Gin machinery modifications to provide “prescription” processing of cotton can result in less lint waste and produce fiber more desirable to textile mills, says Stanley Anthony.
“I think we'll be seeing more of it in the future,” says the director of the USDA Agricultural Research Service's Cotton Ginning Laboratory at Stoneville, Miss.
Prescription processing has increased dramatically since 1997, he notes, primarily because of the IntelliGin system, which is now active in almost 70 gins in the United States.
The improvements will produce equal or better cotton — and more of it — he told members of the Southern Cotton Ginners Association at their summer meeting at Branson, Mo., and they have “substantial potential” for returning several extra dollars per bale to the farmer.
“From the standpoint of reducing production costs, farmers have done about all they can do in terms of maximizing profit from cotton. It's up to the gin crew now to try and help them out by fine-tuning ginning operations.”
In ginning studies, he says, “We found one of the biggest lint losses is with the saw-type lint cleaner. Many times, gins produced cotton that was far too clean and wasted far too much fiber. So we began to look at the internal workings of the machinery.”
By isolating the grid bars in saw-type lint cleaners, Anthony says, “It was easy to see what was happening. The first grid bar did an outstanding job, but beyond that we began losing too much fiber.”
Although the cotton got a little whiter as it went through successive grid bars, “We were seeing a lot of fiber wasted — as much as 10 pounds to 30 pounds per bale.”
One of the studies showed that the first grid bar removed about 7 pounds per bale, and all five removed about 24 pounds.
“If you could get by with only one or two grid bars and still retain acceptable color and leaf, you could end up with several pounds of extra cotton in a bale — good cotton that should have never been removed,” Anthony says.
While there was little or no lint in the first grid bar, 80 percent of the material in the fifth grid bar was good lint, half-an-inch or longer.
“What we basically found was that each grid bar is going to remove material, and the more grid bars you use, the more fiber is going to be in that material.”
The team designed a system of louvers for each grid bar, which could be individually opened or closed. “In effect, it can make one or more of the grid bars inactive, and it can be done on the fly, without changing anything else about the machine.”
When the studies were started in 1998, Anthony notes, 43 percent of the strict low middling cotton in the United States that was examined was leaf grade 2 or 3. “There is no premium or price advantage for either leaf grade 2 or 3, but in ginning for those grades you lose some fibrous material that should remain in the bale. Not only that, every time the cotton encounters a grid bar, it results in more fiber entanglement, neps and short fibers, and lower uniformity.”
Studies using 2, 5, and 10 grid bars, at various moisture levels with several pre-cleaning combinations, showed that most color is gained on the first two grid bars. “Most of the leaf grade improvement will occur on the first two or three grid bars, although you'll continue to get a better leaf grade with successive grid bars. However, neps and short fiber content continue to increase.
“Whenever you can reduce the short fiber content and neps, you'll find the textile mill people that process the cotton will smile at you.”
In taking the studies on through textile mill processing, Anthony says, “In all cases, we saw that one or two grid bars were better.
“The problem, though, is that many times you need more than two grid bars to adequately clean the cotton. So you've got to have a way to automatically select how many grid bars to use for an individual bale, or you might be facing a $15 to $20 per bale penalty on leaf grade and no additional premium in terms of selling the cotton.”
In evaluations of spinning performance at Clemson University, he says, “In terms of processing efficiency, we found more differences as a result of variety than from the number of grid bars used in ginning the cotton. Some varieties will respond quite well to the number of grid bars; others won't. So, you have to be able to control the process.”
In 1999 and 2000, to evaluate how textile mills would respond to prescription-processed cotton, bale lots were ginned with varying numbers of grid bars, from 1 to 10.
“We didn't tell them which was which, and we asked them to rank the cotton as it was processed. It turned out they liked the two-grid bar cotton best. Another mill that has processed 200,000 or so of these bales had similar results. They like it because they feel it produces a better fiber. Least liked was the two-lint cleaner cotton, because it had higher short fiber content.”
Most of the early work was done with a Continental 16D lint cleaner and a Lummus Model 66 lint cleaner. Subsequent work was done with a converted Continental 24D lint cleaner equipped with louvers. Continental Eagle improved the production model of the louvers so only one adjustment was required per grid bar — because the louver was affixed to the end plates for the grid bar — compared to the previous two adjustments.
In processing of 2-grid bar and 8-grid bar cotton at the Clemson Cotton Quality Research Station, fiber quality “was basically the same, with no significant difference in spinning quality,” Anthony says. “Variety had more impact on spinning quality than trash due to grid bars.
“The bottom line is that 2-grid bar cotton is at least equal to, if not better than cotton processed with more grid bars. In most of the studies, cotton variety was more important than the ginning system. I think if we're going to try to optimize quality for ring spinning, we've got to be concerned with integrating variety and grid bars.”
Additional gin machinery modifications are being studied, Anthony says, which show promise of further reducing fiber loss while retaining cotton quality. One new machine can cut fiber waste to about 6 pounds per bale, while delivering higher quality cotton with good mill performance. “The cotton looks rougher, but it is cleaner, with less short fiber, and higher uniformity.”
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