Rieter

Deformation of the yarn in length and width

Index

Fibers can be wound in spirals around other fibers only by increasing their length through exploitation of fiber elongation. When a fiber is extended, its elasticity tries to draw it back. This constant tendency to return to the unextended condition results in a high tension directed towards the core and thus to increase pressure continually towards the yarn interior. These tensions cause the strong compression, and hence great density of the yarn body. The compression leads to a reduction in the diameter of the yarn.

Diameter is thus inversely proportional to twist. However, the tendency to relax also leads to shortening of the yarn (twisting-in, spinning-in). The same effect is produced by the inclined disposition of the fibers relative to the yarn axis. Hence, the length of the spun yarn never corresponds to the delivered length measured at the front roller. The degree of shortening is also dependent upon the raw material and especially upon the number of turns. Johannsen and Walz  [20] indicate that for cotton yarns twisting-in can be derived from Fig. 60 (as an example for Texas cotton).

Fig. 60 – Shortening of yarns with different twist coefficients; A, shortening in %; tex, yarn count ; α, twist multiplier (e, english; m, metric)