I. Introduction
In spinning semifinished products and finished products, there will always be uneven distribution of fibers along the direction of the sliver, that is, uneven thickness. If the sliver unevenness is not controlled, the processed sliver will be behind. During the processing of the segment, the unevenness caused by each step is increased, and these unevennesses will appear in the yarn. Moreover, the initial wavelength of the unevenness will be greatly increased along with the draft of each process, resulting in low yarn strength. The high breakage rate, poor uniformity, and poor quality have seriously affected the appearance and quality of the yarn. Autoleveler is a leveling method used by people to improve the quality of yarns and fabrics. It automatically adjusts the drafting ratio based on the difference in weight (or thickness) per unit length of the semi-finished product fed or spun. The unit weight (or thickness) of the semi-finished product is stable at a certain level, which is the specific application of the automatic control theory in the spinning process. Using this device will improve product quality, shorten the process flow, and increase labor productivity.
(A) The role and type of autoleveller
During the spinning process, there are various forms and irregularities in the sliver, and the autoleveling device can eliminate and adjust these irregularities within a certain range. The function of the autoleveler is illustrated in Figure 7-1 below.
Figure 7-1 Role of the autoleveller
In Fig. (a), an ideal sliver passes through an ordinary draft zone. Due to the imperfect control of the draft device on the fiber, the output sliver produces some short non-uniformity. However, this unevenness is only a short clip, which represents the best situation that can be expected. In fact, the sliver normally fed is uneven. He contains both long and short fragments. When this uneven sliver is fed into a common draft zone, the uneven wavelength will change with the draft multiple, and in addition, a short segment will be formed in the draft zone. The result will be The output sliver has a long fragment unevenness and a short fragment unevenness, as shown in Figure (b). If the normal feeding sliver is fed into the draft zone with an autoleveler, the uneven feeding sliver can be eliminated to a certain extent, although there will still be short-segment unevenness, but the unevenness is Due to the poor control of the drafting device on the fiber, the autoleveling device can substantially eliminate the unevenness of the medium and long segments, and at the same time form short segments in the draft zone, as shown in Figure (C).
Obviously, the self-leveling device can replace and cooperate on the common drafting machine and cooperative use is mainly to improve the random unevenness of the sliver and the unevenness in the negative correlation case, but can not improve the unevenness or synchronization in the positive correlation case. Unevenness, and cooperation is limited. The amount of unevenness that he can reduce is only the unevenness of the feeding sliver divided by the square root of the number of merging, and with the increase of the number of merging, it is increased. Stretch burden, thereby increasing the uneven draft. At the same time, when the unevenness of the feeding sliver is small, the merging effect is the worst, and the opposite effect may even occur when the number of passing slivers is excessive. When the self-levelling device is in correct operation, all irregularities can be substantially eliminated except for the short non-uniformity of the fed sliver. As long as the unevenness of the feeding sliver is within the leveling defense, the uniformity of the output sliver can be achieved as expected, and the leveling device has the same leveling ability for positive correlation unevenness (or synchronization unevenness).
In addition, there is a limit to the amount of unevenness that can be eliminated by cooperative use. After the drafting, the residual unevenness will be extended and more mergers will be needed to make up for it. The use of an autoleveller can continuously and automatically correct and supervise and make the sliver uniformity uniform.
At present, there are various forms of autoleveling devices, but the basic principles are the same, but there are some differences in specific mechanisms. They can be classified from different perspectives.
(1) According to the control method can be divided into open-loop system, closed-loop system and hybrid ring system as shown in Figure 7-2
Figure 7-2 Autoleveling system
The main feature of the auto-leveling device of the open-loop system ((1) in the figure) is the first detection and control, and the control loop in the system is non-closed. This system is mostly used in combed wool spinning. In an open-loop system, as long as the time delay of the control system is matched with the time required between the passing of the sliver through the inspection point and the leveling point, and the change in the draft multiple is completely proportional to the change in the thickness of the sliver, it can be eliminated. The frequency range of non-uniform waves. This type of system works according to the principle of compensation. The leveling effect is good, especially for the fragment length. In the closed-loop system ((2) in the figure), the feeding sliver is tested after passing through the drafting mechanism. Since the detected sliver has been leveled, the difference in the weight of the general sliver is small. Therefore, the closed-loop system often requires a high-power amplifier to amplify the detection deviation signal in order to change the speed of the speed-regulating mechanism and reduce the deviation. . The closed-loop system works according to the feedback principle. It can automatically correct the deviations caused by the fluctuation of various factors, so that the average thickness of the output sliver can meet the normal level, and the thickness of the sliver can be kept stable. However, since the closed-loop system is first tested after leveling, it cannot equalize uneven waves with a wavelength equal to or less than the distance from the leveling point to the detection point. The distance from the leveling point to the detection point is the leveling dead zone, which determines that the closed-loop system is mainly Uniformly uneven sections. Generally, the larger the dead zone is, the larger the length of the segment that can be leveled, and the length of the segment that can be leveled is determined by the length of the closed loop; the ring-shaped autoleveler (Figure (3)), both open-loop and The advantages of the closed loop can not only maintain the leveling effect, but also automatically correct the deviation caused by various fluctuations. From the aspect of adjustment performance, it is relatively perfect.
(2) According to the adjustment effect, there are three types: short fragment autolevelling system, the uniform length of the product is 0.1 ~ 0.12mm; in the fragment autolevelling system, the uniform length of the product is about 3m; long fragment from Leveling the entire system, the uniform length of the product is more than 20m.
(3) According to the structural shape of each component of the autoleveling device, mechanical, hydraulic, electrical, electronic, electromechanical, and pneumatic electronic types may be used.
