There is a theory that attaches great importance to the discharge of cotton in the working box. It is believed that in order to improve the productivity of the sawtooth gin, the residence time of cotton in the working box should first be reduced. In addition, be sure to increase the amount of flower feeding and cottonseed discharge to maintain a balance under high yields.
As shown in Figure 8-22, the fibers on the single-particle cotton are gradually peeled off; when the single-particle cotton first contacts the saw teeth, because the cotton has the largest amount of fibers, the fibers that can be caught by the saw teeth are relatively small. many. As the number of times of padding and stripping increases, there are fewer and fewer long fibers on the cotton, and there are fewer and fewer fibers of single-grained cotton that can be caught by the saw teeth. That is, there are fewer and fewer opportunities for single-grained cotton to be rolled and peeled. In addition, the curve between the progress of single-particle cotton and its residence time in the working box has the abscissa as the asymptote. That is, only when the single-particle cotton stays in the working box for an infinite time can the long fibers on it be peeled off. over. In order to ensure efficient ginning productivity, it is necessary to properly control the cotton wool rate and discharge the cotton in a timely manner.
(1) The discharge process of cotton seeds
In the working box, when the cotton seeds move to the D area, they almost move along the inclined direction of the cotton seeds comb to the saw teeth. Cotton with fibers can be taken away by the saw teeth because the saw teeth directly hook the fibers on it, or the fibers on it are adhered to the single particles of cotton hooked by the saw teeth. Cotton with slight fiber or only short velvet is difficult to be hooked by the saw teeth and loses the conditions for adhesion with other cotton, so it can only be squeezed into the gap of the saw blade. In this way, at the cotton comb, the saw teeth are sorted according to the amount of fiber in the cotton. The cotton seeds that are not selected by the saw teeth and fall into the gap of the saw blade are divided into two situations:
1. The cotton seeds are in direct contact with the side of the saw blade
The cotton seeds that are in direct contact with the side of the saw blade are in direct contact with the saw blade. Friction force P is generated between the blades, and the direction of P is along the tangent direction of the saw blade at the contact point. The friction between the side of the saw blade and the cotton seeds is converted into the impulse on the cotton seeds, as shown in Figure 8-23. Under the condition that the speed of the saw blade roller remains unchanged, the magnitude of the impulse depends on the contact between the cotton and the saw blade. When cotton seeds contain more fibers, the friction impulse is larger, and vice versa.
Suppose the mass of a cotton seed falling into the gap of the saw blade is m, its speed moving along the cotton seed comb toward the saw tooth is v0, and its speed after contacting the side of the saw blade is v. The cotton seed and the saw blade The time of contact between the sheets is t, which can be obtained from the momentum theorem:
mv=mv0+Pt
That is, the cotton seeds are at the cotton combing point The momentum after contact with the side of the saw blade is the combination of Pt and mv0. mv0 is almost a constant. The more fiber there is in the cotton, the greater the influence of mv on Pt. The farther the cotton is thrown, and finally falls on the ginning rib far away from the cotton comb. The flatter upper part. On the contrary, the less fiber the cotton seed contains, the less the mv is affected by Pt, and the closer the cotton seed is thrown, and finally falls on the steeper part of the lower part of the ginning rib that is closer to the cotton seed comb.
2. The cotton seeds are not in direct contact with the side of the saw blade
The part of the cotton seeds that is not in direct contact may be pulled by the nearby cotton that is hooked by the saw teeth, and the length of time the cotton seeds are pulled by the single-particle cotton depends on Depends on the degree of connection between cotton seeds and single-particle cotton. The more fibers there are on the cotton, the closer the connection with the single-grain cotton is, and the longer the cotton is under traction. When the cotton is separated from the traction of the single-grain cotton, it finally falls on the flatter place on the upper part of the ginning rib. On the contrary, the fewer fibers on the cotton seeds, the shorter the time the cotton seeds are pulled by the single-grain cotton, and finally fall on the steeper lower part of the ginning rib.
The cotton seeds falling on the ginned ribs are affected by three forces (because the surface of the ginned ribs is very smooth, the friction between the cotton seeds and the ginned ribs can be ignored), namely the gravity of the cotton seeds themselves, the ginned ribs. The supporting force of the ribs on the cotton and the friction of the side of the saw blade on the cotton. The gravity of the cotton seed itself makes the cotton seed slide down along the surface of the ginned rib; the friction force of the saw blade on the cotton seed causes the cotton seed to move upward along the surface of the ginned rib with the rotation of the saw blade. When the cotton seeds fall on the flat upper part of the ginned ribs, the tangential component of the cotton seeds’ gravity on the surface of the ginned ribs is very small, and the friction force of the saw blade on the cotton seeds plays a dominant role, causing the cotton seeds to move along the surface of the ginned ribs. Move and return to the sub-roll. The cotton seeds falling on the steeper part of the lower part of the ginning rib are greatly affected by gravity, slide down along the surface of the ginning rib, leave the middle box and are discharged out of the machine. In this way, the cotton that falls into the gap of the saw blade is sorted by the saw blade again, and only the cotton with long fibers is discharged out of the machine.
The above description, that is, the “second sorting theory” is a relatively representative statement. There is also a theory that when the sub-cotton roll moves to the cotton comb and encounters a rapidly rotating saw blade roller, because the surface linear speed of the saw blade roller is much greater than the surface linear speed of the sub-cotton roll, a strip is torn apart from the outside to the inside by the saw teeth. The cotton in the cotton roll is discharged along the crack channel under the action of inertial centrifugal force and self-weight.
