Page Banner

United States Department of Agriculture

Agricultural Research Service

Overview Of A Cotton Gin
headline bar
Overview

You may view a photo and a description of each machine by
clicking through the pages above.

Overview of a Cotton Gin

 

Go to CGRU Homepage


Feeder

The stationary head feeder employs a dispersing head with spiked rollers for breaking apart the module. The modules are transported to the stationary dispersing head on a series of beds: each bed is the length of a module and is constructed of flat wire-mesh belts or of chains similar to those of the module truck live bed. A minimum of 1-1/2 beds is required, but additional beds can be added to increase ginning time. The beds can be loaded directly from the module truck once the bed speed and the module truck bed speed are synchronized. After all of the beds are loaded with modules, the ginner selects a bed speed to feed cotton to the dispersing head at a constant rate. When the end bed is emptied, another module can be loaded onto the bed so that ginning is continuous. The modules must be placed end to end to prevent the last part of a module from falling apart as it enters the dispersing head. The stationary dispersing head is equipped with a series of horizontal spiked cylinders that remove cotton from the face of the module and deposit the cotton onto a conveyor or into an air line for mechanical or pneumatic conveying to the gin.

The advantages of module feeding are as follows:
  1. It increases ginning capacity by 10-25 percent by providing a consistent, uninterrupted flow of cotton to the gin plant.

  2. It eliminates suction telescope labor.

  3. It frees the module truck for long hauls by enabling continuous ginning of two to six modules.

  4. It blends wet cotton in the module with dry cotton.

  5. It extracts trash thereby not only reducing the amount of trash entering the gin but also increasing fan and piping life.


Picture



Dryer

In the first stage of drying, heated air conveys the cotton through the shelves for 10-15 sec. The temperature of the conveying air is regulated to control the amount of drying. To prevent fiber damage, the temperature to which the cotton is exposed during normal operation should never exceed 350 F. Temperatures above 300 F can cause permanent physical changes in cotton fibers. Dryer-temperature sensors should be located as near as possible to the point where cotton and heated air mix together. If the temperature sensor is located near the exit of the tower dryer, the mixpoint temperature could actually be 100-200 F higher than the temperature at the downstream sensor. The temperature drop downstream results from the cooling effect of evaporation and from heat loss through the walls of machinery and piping.


Cylinder Cleaner

The drying continues as the warm air moves the seed cotton to the cylinder cleaner, which consists of six or seven revolving spiked cylinders that rotate at 400-500 rpm. These cylinders scrub the cotton over a series of grid rods or screens, agitate the cotton, and allow fine foreign materials, such as leaves, trash, and dirt, to pass through the openings for disposal. Cylinder cleaners break up large wads and generally condition the cotton for additional cleaning and drying. Processing rates of about two bales per hour per foot of cylinder length are common.


Picture



Stick Machine

The stick machine removes larger foreign matter, such as burs and sticks, from the cotton. Stick machines use the centrifugal force created by saw cylinders rotating at 300-400 rpm to "sling off" foreign material while the fiber is held by the saw. The foreign matter that is slung off the reclaimer feeds into the trash-handling system. Processing rates of 1.5-2.0 bales/hr/ft of cylinder length are common.


Picture



Extractor Feeder

The primary function of the extractor-feeder is to feed seed cotton to the gin stand uniformly and at controllable rates, with extracting and cleaning as a secondary function. The feed rate of seed cotton is controlled by the speed of two star-shaped feed rollers located at the top of the feeder directly under the distributor hopper. These feed rollers are powered by variable-speed hydraulic or electric motors and controlled manually or automatically by various interlocking systems within the gin stand. The drive may be designed to automatically start and stop as the gin breast is engaged or disengaged; the system may also be designed to stop feeding seed cotton in cases of gin stand overloads or underloads. Many of the systems are designed to maintain constant seed-roll densities. This is usually accomplished by regulating the speed of the feed rolls in response to feedback control signals from the gin stand. The signals are based on monitoring the power consumption of the electric motor driving the gin stand, measuring displacements of the cove board in the seed-roll box, or monitoring the pressure required to drive the hydraulically powered seed-roll agitator.


