Humidification and drying of sub-cotton. The relationship between moisture content of sub-cotton and sub-cotton processing quality
From the perspective of the physical properties of cotton fiber, its strength and frictional resistance increase as the moisture content of the cotton increases, while its elasticity and rigidity decrease as the moisture content increases. Therefore, the first step in ginning in a ginning mill is to keep the fiber at a suitable moisture level. Good humidity plays an important role in ensuring fiber quality and obtaining large cotton bale value during ginning finishing.
If the moisture content of the sub-cotton is too high (more than 12%), not only is there a risk of mildew, discoloration and reduced strength during storage, but it may even heat up and spontaneously ignite. In addition, during ginning finishing, the machinery may not operate normally and the sub-cotton cleaning is not clean. The surface of the sorted cotton is rough and ugly, which greatly increases the ginning cost and affects its grade and market price.
The effects of excessive moisture content of cotton on the finishing quality of cotton are as follows:
(1) Increase in humidity increases the strength of the fiber, resulting in an increase in the connecting force between the base of the fiber and the cotton; excessive humidity makes the cotton The skin becomes soft, and when the fibers and cotton seeds are separated, simply tear off the skin together. This is one of the important reasons for the generation of fiber-laden cotton seeds.
(2) The increase in humidity leads to an increase in the frictional resistance between fibers, an increase in the adhesion between impurities and fibers, and an increase in the friction on the finishing mechanical surface, making it difficult to remove impurities and reducing the cleaning efficiency.
(3) As the humidity increases, the elasticity and rigidity of the fibers decrease, and the fibers become softer. Under the action of external forces, the fibers will be more entangled and twisted, resulting in more neps and cords in the cotton. Fibrous defects such as cotton directly affect the quality of lint.
(4) The productivity of the cotton gin will be reduced. Because the moisture content of the sub-cotton is too high, the friction factor of the fiber increases and the elasticity decreases, which increases the friction between the wall of the gin working box and the cotton lap, causing the cotton lap to become hardened, resulting in an increase in the shutdown rate during high-speed operation.
(5) Increased humidity and frictional resistance will aggravate the difficulty of cotton brushing during the sawtooth gin finishing process, and may also easily cause rib clogging (fibers embedded in the gaps), affecting the normal operation of the cotton roll, and will not affect the normal operation of the cotton roll. Conducive to safe production.
(6) The clothing loss increases and the grade decreases. High humidity makes it difficult to strip cotton, and the amount of fiber remaining on the cotton (hair ratio) increases. At the same time, the cotton roll formed cannot be in a loose state. After rolling, the lint appears in a strange shape, without luster, dull color or even dark gray.
Generally speaking, there is a one-level difference in the quality of lint after finishing between normal moisture sub-cotton and super-moisture molecular cotton of the same grade. Therefore, the wet cotton must be dried to a more appropriate level in order to achieve optimal cotton bale value.
When the moisture content of the finished cotton is lower, higher grades can be obtained, but the gains are usually offset by the loss of yield and reduction in fiber length. Because static electricity will increase the number of stops, drying will reduce the strength of the fiber. Moreover, when the cotton is over-dried, fiber breakage may occur during the finishing process. The surface brittleness of the cotton increases, and the resistance to compression deformation is weakened. The cotton is easily damaged and broken, and the fiber with debris increases. The elasticity and rigidity of the fiber are affected by moisture. If it is too low, it will increase significantly, thus causing difficulties for packers; over-dry cotton fibers can become very good insulators and can easily generate static electricity due to mechanical friction, causing problems such as incomplete brushing; when the fibers are over-dried, they can also cause problems such as incomplete brushing. May increase drying costs.
If the moisture regain rate of cotton is too high, it will cause difficulties in cotton storage and transportation, causing discoloration, deterioration, and even spontaneous combustion of cotton fibers. If the moisture regain rate of cotton is too low, the expansion force of the cotton fiber will be too large, which will increase the energy consumption of packaging. The cotton bales will not be able to achieve the required density and weight, and a large number of “collapse” phenomena will easily occur during storage and transportation.
When the moisture regain of sub-cotton exceeds 8.5%, it should be dried. Finishers should strive to find the optimal humidity range so that ginning can proceed smoothly, with good cleaning results and low fiber damage rate.
Domestic and foreign production practices and research show that under most production conditions, suitable finishing requires fiber moisture of 7% to 8%. This indicator also applies to plateau cotton, and differences in harvesting methods have no impact on it. Sometimes, this indicator is more difficult for machine-picked cotton because it contains a lot of impurities.
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