Role of the Cotton Gin

The role of the cotton gin has changed dramatically in the last 50 years to keep up with technological and production changes in the cotton industry. At one time, the gin's only function was to remove cottonseed from the fiber. Today, gins must not only separate the seed from the fiber, they must also dry and clean the fiber and package it into bales before it reaches the textile mill.

All gins differ in some aspects of the ginning process. In the Southwest, for instance, gins are equipped with both saw and roller gins: saw gins for ginning Upland cottons, and roller gins for ginning Pima cotton, a cotton grown almost exclusively in this region of the Cotton Belt. Elsewhere in the Cotton Belt, gins use only saw gins in their operation.

The Ginning Process

Stage I: Seed Cotton Conditioning and Cleaning:
Seed cotton - seeds with fiber still attached-usually arrives at the gin in large trailers or modules used for hauling it from the field and for storing it until ready for ginning. From the storage area, conveyor pipes transfer it to the various stages of the ginning process using large volumes of air to make the flow of the cotton easier and faster.

Typically, seed cotton is first dried in large driers using heated air to reduce its moisture content. A cylinder cleaner then removes the leaves and other small trash from the seed cotton by shaking it with spiked cylinders, while conveying it across a screen with small openings that sift the trash released from the seed cotton by the impact action of the cylinders.

Next, a stick machine removes any large sticks or hulls (the dried bolls that form a shell around cotton as it grows) with revolving channel saws. These saws grab the seed cotton and whip it over metal bars to sling off its trash. If the seed cotton requires additional drying and cleaning, gins will often run it through another drier and another cylinder cleaner and stick machine.

Mechanical harvesters made seed cotton drying and cleaning necessary. Although much faster than hand harvesting, mechanical harvesters also pick more trash with the cotton, which usually contains a high amount of moisture. Trash, as well as moisture, can adversely affect the quality of the fiber and lead to costly operating and processing expenses at the gin and at the textile mill.

Excess moisture is common to cotton grown in the more humid regions of the Cotton Belt, while cottons produced in the Southwest can be too dry because of the region's arid climate. Lack of moisture at ginning can also lower the quality of the fiber and contribute to ginning problems.

To prevent fiber damage and to facilitate ginning, gins try to balance the moisture content in the seed cotton during drying, so that it is neither too wet nor too dry. With unusually dry cottons, gins will skip the drying stage and will, at times, add moisture to it with a special humidifier that blows warm, humid air through the gin's conveyor pipes.

Stage II: Ginning the Seed Cotton.
The seed cotton is now ready for ginning. Pima cotton is conveyed to the roller gin, while upland cottons are conveyed to the saw gin for separation of seed and fiber. After being ginned, the cotton fiber is often referred to as lint.

Stage III: Lint Cleaning.
Lint cleaners remove the small trash from the ginned lint left behind by the cylinder cleaner and stick machines. Saw-lint cleaners grab the lint with a cylinder saw and whip it over metal bars to dislodge its trash. Lint cleaning of roller ginned cotton usually involves a combination of three machines: a cylinder cleaner, an impact cleaner which uses cylinders to agitate and release the trash from the lint, and an air-jet cleaner which removes the trash from the lint using high velocity air.

Stage IV: Packaging the Lint.
In the final stage, a bale press compresses the ginned lint into bales that weigh between 450 and 500 pounds. The bales are then wrapped with a protective covering, ready for delivery to the warehouse where they are sold to the various textile mills.