Discussion on the cover plate process of the hotte

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Discussion on the process of carding machine cover plate

the function of the upper cover plate of the carding machine is the most comprehensive and the function principle is the most complex. It not only has the function of combing, but also has the functions of impurity removal, mixing and uniformity; It is not only related to product quality, but also directly related to output, cotton consumption and so on; Due to its extremely complex carding and transfer filling principle, the improvement of the cover plate has been the least over the years. There is still a major breakthrough in the tin part of the metal clothing, but it has not been popularized and applied in the cover clothing. Therefore, the relevant process factors of the cover plate are worth further discussion

1 discussion on the process of rotary cover plate

1.1 the relationship between the force on the fiber on the cover plate needle and the fiber layer between the needles

studying the relationship between the force on the fiber on the cover plate needle and the fiber layer is the theoretical basis for studying the number, speed and rotation direction of the cover plate. The fundamental differences between the force on the fiber on the cover plate needle and that on the cylinder are: (1) the speed of the cover plate is very slow, and there is no centrifugal force; (2) The tooth depth of the cover plate is generally about 4.8mm (the lower knee is 3.5 mm high), which is 7 times greater than the tooth depth of the cylinder (0.6mm). Therefore, it is decided that there is a fiber layer between the needles of the cover plate, and the fiber layer increases gradually with the forward operation of the cover plate, more specifically, with the extension of the carding time (TW) of the cover plate. The change of fiber layer from less to more affects the change of fiber force on the needle when the cover plate travels in different parts (see Figure 1)

in Figure 1: R is the tangential force, mainly manifested as carding force; U is the normal force, mainly including the elasticity of fiber layer; F is friction, f= (rx+ux)· μ。

when the cover plate rotates forward, there are few fiber layers between the needles near the population of the cover plate, so the U force is small; However, the cotton bundles entering the work area here are large, and the carding force is only large. Therefore, it is mainly manifested as ry ≥ uy+f (or uy ≤ ry-f). Therefore, while carding is realized, the fibers fill the cover needle, and the fiber layer gradually increases

with the extension of carding time, the fiber layer gradually increases, the U force increases, and the R force decreases with the decrease (or less) of the cotton bundle. Therefore, the force on the fiber on the needle gradually changes from mainly inward to sometimes inward (needle) uy ≤ ry-f (when the cotton bundle is large and thick), and sometimes outward (needle) uy ≥ ry+f (when the cotton layer on the needle is thin); Or instantly form neither inward nor outward, that is, ry+f ≥ ry-f, and the fiber is held on the needle. Therefore, the fiber is fully combed here, up and down repeatedly, and the spring compensator uses this linear relationship to adjust the deformation through the involute wheel, so as to achieve a constant output tension, ensure the perfection of the combing effect, and thus play a good uniform and mixed role

tests at home and abroad have confirmed that only 14% of the fibers in the working area of the cover plate are brought out by the cylinder at each turn, while most of the remaining 86% of the fibers enter the cover plate needle (that is, uy ≤ ry-f); Most of the remaining 86% of the fibers brought out by the cylinder are sent out from the inside out of the cover needle (that is, uy ≥ ry+f), and most of the fibers sent out come from the fibers that entered the cover needle in the previous 100 revolutions of the cylinder. Therefore, while carding, the cover plate not only has a uniform effect, but also achieves a good mixing effect due to the repeated conversion of fibers inside and outside the needle. All these functions cannot be brought into full play without the existence of fiber layer between needles

however, there is a certain limit to the number of fiber layers. When TW is too large (i.e. the speed of the cover plate needle cloth is too slow or the number of cover plates is too large), there are too many fiber layers, and the U force increases to the extent of uy>ry+f, then at this time, the comb needle has lost its holding ability, the fiber slips outward, and the quality is deteriorated, so it is necessary to go out of the working area immediately. Therefore, in order to ensure good carding effect and prevent too many fiber layers (saturation), we must find out a reasonable cover speed through experiments according to the number of covers, raw cotton conditions and quality requirements, so as to obtain good results

