Ginning Process for Cotton - Spinning, Textile, Yarn

Ginning Process for Cotton - Spinning, Textile, Yarn Production

Ginning:

Cotton Ginning is the process of separating the cotton fibers from the cotton seeds. Perfect ginning operation would be performed if the separation of fibers from seed was effected without the slightest injury to either seeds or to the fiber. A cotton gin is a machine that quickly and easily separates the cotton fibers from the seeds, a job previously done by hand. These seeds are either used again to grow more cotton or, if badly damaged, are disposed of. It uses a combination of a wire screen and small wire hooks to pull the cotton through the screen, while brushes continuously remove the loose cotton lint to prevent jams. The term "gin" is an abbreviation for engine, and means "machine".

Types of Ginning

Previous to the introduction of Modern Machinery, ginning was performed by hand or by machines of a primitive character such as the "Foot Roller" and its improvement the "Churka".

As the cotton industry developed, greater production than these were capable of was necessary, and machines driven by power were introduced. Numerous forms of gins have been tried, but at the present time only three are used to any large extent. They are

• Knife Roller Gin / Roller Gin

• Saw Gin

• Macarthy Gin

SAW GIN

Object: To separate the cotton fibers from the seed.

WORKING: There are two general types of saw gins : (a) the plain type which gins only clean seed cotton that is free from bolls and trash, and is the original type of gin used; (b) the huller gin which separates the seed cotton from the bolls, burrs, leaf, dirt and other foreign substances in a front lower roll box, and then carries the seed cotton into an upper roll box where it sep arates the lint from the seed, thus performing a double ginning operation. The main working parts in both types of gins are the saws cylinder, roll box and means of removing the lint from the saw teeth after separation from the seed. The plain gin (fig. 20) consists of from 6o to 7o saws which are mounted on a shaft and revolve between the interstices of iron grids; against the grids the seed cotton is held whilst the fibres are drawn through, the seeds being left behind. The operation is as follows : seed cotton is conveyed into the feeder hopper and then carried by a lattice to a spiked roller that regulates the seed supply to the hopper or roll box. Whilst in the roll box the cotton is engaged by the teeth of the saws and drawn through the grids, which are set too close to permit the passage of the seeds. The cotton lint is next removed from the saws by a rotating brush which, on account of its higher surface speed, performs a wiping action on the saw teeth. After this removal the cotton lint is drawn through a flue to the surface of a perforated cage by pneumatic action, subsequently to pass between the cage and cage roller and out of the machine to the press box. The discovery that the air blast generated by the brushes played such an important part in re moving the lint from the saws eventually led to the introduction of the pneumatic or air blast gin—a machine in which the lint is removed from the saws by an air blast system instead of by a brush, thereby permitting a higher speed of the saws cylinder and a consequent increase in the productive capacity of the ma chine. The operation of the huller gin is very similar to that of the plain gin, in that the saws cylinder and the method of re moving the lint therefrom are the same. The roll box construction is also the same, except that there is an additional huller roll box in front of the ginning roll box. In hopper, the seed cotton comes into contact with rapidly revolving saw roller (A) saws are threaded on a shaft. As the saws revolve, the teeth carry the fibers forward, but it is impossible for the seeds to follow and also, due to the heavier beating of the rapidly revolving saws on the seed cotton, the fibers are separated from seed and taken round until the brush strips the fiber from the teeth.

Empty seeds husks and other broken seeds are thrown into grid, through which they pass into suitable receptacle. An air current from the cage draw the fibers along the trunk passage, and on reaching the revolving cage are brought under the pressure roller and delivered as a sheet, from which it is taken to the baling press.

PRESSING and BILING OF COTTON

The cotton gin is where cotton fiber is separated from the cotton seed. The first step in the ginning process is when the cotton is vacuumed into tubes that carry it to a dryer to reduce moisture and improve the fiber quality. Then it runs through cleaning equipment to remove leaf trash, sticks and other foreign matter.

Ginning is accomplished by one of two methods. Cotton varieties with shorter staple or fiber length are ginned with saw gins. This process involves the use of circular saws that grip the fibers and pull them through narrow slots.

The seeds are too large to pass through these openings, resulting in the fibers being pulled away from the seed. Long fiber cottons must be ginned in a roller gin because saw gins can damage their delicate fibers. The roller gin was invented in India centuries ago and this concept is still used in modern gins. Long staple cottons, like Pima, separate from the seed more easily than Upland varietie. A roller gin uses a rough roller to grab the fiber and pull it under a rotating bar with gaps too small for the seed to pass.

The raw fiber, now called lint, makes its way through another series of pipes to a press where it is compressed into bales(lint packaged for market), banded with eight steel straps, sampled for classing, wrapped for protection then loaded onto trucks for shipment to storage yards, textile mills and foreign countries. The cotton industry has adopted a standard for a bale of cotton, 55 inches tall, 28 inches wide, and 21 inches thick, weighing approximately 500 pounds. A bale meeting these requirements is called a universal density bale. This is enough cotton to make 325 pairs of denim jeans.

Every bale of cotton is classed from a sample taken after its formation. The classing of cotton lint is the process of measuring fiber characteristics against a set of standards (grades). Classing is done by experts, called classers, who use scientific instruments to judge the samples of lint. All standards are established by the U.S. Department of Agriculture. Once the quality of the cotton bale is determined, pricing parameters are set and the lint may be taken to market. Cotton marketing is the selling and buying of cotton lint. Cotton is priced in cents per pound when sold and the price is negotiated according to the cotton's quality. After baling, the cotton lint is hauled to either storage yards, textile mills, or shipped to foreign countries. The cotton seed is delivered to a seed storage area. Where it will remain until it is loaded into trucks and transported to a cottonseed oil mill or directly for livestock feed.