For getting high quality of yarn, one extra process is introduced which is called combing process. Combing is an operation in which dirt and short fibers are removed from sliver lap by following ways.
- In a specially designed jaws, a narrow lap of fiber is firmly gripped across its width
- Closely spaced needles are passed through the fiber projecting from jaws.
The combing process is carried out in order to improve the quality of the sliver coming out of the card. The process eliminates short fibres, it achieves better parallelisation of fibres, it straightens curls, and it removes neps and residue impurities. It is clear from these functions that the combing process is essentially aimed at obtaining excellent quality yarns and to fulfill this objective raw materials with above average physical and mechanical features must be used from the very beginning of the spinning process.
Depending on what is being produced, waste from combing varies from 12% to 25%, and this can be employed to obtain yarns with a medium coarse count using the open-end process.
As far as parallelisation of curls is concerned, when curls are combed they tend to behave in a very similar way to short fibres and therefore if they do not straighten they are removed, and this produces a notable amount of waste fibres; it is therefore necessary to reduce the curls before the combing stage. Some of the .curls. straighten when drawn in the combing preparation stage.
Furthermore, it is a good idea for the curls to be presented head first to the combing machine, as the latter are to a large extent straightened by devices on the combing machine. The direction of the curls depends on the number of passages the material is subject to following carding, as between one passage and another the direction of the material is inverted and consequentially the curls are too. Therefore, considering that mainly tail curls come out of the card, in order for them to arrive at the combing machine as head curls, it is fundamental to carry out an even number of preparation passages, usually two, one to the drawframe and one to the lap drawing frame.