(4) According to the self-leveling action characteristics, there can be divided into the rear roller shifting mode and the front roller shifting mode.
(B) The composition of the autoleveller and the role of each major part
There are many types of autolevellers, but their basic composition is basically the same. They are all composed of the following four parts (Figure 7-3):
Figure 7-3 Composition of the autoleveler
4.2 Volume feeding carding machine
Most of the country's carding machines still rely mainly on roll-feeding. In general, due to the large number of equipment, the price of self-contained devices is relatively high. Therefore, it should be used economically and reasonably depending on the specific circumstances.
4.2.1 Rotary Spinning of Straight Bars
Some factories commonly use rotor spinning to use waste cotton to spin off the sub-licensed yarn in order to make full use of the fibers available in various types of kicks and carding to obtain limited economic benefits. These waste spun fibers are not suitable, they are processed in parallel, and they are often fed directly. If the user puts forward the quality requirements, they need to install the self-equipment on the carding machine, emphasize the long closed loop of the branch, and emphasize the strength of the strips. Short open loop, both emphasize, use short open loop or mixed loop before.
4.2.2 Combed spinning system
The combed yarn is an upshift product with higher quality requirements. It is a combination of combing systems with more combing than the carding. The preparation process improves the uniformity of the medium and short sections. The mixing ring must be used on the carding machine. Taking into account the improvement of the branching and evenness, combined with a draw frame with an ultra-short section after combing, the quality of the combed yarn is closed.
4.2.3 Carded Spinning System
In general, the self-contained device may not be used, depending on user requirements.
4.2.4 knitting yarn
The quality requirements for knitting yarns are higher than those for woven yarns. Combing knitting yarns, carded knitting yarns or rotor spinning knitting yarns may be used. On the carding machine, the mixing ring must be used in a uniform manner, and the short section or the following on the subsequent draw frame must be used. The short segments are combined from a uniform device, coupled with multiple strands, and the coupling effect of the drafting to improve the quality of the cotton yarn.
4.3 Blowing card
The blowing-carding group has gradually promoted the trend. With the increase in the amount of chemical fiber, the development of this trend has been promoted due to the problem of cotton sticking. However, there are deficiencies in comparison with cotton roll-making.
4.3.1 Cleaning carding process defects
First, there is less on-line self-leveling control on the cotton winding machine; second, less manual adjustment of unqualified light and heavy rolls, ie, less control over long-length fragments; and third, less cleaning. The time-lapse mixing of the horizontal rows of storage rolls and the management and adjustment functions of light and heavy rolls on the carding machine. Many advantages such as continuous, automated, high-yield, high-efficiency, and high labor productivity, etc., have been recognized, but they cannot be promoted if they do not compensate for the above-mentioned defects. The use of uniform devices, except for the inability to delay mixing, is Defects can make up for it.
4.3.2 Continuous Leveling
The pressure switch at the side of the first carding machine controls the feeding speed of the cleaning machine to the cotton roller, so that the upper cotton box of each carding machine can evenly store the raw cotton. The pressure sensor of the lower box controls the upper box feeding roller to feed the raw cotton to the lower box evenly. The lower box is fed into the cotton layer of the card, and then the leveling of the carding machine is accepted. Wuxi Pratt ZNS card cotton box self-leveling, has been successfully applied.
4.3.3 Carding carding machine
There are four types, front, rear open loop, long closed loop, and hybrid loop. There are many models at home and abroad, in China, there are FT025 type of Textile Institute and Zhengzhou Textile Machinery, FT024 type of Qingdao Textile Machinery (mixed ring), Wuxi permanent CCA type, Pratt ZNS series (Figure 7-4), Overseas, there are LOEPFE SLT-4 (short open-loop), Uster UCC-L (long closed loop), Rieter's C4-RR (hybrid ring), TRUTZSCHLER CCD Type (long closed loop) and ICFD + CCD (mixed loop), the type of the PLATNT 2000 (short front open loop). Four types of self-contained device features:
(1) Short open loop after machine
The improvement of sliver shorts is uneven, but the improvement of the long-slice unevenness is limited.
(2) Short open loop before machine
The detection points and control points are all set in front of the machine. The leveling and detection and control of the two points of the card itself can be performed in close proximity to the leveling and external disturbances of the carding machine. If they can be described in sections 3 and 4, they can be The lengths of all segments above the short segment were evenly leveled, but the additional unevenness resulting from the 1.05-2..0 times drafting of the spun birth bar could not be controlled.
(3) Long closed loop
The improvement of sliver support is limited to the improvement of short-segment irregularity. If the equipment is in good condition, the fiber transfer rate of Doffer is stable and can be adapted to the process requirements.
(4) Mixing rings
At the same time, it has the advantages of open and closed loops, and has become a common trend of domestic and foreign textile machinery manufacturers.
4.3.4 Selection of leveling combing carding machines
In general, mixed rings should be considered. For example, limited funds, closed loop or open loop can be considered.
Concluding remark: Since the uniform device and the existing combination and drafting process are combined, the quality of the cotton yarn can be improved, and a better coupling effect can be obtained. The improvement of the evenness of the spun product can reduce the breakage, improve the efficiency, reduce the production cost, and create considerable benefits for the subsequent processes, particularly the weaving process. The existing domestic autoleveling system has been relatively perfect, especially the Pratt ZNS series carding leveling instrument (Figure 7-4) is inexpensive and high quality, which is worthy of deep promotion of the majority of small and medium-sized spinning enterprises.
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Figure 7-4 Schematic diagram of ZNS carding leveling