NEP is one of the important indexes to measure the quality of combed sliver, which directly affects the yarn quality. In practice, we deeply realize that it is very important to do well in equipment management, improve process configuration, strengthen the carding efficiency of cylinder and top carding of comber, and arrange the noil reasonably to reduce the NEP of combed sliver.
01
Influence and control of combing preparation process on combing Neps
Our company adopts the process of strip roll → parallel roll combing preparation. Through a lot of experiments, it is proved that the NEP can be increased by 10% - 20% and the impurity can be reduced by 6% - 10% after the sliver and parallel winding. This is due to the fact that the neps become smaller and larger after the sliver is drawn, which is the main reason for the increase of neps. However, these small neps are difficult to be removed completely because of the limitation of the top comb type.
1) to reduce the increase of Neps in the preparation process, a reasonable drafting multiple is required, which is generally controlled at about 8 times. At the same time, as the length of raw cotton changes, the roller spacing should also change.
2) strengthen the equipment management to ensure that the upper and lower flannelette in the drafting area operate flexibly and the carding knife works well. At the same time, the management of operators should be strengthened, and the impurities such as knots and short fibers on the carding knife should be removed in time to prevent them from falling into the cotton net.
3) the surface of the cot shall be smooth without concave core, bending, flexible rotation and solid pressure. Prevent the occurrence of clinging and rubbing and reduce the increase of neps.
02
Influence and control of small volume ration on Combed Neps
1) according to relevant data of Lida Company, the maximum fixed volume of small volume can be set to 70 g / m. However, in the actual production, the quantitative design of the small roll should not be too large, generally 60 g / M ~ 65 g / m, mainly considering the load on the cylinder teeth and the relationship between the height of the top comb and the thickness of the cotton layer. If the volume is large and the cotton layer is thick, when the relative humidity is too small, the cotton layer is fluffy. Because of the limitation of the top comb height, the bottom fiber cannot be effectively combed.
2) the quantity of small roll is related to the number of fibers and the linear density of cotton fibers. Generally, when the number of cross-section is 38000-40000, the small volume ration can be set at 60 g / m-65 g / m.
03
Effect and control of combing cylinder on Neps
Cylinder is the main carding element of comber. It is responsible for carding the front end of the fiber bundle, straightening and paralleling the fibers, and removing the short fibers and neps. Therefore, there is a direct relationship between the reduction of neps and tin.
1) sawtooth cylinder is used on FA261A comber, and Nakagawa 1449 cylinder is used, which is composed of four needle plates. According to the arrangement principle of tooth height from deep to shallow, tooth density from thin to dense and tooth plate from thick to thin. The cotton layer held by the clamp plate is combed by the cylinder from front to back, so as to gradually eliminate such sundries as lint, neps and impurities. If there are broken teeth or crooked teeth in Xilin, the carding effect will be affected and neps will not be easily eliminated. Generally, the number of damaged teeth in the longitudinal and transverse direction of the cylinder shall not exceed 2, and those exceeding shall be replaced in time. If caulking is found in the tin, the cause should be found out and eliminated thoroughly.
2) in order to pursue the output and improve the speed of the cylinder, some enterprises will increase the neps. At this time, the corresponding control measures should be taken to change the process parameters, adjust the separation and joint time, reasonably select the drop rate and control the increase of neps.
04
Influence and control of top carding on Neps
The effect and control of top carding on Combed neps; the top carding is fixed on the clamp bracket, which is used to comb and separate the back end of the fiber bundles. Although there is only one row of carding needles, the top carding has a very large effect.
1) the top comb density shall be determined according to the fiber linear density, the type of spinning and the drop percentage. Generally, 14.5 tex yarn has a drop rate of 14% - 18%, and 26 teeth / 10 mm can be selected; under 10 tex yarn, the drop rate is 10% - 25%, and 28 teeth / 10 mm-30 teeth / 10 mm top comb can be selected. The experiment shows that when the insertion depth of top carding is the same and the drop rate is the same, the specification of top carding has a certain relationship with NEP.
2) the high and low position of top comb not only affects the landing rate, but also affects the removal of neps, which is generally controlled between - 0.5 and + 0.5 scales. If the inserting depth is too deep, the root of top comb will be seriously embedded, which will affect the next carding, and the effect of removing neps is poor, causing serious holes in the cotton mesh; if the inserting depth is too shallow, the bottom of the clump must not be combed by top comb, and some neps will be left in the cotton mesh, resulting in the increase of neps. In the production process, we can turn the clamp plate to the front position, open the adjacent separation rubber roller pressure piece, and observe whether the depth of the top comb inserted into the whisker is appropriate, otherwise we need to adjust.
