Rieter

General

Index

Whereas synthetic and cellulosic man-made fibers are usually „clean“, i.e. free of trash and extraneous material (with the exception of coarse fibers and packaging residues), raw cotton always contains a certain amount of organic and inorganic trash, dust, and vegetable and extraneous particles. The majority of disturbing impurities can be eliminated by efficient cleaning of the cotton with the appropriate number of cleaning positions in spinning preparation and careful carding (see  Fiber Preparation). Modern blowrooms are capable of removing up to 97% of the trash contained in raw cotton (trash content of the carded sliver compared to the raw cotton fed to it).
However, depending on the method of harvesting and the „cleaning propensity“ of the cottons used, certain disturbing extraneous materials can survive the cleaning and carding process. These are mainly:

  • fine and very fine dust (especially critical when adhering tenaciously to the fibers);
  • extraneous fibers (especially bale packaging material);
  • vegetable residues (seed coats, leaves, cotton plant stems);
  • larger trash particles when the cotton has not been adequately cleaned.

While trash removal on the rotor spinning machine is capable of effectively removing larger trash and extraneous particles, dust and other very light extraneous material can reach the rotor in the air current and be deposited there in the rotor groove.
Coarser particles (mainly seed coat fragments) stay caught in the rotor groove. They can prevent yarn formation at this point, and this in turn can result in ends down, mainly when spinning finer yarn counts. On the other hand, fiber agglomeration at the particle results in a thick place at the agglomeration point, and immediately thereafter a thin place where the agglomerated fibers are absent in the groove. The resulting defect (thick/thin place) is absolutely periodic and leads to a moiré effect if the affected yarn is worked into a fabric.
Small dust particles lead to slow but persistent filling-up of the collection groove in the rotor. If this is originally narrow, it becomes steadily more open and wider as it fills up. The fiber bundle, which was extremely condensed in the narrow groove to produce a compact yarn, becomes steadily less compressed; the yarn thus becomes gradually more open and bulky. The yarn character and quality thus change gradually and unnoticed over a long period. The same effect is observed in spinning synthetic fibers if the spin finish can accumulate in the rotor.
Clean raw material is therefore a precondition for spinning yarn on the rotor spinning machine. Rieter Ingolstadt recommends that the following residual trash content should not be exceeded in the feed sliver:

  • up to Nm 10/ Ne 6/ 100 tex : 0.3 %
  • up to Nm 34/ Ne 20/ 30 tex : 0.2 %
  • up to Nm 50/ Ne 30/ 20 tex : 0.15 %
  • above Nm 50/ Ne 30/ 20 tex : 0.1 %.

These requirements imply that the “cleanest possible” cotton should be sought out at the purchasing stage and furthermore that good preparation equipment, giving a high cleaning and dust-removal effect, is of great benefit for the rotor spinning process. In addition, several machine manufacturers have fitted their machines with trash-removal devices.