1.2 relationship between the number of working cover plates and the speed of cover plates

the number of working cover plates is closely related to the speed of cover plates, which can be explained by the time TW of cover plates participating in carding:

tw= width of each cover plate × The number of working covers/cover speed (1)

in formula (1), the cover width is a constant, about 35mm, so the number of working covers is linearly related to the cover speed, that is:

tw=35 × The number of working cover plates/speed of cover plates (2)

it can be seen from formula (2): a large number of working cover plates require a fast speed to ensure that the time TW of the cover plate clothing participating in carding is not too long, so that the degree of fiber filling between the cover plates is not too serious and affects carding; On the contrary, when the number of cover plates is small, the speed can be lower to maintain the approximation of tw. For example, when there are 43 Working covers, speed 2) screw the round steel brush to the drill pipe and the electric drill into a cleaning tool, and the degree should be 172 mm/min, which is similar to the tw when the speed of 30 covers is 120mm/min, that is, the tw value is 9min. It is inappropriate to evaluate the number of cover plates independently without considering the speed

tw is the time when the cover plate participates in carding, not the time RH when the fiber layer in the cover plate is oversaturated. Therefore, in order to ensure the good effect of the combing needle, it is necessary to make TW from the perspective of carding. The number of cover plates is large and the speed is fast, while the number of cover plates is small and the speed is slow. Although the value of TW is similar, the working surface (arc length) of the former cylinder and cover plate is large, which is conducive to carding and even mixing. From the perspective of impurity removal and cotton use, when the number of cover plates is large and the speed is fast, the flower weight of each cover plate can be similar to that when the number of cover plates is small and the speed is slow, but the flower rate of cover plate increases. The increase of cover flower rate can increase the impurity removal rate on the one hand, but on the other hand, it will increase the cotton consumption. Therefore, by comprehensive comparison, under the condition of TW approximation, there is no significant difference in the number of 30 working covers and 40 working covers, which should be mainly determined according to the quality requirements. For example, 43 Working covers are used when spinning combed yarn. Although there are many lints, the yarn quality of combed yarn can be guaranteed

the carding machine produced by Rieter company of Switzerland has been restored from the original 30 working covers to the current 40-42 (the center of the cylinder will be raised in order not to hinder the installation of front and rear fixed covers). Italy's Marzoli company has also changed from 20 working covers of the CX400 carding machine to 30 of the new C501 carding machine. This shows that it is not feasible to reduce the number of cover plates too much. Because TW is too small if the speed is still 40 when 20 cover plates are used; It will certainly increase the fiber content of the cover flowers and cause waste of raw cotton. If the speed is reduced by half to make it the same as the tw at 40 pieces, the number of cover plates with more clean cover plates and fiber layers will be reduced in the same proportion, and the working face (arc length) combing with the cylinder will also be reduced, which will inevitably lead to poor combing quality

1.3 the influence of the number of working cover plates and the rotation direction of cover plates on the yarn quality (see Figure 2)

according to the above test data provided by Trutzschler company, the influence of the number of working cover plates and the rotation direction of cover plates on the yarn quality at the speed of 120 mm/min is analyzed:

(1) when there are 30 working cover plates, the reverse rotation has the best quality indicators, followed by the forward rotation of 30 cover plates. The yarn quality of 43 cover plates is the worst regardless of forward rotation and reverse rotation. This shows that in this case, the number of working covers plays a decisive role. If the number of covers is large, the carding time TW of the cover in the working area is long, from tw=9 min at 30 to tw=12min at 43. Therefore, the fiber filling between needles is serious, and the carding effect is deteriorated

