In all other spinning processes, an uninterrupted stream of fibers proceeds continuously, but with gradual attenuation, from the feedstock to the take-up package. In open-end spinning, this flow of fibers is interrupted, the fiber strand being opened into individual fibers at a predetermined position, usually by means of an opening roller, followed by airborne fiber transport. This interruption or break in the fiber flow is physically achieved by increasing fiber speed locally to very high levels (up to 100 m/s), so that – according to the equation of continuity – the number of fibers in the cross-section drops to such low values that the fibers lose contact with each other. This enables twist to be imparted merely by rotation of the yarn end, which in turn leads to a significantly higher potential rotation speed. However, the break in fiber flow also leads directly to one of the most important and difficult tasks in open-end spinning, namely to control the configuration of the individual fibers, airborne at high speed, and the need to re-collect these fibers without losing their elongated configuration, which is essential to the formation of a new fiber strand. This very tricky problem of open-end spinning can be dealt with schematically as described below (see Fig. 1).
A constant stream of separated, individual fibers is allowed to flow to a rotating yarn end. The brush-like, open yarn end grasps the fibers brought into contact with it and continuously binds them into a yarn with the aid of the continual rolling movement. The continuously formed yarn has only to be withdrawn and taken up onto a cross-wound package. On the basis of the device used to reassemble the separated fibers, distinctions are drawn between:
- rotor spinning;
- electrostatic spinning;
- air-vortex spinning;
- friction spinning; and
- disc spinning.
Rotor spinning has meanwhile become so widespread worldwide in the market that this very important and well-established spinning system is dealt with in a separate volume. The other open-end processes are described hereafter.