Picture



Gin Stand

The modern gin plant typically has multiple gin stands. Cotton enters the gin stand through a huller front. The saws grasp the cotton and draw it through widely spaced ribs known as huller ribs. The locks of cotton are drawn from the huller ribs into the bottom of the roll box. The actual ginning process--separation of lint and seed--takes place in the roll box of the gin stand. The ginning action is caused by a set of saws rotating between ginning ribs. The saw teeth pass between the ribs at the ginning point. Here the leading edge of the teeth is approximately parallel to the rib, and the teeth pull the fibers from the seed, which are too large to pass between the ribs.
Ginning at rates above those recommended by the manufacturer can cause fiber quality reduction, seed damage, and chokeups. Gin stand saw speeds are also important. High speeds tend to increase the fiber damage done during ginning.


Picture



Lint Cleaner

It is very important for cotton to flow uniformly and be well dispersed, particularly as it leaves the gin stand. Cotton is conveyed from the gin stand through lint ducts to condensers and formed again into a batt. The batt is removed from the condenser drum and fed into the saw-type lint cleaner. The batt should be of uniform thickness and be evenly spread over the entire width of the lint cleaner; otherwise, poor cleaning and excessive fiber loss will result.
Inside the lint cleaner, cotton passes through the feed rollers and over the feed plate, which applies the fibers to the lint cleaner saw. The saw carries cotton under grid bars, which are aided by centrifugal force and remove immature seeds and foreign matter. It is important that the clearance between the saw tips and grid bars be properly set. The grid bars must be straight with a sharp leading edge to avoid reducing cleaning efficiency and increasing lint loss. Increasing the lint cleaner's feed rate above the manufacturer's recommended rate will decrease cleaning efficiency and increase loss of good fiber. Lint cleaners can improve the grade of cotton by removing foreign matter. In some cases, lint cleaners may improve the color of a lightly spotted cotton by blending to produce a white grade. They may also improve the color grade of a spotted cotton to light spotted or perhaps white color grade. All ginners must compromise between degree of cleaning and fiber damage. Fiber length can be damaged by excessive lint cleaning, especially when the cotton is too dry. Ginners should determine the number of lint cleaners that gives maximum bale value based on a compromise between increased grade, reduced staple length, and reduced turnout.


Picture



Bale Press

The cleaned cotton is compressed into bales, which must then be covered to protect them from contamination during transportation and storage. Three types of bales are produced: modified flat, compress universal density, and gin universal density. These bales are packaged at densities of 14 and 28 lb/ft3 for the modified flat and universal density bales, respectively. In most gins cotton is packaged in a "double-box" press wherein the lint is initially compacted in one press box by a mechanical or hydraulic tramper; then the press box is rotated, and the lint is further compressed to about 20 or 40 lb/ft3 by modified flat or gin universal density presses, respectively. Modified flat bales are recompressed to become compress universal density bales in a later operation to achieve optimum freight rates. In 1996, about 96 percent of the bales in the United States were gin universal density bales. Bales should be packaged and tied only in material approved for storage by the Commodity Credit Corporation loan program.


Picture



Process Control

Cotton ginning systems consist of several different types of processing machines and each is designed for specific tasks. Each machine influences several physical properties of the cotton fiber and many of those properties must be measured with complex laboratory instruments. The decision about the use of an individual machine involves a tradeoff, i.e. a cleaning machine will remove foreign material but also removes some valuable cotton and does some damage to the remaining fiber. A computerized process control system can optimize fiber quality by "prescription" processing the cotton.

Picture



Process Control System

The first computerized process control system was installed in a small-scale research facility at Stoneville, MS, and used special routing valves to bypass or select any combination of four seed cotton cleaners, two multi-path driers, and three lint cleaners as directed by a computer. The current design uses three color/trash/moisture measurement stations in the gin system: in the feed control or module feeder, immediately behind the gin stand (before the lint cleaning), and after the lint cleaning. Station 1 evaluates seed cotton whereas stations 2 and 3 evaluate lint. The lint moisture, color, and trash measurements are used to predict the value of the cotton after treatment by all combinations of equipment which are available in the gin. Similar installations in six full-scale gins have also been evaluated.


