After the pretreatment process, the cotton enters the ginning process. Ginning uses mechanical action to separate the long fibers growing on the cotton seeds from the cotton seeds to form lint, while retaining the short lint on the cotton seeds. The machine that separates cotton seeds from long fibers is called a gin.
1. Ginning Mechanism
The basic task of the ginning process is to separate long fibers from cotton seeds. To achieve this goal, two conditions must be met, namely internal factors and external factors.
The internal reason for the separation of long fibers and cotton seeds is that the absolute strength of the cotton fibers themselves must be greater than the fixation strength of the fibers on the cotton seeds. This depends on the physical properties of the cotton itself. Cotton fiber is extended from the epidermal cells of the seed, and its base is part of the epidermal cells of the cotton seed. As shown in Figure 8-1, it can be seen that the base of the cotton fiber is relatively weak, which is conducive to the separation of the fiber from the cotton seed epidermis. Therefore, during ginning, the slightly upper part of the fiber base is most susceptible to breakage. Experimental data also proves this. The fixing force of a single fiber on cotton is 40% to 60% of its own breaking strength, and the absolute strength of a bundle of fibers is 12 to 15 times the fixing strength. The internal condition of cotton fiber is a necessary condition for the separation of fiber and cotton seed, and is also the basic principle guiding ginning work.
The fixing power of sub-cotton fibers has a great relationship with the degree of dryness. The fiber strength and fixing power of wet sub-cotton fibers are higher than those of dry sub-cotton fibers. Figure 8-1 The structure of the cotton fiber base and the cotton seed shell. The fixing force of the fiber on the cotton seed is also related to its location. The fixing force of the cotton seed tip is greater than the fixing force of the cotton seed middle. Therefore, the fibers at the tip are generally not easy to roll off. The blunt end (chaleal end) of cotton seeds has a thin shell, and the cohesion of cotton fibers is small. The fibers at the blunt end are easy to separate from the cotton seeds during ginning, but the shells are easily broken, resulting in cracks and fiber scraps.
The external condition for the separation of long fibers and cotton seeds is that there must be mechanical action, so that the fibers and cotton seeds are acted upon by external forces at the same time, and the resultant force of these external forces acting on the base of the cotton seeds’ epidermal fibers is greater than the fiber (1) The cotton seeds are blocked At the same time, the fibers are pulled by external forces.
(2) The fibers and cotton seeds move under the action of external forces at the same time. Due to the different magnitude and direction of the external force and the different masses of the fibers and cotton seeds, the speed difference between the two creates a relative motion, causing the cotton fibers and cotton seeds to separate.
(3) While the fiber is pulled by an external force, the cotton seeds are impacted by an external force in the other direction.
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