What does yarn evenness mean?

Evenness of yarn

(Poor linear density, uniformity of linear density)

Unevenness refers to the degree of variation in thickness along the length of the yarn, and can also be expressed as unevenness of yarn evenness. The quality of textiles depends largely on the yarn evenness. The unevenness of yarn is divided into short-section unevenness, medium-section unevenness and long-section unevenness. The length of the interval where the unevenness occurs is 1-10 times the fiber length, and the unevenness of the interval below about 1m is called short segment unevenness; the length of the uneven interval is 10-100 times the fiber length, and the interval is about a few meters. The unevenness is called the unevenness of the middle segment; the length of the interval where the unevenness occurs is 100-3000 times the length of the fiber, and the unevenness of the interval is about tens of meters, which is called the unevenness of the long segment.

When weaving yarns with high unevenness in short segments, there is a greater probability that several thick knots or details will be juxtaposed on the fabric surface, and fabric defects are prone to appear, which will have a greater impact on the quality of the fabric; long uneven yarns The cloth surface woven by thread will have obvious horizontal stripes, which will have a greater impact on the cloth surface. Relatively speaking, the chance of defects on the cloth surface is slightly lower when the yarns with uneven fragments are woven, and they are related to the width of the cloth. Obvious defects (stripe shadows or cloud spots) will appear when a multiple relationship. In addition, during the weaving process, the end breakage rate will increase and the production efficiency will decrease. Therefore, the evenness of yarn is an important index for evaluating yarn quality.

The main reason for uneven yarn evenness

(1) Differences in fiber properties: The length, fineness, structure, and shape of natural fibers are uneven. This unevenness is not only manifested between roots, but also in different parts of the same fiber; chemistry The unevenness of fibers is better than natural fibers, but there are still some differences in properties. The unevenness of the fiber properties or the difference in performance will cause unevenness of the yarn evenness, which is manifested by the increase of the CV value and the increase of the spectrogram.

(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 from defects, the yarn will still be uneven. This is because the number of fibers reported in the cross-section of the yarn is randomly distributed. This unevenness is the lowest limit unevenness, also known as the limit unevenness, which can be calculated by formula (2-11).

(3) Unevenness caused by accidents: This kind of unevenness is often due to special reasons, such as fly stick adhesion, gear intarsia, traverse guide rod out of position, poor operation, air-conditioning failure, cotton candy sticky roller, etc., most of the time. It is the rise of defects or the appearance of extra-large defects, sometimes manifested as mechanical waves.