The assessment of yarn quality includes two aspects: internal quality and appearance quality.

Basically, it is based on physical indicators and appearance defects. However, the physical index items and appearance defect items of different types and uses of yarns are different.

The quality standards for yarn include national standards (approved and promulgated by the State Science and Technology Commission), ministerial standards (approved and promulgated by the Ministry of Textile Industry), and enterprise standards (formulated by provincial and municipal industrial departments).

The basis for evaluating the quality of common yarns and the classification and grading situations are as follows:

Quality assessment of cotton yarn

Cotton yarn refers to all cotton-type yarns. The production volume of three shifts per day and night is taken as one batch for evaluation. Its grades are classified as excellent, first grade, second grade and third grade. Excellent is equivalent to the international advanced level, and first-class is equivalent to the international average level.

Items for evaluating cotton yarn

Coefficient of variation of breaking strength of single yarn

2. Coefficient of variation in weight per 100 meters

3. Uniformity of the strips

4. The number of cotton grains formed within one gram

5. The total number of impurities in cotton knots within one gram

The basis for evaluating cotton thread: 1.2.4.5.

The grading method: The grade is determined based on the lowest item from 1 to 5. Then, look at 1.2. Whether it exceeds the range. If one or two items exceed the range, it is downgraded by one grade to two. For superior cotton yarn, an additional 100,000 meters of yarn defects are added as the classification index.

1. Single yarn (thread) breaking strength, coefficient of variation of breaking force

Measure the single yarn 60 times and the strand 30 times. It can be obtained by substituting into the formula of the coefficient of variation. The formulas are different when n>50 or n<50.

2. Coefficient of variation in weight per 100 meters

30 yarns, 1 meter per week, 100 weeks. Weigh each item separately and substitute them into the coefficient of variation formula. Based on this, search for products, etc. in the technical index specification table.

3. Weight deviation within 100 meters

Actual specials and design specials

The percentage deviation between the two is called weight deviation or specific number deviation. In actual assessment, the weight deviation per 100 meters is used for measurement.

4. Uniformity of the strips

Either the coefficient of variation of strip dryness uniformity (measured by an electronic uniformity meter) or the blackboard strip dryness uniformity can be adopted. In case of any dispute, the former shall prevail.

Blackboard strip uniformity determination: Randomly select 10 tubes and evenly shake 10 blackboards, each measuring 250mmx220mm. Under specified light, compare them one by one with the standard sample of the strip. Based on their shadows, thick nodes, severe defects, and severe irregular unevenness, evaluate them respectively. Those that are better than or equal to "excellent" are rated as "excellent", those that are better than or equal to "first" are rated as "first", those that are worse than "first" or have serious defects are rated as "second", and those with serious regular unevenness are rated as "third". Finally, based on the proportion of excellent grade, first grade, second grade and third grade among the 10 blackboards, the uniformity of the blackboards was determined.

5. The number of cotton grains within 1g and the total number of impurities in cotton grains within 1g

Count the number of cotton knots and impurity grains within the 10 blank Spaces on both sides. The total number of cotton knots na and the total number of cotton knots and impurity grains nb within 10 blackboards can be calculated as follows:

The number of cotton grains within 1g =na/ Ntex x10

The total number of impurities in the cotton knot within 1g =(na+nb)/Ntex x10

6. One hundred thousand meters of yarn defect

Yarn defects refer to major flaws adhering to the yarn, which are classified into three categories: short coarse knots (more than 100% thicker than normal, with a length less than 200px), long coarse knots (more than 45% thicker than normal, with a length greater than 200px), and long fine knots (30 to 70% thinner than normal, with a length greater than 200px). It affects the quality of the fabric surface and causes short ends. Its inspection requires a large sample size; otherwise, it will be difficult to detect. Therefore, a sample length of 100,000 meters is taken. It is carried out on the yarn defect tester.