Operating principle of the rotor spinning machine


The feedstock is in the form of either  drawframe sliver (almost always) from first- or second-passage drawing or  carded sliver (a) (see Fig. 7). The sliver runs from a round or rectangular can beneath the spinning unit through sliver guide (b) via  feed roller (d) and feed table (c) to rotating  opening roller (e). The rotating feed roller grips the sliver and pushes it over the feed table into the opening roller housing. The feed table is spring-loaded to ensure firm clamping of the sliver toward the feed roller.

In the event of a yarn end down, sliver feed is automatically stopped by disengaging the feed clutch and thus stopping rotation of the feed-roller. The signal pulse causing this is generated by a yarn-sensing device (thread monitor).
In the conventional  ring spinning process the fiber bundle – i.e. the drawframe sliver – at the in-feed is maintained as a coherent structure and is merely attenuated during spinning. In rotor spinning the fiber bundle is opened into individual fibers. This task is performed mainly by the opening roller. This roller, which is usually clothed with saw teeth, combs through the fiber beard projecting from the nip between the feed roller and the feed table; it transports the released fibers to fiber channel (f).
An air current is needed to transport the fibers from the opening roller via the  fiber channel to the rotor. This is generated by main duct (h) in the sections and then via a vacuum in the rotor housing (i). The vacuum is created by a central fan that draws air by suction through small ducts from each rotor housing. To facilitate generation of this negative pressure, the rotor box must be hermetically sealed as far as possible. Most of the transport air enters only at the  trash removal slot and only a small amount via the draw-off tube.

One result of the centrifugal force of the opening roller is that impurities carried with the incoming sliver are expelled through an outlet of the opening roller housing. The expelled waste falls onto conveyor belt (g), which carries it either to one or to both ends of the spinning machine, where it is removed by suction nozzles on each side of the machine.
The suction current in the fiber channel lifts the fibers off the surface of the opening roller and leads them to rotor (k). In the course of this movement, both the air and the fibers are accelerated due to the converging shape of the feed tube. This represents a second draft following the nip trough / opening roller and results in further separation of the fibers. Moreover, partial straightening of the fibers is achieved in this air current. A third draft arises upon arrival of the fibers on the wall of the rotor, since the peripheral speed of the rotor is several times the speed of the fiber. This is a very important feature, since it contributes significantly to good orientation of the fibers. Final straightening of the fibers occurs as the fiber slides down the rotor wall into the groove under the influence of the enormous centrifugal forces acting within the rotor.
On average, one to five fibers (in section) emerge simultaneously from the exit of the fiber channel. After sliding down the rotor wall, they come to rest in a longitudinally oriented form in the rotor groove. Because the rotor is turning continuously under the stationary exit of the fiber channel, continual deposition of fibers in the groove is achieved (i.e., fiber is laid on fiber). In this way, a continuous fiber ring is built up in the groove. This operation is referred to as back-doubling (refer to section  Fiber collection in the rotor groove (back-doubling)).

If nothing further were done, the rotor would be choked in no time. However, since the whole purpose is to form these fibers into a new yarn, the free end of yarn (l) is allowed to extend from the rotational axis to the rotor periphery. Centrifugal force (more than 100 000 times the weight of the fiber) acting at this point presses the yarn end firmly against the wall of the collecting groove, exactly as in the case of the fibers in the ring. The yarn end therefore adheres to the rotor wall. As the rotor turns, it therefore carries the yarn along, and the latter rotates around nozzle (o) like one arm of a crank.
Each revolution of the rotor generates one turn of genuine twist in the yarn. When the yarn has reached its maximum twist level as determined by the prevailing force conditions, the yarn end begins to turn about its own axis, i.e., it rolls in the rotor groove. Now the open yarn end is resting in the binding-in zone on a strand of parallel fibers; rolling of the yarn end therefore causes the brush-like yarn end to grasp fibers from the ring and twist them in to give a new yarn portion, which proceeds to grasp the next fibers and twist them in, and so on. A yarn is thus spun continuously. It is simply necessary to pull this yarn out of the rotor via yarn compensation bar (p) by means of take-off rollers (m + n) and wind it up on winding drum (q) into crosswound package (r).

Machine automation by means of operating robots as well as package removal systems are described in the section  Machine automation in rotor spinning and transport automation in the section  Transport automation in the rotor spinning mill.

Fig. 7 – Path of the fibers from sliver feed into the spinning box to winding of the yarn onto cylindrical or conical cross-wound packages