In the carding system, the processes after carding basically no longer have the functions of opening, carding and removing impurities, so the quality of the card sliver, especially the knot content, directly affects the quality of the yarn.
Therefore, quality control of raw strips is particularly important.
Raw strip quality index:
The quality indicators of raw sliver can be divided into two categories: regular inspection items and reference items in operation and production.
1. Regular inspection items:
1. Unevenness of raw strips
The unevenness of the raw sliver reflects the uneven thickness of each meter of the raw sliver. There are two inspection indicators: Sabouraud sliver and Ubbelin sliver. Generally, the sliver sliver should be controlled at 14% to 18%. Within the range, the CV value of Ubbelohde’s special dry bar is controlled below 4%.
2. Raw sliver weight unevenness
It reflects the uneven thickness of the 5-meter segment of the raw sliver, and the weight unevenness should be controlled below 4.0%.
3. Card sliver neps and impurities
It reflects the number of neps and impurities contained in each gram of raw sliver. This indicator is determined by the enterprise according to the product requirements.
4. Raw sliver short staple rate
Refers to the percentage of fibers below 16mm in the raw sliver. The carding process both eliminates short lint and produces short lint to a certain extent. The lint production volume of ordinary carding machines is greater than the discharge volume, so the lint content in the card sliver is generally more than that in the cotton lap. After using multi-point suction, the carding machine can greatly increase the amount of short lint and dust removal, which can make the short lint content in the card sliver less than that of the cotton roll. Generally, the short lint rate of the card sliver is controlled within 4%.
2. Reference indicators:
The clarity of the cotton web is a comprehensive indicator that reflects the structural status of the cotton web. By visually observing the straightness, separation and uniform distribution of the fibers in the cotton web, we can quickly understand whether the mechanical state of the carding machine and the process configuration are reasonable.
Control of neps and impurities in card slivers:
Neps and impurities in the card sliver directly affect the knots and surface defects of the carded yarn, and affect the normal movement of the fiber during drafting in the doubling, thickening and thinning processes and the normal movement of the traveler when the spun yarn is twisted and wound. , causing evenness to deteriorate and yarn defects and ends to break to increase. Therefore, it is necessary to control and reduce the number of foreign particles in the raw sliver. In production, it is necessary to strengthen control and management and rectify backward machines to reduce the dispersion of the number of nep impurities between machines as much as possible.
Since the fibers are subject to strong impact and careful carding during the cleaning and carding processes, the number of neps increases. Especially in the carding process, the immature fibers undergo the impact and friction of the saw teeth of the licker-in, and are formed in the tin Repeated rubbing in the working area of forest and cover board can easily twist into neps; in addition, some fiber impurities, stiff cotton or fiber clusters and bundles produced in cleaning cotton can also be easily transformed into neps. Therefore, from raw cotton to card sliver, the weight percentage of impurities decreases rapidly, but the number of impurities gradually increases, and the weight of each impurity decreases. After the card sliver is combined and roughened, the number of knots and impurities increases. However, in the spinning process, some of the nep impurities are wrapped inside the yarn sliver, so the number of knots and impurities in the yarn is 20% to 40% less than that of the card sliver. %.
The control of nep impurities should be based on the properties of raw materials, cotton roll quality and yarn quality requirements, starting from process deployment, and giving full play to the dust removal effect at the rear belly and cover. Its main measures are:
1. Configure the carding process:
Combining the carding process with “four fronts and one accuracy” and “tight gaps” can increase the percentage of single fibers in the cotton web, promote the fibers to straighten and parallelize, fully separate the fibers from impurities, and improve the carding machine’s removal of cotton. The ability to bind impurities.
2. Get mixed up early and at the right time:
There must be a reasonable division of labor for impurity removal in the cleaning and carding processes, as well as a reasonable division of labor for impurity removal in each part of the carding machine itself. For impurities that are generally larger and easy to separate, the principle of falling early and breaking less should be implemented; impurities with greater adhesion, especially impurities with long fibers, should not fall early when they are not separated from the fibers, and should be removed during carding. It is more advantageous to clean it after sufficient combing on the machine. When the maturity of raw cotton is poor and there are many fiber impurities, the waste and impurity removal burden of the carding machine should be appropriately increased.
