Rieter

Fiber count

Index

In rotor spinning fiber count and thus the number of fibers in the yarn cross-section probably have the greatest influence on yarn and spinning results. Fiber count (Micronaire or dtex) defines the spinning limit, i.e. the ratio of fiber count to yarn count from which stable spinning behavior is assured. Due to the markedly different yarn structure of rotor-spun and ringspun yarn, resulting in less pronounced parallelization of the fibers in rotor-spun yarn, the material utilization of fiber tenacity and thus also yarn tenacity (with the same fiber count and thus the same number of fibers in the yarn cross-section) is some 15 - 25% lower than in ring-spun yarn. In order to compensate for these system-related differences, i.e. in order to ensure stable spinning conditions and also achieve good yarn tenacity, rotor-spun yarns must be spun with a higher number of fibers (at least 90 - 110 (120)) in the yarn cross-section. The relationship between the fiber count of cotton and man-made fibers and the resulting spinning limit is shown in Table 8. The spinning limit (Nm/Ne/tex) can be calculated as follows:

spinning\ limit\ tex\ (Y) =\frac {dtex (F) \times n_F}{10} = \frac {Mic \times n_F}{25.4}

spinning\ limit\ Nm\ (Y) =\frac {10\ 000}{dtex (F) \times n_F} = \frac {25\ 400}{Mic \times n_F}

spinning\ limit\ Ne\ (Y) =\frac {5\ 917}{tex (F) \times n_F} = \frac {15\ 030}{Mic \times n_F}

nF = number of fibres given for the spinning limit in the table 8 (90 to 110 fibres)

Derived from this, the number of fibers in the yarn crosssection (nF) is calculated as follows:

number\ of\ fibers\ n_F =\frac {tex (Y) \times 10}{dtex (F)} = \frac {5\ 917}{Ne (Y) \times dtex (F)} =\frac {10\ 000}{Nm (Y) \times dtex (F)}

number\ of\ fibers\ n_F =\frac {tex (Y) \times 25.4}{Mic} = \frac {15\ 030}{Ne (Y) \times Mic} =\frac {25\ 400}{Nm (Y) \times Mic}

nF = number of fibers in the yarn cross-section 
Mic = Micronaire
Y = yarn
F = fiber

In blends the arithmetic mean fiber count (dtex or Micronaire) is calculated according to the percentage content of the individual components:

Example:
67% polyester 1.3 dtex/33% cotton 4.2 Micronaire = 1.65 dtex (dtex cotton = Micronaire x 0.394)

Øfiber count = 100/{[67/1.3] + [33/1.65]} = 100 / [52 + 20] = 1.4 dtex

The cottons used for rotor-spun yarns are mostly in the count range of 3.5 to 4.6 Micronaire, although in some applications very fine cottons from 2.8 Micronaire (for very fine yarns) up to very coarse yarns up to 5.0 Micronaire (in the coarse yarn range) are used. Care is required especially with very fine fibers – <3.0 Micronaire – since in this count range the danger of immature fibers increases. In this context a fundamental comment on the Micronaire value:
when using the Micronaire value it should be borne in mind that this value does not always correspond to the current count, since it is influenced by the maturity of the fiber. It has been established that for certain Micronaire values the current count corresponding to the maturity varies, and can thus also influence the spinning limit. Accurate fiber count values are obtained by measuring fiber count in mtex or dtex. However, since the Micronaire value is still mostly used in practice, the following statements are also based on this value.
Through careful selection of correspondingly fine and well matured types of fiber, carded cotton yarns up to Ne 60 / Nm 100 / tex 10 can now also be spun industrially, i.e. with stable spinning conditions and good yarn values, using the rotor spinning system.
Man-made fiber manufacturers recognized the importance of finer fibers for rotor spinning very early, and have offered increasingly fine fiber counts on the market. Whereas fibers were offered with 1.5 den as the finest count at the beginning of the nineteen-eighties, only a few years later fibers with 1.2 den and within a few more years fibers with counts of <1.0 den, so-called microfibers, were already available. The availability of these very fine fibers has enabled yarn manufacturers to produce increasingly fine yarns with increasingly high yarn quality. By using microfibers, manmade fibers with counts of up to Ne 60 / Nm 100 / tex 10 can also be spun on rotor spinning machines.
If finer fibers are also used for coarser yarns, i.e. the number of fibers in the yarn cross-section is increased, this has a positive influence not only on the yarn characteristics; in particular, yarn twist can be significantly reduced, which in turn substantially improves the hand of the yarns in the end products. These advantages have been exploited by those yarn manufacturers who prefer to manufacture yarns for end products where wearing comfort plays a major role. This applies in particular, for example, to T-shirts (in which rotor-spun yarns are now dominant both in the US and also in Europe), but also to leisurewear and lightweight men‘s and women‘s outerwear. Fig. 68 clearly shows the influence of fiber count, i.e. the number of fibers in the yarn cross-section, on yarn tenacity.
Yarn counts of yarns produced from wool and bast fibers, even if they are spun in blends with cotton or man-made fibers, depend largely on the available (and also widely varying) fiber counts. However, since the fibers of these raw materials are usually coarser than those of cotton or manmade fibers, the finally spun yarn counts are usually in the coarser count range ≤ Ne 12 / Nm 20 / tex 50. Yarns in counts up to Ne 24 / Nm 40 / tex 25 are produced only with very fine wool grades or angora wool, usually in blends with cotton or PES (the figures given are only approximate values).

Table 8 – Spinning limit for cotton and man-made fiber yarns as a function of fiber count

Fig. 68 – Relationship between fiber count (B) and yarn tenacity (A)