Test method for yarn diameter

1. The optical projection method places the yarn under a microscope equipped with an eyepiece test ruler at about 100 times, or under a projector with the same magnification, with a predetermined tension, and after focusing, the projected shape of the yarn surface can be obtained. Determine the diameter standard after removing hairiness, randomly select detection points on the yarn at a certain interval, and after more than 300 observation values are obtained, the average value of the yarn diameter is calculated by statistical method. Due to the fuzzy characteristics of the yarn diameter boundary, the artificial definition of the yarn diameter to remove the fuzzy boundary of the yarn hairiness is affected by human subjective factors. 

This method has human observation and visual error, but since the yarn has been magnified 100 times during the test, the accuracy of visual inspection has been improved, and the test results are still relatively correct. The disadvantage of this method is that there are many test points required for the sample, the operation is time-consuming and laborious, and the test efficiency is low. 

2. Indirect calculation method Due to the shortcomings of measuring diameter by optical projection method, a diameter calculation method derived from the formula of yarn fineness is produced. Let the yarn be a cylinder, the length is L (mm), the weight is G (mg), and the cross-sectional area is S (mm)²), the volume weight isδ(g/cm³), the diameter is d (mm): the relationship between the diameter of the yarn and the yarn special number Nt, the metric count Nm, and the fineness D is: the volume weight of the yarnδIt is related to the nature of the fiber and the twist of the yarn. The common yarn volume weight values are shown in the table: if it is expressed by a general formula, the expression of the yarn diameter can be written as where Kd is called the yarn diameter coefficient in order to find a certain value. The diameter of a kind of yarn must be measured by its diameter coefficient. The diameter coefficient of the yarn is also determined by the optical projection method, so the direct calculation of the diameter is essentially an optical method test. The disadvantage of this method is that the yarn diameter coefficient Kd is related to the volume weight of the yarnδrelated. With different yarn varieties, different blending ratios and the emergence of new fibers, the volume weight of the yarn changes greatly, and the diameter calculated by the diameter coefficient of the yarn is greatly restricted.

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