The roller gins are classified as oscillatory knife gin and rotary knife gin depending upon the type of motion of moving knife. Oscillatory type gins are further classified as single roller (SR) and Double roller (DR) depending on the number of rollers used per machine.
The principle of working of single roller gin is popularly known as McCarthy principle named after its proponent.
It lies in picking and then moving the cotton fibres between the roller and fixed knife preventing the seeds to pass through. The seed cotton, when thrown into the hopper, passes through the machine. While the machine is working, at each elevation of the moving knife the grids lift the cotton to the level of the stationary knife-edge and of the exposed surface of the rollers. The free ends of the fibres are gripped, in the grooves of the rotating roller, and dragged forward till the seeds reach the edge of stationary knife. The edge where the fibre is caught is the ginning point. By the downward motion of the moving knife, the seeds are detached from the cotton at the ginning point and are thrown out through the slots of the grid. It is important that the grooves of the rollers should be kept well open and when the leather roller becomes smooth, rough file should be applied occasionally to the surface to keep the same grip and pull on the fibre. The seeds are then hammered by means of the rapidly moving knife whereby some fibres are separated. In subsequent cycles, the remaining fibres also get separated. This process is continued till all the fibres from the seed get removed.
The Single Roller McCarthy Gin technology is most suitable for handpicked, low trash cottons of medium, long and extra long staple length. This technology retains maximum natural fibre parameters of the cotton during the ginning hence treated best.
Double Roller is the improved version of McCarthy Single Roller Gins. In a double roller (DR) gin, two spirally grooved leather rollers, pressed against two stationary knives with the help of adjustable dead loads, are made to rotate in opposite directions at a definite speed.
The three beater arms (two at end and one at the centre of beater shaft) are inserted in the beater shaft and two knives (moving knives) are then fixed to the beater arms with proper alignment. This assembly is known as beater assembly, which oscillates by means of a crank or eccentric shaft, close to the leather roller. When the seed cotton is fed to the machine in action, fibres adhere to the rough surface of the roller and are carried in between the fixed knife and the roller such that the fibres are partially gripped between them. The oscillating knives (moving knives) beat the seeds from top and separate the fibres, which are gripped from the seed end. This process is repeated a number of times till all spin-able fibres are separated from the seeds, which are carried forward on the roller and doffed out of the machine. The ginned seeds drop down through the slots provided on seed grid, which is part and parcel of beater assembly, which also oscillates along with the moving knives.
This technology also retains maximum natural fibre parameters of the cotton similar to McCarthy Single Roller Gin but produces double or more quantity of fibre at same electrical power and processing cost hence most cost effective. Therefore maximum McCarthy Single Roller Gins have been replaced by this technology in case of hand picked cotton. In Double Roller Ginning Technology one can gin all types of cotton of the world by simple setting adjustments, hence this technology has rapidly replaced majority of McCarthy Single Roller Gins and has become most preferred technology for hand picked cotton where trash contents are lower in the seed cotton.
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