Station 1


Station 2


Station 3

Experience
The gin process control system developed at the Stoneville Ginning Lab has operated successfully for several years. Research and field experience clearly demonstrates that process control designed to maximize farmer monetary returns will also minimize the damage to cotton fiber during gin processing. W.S. Anthony and R.K. Byler adapted the design and coordinated the installation and validation of the system in several commercial gins. Components of the CGPCS were initially field tested at Burdette Gin near Leland, MS, in 1989. After successful validation, the components were installed at Westlake Gin, Stratford, CA and Servico Gin, Courtland, AL. Excellent results have been achieved at Westlake since 1992. The Servico system processed about 40,000 bales successfully in 1994 and improved monetary returns to the farmer as well as provided cotton of a higher spinning quality. It also helped identify several additional opportunities for improvements during the gin process. The CGPCS at Servico was improved and operated in 1995, yielding even better results for the farmer and spinner. Based on the successes in 1994 and 1995, Zellweger Uster licensed several USDA patents (with W.S. Anthony, R.K. Byler, and O.L. McCaskill inventors) to enable them to make the CGPCS available to the cotton industry. In 1996, the CGPCS at Servico was upgraded with Zellweger Uster cameras. Again, the upgraded CGPCS was very successful. Prior to the 1997 season, new Zellweger Uster manufactured sampling stations, flash cameras, spread spectrum data transmission equipment, and other improvements were installed at Servico. The new system essentially operated on "automatic pilot" during the 1997 season. Experiences with the cotton from Servico at one textile mill have been exceptionally favorable. The same mill has purchased the entire gin production for 1998.
New beta sites were also installed prior to the 1997 season at Marianna and Dumas, AR, and were Zellweger Uster's first installations. Additional CGPCSs are being installed for the 1998 season. Thus, this new technology is now available to the cotton industry on a limited basis.

Monetary Returns

Evaluation of computer simulation models for process control suggest that bale values could be increased from $6.86 to $23.38 per bale (based on base price of 60.9 cents per pound for strict low middling and an initial lint moisture content of 6.0%). Obviously, adjustments are required to reflect current market prices. Field experience at commercial gins indicate that these numbers are reasonable and are likely too low for current raw cotton and market conditions. One commercial ginner reported farmer profit increases of over $40 per bale using the gin process control system. He also reported dramatic improvements in fiber quality based on HVI measurements. Mill processing experiences with the cotton produced from gins equipped with the IntelliGin have been exceptionally good with higher quality yarn produced at lower costs.

Fiber Improvement by Process Control

Control of the cotton ginning process minimizes machinery usage as well as drying. Obvious benefits result both in monetary rewards and fiber quality. Control of fiber moisture will: 1) increase length about 4%, 2) reduce short fibers about 47%, 3) increase seed-coat fragment size about 18% and improve removabiliy at the textile mill, 4) decrease the number of seed-coat fragments about 36%, 5) increase measured strength by 5%, and 6) increase fiber yield about 3%.

Future

Rapid expansion of automated and intelligent process control systems for cotton gins will vastly improve the quality of cotton. The capability to rapidly determine the essential fiber quality features of cotton and to consider the ability of individual cotton machines to modify those fiber quality characteristics every few seconds, and to make those measurements at multiple locations in the ginning process and refine the machinery selection is the basis for a new frontier in cotton ginning. Armed with a full spectrum of knowledge concerning the fiber qualities of cotton online during processing and the capabilities of gin machines to influence those fiber qualities, this new frontier will represent many future opportunities for improved ginning processes. It will also serve as a platform for major advancements in gin machinery, in fact, some are already in the patent process. New, less aggressive and less damaging machines can be developed and integrated into existing gin systems that can now monitor the performance of those machines. Ginners will now be able to achieve the desired fiber qualities based upon guidance from the farmer or textile mill within constraints of initial fiber quality characteristics. Farmers, ginners, gin managers, and the textile industry now have acccess to instantaneous online measurements of cotton quality. Interactive, responsive processing at the gin can now be controlled remotely by the buyer of the cotton. Enormous opportunities exist for re-engineering the post harvest processing of cotton to deliver textile mills precise products that meet their specifications. With control of the cotton fiber quality characteristics comes the opportunity for improvements in the textile industry. The stage is now set fro ginning to be the next new frontier in cotton processing.