3) the top comb teeth shall be complete, and no broken or combined needle is allowed. If any, it shall be replaced in time. At the same time, the operator should clean the top comb thoroughly and carefully in strict accordance with the requirements to reduce the phenomenon of needle teeth hanging.
4) when adjusting the noil spacing, whether it is increased or decreased, the position before and after the top comb shall be corrected repeatedly and carefully, otherwise the depth of the top comb inserted into the whisker will change. In practice, it is found that there is a gap of 1mm between the top comb and the setting gauge, and the height of the top comb is raised by about 0.1mm correspondingly, that is to say, the depth of the top comb inserted into the whisker bundle is reduced by about 0.1mm, which is very important. Therefore, the maintenance workers should pay attention to the operation, otherwise the depth of the top comb inserted into the whisker bundle is not consistent with the actual situation.
05
Influence and control of brush on Combed NEP
The function of the brush is to remove the knots and short fluff on the cylinder needle teeth, keep the next carding normal, and keep it in good operation state.
1) the diameter of the brush must be the same as that of the same machine. If the cleaning of the whole cylinder is poor, the first reason is that the speed of the brush becomes slower, which is caused by the relaxation of the triangular tape of the brush; the second reason is that the diameter of the brush becomes smaller with the extension of the running time, the depth of the brush inserted into the cylinder decreases, and the cleaning effect on the cylinder decreases. If there is a bad cleaning of the cylinder in one eye, resulting in a sharp increase of Neps in the cotton net, it is necessary to check the looseness of the brush in time, and remove the flying flowers in the air scoop.
2) the brush is inlaid with flowers, which is not conducive to the cleaning of the cylinder, and the knots on the brush are thrown into the human cotton net. The brush should be replaced immediately, and the distance between the brush and the triangular air flow plate should be adjusted at the same time.
3) the ratio of brush speed to cylinder speed is a key process parameter value. Proper selection can reduce neps. In addition, when the speed of the brush is constant, the diameter of the brush is reduced, and the linear speed is also reduced. In order to clean the cylinder and reduce neps, the speed of brush should be selected according to the actual situation.
4) in order to improve the carding effect, the automatic deceleration device of the comber is used reasonably. The cleaning interval is generally set as 30 min, and the cleaning time is set as 10-20 s each time, so as to keep the cylinder in a good clean state. This not only stabilizes the dropping rate, but also greatly reduces the production of neps and impurities.
06
The influence and control of the separation and joint of comber on Neps
After the separation and joining, we found that there were more neps and larger neps in the end of the comb. The reason is due to the improper matching between the forward rotation time of the separating roller and the swing time of the clamp plate. It is known from the relevant data that when the pendulum shaft swings backward, the clamp plate moves backward accounting for 136 °, the pendulum shaft swings forward, the clamp plate moves forward accounting for 224 °, and the travel speed ratio coefficient is 1.647, which indicates that the clamp plate moves backward quickly. Therefore, the top comb can also be pulled out from the cotton layer at a fast speed. At this time, the separation roller has not finished its clockwise rotation, and part of the end of the cluster has not been combed by the top comb, so there are more neps at the end of the cluster. Therefore, according to different fiber lengths, the separation and jointing time should be adjusted reasonably to reduce the neps at the end of the bundle.
07
The influence and control of noil rate and feeding length on Combed NEP
The size of the drop rate and the selection of the feeding length directly affect the NEP of the comber. Therefore, in the production process of combed yarn, the reasonable drop rate and the feeding length should be selected according to the actual situation, and the following two points should be paid attention to.
1) the drop rate shall be determined according to the requirements of the product quality and in combination with the quality of the cotton roll including lint, neps and combs. The larger the drop rate of the same roll, the less neps there are in the comber, but the number of effective fibers in the drop rate should be considered.
2) the feeding length should be determined according to the fiber length, the drop rate and the supply-demand relationship of the output. The shorter the feeding length of the same cotton roll, the better the carding effect, and the less neps in the comber strip, but the output demand should be considered.
The control of Neps in combed sliver is a systematic project, which has many factors. In daily production, neps are often caused by the combination of several defects. Therefore, according to the specific conditions of different raw cotton, process, equipment, temperature and humidity, the main and secondary problems should be found out, and effective control measures should be taken to keep the combed neps under control all the time, so as to achieve the purpose of stabilizing product quality.
