Neps and lint are the key factors affecting the yarn quality. The existence of neps is easy to cause white stars after dyeing, which greatly affects the quality of the fabric; the existence of short fiber easily causes coarse knots and details on the yarn body, and affects the appearance and weaving efficiency of the fabric. Therefore, in order to improve the quality of yarn, it is necessary to adopt systematic and appropriate methods to reduce the impurities and short fibers of semi-finished products before spinning process.
1、 Selection of raw materials
1. The selection of raw materials should consider the equipment condition and variety requirements
We should give full consideration to the equipment condition and variety requirements of our factory, and give priority to the raw cotton with good grade, suitable fineness and maturity, low short fiber rate and impurity rate.
Due to the influence of many factors, such as the origin, picking period, variety, ginning method and so on, the performance of raw cotton is very different. In actual production, we can only adjust the technology of raw cotton with different quality indexes according to the existing equipment, and it is impossible to use them properly. Therefore, when selecting raw materials, we should fully consider the equipment condition and variety requirements of our factory, so as to give full play to the characteristics of raw cotton.
Practice has proved that raw cotton has good grade, moderate fineness and maturity, low short fiber rate and impurity rate, and less neps and impurities in raw sliver after blowing and carding process. This is because there are few short fibers and impurities in the fiber, and the probability and degree of diffusion of short fibers and impurities are small in drafting and carding blow. At the same time, the amount of short fibers and impurities adhering to various parts of the spinning channel is also small, and the impurities generated after the same amount of drafting and carding blow are also less. However, good grade of raw cotton will increase the spinning cost. Therefore, reasonable selection should be made in combination with the sales price and the user's use and quality requirements.
2. Strictly control the difference of lint and the number of back blooming
After drawing, the fiber has been fully straightened and parallel. If it goes through the cleaning and carding process again, it will be beaten and combed, or it will be broken into short fibers, or it will be kneaded into neps. If the raw cotton with large difference in short staple fiber is used, its pertinence will be poor when short fiber is excluded, which will cause waste or insufficient elimination. Therefore, it is necessary to strictly control the difference of short hair and the number of back flowers. In order to reduce neps and impurities, raw cotton with lint ratio more than 14% is generally not used in cotton blending scheme, and the average short fiber rate is generally controlled below 11.2%.
2、 Opening and cleaning process
Pay attention to the process flow and parameter setting of opening and cleaning process
The influence of opening and cleaning process on the subsequent process is not paid attention to by many manufacturers as much as carding process. In fact, the control of neps and short fibers has begun when the cotton grabber starts to grab cotton. The selection of opening and cleaning process plays a very important role in carding quality. Too large cotton block grabbing, improper setting of clearance striking point spacing, improper striking air flow, resulting in poor dust removal and noil, and failure to eliminate impurities and short fibers in time may bring additional task of eliminating impurities in carding process, and the elimination of impurities and short fibers in carding process is limited. Therefore, attention should be paid to the opening and cleaning process and process setting as much as the carding process.
Some problems should be paid attention to in the process selection
(1) Try to use a short process, combined with early drop, less broken, more row, reasonable opening. With the development of new technology, the process of flower cleaning is developing to be short and precise. This can be seen from the mainstream blowing carding units abroad. The selection of technological process should be combined with the actual situation of raw materials containing impurities, combined with the process principle of early drop, less crushing, more row, reasonable opening and clearing, so as to avoid crushing impurities and damaging fibers.
(2) Give full play to the role of free opening and holding the blow properly. For example, fa103 biaxial flow and fa031 corner pin beater in blowing carding unit process system are free opening, and a slightly higher speed should be selected to give full play to their free opening function; fa106b saw blade roller and fa108e saw tooth roller belong to grip opening, so it is not suitable to strike excessively to avoid crushing impurities and damaging fiber when the opening conditions are met. Adjust the noil process, dust bar, dust knife, carding bottom gap, and organize the air distribution to ensure that each machine can absorb enough air volume of noil, which can meet the requirements of gradual opening and slow beating, early falling, multi row, less damage and breakage, and reduce the impurity.
(3) The cotton roll should be light weight, and the bundles and lumps should be as small as possible. In this way, the carding load in the working area of the carding rotary cover can be reduced, the deformation and damage of the cylinder and the card clothing of the rotary cover can be reduced, and the carding effect is better. The results show that the degree of single fiber in the web is high, the number of neps is small, and the amount of impurities in the web is more.
3 requirements for flower cleaning machinery
The opening parts should be smooth, the air flow in the front and rear machines should be smooth, the spacing of each component should be accurate, the carding pipe should be smooth and clean without hanging flowers, so that the raw cotton will not return to the flower, hang or entangle in the processing process. Good sealing of cotton conveying pipe and cotton box, keeping enough air volume and pressure, smooth cotton conveying, no sticking, extrusion and blocking, and smooth transfer are beneficial to reduce neps. A series of old machine should pay attention to the transformation of the hitter.
