What is yarn evenness?
Evenness of yarn (poor linear density, evenness of linear density)
The evenness refers to the degree of change in the thickness along the length of the yarn, and can also be expressed as the evenness of the yarn. The quality of textiles depends largely on the evenness of yarn.
Yarn evenness is divided into short segment unevenness, medium segment unevenness and long segment unevenness. The interval length of unevenness is 1-10 times of the fiber length, and the interval unevenness below about 1m is called short segment unevenness; The interval length of unevenness is 10-100 times of the fiber length, and about a few meters is the interval unevenness, which is called middle segment unevenness; The interval length of unevenness is 100-3000 times of the fiber length, and about tens of meters is the interval unevenness, which is called long segment unevenness.
When weaving with short segment yarn with high unevenness, the probability of several coarse knots or details juxtaposing on the cloth surface is high, and the cloth surface defects are easy to appear, which has a great impact on the cloth surface quality; The fabric surface woven from long and uneven yarn will have obvious horizontal stripes, which also has a great impact on the fabric surface; Relatively speaking, the probability of defects on the cloth surface is slightly lower when weaving the yarn with uneven segments, and it is related to the cloth width. When it presents a certain multiple relationship, it will appear obvious defects (stripes or cloud spots). In addition, during the weaving process, the breakage rate will increase and the production efficiency will decrease. Therefore, yarn evenness is an important index to evaluate yarn quality.
Main causes of yarn unevenness
(1) Differences in fiber properties: the length, fineness, structure and shape of natural fibers are uneven, which is not only between roots, but also in different parts of the same fiber; The heterogeneity of chemical fiber is better than that of natural fiber, but there are still some differences in properties. The unevenness of this property or the difference in performance of the fiber will cause the unevenness of the yarn, which is manifested by the rise of CV value and the rise of the spectrum.
(2) Random arrangement of fibers: If the fibers are of equal length and thickness, and the fibers in the yarn are straight and parallel, and the spinning equipment and spinning process are free of defects, the yarn will still be uneven. This is because the fiber count in the sliver section is randomly distributed, which is the lowest limit unevenness, also known as limit unevenness, which can be calculated by formula (2-11).
(3) Unevenness caused by accidental events: This kind of unevenness is often caused by special reasons, such as flying flower adhesion, gear intarsion, lateral guide rod dislocation, poor operation, air conditioning failure, cotton candy sticking roller, etc. Most of the time, it is manifested as the rise of defects or the appearance of extra-large defects, and sometimes it is also manifested as mechanical waves.
