Fiber length


The influence of fiber length on the processing properties and the quality of the yarns produced is less significant in rotor spinning than in ring spinning, but should nevertheless not be underestimated. Fig. 69 shows the influence of different fiber lengths on yarn tenacity and yarn irregularity.

Table 9 shows the relationship between staple lengths and the yarn counts produced from them. It should be noted here, however, that this relationship is not governed solely by staple length, but that fiber count plays a role inasmuch as shorter fibers are often quite coarse, but longer fibers are available in finer counts.
This table also shows clearly that cotton and cotton waste with a high short fiber content (<1˝/25.4 mm) can be processed successfully using the rotor spinning principle. Cotton waste is therefore in demand as a raw material for certain ranges of application. However, it should be borne in mind that yarn quality declines alongside staple length; this affects yarn tenacity and yarn purity (imperfections) in particular. Yarns produced from shorter fibers usually also have to be spun with higher twist multiplyers. However, physical textile properties such as tenacity and regularity play only a subordinate role in the end products usually produced from these yarns, such as sheets, which are subsequently napped, while the high number of fiber ends has an especially favorable impact on the napping effect of the final fabrics (short fibers result in a high number, whereas longer fibers result in a lower number of fiber ends for the same yarn length).
If the rotor diameter is too small for the intended fiber length, twist integration in the rotor groove is considerably disturbed. However, the tolerance range is larger than is often described in the literature. As a rule of thumb, fiber length (mm) should not significantly exceed rotor diameter (mm). However, in mill practice fibers with a staple length of 40 mm, for example, are successfully spun in large quantities on rotors with a diameter of 30/32 mm.
Finally, it must be reiterated that in rotor spinning fiber length is not the dominant fiber characteristic it is in ring spinning; in the rotor spinning machine, this role is assumed by fiber count.

Table 10 shows the yarn counts of man-made fiber yarns as a function of fiber length.

The influence of staple length compared to fiber count is also of secondary importance for man-made fibers. The graduation of yarn count in accordance with fiber length results from the fact that, in contrast to cotton, shorter fibers are supplied in finer counts and longer fibers in coarser counts.

Fig. 69 – Relationship between staple length in inches (B) and yarn tenacity (A)

Table 9 – Yarn counts for cotton yarns as a function of staple length

Table 10 – Yarn counts of man-made fiber yarns as a function of staple length