Cotton Fibers – the king of fibers

Cotton Processing: Harvesting

Cotton processing begins at harvest. Once the cotton bolls have matured, they are mechanically removed from the plant by either of two harvest methods: cotton strippers or cotton pickers. A cotton harvester is self-propelled with special heads that harvest the cotton and a basket to hold the seed cotton. In some parts of the world, cotton is still harvested by hand.

Cotton was once harvested by hand, often by slave labor or tenant farmers. As recently as 1965, over a fourth of the U.S. cotton crop was picked by hand. Today, harvesting cotton is highly mechanized.

Cotton Strippers

Harvesting machines called strippers and pickers efficiently remove the cotton while leaving the plants undisturbed. A spindle harvester, also called a picker, has drummed with spindles that pull the cotton from the boll in one or two rows at a time. Even a one-row mechanical picker can do the work formerly done by 40 hand pickers.

In stripper harvesting, the stripper moves along rows of plants, passing them between revolving rollers or brushes that pull off the cotton. Strippers also pull twigs and leaves with the cotton.

Pickers remove only the seed cotton from the boll, leaving the burrs (dried locules) and the plant intact in the field. Cotton pickers utilize a series of spindles stacked on a spindle bar in the picker drum. The spindles, which rotate, are round, tapered, and fluted with barbs. The entire spindle bar is rotating as it enters the row of cotton plants. As the rotating spindles come in contact with the seed cotton on the plant, the cotton is pulled out of the burr (locule).

The bar continues to rotate and comes into contact with a spinning doffer that wipes the cotton off the spindle and into a pneumatic conveying system that moves it to the basket.

Strippers are used in areas with stormproof cotton varieties (these varieties minimize field losses from weather). The seed cotton is held in the boll until the plant is killed by cold weather or chemical harvest aids. The cotton stripper removes the complete boll from the plant utilizing two counter-rotating stripper rolls consisting of nylon brushes and rubber bats. This method of the harvest will result in a higher trash content of harvested seed cotton. Some strippers have field cleaners that can separate the burrs and sticks from the seed cotton that goes into the basket, leaving the trash in the field.

The harvester basket full of seed cotton is then dumped into a module builder. The module builder can pack the cotton into an eight to twelve bale module. The module of cotton is left in the field to be picked up by a module truck and taken to the yard of the gin to wait for ginning.

The stripper’s head consists of two counter-rotating rolls with long brushes and rubber batts spaced close together and slanted towards the ground. As the stripper moves, plants enter the head and the whole boll is snapped off of the dried plant by the bats. The boll is conveyed up to the basket by augers and pneumatic conveyors.

Mechanical cotton stripper

The name comes from the fact that it removes the complete boll from the stalk of cotton. The stripper is driven through the field with a stripper’s head for each row of cotton (up to eight rows). The plants enter the head and the counter-rotating batts snap off the complete bolls, leaving the dry stalk standing in the field. Newer strippers have a field cleaner on board that removes the trash (burrs, sticks, and fine trash). The trash drops from the field cleaner via a chute behind the front tire.

It removes only the seed cotton from the open boll, leaving plants in the field. The cotton picker moves down the rows of cotton plants, picking the cotton from the bolls. The cotton is conveyed to the cotton basket. The picker head has a stack of rotating spindles on a spindle bar. The entire spindle bar rotates also. As the picker moves down the row, plants enter the picker head and the spindles come in contact with the cotton, pulling it out of the open boll. A doffer wipes the cotton off of the spindle.

 

 

Cotton Module Builder

The harvester basket full of seed cotton is dumped into a module builder. A module builder is a metal box with no top or bottom and a moveable tramper that packs the cotton into an eight to twelve bale module, much like a trash compactor. When finished, the rear door opens, the builder is lifted by hydraulics and pulled away from the module by a tractor to another location where the next module can be compacted. The module of cotton usually has a tarp pulled over the top. It is left in the field to be picked up by a module truck and taken to the gin. The development of the module builder as a replacement for cotton trailers helped eliminate storage and handling problems between the field and the gin.

Cotton gins separate the fibers, called lint, from the seeds. After ginning, the cotton goes to the bale press that packs it into 480-pound bales about the size of a large refrigerator.

Module builder receiving a load of cotton from a harvester. When the module is completed, the builder has pulled away to the next site and filled it again. A module truck from the gin will pick up the modules in the field.

Cotton Ginning

Harvested cotton is called seed cotton because the fibers are still attached to the seed. The ginning process removes the seeds and cleans the fiber. Clean cotton is important because a bit of trash incorporated into a spun yarn can cause the yarn to break. When the bale of fiber comes out of the bale press, a sample is taken for cotton classing (fiber evaluation).

From the field, seed cotton moves to nearby gins for the separation of lint and seed. The cotton first goes through dryers to reduce moisture content and then through cleaning equipment to remove foreign matter. These operations facilitate processing and improve fiber quality. The cotton is then air conveyed to gin stands where revolving circular saws pull the lint through closely spaced ribs that prevent the seed from passing through. The lint is removed from the saw teeth by air blasts or rotating brushes and then compressed into bales weighing approximately 500 pounds. Cotton is then moved to a warehouse for storage until it is shipped to a textile mill for use.

The principal function of a cotton gin is to convert the farmers’ harvested seed cotton into salable commodities, i.e., fiber and seed. Thus, Ginning is the bridge between cotton production and cotton textile manufacturing. To satisfactorily convert today’s mechanically harvested cotton into salable commodities, gins have to dry and clean the seed cotton, separate the fibers from the seed, further clean the fibers and place the fibers into an acceptable package for commerce.

Cottonseed is sold to dairies for feed, to oil mills for the production of many valuable products, or saved for planting next year’s crop. The fibers are the more valuable product, however, and the design and operation of cotton gins are oriented toward fiber production. In essence, the modern cotton gin enhances the value of the cotton by separating the fibers from the seed and by removing objectionable non-fiber matter, while preserving as nearly as possible the inherent qualities of the fiber.

The module of cotton is opened and cotton is moved with an airstream into the gin, first pass- ing through a boll trap that removes green (un-opened) bolls and rocks. The airline cleaner takes out fine trash and sand (for stripper harvested cotton). The separator removes the cotton from the air stream, dropping it into the feed control, which regulates the flow of cotton into the ginning stream. The tower dryers dry the cotton if it is wet or harvested before the plant was completely dry.

The inclined cleaners (or cylinder cleaners) are a type of cleaner that removes fine trash. The CBS (combination burr and stick) machine in a stripper cotton gin removes sticks and burrs. In a picker cotton gin, a stick machine, at this location, removes sticks and green leaf. The cotton then goes through a second dryer, another inclined cleaner, and a second stick machine (in a stripper gin). Another separator takes cotton out of the conveying air stream and drops it into a conveyor distributor. The distributor delivers cotton to each of several extractor-feeders, which feed the gin stands uniformly and at a controlled rate.

Recommended gin machinery for machine-stripped and machine-picked cotton

The gin stand is the heart of the ginning process where the fibers are removed from the seed. Most gins are equipped with two lint cleaners that remove small trash that remains in the lint after ginning. These cleaners are equipped with bypasses to regulate the amount of cleaning required. The fiber then goes into a gin press where it is compressed into a 480-pound bale suitable for commerce.

A typical gin will process about 12 bales per hour, while some of today’s more modern gins may process as many as 60 bales an hour.

 

Inside the Cotton Gin – Video