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  • Cotton ginning machinery

    Chapter 2 - Cotton value addition - Impact of varieties and production practices 

     
     

    The principal function of the cotton gin is to separate lint from seed and produce the highest total monetary return for the resulting lint, seeds, etc. under the prevailing marketing conditions. These marketing quality standards most often reward cleaner cotton and a certain traditional appearance of the lint. The gin then must also be equipped to remove a large percentage of the foreign matter from the cotton that would significantly reduce the value of the ginned lint, especially if the cotton is machine harvested. A ginner must have two objectives: to produce lint of satisfactory quality for the grower’s classing and market system; and to gin the cotton with minimum reduction in fibre spinning quality so that the cotton will meet the demands of its ultimate users, the spinner and the consumer. Thus, quality preservation during ginning requires the proper selection and operation of each machine that is included in a ginning system. The ginner must also consider the weight loss that occurs in the various cleaning machines. Often the weight loss to achieve higher grade results in a lower total monetary return.

     

    Figure 2.5: Minimum machine sequence used to process clean, hand-picked cotton

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    The minimum machinery required to process clean, hand-harvested cotton consists of a dryer and/or moisture restoration device followed by a feeder to uniformly meter seed cotton into a gin stand. The ginner must be able to adjust the moisture of the cotton up or down, individualize the locules of cotton, meter the locules uniformly into the gin stand to separate the fibre from the seed, and then package the fibre and seed for market. The simplified machine sequence in figure 2.5 illustrates the minimum machinery necessary to produce marketable fibre. This simplified sequence, however, does not provide versatility to properly manage cotton that has excessive moisture or trash, or cotton that must meet specialized textile needs. Since saw-type lint cleaning is not included in figure 2.5, the baled fibre will contain imperfections such as motes and trash, and will not have a smooth appearance. A more extensive machine sequence such as that shown in figure 2.6 provides the flexibility to meet almost any situation for hand- or machine-picked cotton.

    Foreign matter levels in seed cotton before gin processing usually range from 1% to 5% for hand harvested, from 5% to 10% for spindle-harvested, and from 10% to 30% for stripper-harvested cottons. The level of foreign matter dictates the amount of cleaning needed.

    Figure 2.6: Representative cross-sections of typical types of gin machinery arrayed in a sequence used for spindle-picked cotton

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    The quality of ginned lint is directly related to the quality of the cotton before ginning. High grades will result from cotton that comes from clean fields. Lower grades will result from cotton that comes from grassy, weedy fields in which poor defoliation or harvesting practices are used.

    When gin machinery is used in the recommended sequence, 75%–85% of the foreign matter is usually removed from the cotton. Unfortunately, this machinery also removes small quantities of good quality cotton in the process of removing foreign matter, so the quantity of marketable cotton is reduced during cleaning. Cleaning cotton is a compromise between foreign matter level, and fibre loss and damage. Trash removal efficiency and fibre damage are inversely related to fibre moisture.

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    Cotton Exporter's Guide

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