Cotton ginning is the process of separating cotton seed from the lint so that the lint will be baled and goes to textile industries for further processing whereas the cotton seed is milled by oil mills to produce edible oil.
Cotton ginning, therefore, requires the unprocessed raw cotton, and then is applied on the cotton ginner in order to produce baled cotton and cottonseed.
The major unit operations involved in cotton ginning are: -
- Lint cleaning
Schematic diagram of cotton gin production
1. Raw cotton from the storage
hall is manually transported to an intake separator where the cotton is screened out and allowed to pass to the next machine. Modern separators have rotating sealed wheels and curved screens which permit the air currents to pass directly to a fan. The separation process involves equipment like the separator, feeding hopper, fan with tubular air ducts.
2. After the seed cotton (raw cotton) is separated from foreign materials (possibly carried over from cotton farms and during transportation), it is then passed to a hot gas drier. Here the seed cotton that is damp or wet will be dried. If seed cotton is wet some of the lint will be cut by the saws or packed into small dense tufts. The saws may become so clogged that the gin will not run at all. Hot gas dryers can be bypassed when ginning during dry weather.
3. Cleaners are types of machines having concave screens or grid bars utilizing beater cylinders and are frequently supplied with a down wash of hot air. Cleaners would, therefore, clean the seed cotton by threshing over screens.
4. Extractors are equipment that employ a toothed "carding" action on the locks of cotton in conjunction with stripper cylinders that beat off the hulls, burs and stems, while the lock passes onto a doffing brush. Extractors perform functions of cleaning and extracting of large piece of foreign materials.
5. Cotton gins (ginneries) use mechanical forms of distribution between overhead machinery and the feeders on the gin stands. Each gin stand in a multiple of gin stands is supplied with all the cottons it can handle. Distributors thus supply cotton to all gin stands installed in the ginnery.
6. Feeders are devices, located over each gin stand, that supply the gin saws with a regulated streams of clean, dry seed cotton. Feeder takes the form of regulated rollers with spiked drum and screen.
7. Ginning is the process of separating the seed from the lint. This is accomplished by gin saws. These are steel disks approximately 0.037 inch thick and provided with about seven teeth per inch of periphery. Improved huller gins use saws 12 inches in diameter, having from 264 to 282 teeth and running at speeds from 650 to 700 revolutions per minute for maximum capacity.
Ribs of tough, highly polished iron are used in cotton gins to form grids through which the saws may pass. Ginning ribs are spaced about 1/8 inch apart, so that the saws carrying the lint may pass while the seeds are excluded.
The cotton gins employ rotating brushes to remove the cottons from the saw teeth. After the seed is separated from the lint, it is discharged in to self-cleaning belt and then in to self-cleaning blowpipe systems. The lint removed from the saws is carried by air blast to the condenser, which consists essentially of a large roller covered with wire screen and smaller wooden roller. From the condenser, the cotton drops in to the press box, over the bottom of which has been spread bale bagging. As the cotton collects in the box it is packed every minute or so by mechanical trampers. After enough has been accumulated to make approximately 750lbs bale, heavy pressure is applied by hydraulic press. When the cotton is under pressure, the bagging is fitted over the sides of the bale and six steel ties are put around it and fastened. Pressure is then released, and the cotton expands somewhat but is held firmly in a compact bale by the bagging and ties. The bale is now complete. The seed produced is bagged in hessian sacks and are dispatched to oil mills. The process is environmentally friendly since it does not emit any toxic chemical