 = 10.284 m, and weigh the total yarn mass m = 0.0494 g. Calculate the linear density T of the spandex filament specimens according to the formula and convert the linear density unit. T = 0.0494×1000 / 10.284 ≈ 4.8 tex (43.2 D) That is, the linear density of the spandex is measured to be 43.2 D. The deviation rate of its linear density is 8.0%.

[0072] After testing, the deviation rate of the linear density of all the test data in Examples 1 - 9 is controlled within 4%, which means that the accuracy of the test data reaches more than 96%, completely within the standard error range. This result strongly proves that the method for detecting the linear density of spandex long filaments in knitted fabrics proposed by the present invention can accurately measure the linear density of spandex long filaments in blended yarns. Through actual testing, the accuracy and reliability of this method have been fully verified. And according to the nominal linear density and the measured linear density of the spandex long filament samples, the deviation rate of the linear density of Comparative Examples 1 - 4 is calculated. The deviation rate of the linear density = (measured linear density - nominal linear density) / nominal linear density × 100%. The deviation rates of the linear density of Comparative Examples 1 - 4 are all above 7%, and the test accuracy is not high. Compared with the comparative examples, the examples have higher detection accuracy.

[0073] In addition to the above embodiments, the present invention also includes other implementation manners. All technical solutions formed by equivalent transformation or equivalent substitution shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for detecting the spandex thread density in the yarn removed from a knitted fabric, characterized in that: It includes the following steps: a. Preparation of spandex filament specimens: Select a fabric sample containing spandex filaments for conditioning treatment. Remove the yarn from the fabric sample, untwist the yarn and extract the spandex filaments inside to obtain spandex filament specimens. b. Take a group of spandex filament specimens, with the number of spandex filament specimens being M. Cut the spandex filament specimens into a fixed length with a fiber cutter. Apply a pre-tension to the lower end of the spandex filament specimens to make each spandex filament specimen hang naturally. After waiting for several seconds, measure the length L0 before boiling water treatment with a chemical fiber heat shrinkage tester. c. Conduct a heat shrinkage rate test on the spandex filament specimens in step b. Measure the length L1 of the spandex filament specimens after boiling water treatment with a chemical fiber heat shrinkage tester. d. Calculate the recovery rate S of each spandex filament specimen after boiling water treatment, and find the average recovery rate S1. e. Take another group of spandex filament specimens, with the number of spandex filament specimens being N. Apply a pre-tension to this group of spandex filament specimens to make each spandex filament specimen hang naturally. Measure and record the straightened length of each spandex filament specimen with a steel ruler, calculate the total yarn length L2, and weigh the total yarn mass m. Calculate the original length L3 of the spandex filament specimens through the shrinkage rate. f. Calculate the linear density T of the spandex filament specimens according to the formula.

2. The method for detecting the spandex yarn density in the yarn removed from a knitted fabric according to claim 1, characterized in that: In steps b and e, according to the nominal linear density of the spandex filament specimens, look up Table 1 of the pre-tension selection table in Section 8.1 of FZ / T 50005-2013 "Test Method for Linear Density of Spandex Yarn" to determine the pre-tension of the spandex filament specimens.

3. A method for detecting the spandex thread density in the yarn removed from a knitted fabric according to claim 1, characterized in that: In step c, according to the nominal linear density of the spandex filament specimens, select the boiling water treatment duration to ensure full shrinkage of the spandex.

4. A method for detecting the spandex yarn density in the yarn removed from a knitted fabric according to claim 1, characterized in that: In step d, the calculation formula for the recovery rate S after boiling water treatment is as follows: 。 5. A method for detecting the spandex yarn density in the yarn removed from a knitted fabric according to claim 1, characterized in that: In step e, the calculation formula for the original length L3 of the spandex filament specimens is as follows: L3 = L2 × (1 - S).

6. A method for detecting the spandex yarn density in the yarn removed from a knitted fabric according to claim 1, characterized in that: In step f, the calculation formula for the linear density of the spandex filament specimens is: 。

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