(2) Factors affecting the discharge of cotton seeds
If the lint rate of discharged cotton seeds is too large, it will increase the clothing loss; if the lint rate of discharged cotton seeds is too small, it will affect the quality of cotton lint and ginning and stripping. Therefore, the cotton wool rate should be controlled within an appropriate range. The national standard “Cotton Fine Staple Cotton” (GB1103-1999) stipulates that the cotton lint rate should not exceed 0.4% when processing grade 1 and grade 2 cotton, and should not exceed 0.4% when processing grade 3 to 5 cotton. greater than 0.6%.
Whether the cotton seeds are discharged smoothly or not has a great influence on the cotton seed hair rate and the uniformity of the cotton seeds. Cotton seeds are not discharged smoothly. When the flower feeding speed is above the middle gear, the cotton roll will be very tight. When the flower feeding speed is at the high gear, the cotton roll will stop spinning. If the cotton seed is discharged smoothly and the cotton feeding speed is above the middle gear, the cotton seed roll will not be tight; when the cotton feeding speed is at the high gear, the cotton seed roll will keep rotating. Therefore, it is very important whether the cotton seeds are discharged smoothly or not. It is mainly affected by the following factors:
1. Working box geometry
A working box with a reasonable shape can create better conditions for the cotton to be rolled out of the fiber to be discharged from the working box in a timely manner.
2. Tightness of sub-cotton roll
Cotton is easy to fall out when the sub-cotton roll is loose. Because the sub-cotton rolls are loose, the holding effect between the cotton seeds and the sub-cotton rolls is weak, and the cotton seeds are easily separated from the sub-cotton rolls and discharged smoothly. Especially when the cotton roll comes into contact with the saw teeth at the cotton comb, due to the sudden acceleration of the movement of single particles of cotton, a crack is torn open in the cotton roll by the saw teeth, so that the cotton can be discharged smoothly. When the sub-cotton roll is tight, it is difficult to form a row of crack channels when the sub-cotton roll encounters saw teeth. Moreover, the binding effect between the cotton seeds and the sub-cotton rolls is strong, which can easily cause poor cotton discharge. In order to discharge the cotton seeds smoothly, the curvature radius of the working box and the plate can be adjusted to the maximum and the cotton roll density to the minimum, which is conducive to the discharge of cotton seeds.
3. Adjustment of the cotton comb
Adjusting the inclination of the cotton comb is crucial to the smoothness of the row and to controlling the lint rate of the discharged cotton. When the cotton comb is lifted upward, the local density of the cotton roll at the cotton comb increases, and the cotton is less likely to be discharged; conversely, when the cotton comb is tilted downward, the cotton is easily discharged. Therefore, the degree of regulation and control of the cotton comb has a great relationship with the position and structure of the cotton comb. In addition to the inclination adjustment, the cotton comb of the new sawtooth gin can also be adjusted forward and backward to adjust the gap between the cotton comb and the gin rib row.
This two-way adjustable cotton comb strengthens and improves the regulating effect of the cotton comb, and is more conducive to the discharge of cotton.
4. The size of the platoon channel
The platoon channel is the channel between the embossed rib row and the shell rib row. During ginning, the channel is divided into many “well”-shaped channels in the length direction by the saw blade roller. The size of the pavilion is determined by the length and width of the “well”-shaped channel. The length and width of the “well”-shaped channel are determined by the gap between the embossed rib row and the shell rib row and the saw blade pitch. Under other conditions being the same, if the gap between the embossed rib rows and the shell rib rows is large, the cotton seeds are easily ejected to the steeper lower part of the ribs, and the cotton seeds are easily discharged; conversely, the cotton seeds are easily ejected to the flat upper part of the ribs. Cotton seeds are not easily discharged. The embossed rib row and the shell rib row can be adjusted within a small range, but it should be ensured that the embossed ribs do not collide with the saw blade roller spacer, and the height of the saw blade extending beyond the shell ribs should be ensured. Under the same conditions, if the saw blade pitch is large, the cotton seeds are easily discharged; on the contrary, the cotton seeds are not easy to be discharged, so the reduction of the saw blade pitch is limited.
5. Saw blade spacing and sawtooth status
When the saw blade spacing is large, the number of cotton seeds falling between the two saw blades is relatively large, and the number of cotton seeds in contact with the side of the saw blade is relatively small, that is, there is no There are many cotton seeds affected by the impulse. It is relatively easy for most cotton seeds to overcome the coupling force of the cotton rolls and the friction of the saw blade due to the action of gravity, and the cotton seeds are easily discharged. If the pitch of the saw blade is small, there will be more cotton in contact with the saw blade and it will be difficult for the cotton to be discharged.
If the saw teeth are not sharp and have too many defects, they will seriously affect the hooking of the fiber-laden cotton by the saw teeth at the cotton comb, resulting in a high rate of discarded cotton wool and serious loss of clothing hem.
6. The inclination of the embossed ribs
When the embossed ribs are adjusted in the vertical direction, the lower part of the row is expanded, and the flatter part of the upper part of the rib tends to be inclined, which enhances the gravity of the cotton seeds on the row. The function is to make the rows smooth. When the embossed ribs are adjusted in the opposite direction, it will affect the row.
(3) The motion trajectory of cotton seeds in the working box
In order to discharge the cotton seeds that meet the requirements of hair rate from the machine in time, in addition to adopting reasonable process parameters and improving operating methods on the existing machine models In addition, another method is to innovate the existing platoon mechanism.
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