(2) Figure 2 shows that when the number of working covers is small, the reverse rotation quality is the best, which fully reflects the advantage of the reverse rotation of the carding cover. However, when the number of cover plates is large, the reverse rotation has the worst quality. This is because during the reverse rotation, the fibers on the cylinder at the population part of the cover plate are the fibers that have been combed by the rear cover plate, so there are relatively few cotton bundles and non single fibers, so the carding force R is generally small, and the component force ry in the fiber needle is small, so more clean cover plates can be obtained than that during the forward rotation, so the yarn quality is the best. However, when the number of covers is large and the cover rotates in reverse, when the cover runs to the outlet, there are many fiber layers between the cover needles, so uy>ry+f, it is difficult to grasp the large cotton bundles that have just been brought into the working area by the cylinder and have not been properly combed for carding, which is easy to cause the fibers to roll between the needle surfaces and deteriorate the quality. Therefore, the number of cover plates should be less during reverse rotation and more during forward rotation. When the number of cover plates is the same, the reverse rotation is required to be faster than the forward rotation. The lowest limit of cover plate speed is the limit of serious cover plate filling and loss of carding ability. And the highest speed is subject to not bringing out too many spinnable fibers

2 selection of function and number of fixed cover plate

2.1 function of fixed cover plate

since the fixed cover plate is fixed, the first thing to consider when realizing carding is to prevent the deposition of fiber layer between needles. Therefore, it is necessary to keep the tooth height h as low as possible and the working angle. Enlarge as much as possible to reduce the possibility of fiber filling into the needle (see Figure 3)

therefore, the tooth height is generally 4.5 mm, which has been reduced to about 3 mm abroad, basically eliminating the space generated by the fiber layer. The working angle is generally 850~900, and the component ry (ry=rcos) that makes the fiber fill the needle α) Basically very small or not at all. Currently considered. It is too large, which is bad for holding the fiber. Therefore, the working angle of the front fixed cover plate α Reduce it to 700 and lower the tooth height h (at least 2.69mm) to compensate each other. In this way, the fixed cover plate can realize carding without forming fiber plastic, but it is also a flammable high molecular material component, which greatly improves their design freedom and product aesthetics layer and hinders carding, so as to ensure that the fixed cover plate can play the role of carding for a long time without moving out of the machine for cleaning, so as to achieve the purpose of fiber only staying on the needle for a short time - both carding and transfer. Compared with the carding effect of the front and rear fixed cover plates, the carding effect of the former fixed cover plates is stronger. The uniform effect of the fixed cover plate is also certain, especially the rear fixed cover plate, which combs the larger cotton bundles on the cylinder and the thicker cotton layer on the cylinder, playing a better uniform effect

the fixed cover plate currently has a dust suction mechanism, which is composed of a dust knife and an air suction device to achieve its cleaning effect. Early seen in the weblean.k.r removal mechanism in truzler, and the Trex removal mechanism of Lida also strengthened the ability to remove dust and lint. So far, the fixed cover plate has made great progress in combing, cleaning, mixing and other aspects

2.2 the number of fixed cover plates

whether the number of fixed cover plates can be increased too much, and whether all fixed cover plates can be used to replace rotary cover plates is negative from the current situation abroad. The CX400 carding machine of mazzoli company in Italy increases the number of fixed covers to the last 14 and the first 9 (correspondingly, the number of rotary covers is reduced to 20). Compared with other domestic and foreign models, there are 10 more rear fixed covers and 6 more front fixed covers. However, it was soon replaced by the front and back of the C501 carding machine produced by mazoli company (the number of rotary cover plates was changed from 59 to 75 again). The above is an example of not increasing the fixed cover plate too much and reducing the rotary cover plate. At present, most carding machines use three to four fixed covers at the front and rear

now, whether we can use more fixed cover plates, or use all fixed cover plates instead of rotary cover plates, we will analyze and demonstrate the combing function, mixing function and uniformity function of the fixed cover plates

3.1.1 carding action

because the fixed cover plate is fixed, it is not allowed

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