The opening roller‘s task is to open the carded or drawframe sliver fed to the 
spinning box into individual fibers and at the same time to separate the fibers from the trash. The shape, geometry and design of the opening roller are, alongside the rotor, of the greatest importance for faultless spinning results. Its function with regard to releasing individual fibers from the fiber sliver, its influence on trash removal and fiber transport to the fiber transfer point in the fiber guide channel is described in detail in section opening unit.
The point and front flank of the clothing tooth in particular are exposed to wear. The wear is greater, the more aggressive the raw material used, for example when processing cotton containing mineral dust or man-made fibers containing delustring agents (titanium dioxide TiO2). The service life of the opening roller clothing is significantly improved if the teeth are coated. In this case the clothing is either given a nickel coating or diamond powder with a grain size of several microns is embedded in the nickel layer for even better wear resistance. The service life of nickel-plated clothing is about twice that of steel clothing that has only been hardened, while diamond/nickel-treated clothing lasts about 4 times as long.
Worn opening roller clothing usually first becomes apparent when ends down increase and yarn irregularity and imperfections deteriorate with otherwise identical raw material and spinning conditions. As a rule of thumb, clothing can be described as worn when ends down rates double and yarn irregularity deteriorates by more than 1 CVm%.
Clothing shape and opening roller speed must be coordinated with the raw materials being processed (see Fig. 73). Clothing differs mainly in tooth shape, the gradient of the front flank of the clothing tooth and tooth density (pitch) relative to clothing surface area:
- For carded and combed cottons and viscose, clothing with a large, i.e. more aggressive front flank, higher tooth density and sharper points (type B 174) is usually used.
- For critical cottons, also those containing a small amount of honeydew, the use of clothing type B 174-4.8 is recommended, which is characterized by a modified clothing shape and wider tooth spacing (4.8 mm instead of 2.5 mm as in B 174).
- Clothing shape S 21 is characterized mainly by a less sharply inclined and thus also less aggressive front flank, which is suitable for gentle processing of thermally more sensitive man-made fibers in particular, especially polyesters and their blends.
- Clothing with low tooth density and low tooth height, type S 43, is used in particular for man-made fibers with a tendency to lap due to high metal/fiber cohesion, such as polyacrylic. Especially gentle opening is possible with this clothing and at the same time the fibers are more readily released from the clothing.
Besides the clothing specification, opening roller speed has a decisive influence on spinning results, as regards both the running behavior of the rotor spinning machine and yarn quality. The ideal speed for a given raw material and a given yarn is preferably defined by a series of trials at several opening roller speeds. The most suitable speed can be chosen on the basis of yarn quality. A series of trials of this kind can even provide a rough idea of running behavior. If 2 or 3 thread breaks already occur during a half-hour spinning trial on 10 spinning positions, this opening roller speed is unsuitable for stable spinning conditions, despite possibly good yarn values. Empirical values for basic settings are usually provided by machinery/component suppliers.
The following factors apply in principle when specifying the opening roller speed:
- A higher opening roller speed should be selected, the higher the material throughput per unit of time, for example with coarse yarns and/or high delivery speeds, or the more heavily contaminated the raw material and the more effective trash removal therefore has to be.
- The opening roller speed selected should be lower, the more sensitively the fibers react to mechanical and thermal stress and would be damaged at excessively high speeds.
- Certain raw materials, especially very fine and/or very long man-made fibers or fibers with high fiber/metal adhesion, have a tendency to lap in the opening roller clothing. In these cases especially careful definition of the opening roller speed is required, and this can ultimately only be specified by spinning trials.
Opening roller clothing, especially the teeth, is particularly susceptible to mechanical damage. If certain spinning positions display especially high ends down rates, or yarn quality deteriorates particularly severely at certain spinning positions, this is often attributable to broken or bent teeth, usually caused by incorrect handling when installing or replacing the opening roller. Maintenance and operating personnel must be specially instructed to handle opening rollers carefully and gently.
Fig. 73 – Tooth shapes of the opening roller clothing and their range of application
