recent advances in ginning for lowering cost and ... - Bajaj Group

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(RECENT ADVANCES IN GINNING FOR LOWERING COST AND IMPROVING OF EFFICIENCY) # 2 # cottons having length up to 27-28 mm. The single roller gins and double roller gins can be used for cottons of all staple categories while Rotobar gin is used for long and extralong cottons particularly black seeds only. Among all the types of roller gins, double roller gins are most commonly used in India and other countries due to its advantages over other ginning technologies. The ginning operation needs to be carried out carefully so that the fibres are not damaged or broken during the process and the overall quality of lint remains practically unchanged. For ensuring this, machinery used for the ginning process requires proper adjustments and regular maintenance. The details of each ginning machine is elaborated below: Figure 3.1 Improved version of charkha gin 3.2 Saw Gins The Saw Gin belongs to second-generation tool invented by Eli Whitney in 1794, in the USA and the latest version is shown in Figure 3.2. It consists of a series of circular saws, 305 to 407 mm (12 to 18 inches) in diameter. All the saws are mounted closely on an axle and are made to revolve at high speed in order to tear the lint away from a roll of seed cotton. The saw projects slightly between bars or ribs, which are so, spaced that they prevent the seed from going forward. Fibres are thus torn away from the seeds with high speed. The seed cotton is fed continuously into a rounded box or hopper. The action of the saws keeps it revolving in a loosely compacted roll. The seed falls through a grid into a collecting box or seed conveyor. The lint is whipped off the teeth of the saws by high-speed brushes or an air blast. Figure 3.2 Saw Gin stands in ginnery in USA Contd. …3.
(RECENT ADVANCES IN GINNING FOR LOWERING COST AND IMPROVING OF EFFICIENCY) # 3 # The average saw gin turns out about 500 kg of lint per hour. However, saw gin gives about 1% to 3.5% less ginning percentage than single and double roller gin. Although the ginning output of saw gin is very high, these gins are not suitable for ginning extra-long staple (ELS) varieties and the lint is more nappy than the roller ginned lint. The maintenance of saw gin is very costly because there are many moving parts which are of special construction and many times are not readily available. Further, a qualified and experienced technician is required to operate saw gin stand to get the optimum output and to replace the worn out parts and adjust the gin for uniform processing of seed cotton. In view of limitations in respect of ginning short and medium staple cotton only, fibre length cutting and higher neps, saw gin in the countries like India where different varieties of different fibre parameters are grown has been phased out completely by double roller gins. 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 while Rotary Knife gin is called Rotobar. 3.3.1 Single roller gin - McCarthy gin The principle of working of single roller gin is popularly known as McCarthy principle named after its proponent and shown in Figure3.3. Figure 3.3.1 Single Roller Gin 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 gins have been phased out in India by Double Roller Gins due to lower production in single roller gins at same electrical power and manpower cost. Contd. …4.
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