The carding roller part of the carding machine is a key impurity area. Broken seeds, stiff flaps and impurities with short fibers should be discharged in this area to prevent impurities from being crushed or stuck between the cylinder needle teeth and affecting the separation. combing effect. Therefore, except for a small amount of adhesive impurities, the licker-in part should fall off early and fall off more. Reasonable configuration of the licker-in speed and the rear turning process has a significant effect on improving the impurity removal efficiency of the licker-in part and reducing the impurity of the card sliver. The cylinder and cover parts are suitable for removing small impurities, neps and short lint with fibers of different lengths. The specifications of the cylinder and flat card clothing and the distance between the two needle surfaces, the position of the upper front cover plate, the distance between the front upper cover plate and the cylinder, and the speed of the flat plate also affect the cotton in the sliver. The amount of junction impurities. For raw cotton that is less mature and contains more harmful defects, special attention should be paid to the role of the cover work area in eliminating impurities.
3. Reduce fiber twisting:
According to the tightness of the fibers in the neps, they are divided into loose neps and tight neps. Most of the tight neps contain impurities. A nep is generally composed of dozens of fibers, most of which are thin-walled fibers with low maturity coefficients. Such fibers have low rigidity and high moisture regain. On the carding machine, due to the impact and friction of the licker-in and the cylinder cover, Repeated rubbing between boards can easily cause neps to form. In addition, when Xilin,When the blade and doffer needle teeth are blunt or have burrs, the fibers cannot transfer repeatedly between the two needle surfaces and tend to float between the two needle surfaces, where they are rubbed by other fibers and form more neps. The distance between the lick-in roller and the cylinder is too large and the serrations are not smooth, which can easily lead to poor peeling between the lick-in rollers and return of the lick-in rollers, resulting in a significant increase in neps. The needle surface of the cylinder is rough due to grinding, there are oil stains and rust spots on the needle surface, and the distance between the cylinder and the doffer is too large, which can easily cause the cylinder to wrap around and increase neps.
4. Strengthen temperature and humidity control:
Temperature and humidity also have a great impact on nep impurities. When the moisture regain of raw cotton and cotton laps is low, impurities tend to fall, and neps and bundles can also be reduced. The moisture regain control range is: 8% to 8.5% for cotton laps and 10% to 11% for raw cotton. The carding workshop should control a low relative humidity, generally between 55% and 60%, to release moisture from the fiber, increase the rigidity and elasticity of the fiber, and reduce the friction between the fiber and the needle teeth and the filling of the tooth gaps. However, if the relative humidity is too low, on the one hand, it is easy to generate static electricity, and the cotton mesh is easy to be damaged or broken, especially when spinning chemical fibers. This phenomenon is more obvious. On the other hand, it will reduce the moisture regain of the card sliver, which is detrimental to the drafting of the subsequent processes. .
Control of raw strip uniformity:
Raw sliver unevenness is divided into two types: raw sliver weight unevenness and raw sliver dryness unevenness. The former represents the weight difference between long segments of the sliver (5m), and the latter represents the unevenness of each meter of sliver segment. Condition.
1. Control of dryness uniformity of raw strips:
Card sliver evenness affects the weight unevenness, evenness and strength of the yarn. The main factors that affect the unevenness of the card sliver include the carding quality, the uniformity of fiber transfer from the cylinder to the doffer, the mechanical state, and the cloud spots, holes and broken edges of the cotton net, etc.
When the carding quality is poor, there will be more residual fiber bundles, or clusters of aggregated fibers of different sizes will appear in the cotton net, forming cloud spots or fish-like defects. Poor mechanical conditions, such as inaccurate gauge, periodic changes in gauge caused by vibration of the licker-in, cylinder and doffer, poor gear meshing in the coiler, etc., will increase the unevenness of the slivers. In addition, if the distance between the stripping rollers is incorrect, the drafting of various parts between the doffer and the coiler and the cotton web tension are too large, and the sliver quantity is too light, etc., it will also increase the unevenness of the sliver.
2. Control of raw sliver weight unevenness:
There is a certain relationship between the card sliver weight unevenness and the spun yarn weight unevenness and weight deviation. The sliver weight unevenness should be controlled from two aspects: internal unevenness and external unevenness. The main factors that affect the unevenness of the card sliver weight include the uneven weight of the cotton lap, the difference in the noil rate between the various machines of the carding machine, and the poor mechanical condition. To control the internal unevenness of the card sliver weight, the unevenness of the cotton roll weight should be controlled to eliminate the sticky layer, holes and poor roll change joints of the cotton roll. To reduce the external unevenness of the card sliver weight, the spacing and noil rate of each carding machine spinning yarn with the same linear density are required to be uniform, to prevent the wrong use of the drafting conversion gear, and to do a good job in maintaining the condition of the equipment to ensure Mechanically in good condition.
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