After opening, the fibers must be supplied to the rotor. For this purpose, a closed fiber channel in the shape of a flow passage serves as a means of guidance. Centrifugal forces of the opening roller and a vacuum in the rotor housing cause the fibers to disengage from the opening roller. Transport of the disengaged fibers through the fiber channel to the rotor is effected by an air current generated by suction of air from the hermetically sealed rotor housing. The partial spinning vacuum on spinning systems with perforated rotors is generated by the rotors and thus depends on rotor size and rotor speed. The partial spinning vacuum therefore declines as rotor diameters become smaller or if dirt (trash, dust, fiber fragments) accumulates in the openings in the base of the rotor.
The shape of the fiber guide channel (Fig. 14, a) is crucial for fiber transport and the desired longitudinal orientation of the fibers. The inlet and outlet openings of the fiber guide channel must be designed and produced so that the transfer of fibers from the opening roller, fiber transport in the guide channel itself and the transfer of fibers to the inside wall of the spinning rotor (Fig. 14, b) are trouble-free. The fiber channel narrows toward the rotor, which causes acceleration of the air and fiber flows. This acceleration is of great significance because it leads to further separation of the fibers, down to between one and five fibers in section, and also straightens the fibers. The narrowing region represents a second draft zone (following the feed roller/ opening roller). Spinning box systems with both one-part and two-part fiber guide channels are used in mill operations. A two-part fiber guide channel is necessary in these systems on design grounds in order to facilitate opening of the rotor cover. The interface on the two-part fiber guide channel must be hermetically sealed in order to prevent the entry of secondary air and also be designed so that no air turbulence can occur. After leaving the exit port of the fiber channel the fibers are guided directly onto the rotor wall for deposit in the rotor groove, while the air – together with the remaining dust – flows over the rotor rim to the central filter housing. The outlet opening of the fiber guide channel must be positioned very close to the rotor wall to ensure that good fibers are not also sucked out over the edge of the rotor. Interchangeable channel inserts – in which the fiber guide channel is integrated – are available for this purpose and used depending on the given rotor diameter. Extensive mill trials have demonstrated that several rotor diameters, albeit in close proximity with each other, can be served by one channel insert. This significantly improves flexibility when changing spinning parameters, since the complete rotor cover does not need to be replaced with every change in rotor diameter. The channel inserts are sealed against the rotor housing to prevent air losses in the rotor housing.
However, if the distance between the fiber guide channel and the rotor wall is outside the optimum range, for example due to using channel inserts that are too small, good fibers can pass uncontrolled into the extraction system: this becomes apparent not only through an increase in ends down, but also – which is much more serious – through a change in yarn count (usually undetected) and the resulting enormous costs arising from defective final fabrics.
Channel inserts equipped optionally with a so-called SPEEDpass (Fig. 15) are a special feature. This is an additional opening in the fiber guide channel through which a certain proportion of the fiber transport air is extracted in order to increase the air volume and thus the rate of flow in the fiber guide channel. This promotes the disengagement of fibers from the opening roller clothing and is thus especially suitable for processing man-made fibers and blends containing more than 50% man-made fibers. At the same time the higher volume of air proves especially beneficial in the manufacture of coarse count yarns and thus for high material throughput.
Cotton dust (finishing abrasion in the case of man-made fibers) is also extracted through this opening. Fine dust therefore does not accumulate in the rotor groove, and yarn characteristics and yarn values remain stable.