An Overview of Open End Spinning

Open end Spinning:
Open end spinning or open-end spinning is a technology for creating yarn without using a spindle. It is also known as break spinning or rotor spinning. In this process the fiber sliver is separated into single fibers and in which the separated fiber material is brought by an air stream to a collecting surface from which it is drawn off while being twisted. It is a more recent method of yarn formation compared to Ring Spinning.

This is normally used in cotton carded spinning. The frame is fed with slivers from the drawframes which transform the yarn directly into packages, eliminating the passage on the roving frame and, in many cases, further packaging operations. The figure below represents an example of rotor (or open-end) spinning frame.
Open End Spinning Frame
Open End Spinning Frame

The main function of the spinning unit is as follows:
The sliver from the drawframe is introduced by a feeder cylinder and is subject to the action of an opener with saw-toothed wiring which rotates at a speed of between 6000 and 9000 rpm, separating the sliver into single fibres, then the fibres are sent to the rotor through a vacuum channel. The rotor, whose diameter is between 32.5 and 54 mm, rotates at a very high speed over 100,000 rpm, and compacts the fibres partly thanks to its special shape, twisting the fibres at the same time.

The processing data of an open-end frame for cotton are normally as follows:
  • Sliver count Ne 0,10 . Ne 0,27 ( Tex 5900 . Tex 2180)
  • Yarn count Ne 5 . Ne 40 (Tex 120 . Tex 15)
  • Draft range 16 . 250
  • Twists 300 . 1500 T/m.
The yarn formed in this way then passes to the winding unit which makes the packages, that are either cylindrical or conical. The cylindrical packages can have a diameter of 300 x 152 mm and the conical ones a diameter of 270 x 152 mm. The winding speed can reach up to 200 m/min.
Diagram of rotor spinning frame
Diagram of rotor spinning frame

The yarn produced by the rotor spinning frame presents different features from the conventional ring yarns, as the fibres tend to be arranged around the edges of the rotor in a casual manner, rather than as a result of the length of the fibres themselves or with a preferential migration of fibres.

It follows that a regular yarn is formed but with the presence of longer fibres in the yarn that also hold other fibres, giving the yarn a characteristic look and a higher degree of hairiness.

Modern rotor spinning frames, due to some technical improvements such as more efficient cleaning, thanks to pneumatic evacuation of impurities in the channel, the self-aspirating rotor system, the particular design of the rotor transport channel, the adoption of separators with particular profiles that determine a better distribution of fibres in the groove of the rotor, are able to produce yarns of a better quality and more similar to those made on ring spinning frames 

The following figures show a macroscopic view of the structure of the two types of yarn, the first produced on a modern rotor spinning frame (100% cotton Ne 30), the second on a conventional machine (100% cotton Ne 30).

It can be seen that the first yarn presents better evenness and less hairiness. As a consequence, the improved parallelisation of the fibres and more regular final structure will give the yarn better elongation resistance, and therefore generally offer more sophisticated performances.

Furthermore, the waxing system is able to guarantee distribution of the wax over the yarn in a regular manner according to the quantity desired. The machine is automated by carriages for automatic piecing of the thread and package doffing of a number variable between 1-2-4 per machine.

A machine normally has two completely independent sides, with automatic distribution of empty tube yarn piecing carriage, package doffer and rotor cleaning. The machine is generally mounted with modules of 24 units on 2 sides and carries a maximum number of 288 units per machine.

The machine also has a system for quality control, productivity and maintenance. The computerised system automatically controls production, it manages the spinning units and shows output data for each individual unit. Furthermore, the system is capable of self-diagnosis when machine alarms occur and in the eventuality of inefficient individual units. It is also possible to apply electronic yarn clearing systems to eliminate yarn defects directly on the spinning frame.

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