1. Introduction
All the natural fibres including cotton have considerable amount of impurities in them which have to be removed to produce a clean yarn. On other hand short staple man made fibres just require opening but no cleaning. The amount and type of cleaning required for a particular lot of fibres depends upon size and amount of impurities present in it. Greater the trash content in fibres greater no of cleaning points are used during various stages of the spinning process. Cleaning is generally associated with opening. As the fibre opening takes place, the impurities also get separated and removed.
(Zone 2): The course cleaning machine directly gets it feed from the hopper feeders or from top feeders. The striking and beating elements in the zone are widely spaced and hence the opening of the fibres is also very minimal. The main purpose of these machine is to open up the mass of fibres in to large tufts. Which are then converted in to smaller tufts by using more intense opening and cleaning machines in the next zones. The machine in these zones are sometimes not even fitted with cleaning devices or even if these cleaning devices are present, they can only remove fraction of the impurities.
2. Cotton Impurities
Any foreign material other than fibres is classified as impurities. The removal of impurities also results in the loss of useful fibres. The impurities in cotton fibres are:-
a)Seed-It is present in raw cotton as largest impurities includes ginned seeds, un-ginned seeds and part of seeds.
b)Chaff– It is vegetable fragments consisting of leaf particles, bract ,shale and stalk of cotton plant.
c)Dirt– It includes soil and sand particles that may be handle from the cotton field due to mishandling, fibre pickup dust and during transportation .
d)Micro dust– The micro-dust includes very fine particles of chaff, dirt, small fibre fragments and spore of mildew.
e)Abnormal impurities– This includes pieces of stones, pieces of iron, cloth fragments, foreign fibres such as jute, poly propylene etc. This found very rare in the cotton fibres.
3. Cleaning Machines
Different machine manufacturers have developed various types of course cleaning machine. The most commonly used ones are:
A. The Step Cleaner
The step cleaner is very standard type of cleaning machine that is produced by several manufacturers. As the material falls in to this machine it is subjected to first beater which not only does the initial opening but also transports the fibres upwards where sometimes 4 or 6 beaters are placed closed to one another and inclined at an angle of 45˚. The surface of these beater rollers are covered with blades or bars. The cleaning of impurities takes place as the material continuously passes from one roller to the roller with the help of grids placed beneath each of the other. The speed of the beaters and the grids are both adjustable.
B. Uni-Cleaner
The uni-cleaner or the mono-cylinder cleaner relies on the use of single beater roller having its surface covered with spikes. The fibre material enters to the machine from one side due to a suction effect produced at the other side of the machine. To ensure that fibres may not pass the exit pipe untreated by the beater, following arrangement is done.
- The hood of the machine around the beater is designed in three portions in such a way that the fibre mass is forced to fall back in to region of the beater after being beaten. In this way the fibres are forced to circulate the beater many a times to give required opening and cleaning.
- The exit opening of the machine is kept higher than the in-feed opening of the machine that also ensures that only the smallest tufts can pass straight through but the bigger tufts are always subjected to the beater action of the beater.