3、 Carding process
Carding process is the key process to reduce neps and remove short fibers. Carding machine is the last machine of blowing carding unit, and it is also an effective machine for carding to remove neps and fine impurities, especially neps. During opening and cleaning, neps increase exponentially, only carding can remove about 80%. In order to reduce cluttering and short pile, the following problems should be paid attention to:
1. Reasonable selection of metal card clothing
Reasonable selection of carding metal card clothing is an important prerequisite for reducing short fiber, reducing neps and ensuring yarn quality.
(1) The following factors should be considered in the selection of card clothing:
The matching of cylinder and doffer card clothing should help to improve the fiber transfer rate, improve the holding efficiency, reduce the cylinder fiber return and fiber mesh holes; the card clothing should be sharp, smooth, high wear resistance, flat after wrapping, ensure the carding effect and smooth transfer, and the spacing can be wide, so as to reduce the risk of needle connection and facilitate maintenance; it can be used for the transmission of various cotton and cotton chemical fibers To meet the requirements of high production and high speed, it is necessary to select the appropriate pin tooth density with good quality stability, and pay attention to the matching of cylinder, doffer, cover plate and taker in roller clothing.
(2) Popularization and application of the new type of clothing:
Whether it is cylinder, doffer clothing, or cover, roller clothing, has made great progress in recent years, the continuous introduction of new clothing to reduce neps and short hair to open up the imagination. According to the comparative experiments of the new type of card clothing popularized and applied in many spinning mills, the neps of sliver and yarn are greatly reduced, especially the neps. The comparative data of many spinning mills show that the NEP of sliver can be reduced by 25% - 50%, and the NEP of yarn can be reduced by 20% - 60%. No other measure can compare with the great reduction of sliver and yarn nep.
2. Select the suitable grinding cycle of card clothing
The selection of the grinding cycle of card clothing not only affects the cost, but also has a close relationship with the generation and elimination of neps and short fibers. The comparison of several schemes for selecting the grinding cycle of carding card clothing is as follows:
(1) According to the fixed cycle, the needle cloth is grinded and replaced. Generally, the replacement period of card clothing is two years, and the period of needle grinding is half a year. However, due to the gradual decrease of needle height and the gradual increase of needle density in modern clothing, excessive needle grinding will damage the needle tip and reduce the carding effect, which is unfavorable to the elimination of neps and short fibers.
(2) Grind according to the output. The general service life of imported card clothing is 600-700t, and the needle grinding cycle is 250t. Compared with the imported card clothing, the service life and grinding cycle of domestic card clothing are shortened to varying degrees. However, due to the influence of variety, speed and state, it is not easy to grasp accurately, so it is less used.
(3) According to the quality of sliver web combined with the use of time to grind. This is a more scientific and practical method. Most spinning enterprises test and check the sliver and web quality more than once a week, so it is timely and convenient to confirm whether it is necessary to grind according to the quality index of cotton web, sliver and other quality indexes combined with service time.
3. Increase the fiber transfer rate
The purpose of increasing the fiber transfer rate between cylinder and doffer is to reduce the needle load of cylinder, improve carding efficiency and prevent the fiber from being excessively combed into short fibers and neps. The factors influencing the transfer rate are summarized as follows.
(1) The influence of rotation speed: when the rotation speed between cylinder and doffer is high, the transfer rate is large.
(2) The smaller the difference of the density of the two needles, the higher the transfer rate. The larger the height difference between them, the greater the transfer rate. Therefore, the higher the doffer's density is, the higher the transfer rate will be.
(3) Spacing: when the distance between cylinder and doffer is small, the transfer rate is high. If the distance between the cylinder and the lower edge of the front lower cover plate is large, the transfer rate is high.
4. Add fixed cover plate, cotton net cleaner and other accessories to ensure the elimination of lint and neps
This is for the old carding machine. The factory test shows that the neps and impurities of sliver are reduced, the sliver evenness is improved, and the neps of sliver become finer and smaller.
5. On the premise of ensuring the basic work of "four front and one alignment", we should pay attention to the reasonable selection of wire speed ratio of cylinder, licker in roll surface and cover plate speed
Generally, the linear speed ratio of cylinder and taker in roller is about 2:1, and the speed of cover plate is more than 120mm / min, which is beneficial to reduce neps.
4、 Merging and roughing process
The influence of blending and roughing process on short fiber and NEP in yarn formation was ignored before. In fact, blending and roughing process also has certain influence on short fiber and NEP. The experiment shows that if the roller gauge is not proper, neps and short fibers will increase. The increase of lint is due to the breaking of some fibers in the drawing process, and the increase of neps is caused by sliver grinding, roller winding, etc.
5、 Influence of temperature and humidity
In fact, the influence of humidity is very important, and many textile mills pay more attention to it, especially in high temperature and humidity seasons or when using cotton with high sugar content. If the temperature and humidity are not suitable, the draft and carding of the fiber are unfavorable, and neps or short fibers are easily produced. The temperature difference between the blowing workshop and carding process is too large, and it is easy to produce sticking coil, fiber thermal expansion, not easy to carding, etc., which is not conducive to reducing neps and short fibers.