The ginning process requires ginning the long fibers on the cotton without damaging the natural physical properties of the fibers. According to the ginning mechanism, to achieve this requirement, cotton seeds and long fibers must be subjected to external forces in different directions. The middle box of the sawtooth gin creates the conditions for it. The geometry of the middle box can make the cotton rolls form. The position of the saw blade roller in the middle box is used to make the saw teeth pull the cotton fibers and align the cotton rolls at the same time. An acting moment is generated to cause the cotton roll to rotate. It is precisely because of the rotation of the cotton roll that the saw teeth can pull the fibers in a balanced and efficient manner; at the same time, the cotton cotton with clean fibers can be smoothly discharged. Because there are differences in the rotation speed and direction of the sub-roll and the saw blade drum, especially at the working points of the ginning rib rows, the mechanical conditions of ginning can be met.
(1) The formation process of sub-roll movement
Before ginning, put a certain amount of sub-cotton in the middle box so that the sub-roll can be formed quickly after starting the machine. When ginning, the cotton in the front box is pulled by the sawtooth hook and enters the middle box through the upper gap of the rib row of the resistance shell, and is distributed on the outer surface of the cotton roll, as shown in Figure 8-15.
Along the arc length of the saw blade from the cotton comb to the working point of the embossed rib row, the saw teeth continue to pull the cotton fibers. The cotton pulled by the saw teeth moves with the saw blade, but the cotton is also restrained by the cotton roll, so some of the fibers in the fiber bundles hooked by the saw teeth are pulled off the cotton. At the working point of the embossed rib row, the sawtooth pulls the cotton fibers into the rib gap, and most of the fibers are separated from the cotton. The sub-cotton that has been pulled out of some fibers is blocked by the embossed ribs and remains in the middle box. Since the subsequent saw teeth continuously leave the cotton with part of the fiber pulled out above the working point, the cotton here is squeezed very tightly and squeezes upward along the surface of the ginned rib row, pushing the cotton in front to move upward. As a result, the cotton in area A moves to area B, and then moves to areas C and D, forming a movement of the outer layer of cotton rolls. When the cotton moves to the vicinity of the cotton comb, it meets the newly entered cotton in the middle box, and is pulled into its own area by the sawtooth hook again. The cotton with clean fibers is discharged from the machine near the cotton comb. This process goes over and over, constantly taking away fibers and discarding cotton seeds, and constantly hooking in cotton seeds to replenish them. The cotton seeds in the middle box are always in a stable rolled state, constantly moving along the inner wall of the middle box.
Cotton roll is a mixture of cotton, wool, free fiber, cotton, etc. Although the inner layer of cotton in the cotton roll is not in contact with the saw teeth, because the inner and outer layers of cotton are restrained and embraced by each other, when the outer layer of the cotton roll rotates, the friction between the layers pulls the inner layer of cotton along. The outer layers move together. In this way, the entire sub-cotton roll rotates around a certain center, which also creates conditions for the cotton fibers to be smoothly peeled off from the sub-cotton.
(2) Basic conditions for the movement of sub-rolls
The normal operation of sub-rolls is an essential condition to ensure good ginning status. In order to ensure that the saw teeth draw the cotton fibers continuously and evenly, the following conditions must be met for the normal operation of the cotton roll:
(1) The cotton roll should have a certain density. For sub-cotton rolls with a certain degree of compactness, each single particle of cotton can properly squeeze each other and form a certain friction force to transmit torque, causing the inner and outer layers of the sub-cotton roll to pull each other to form an overall movement.
(2) The traction torque of the saw teeth on the cotton roll must be greater than the frictional resistance torque of the working box wall on the cotton roll. In order to increase the traction torque of the saw teeth on the cotton roll, the following measures can be taken:
① Raise the saw blade drum and increase the number of working teeth of the saw blade in the work box.
②Keep the sharpness of the saw teeth; keep the teeth straight and do not reverse the teeth; brush the cotton cleanly.
③Appropriately reduce the pressure angle.
In order to reduce the frictional resistance moment of the working box wall to the cotton roll, the following measures can be taken:
① Improve the smoothness of the inner wall of the working box and the surface of the embossed ribs, especially the upper heel fixation of the embossed ribs. Flat and smooth.
② Appropriately increase the gap above the working point of the embossed rib row, expand the diameter of the top hole, and improve the smoothness of the side and top holes of the embossed rib working point and above.
③ Install and adjust the cotton comb correctly to prevent the comb from being misaligned and obstructing the row.
④After turning on the machine for a certain period of time, the cotton roll should be replaced or cleaned. Because there are often impurities in the center of the cotton roll, they cannot be pulled out by the saw teeth, and they are not easily discharged with the cotton. As the processing time is extended, the number of impurities increases, and some of the impurities will block the embossed rib rows. The gap causes the sub-roll to stop rotating.
⑤ Control the density of the sub-roll to prevent the sub-roll from being too tight, which will cause the frictional torque to increase sharply and affect the operation of the sub-roll.
(3) The distance between saw blades should not be too large, generally within 20mm. If the blade distance is too large, it is difficult for the cotton between the saw blades to obtain traction, and it is difficult to move with the cotton roll.
(3) Composition of sub-cotton rolls
The fibers on the single-grain cotton cannot be completely pulled through one sawtooth hook, that is, the rolling and peeling process of the single-grain cotton is completed within a certain time interval, so the work The sub-cotton rolls in the box are composed of single particles of cotton in different stages of rolling and peeling. However, the composition of sub-cotton rolls is not fixed. The proportion of sub-cotton groups in different rolling and stripping stages is related to the operating process of the gin (especially the flower feeding speed). Changing the feeding speed will change the proportion of sub-roll components and other parameters, such as sub-roll speed, sub-roll weight, sub-roll density, etc. It can be seen from Table 8-6 that the number of cotton seeds with clean fibers in the cotton rolls increases with the increase of the productivity of the gin.Tilt downward, the lower part of the sub-rolls expands into a cone shape, the row is unobstructed, the density of the sub-rolls decreases, and the movement speed also decreases.
3. Saw blade drum speed and gin productivity
The relationship between the movement speed of the sub-roll, saw blade drum speed and gin productivity is shown in Figure 8-18. Under the same productivity conditions, increasing the rotation speed of the saw blade drum will make the sub-cotton roll looser and slow down the movement speed; under the same conditions of the saw blade drum rotation speed, increasing the productivity of the gin will make the sub-cotton roll become tighter and speed up the movement speed. .
4. The position of the embossed rib row
Changes in the position of the embossed rib row will cause the following changes:
(1) R 1 (the distance from the center of the cotton lap to the rib) changes, which will cause the Changes in the shape and circumferential density of cotton rolls;
(2) Changes in the width of the row, thus affecting the speed of the row;
(3) Changes in the relative position of the embossed rib row and the saw blade drum, thus changing the speed of the row. Change the force exerted by the saw teeth on the cotton roll at the working point.
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