High-Speed Roller Ginning Takes Center Stage
March 17, 2010 Roller ginning has historically been used to gin only Pima cotton. Pima has inherent fiber advantages over upland cotton such as length, strength, and fineness. On a production per-unit-width basis, roller ginning is about five times slower and, therefore, more expensive than saw ginning, but because the value of Pima cotton is considerably higher than upland cotton, the higher cost of roller ginning Pima cotton is justified.
Roller ginning compared to saw ginning produces fiber of better quality. USDA researchers S.E. Hughs and W.F. Lalor showed that roller ginning different cultivars of cotton improved fiber length, length uniformity, and nep count when compared to saw ginning. M.N. Gillum and I showed that roller ginning upland cotton, when compared to saw ginning, produced upland fiber that was more than one staple length longer, had fewer short fiber and neps, and higher turnout. However, upland cotton has a higher fiber-to-seed strength of attachment than Pima cotton and is more difficult to gin, adding to the already higher cost of roller ginning.
In recent field tests, numerous conventional roller gin stands were modified to run at high speed in commercial ginning plants. The high-speed stands ginned both Pima and upland cotton. Results from a field test at a commercial ginning plant that compared roller ginning (including one high-speed stand) and saw ginning using one upland cultivar, showed that high volume instrument (HVI) color grade, staple length, uniformity, and fiber value were improved when using the roller gin stands.
Results from the California test crop showed similar improvements in staple length and uniformity when comparing roller-ginned upland cotton (which included conventional and high-speed stands) and saw-ginned upland cotton. Textile mills that value the significance of improved fiber properties were willing to pay a premium for roller-ginned upland cotton.
Research also indicated that it is possible to roller gin upland cotton at a rate nearly equal to a conventional saw gin stand. In addition, the horsepower requirement of the high-speed roller gin stand was equal to that of a conventional saw gin stand. The high-speed roller-ginned upland cotton had the same fiber quality advantages as conventional roller ginning in that it did not damage the fiber. In the study, bale value was not significantly different between roller and saw ginning, but this was because the pricing system does not reward for upland cotton staple lengths longer than 37, and there is no premium for lesser amounts of short fiber. However, export markets, which now use about 75 percent of U.S. upland cotton, value the significance of increased staple length and decreased short fiber and neps, and some textile mills are paying an extra 13 to 26 cents/kg (6 to 12 cents/lb) for roller ginned upland cotton.
Results of the Study
In a 2007 USDA study, a Consolidated HGM roller gin stand was converted from conventional speed to high speed. This research was a cumulative effort that had built upon earlier work that determined the optimum designs of the rotary knife and stationary knife. After work was completed on the Consolidated HGM roller gin stand, interest from the ginning industry led to a field test that converted a Lummus roller gin stand to high-speed. The motivation for research on high-speed roller ginning was to make it more feasible to gin upland cotton, but the benefit of running high speed also allowed Pima cotton to be ginned at a higher rate.
Commercial roller ginning plants in Arizona, California, and New Mexico converted numerous conventional roller gin stands and feeders to high speed during the 2005 and 2006 ginning seasons. In 2005, one Arizona ginning plant converted a conventional roller gin stand to high speed. All of the remaining conversions occurred in 2006. Some of the roller ginning plants in California and New Mexico made only partial conversions to their equipment. These partial conversions consisted of only increasing the throughput of seed cotton in the feeder, or only slightly increasing the speed of the ginning roller and rotary knife (but not by enough to require a cooling system).
The partial-conversion roller gin stands and feeders did not achieve the same ginning rate as the full-conversion high-speed stands. The partial-conversion stands were estimated to gin at about 436 kg m-1 h-1 (2 bales m-1 h-1) compared to about 1000 kg m-1 h-1 (4.5 bales m-1 h-1) on a fully-converted stand. During the 2006 ginning season, two full-conversion high-speed roller gin stands operated in Arizona, and 14 operated in California. During the same year, 52 partial-conversion stands operated in California and four in New Mexico.
Prior to running the field test, about one module of upland cotton (12 bales) was ginned to check the initial start-up of the high-speed roller gin stand. The high-speed stand roller gin averaged a ginning rate of 1046 kg m-1 h-1 (4.8 bales m-1 h-1). This compares to a ginning rate on a conventional roller gin stand of about 273 kg m-1 h-1 (1.25 bales m-1 h-1). During start-up, the high-speed roller stand performed well. Roller temperature averaged about 93˚C (200˚F), and there were no choke-ups. The only modification made at start-up involved changing a sheave on the feed-rollers drive on the feeder to increase the throughput of seed cotton.
Leaf grade, micronaire, and strength were not different between roller and saw ginning treatments and averaged 2.66, 3.56, and 29.5 g/tex, respectively. Color grade was different between ginning treatments, averaging 104.7 and 104.3 (old code) on the roller and saw gin, respectively. These color grades equate to a new code color grade of 11 and 21 for the roller and saw gin, respectively. Reflectance and yellowness were different between ginning treatments. Reflectance averaged 81.3 and 82.4 on the roller and saw gin, respectively, and yellowness averaged 8.78 and 8.04 on the roller and saw gin, respectively.
New markets may open up due to the improved fiber quality of roller ginned upland cotton. And as processed roller ginned upland cotton receives a premium, numerous roller gin stand conversions are planned in the future. A better evaluation of roller life will ensue as more high-speed roller gin stands are used. •
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