Rieter

Fiber flow to the rotor

Index

At the start of the development of rotor spinning, the fibers were mistakenly guided directly into the fiber collecting groove. The disadvantage of this was that the fibers inevitably collided with the radial yarn end during the acceleration that had to occur. This led to deterioration in fiber orientation. Yarn produced in this way had the typical „sauerkraut“ structure, with very low strength.
In current rotor spinning machines, the fibers flowing into the rotor are headed for the top of the rotor wall, above the groove. It is important that the rotor wall has a higher peripheral speed than the fibers colliding with it. Thus a drafting effect is taking place, which ensures that the fibers are straightened and aligned. The necessity to operate with a draft at this point places a lower limit on the rotation speed of the rotor, which is therefore limited not only upward but also downward.

The air flows are also very important in this zone. There should be no air turbulence between the fiber channel and the rotor wall. The aim is to generate a uniform, rotating air current that helps to forward the fibers onto the rotor wall in a straight condition. This depends, among other things, on the distance between the exit of the fiber channel and the wall and the shape of the rotor channel insert that contains the fiber channel. Accordingly, all manufacturers use replaceable channel inserts matched to the diameter of the rotor, which is also replaceable. The amount of air – which is necessary for the fiber flow – is extracted by the main fan through the gap between channel insert and rotor cup.

An incoming fiber strikes an inclined wall and is pressed outward by an enormous centrifugal force – over 100 000 times the weight of the fiber. This causes the fiber to slide downward on the rotor wall while being accelerated in the peripheral direction and to be deposited on the other fibers in the collecting groove.
Due to the fact that the fibers are continuously accelerated from the moment they are released from the sliver by the opening roller until they are deposited in the rotor groove, they are well extended longitudinally, also compared to other OE processes. This extension is also maintained in the finished yarn due to the high centrifugal force with which the fibers are then pressed into the rotor groove. Only in the outer layers of yarn are the fibers of rotor-spun yarn (core twist) less accurately aligned than in ring-spun yarn (surface twist, refer to section  Yarn structure and physical textile characteristics).