Changes of Sliver Irregularity in Two-Zone Roller Drafting

A theoretical calculation is made to simulate the effect of drafting upon the sliver irregularity in two-zone drafting of three-over-three roller system. Two types of slivers, i.e., random sliver and optional sliver are considered. The effects of sliver count, staple fiber length, fineness of fiber, draft distribution between two drafting zones, maximal moving distance and distribution type of speed changing point are calculated on a computer. Furthermore, we have a try for clarifying the relation between irregularity of the supplied sliver and irregularity due to the movement of speed changing point upon irregularity of sliver after drafting.The results are as follows:(1) When the maximal moving distance of speed changing point is 0, the number of fiber ends in every increment remains unchanged, but the sliver thickness is reduced by the drafting action. Therefore, the coefficient of variation in the drafted sliver increases by the square root of the draft ratio.(2) When the maximal moving distance of speed changing point is not 0, sliver irregularity vary with the increase in this distance. The increase ratio of sliver irregularity decreases with the increase of British count of sliver, fineness of fiber and staple fiber length. And the staple fiber length has the strongest influence on it. Furthermore, the coefficient of variation varies with the draft distribution and the moving condition of speed changing point on two drafting zones. It can be seen that there is an optimal draft distribution which makes the coefficient of variation minimum, and that the range of the first drafting ratio is about 1.5-3. When the distribution type of moving distance is the same one in each drafting zone, the difference between the maximal and the minimal value of coefficient of variation is the smallest one.(3) It is also found that the correlation between the irregularity of the supplied sliver and the irregularity due to the movement of speed changing point is almost always a negative value on each drafting. On the first drafting and the second drafting in which the moving distance of speed changing point is 0, those correlations are regarded as independent of each other because of the small value (Max. -0.2). However, on the second drafting in which the moving distance of speed changing point is not 0, the correlation is not regarded as independent because of the large value (Max. -0.7).