Compared with hand-picked cotton, machine-picked cotton has less labor, low cost, and low corresponding cotton price, which is widely used in textile enterprises, but the proportion of short fiber and immature fiber of machine-picked cotton is large, and the content of harmful defects such as infertile seeds and soft seed epidermis is higher, which brings more unfavorable factors to the production of enterprises.
In the processing process of machine-picked cotton, due to the large number of striking points, immature fibers, infertile seeds, soft seed skins, stiff spots, etc. are easy to be damaged and crushed to form a large number of harmful defects, and eliminating or reducing impurities and fine defects in machine-picked cotton has become one of the difficulties in the opening, impurity removal and carding process of spinning enterprises. Therefore, it is the key to reduce the harmful defects of machine picking cotton by formulating a reasonable plan for opening, removing impurities, removing linter and carding in a targeted manner.
Since 2017, with the gradual maturity of defoliant spraying technology and the update of machine harvesting equipment, the quality of cotton harvesting machine in Xinjiang has improved significantly, but the overall index of machine cotton picking in Xinjiang in 2022 has deteriorated significantly compared with previous years (see Table 1), especially the number of impurities and linters have increased significantly.
Table 1 Comparison of HVI quality data of cotton in each year
Judging from the above indicators in Table 1, the carding configuration scheme should be mainly designed from the aspects of short linter and impurities when harvesting cotton.
First, the problems that are prone to occur in the production of machine-picked cotton
1.1 Machine picking cotton production process
In the process of cotton ginning, due to the long processing process of machine-picked cotton, the blow to cotton is stronger than that of the cotton cleaning process, so that the volume of neps, impurities, fiber chips, and soft seed skin becomes smaller, the number increases, and the defects generally increase by more than 5 times compared with hand-picked cotton. Many defects are in the form of fibre chips, which are small and lightweight, and can easily be transferred with the fibres to the next process during the spinning process.
In the process of opening and removing impurities in the opening and cleaning process, it is difficult to be effectively removed because these defects are small in size, light in weight or mixed in the middle of the fiber, which increases the burden of opening, removing impurities and carding in the carding process, so the carding requirements for the carding machine are more stringent.
Generally speaking, about 30% of the defects that are not removed in the cotton cleaning process cannot be removed in the carding process, and the small defects formed by machine cotton picking are more difficult to remove. Even if the carding process is continuously improved, there are still about 50-60% of small defects such as fiber chips that cannot be removed, which is also a major technical problem that textile mills have difficulty solving when using machine cotton picking in recent years.
1.2 The influence of machine cotton picking on the quality of semi-finished products and finished products
In the spinning process, machine picking cotton is easy to increase the number of defects of semi-finished products, especially the neps, fiber chips and linter rates in the carding and combing processes are much higher than those of hand-picked cotton.
Generally speaking, the raw nep of machine-picked cotton is 20-50% higher than that of hand-picked cotton, 30-80% higher with fiber seed chips, 1.5-4.5% higher than the linter rate, and 0.5-2.5% higher than the carded cotton drop rate. That is to say, machine picking cotton not only has a large number of defects, but also has a high production cost.
In the combing process, the nep of cotton combed strips is 30-50% higher than that of hand-picked cotton, the cotton drop rate is 2-8% higher, and the short linter rate is 0.5-2.0% higher. In the spinning process, the number of defects in the spinning process of machine-picked cotton is high, the content of short linter rate is high, the cotton drop rate is more, and the quality of semi-finished products is poor, resulting in more yarn defects.
Second, the configuration of the carding components
Carding process is the key process in the spinning system, its main task is to comb the cotton block and bundle fibers into a single fiber state, effectively remove linters, impurities and neps, remove dust in the fibers, and improve the straightness, parallelism and separation of the fibers under the interaction of the carding elements, so that the fibers in the green strips are mixed more evenly, and finally improve the quality indicators such as dryness, strength and IPI yarn defects of the yarn sliver.
In the carding process, through the selection of carding elements and the optimal configuration of the process, it is an important means and method to improve the quality of machine-picked cotton yarn while ensuring that most of the defects formed by immature fibers are removed, and reducing fiber damage.
2.1 Selection of main carding parts
Card clothing is the "heart" of the carding machine, and the performance of the card clothing of the carding machine, whether the card clothing is suitable and whether the carding process parameters are reasonable have a very important impact on the carding quality and even the quality of the finished yarn. Therefore, it is particularly important to choose and match the carded card clothing correctly. In the spinning process, different origins, different grades (length, maturity, ginning quality), and different varieties of cotton fibers should also be emphasized.
2.1.1 Cylinder wires
The key to the selection of carding parts for the carding machine is to first choose the right cylinder card clothing. According to the characteristics of machine-picked cotton impurities and leaf impurities, we selected AC2040×01850-II double-tooth cylinder card clothing, which can not only increase the carding area between the cylinder and the cover plate, the cylinder and the fixed carding plate, but also enhance the pre-carding ability of the cylinder and the thorn roller, increase the transfer rate of the surface fibers of the doffer and the cylinder, and increase the carding effect. The improvement of carding efficiency can not only improve the output of the carding machine, but also stably improve the quality of the green strips, and is more conducive to the removal of fine impurities, fiber seed chips, dead cotton and white stars in the cotton layer. Table 2 shows the main card clothing configuration of the FA221B card, and Table 3 compares the quality of the green strips between single-tooth card clothing and double-tooth card clothing under different vehicle speeds.
Table 2 The main card clothing configuration of FA221B carding machine
Table 3 Comparison of the quality of raw strips of single-tooth and double-tooth cylinder wires
According to the comparative data in Table 2, the use of double-tooth cylinder card clothing reduced the linter rate of green strips by 16.4%, neps by 24.2%, and the number of impurities by 36.6%.