Gin Machinery Impact on Fiber Quality

Knowledge of the performance characteristics of gin machinery is the basis for controlling the gin process. W.S. Anthony developed the performance characteristics of each type of gin cleaning machinery and combination of machines in terms of their effect on fiber quality as a function of moisture and trash levels as well as cotton varieties. The study included three moisture levels (4.1, 5.5 and 8.4%), and three trash levels (3.0, 4.1 and 7.8%) based on the Shirley Analyzer visible foreign matter.
Samples were taken before gin processing and at the feeder apron and lint slide to determine the characteristics of the seed cotton as well as the characteristics of the lint cotton. Foreign matter and moisture analyses were performed by the Cotton Testing Laboratory (CTL) at Stoneville. HVI and Smith-Doxey classifications were done by the Agricultural Marketing Service at Greenwood, MS. Neps, seed-coat fragments and short fiber content were determined at the CTL at Stoneville, MS.

Foreign Matter

The visible and total foreign matter remaining in the ginned lint were a function of the variety, moisture, and machinery treatments. Visible lint foreign matter ranged from 3.9% to 6.2% as moisture increased, and from 2.0% to 7.4% as ginning machinery was changed.

Length Measurements

Staple length ranged from 36.0 for the EFGS only to 35.1 for the 3-lint cleaner treatment. All lint cleaner treatments decreased staple length. HVI length corresponded directly with moisture level and was 1.10, 1.11 and 1.12 in. respectively, for the low (4.1%), medium (5.5%), and high (8.4%) moisture levels. No difference existed in length values for the seed cotton cleaners. However, each lint cleaner reduced the length by 0.01 in.
Mean lengths, as measured by the Peyer 101, for machinery ranged from 0.86 in. for the three lint cleaner treatment to 0.92 in. for a treatment with no lint cleaners. Mean length decreased from 0.93 in. to 0.87 in. as lint moisture decreased from 8.4% to 4.1%. The short fiber content (fibers less than 0.5 in. in length) by weight increased from 4.6% to 8.7% as moisture decreased from 8.4% to 4.1%. Seed cotton cleaners did not increase the short fiber content but lint cleaners did. Lint cleaners increased the short fiber content to 6.8, 8.8 and 9.6%, respectively, as one, two and three stages of lint cleaning were used.

Length Uniformity and Strength

The uniformity was higher for the high moisture level, 82.8, than for the medium, 82.2, and low, 81.9, moisture levels. The Machinery treatments caused the mean uniformity to vary from 81.4 (three lint cleaners) to 82.8 (extractor-feeder and gin stand (EFGS) only or stick machine with EFGS) with lint cleaners decreasing uniformity about 1.0. Strength means for moisture were 28.0, 28.6 and 29.2 g/tex, respectively, for cotton processed at 4.1, 5.5 and 8.4% fiber moisture.

Seed-coat Fragments and Motes

The number of seed-coat fragments per 3 grams of lint were about 50% higher at the low moisture level than at the two higher levels. Machinery did not significantly influence the number of seed-coat fragments. The weight of seed-coat fragments was significantly influenced by Moisture and Machinery. Means for the high moisture level were significantly higher (33.8 fragments) than for the other two moistures (28.5 fragments). Machinery strongly influenced fragment weight with the seed cotton cleaners having no effect and lint cleaners decreasing the weight dramatically. The number and weight of motes were decreased dramatically by saw-type lint cleaners.

Neps

Small entanglements of cotton fibers called neps increase each time that cotton is manipulated. G.J. Mangialardi studied samples of cotton fiber collected in seven locations in a gin system and found that neps were increased from 6 to 16 per 100 in.2 of web by simply removing cotton from the trailer pneumatically. Two stages of lint cleaning increased the number of neps dramatically from 18 to 34. W.S. Anthony reported that neps averaged 13.1 and 6.7 per 100 in.2 of web for lint moisture contents of 4.1% and 8.4%, respectively, a decrease of 49% across all machines. He also reported that neps decreased by 15% and 42%, respectively, when one and two stages of lint cleaning were bypassed.


Last Modified: 5/22/2013