1. Cut off weighing method. Use the yarn length measuring device to obtain several twists of a certain length of skein, each twist is called a segment, and the weight of each twisted yarn is weighed separately, that is, Xi is obtained. Substitute into formula (2-12) to obtain the uneven weight , substituting into equation (2-13) to obtain the unevenness between segments. The length of the segment is 100m for cotton yarn, 50m for box-carded yarn, 20m for combed yarn, 50m for ramie yarn of 49tex and above, 100m for below 49tex, and 450m for raw silk.
2. Visual inspection method, also known as blackboard dry method. It is to use a blackboard winding machine to evenly wind the yarn on a blackboard of a certain specification at a certain density, and then place the blackboard under the specified light and position in the dark room, and observe the shadows, thick knots, serious defects, etc. of the blackboard with eyes. Compare with the standard sample to determine the evenness level of the yarn. The evenness grade of cotton yarn is divided into first-class, first-class and second-class, and third-class except second-class. Wool yarns are evaluated for evenness first-class rate. The unevenness of the yarn tested by the visual inspection method reflects the uneven thickness of the short segments of the yarn. The test is fast and simple, but quantitative data cannot be obtained, and the test results will vary from person to person. The picture is the YG381 shaking blackboard machine.