2.1.2 Card clothing
The card clothing takes on about 80% of the carding and nep removal tasks during the carding process. When harvesting cotton in the production machine, the configuration of the cover card clothing should focus on the elimination of fine impurities.
BH550-81 high-density elastic cover card clothing was selected through the test, and the thickness of the needle tip was only half of the cross-section of the cylinder teeth, which had strong puncture ability, reduced the slippage in the carding process and reduced the probability of fiber breakage.
2.1.3 Felting roller card clothing
Our FA201 carding machine is a grooved barbed roller, which cannot increase the density of the transverse needle teeth, only the longitudinal tooth density.
When the production machine picks cotton, the carding and holding effect of the fiber are enhanced by increasing the density of the needle teeth, and the speed of the barbed roller is reduced at the same time, which enhances the carding and protects the fiber, reduces the damage of the fiber, reduces the green strip and linter, and reduces the cotton drop rate. Table 4 shows a comparison of the effects of different types of felting card clothing on the quality of the sliver.
Table 4 Effect of different types of felting card clothing on the quality of the AFIS of the green strip
From the above comparative data, it can be seen that after replacing the encrypted barbed roller, the carding cotton drop rate was reduced by 1.17%, the green nep was reduced by 10.9%, the short linter rate was reduced by 12.1%, and the impurities were reduced to 0.
2.2 Pay attention to the role of additional carding elements of the carding machine
The additional carding elements of the carding machine mainly include: pre-carding plate, front and rear fixed cover plate, and cotton net cleaner.
2.2.1 Pre-carded plates
The pre-carding plate is installed below the barbed roller, so that the barbed roller and the pre-carding plate are freely carded, the fibers before entering the cylinder are separated and carded, the separation degree of the fibers is improved, some impurities are excluded, and the large cotton bundle is decomposed into small cotton bundles, which plays the role of pre-carding, which can relieve the partial carding pressure of the cylinder and the main carding area of the cover plate, and improve the carding quality.
Preferred fixed carding plate density: We used 100% Xinjiang machine-picked cotton on CPJC9.8tex variety, and used 60, 90 and 120 teeth/cm2 pre-carded plates, respectively, and carried out AFIS comparative tests on the green strips, and the results are shown in Table 5.
Table 5 AFIS data of green strips with different comb rack densities
It can be seen from the test data in Table 5 that the tooth density of the pre-carding plate is not as large as possible, because after the increase of tooth density, the fibers and impurities are decomposed into more fine, although some of them are excluded, but the short colluts increase significantly. It can be seen that the selection of moderate tooth density has a significant effect on improving the quality of green strips.
2.2.2 Fixing the cover
The fixed cover plate can be divided into two kinds of front fixed cover plate and rear fixed cover plate, the fixed cover plate is an additional carding element installed between the front and rear cover plates, the front fixed cover plate is installed before the doffer transfer area, and the rear fixed cover plate is installed before the cylinder and the cover plate carding area, they play an important role in improving the quality of carding.
(1) Front fixed cover. The front fixed cover plate mainly plays the role of finishing and carding, improving the straightness and parallelism of the fiber, because the fiber has become a single fiber state, so the process interval can be appropriately controlled by small part. The fine cotton bundles and adhesive fibers remaining in the fiber layer on the cylinder needle surface after carding in the main carding area were further supplemented and carded to improve the straightness and parallelism of the fibers and improve the arrangement structure of the fibers in the green strips.
(2) Rear fixed cover. The fibers after carding through the barbed roller are pre-carded to improve the arrangement direction of the fibers on the cylinder needle surface entering the main carding area, improve the straightening parallelism of the fibers, facilitate the carding of the fibers between the cylinder and the cover plate, and focus on reducing the load of the main carding area.
(3) The influence of different fixed cover configurations on product quality. The purpose of the carding machine is to increase the free carding area, so as to effectively improve the separation between fibers and increase the amount of neps and impurities.
The carding load borne by the needle surface of the front fixed cover plate is relatively small, the carding is soft and delicate, and the tooth density should be large and mastered, generally selected at 400-800 teeth/(25.4 mm)2;
The carding load of the rear fixed cover plate is relatively large, and the tooth density should be smaller, generally 80-350 teeth/(25.4 mm)2, and the configuration is gradually densified and stepped segments.
According to the characteristics of machine picking, we have made detailed adjustments in the selection of the tooth density of the front and rear fixed cover plate card clothing to optimize the carding curve and make the carding more detailed and soft, and the indicators have achieved good results, as shown in Table 6, Figure 1 and Figure 2.
Table 6 Optimization test results of fixed cover tooth tightness
According to the characteristics of Xinjiang machine-harvested cotton, combined with the fiber carding movement state, through the optimal configuration of the teeth density of the front and rear fixed cover plates, favorable conditions were created for the main carding area, so that the fiber bundle was further opened and decomposed, and the impurities and linters were further separated from the fiber, so as to achieve the effect of fiber homogenization. Table 7 shows the comparison of AFIS quality indexes of carded green strips before and after the optimization of the needle tooth density arrangement of the fixed cover.
Table 7 Comparative test of the optimization of the needle tooth arrangement of the fixed cover
It can be seen from the comparative test results in Table 7 that after the optimization and adjustment of the tooth density of the front and rear fixed cover card clothing, the carding curve is more flexible, the quality of the green strip is significantly improved, and the optimized nep is reduced by 25% year-on-year, the weight of the linter rate is reduced by 6.4%, the number of velvets is 3.1%, and the impurities are reduced to 0.
(To be continued)
Source: Ma Jingbao, Weiqiao Textile Co., Ltd
Editor: China Yarn Network New Media Team
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