Weft insertion mechanism
1. Air source purification In order to ensure the good operation of the air-jet loom, the quality of the compressed air supplied to the loom is extremely important. The compressed air output from the compressor contains some moisture, oil droplets and dust. If it is used directly for weft insertion, it will cause the attachments in the main and auxiliary nozzles and pipelines to gradually increase, and the pressure loss along the air flow will increase, resulting in increased energy consumption. In severe cases, it will cause blockage of the air path; cause the solenoid valve action sensitivity to decrease, affecting the accuracy of the action timing; cause the pressure regulating valve sensitivity to decrease, affecting the stability of the weft insertion air pressure; cause parts to rust, contaminate the spinning yarn, produce defects, and affect the stability of the weft insertion air pressure. The first-class product rate of fabrics coming off the machine. Therefore, the compressed air needs to be processed by an air source purification device to filter out various debris with larger particle sizes before it can be used for weft insertion. The compressed air processed by the air source purification device is not very pure and still contains a certain amount of tiny water, oil particles and fine dust. The purity of compressed air is determined by the accuracy of the filter in the air source purification device. Of course, the cleaner the compressed air, the better, but the higher the precision of the filter, the greater the pressure drop it generates, that is, the greater the energy consumption and the smaller the air flow, so the air filter must be selected reasonably. The general requirements for filter accuracy are that the oil content is less than 0.01mg/kg and the dust removal accuracy is 0.3μm.
2. Air pressure adjustment device The output air pressure of the air compressor used for air-jet looms is generally 0.7MPa (7kg/cm2). It is required that the air pressure when transported to the loom is usually not less than 0.55 MPa(5.5kg/cm2). The main nozzle, auxiliary nozzle, shear spray, normal spray, draft spray and other jet airflows have different functions, and have different requirements for air pressure. Therefore, air-jet looms must be equipped with air pressure adjustment or air flow adjustment devices to meet different needs for air pressure or flow. The function of the air pressure regulating box is to adjust the pressure of the compressed air supplied to each nozzle according to the different needs of each jet air flow for air pressure. The air flow pressure of each nozzle should be adjusted separately. Therefore, each jet air flow has a corresponding pressure regulating valve or throttle valve. The higher the air pressure, the faster the airflow speed, and the greater the traction force on the weft yarn, which is beneficial to weft insertion. However, when the air pressure is too high, it is easy to cause weft insertion failures such as weft breakage; when the air pressure is too low, weft insertion failures may occur, such as the weft yarn not being inserted in place or the weft yarn arriving at the specified position with a time lag. In addition, air pressure and energy consumption are directly proportional. The higher the pressure, the greater the energy consumption. Therefore, the pressure supplied to each nozzle must be reasonably adjusted. On the premise of ensuring smooth weft insertion, the air pressure should be as low as possible. The names and functions of each pressure regulating valve: (1) Normal spray pressure regulating valve: It is a pressure regulating valve that sets the size of the normal spray flow of the main nozzle. The function of the constant jet flow is to control the weft yarn during non-weft insertion time so that it does not escape from the main nozzle to ensure the continuity of weft insertion. (2) Shear jet pressure regulating valve: It is a pressure regulating valve that sets the size of the shear jet flow of the main nozzle. The function of the shearing jet flow is to control the weft yarn when the scissors on the yarn supply side are acting, to prevent the weft yarn from breaking away from the main nozzle under the action of tension, so as to ensure the continuity of weft insertion. (3) Main nozzle pressure regulating valve: It is a pressure regulating valve that sets the size of the main nozzle weft insertion airflow. The function of the weft insertion airflow is to pull the weft yarn through the fabric fell with the cooperation of the auxiliary airflow to complete the weft insertion. (4) Auxiliary nozzle pressure regulating valve: It is a pressure regulating valve that sets the size of the weft insertion airflow of the auxiliary nozzle. The function of the auxiliary jet weft insertion airflow is to supplement the energy of the main jet weft insertion airflow to keep the speed of the weft insertion airflow constant and ensure effective traction of the weft yarn within the specified range. When the speed of the loom is increased, the pressure of the main and auxiliary nozzles should be increased accordingly. 3. Air path: There are various specifications of plastic pipes, pipe joints, multi-purpose seats, one-way valves, and throttle valves used to purify the air source, adjust air pressure, main and auxiliary air bags, solenoid valves, main nozzles, and auxiliary nozzles. Wait for them to be connected in a certain order. Form an airflow channel that meets the usage requirements. The sizes and specifications of hoses and pipe joints are determined according to different air flow rates. A slightly larger diameter will help reduce pressure loss along the way. 4. Main nozzle The main nozzle is a key part of airflow weft insertion, and its performance directly affects the weft insertion effect. On an air-jet loom, the weft insertion work is mainly completed by the main nozzle, auxiliary nozzle and special-shaped reed. The function of the main nozzle is to modulate the compressed air entering the main nozzle according to the process requirements, accelerate and fully act on the surface of the weft yarn, so that the weft yarn accelerates from rest to the flight speed required for weft insertion. Transport the weft yarn into the special-shaped reed groove and determine the correct angle and position of the weft yarn entering the special-shaped reed groove. The number of main nozzles of the air-jet loom is determined according to the fabric, including single nozzle, double nozzle, four nozzle, six nozzle and eight nozzle. When weaving single-color fabrics, one or two can be set. Weaving single-color fabrics with double jets can improve the fabric surface quality and loom speed. This is because the two main nozzles take turns supplying weft, which can relatively reduce the unwinding speed of the weft yarn on the package, reduce the weft yarn breakage rate, and reduce the number of weft yarns. The impact of uneven evenness on fabrics. In order to achieve stable weft insertion at high speed, the new air-jet loom is equipped with an auxiliary main nozzle. The auxiliary main nozzle and the main nozzle form a series combination relationship, which can shorten the weft acceleration time, thereby increasing the operating speed of the air-jet loom or broadening the reed width manufacturing conditions. The structure of the 2A type main nozzle is shown in Figure 2-5.
The main nozzle of the air-jet loom is composed of three parts, namely, the nozzle body B, the nozzle core A, and the yarn guide tube C. The airflow channel in the nozzle consists of an airflow acceleration zone.��It consists of weft yarn injection zone and weft yarn acceleration zone. The weft yarn introduced by the weft feeder enters the weft insertion flow channel l from the entrance k. The high-pressure airflow from the main air bag enters the nozzle from the airflow inlet a. 5. The auxiliary main nozzle is used to accelerate the weft yarn with lower air pressure in conjunction with the main nozzle, which can reduce the weft yarn breakage rate and has obvious application effects in situations where the weft yarn tension is large, such as wide width or high-speed operation. It will increase the air consumption of the loom and should not be used when weaving in narrow width or medium or low speed. The air chamber b is annular. When the airflow enters the air chamber, it flows along the axis and circumferential directions, generating high-speed vortex. The rectifying groove c is a number of axial grooves distributed along the circumference. When the high-speed eddy current in the air chamber flows through the grooves, the flow direction is adjusted and becomes an axial air flow. The second air chamber d is also annular, but the air flow in the second air chamber has become an axial flow of high-pressure air flow. Then, the airflow is accelerated by the cone-shaped shrink tube e, reaching a flow rate close to the speed of sound. The throat f is an annular gap flow channel with a small cross-section. After the airflow passes through the throat, the flow speed can reach the local speed of sound. After passing h, the flow rate will drop rapidly. The yarn guide tube C is a variable cross-section tube flow channel. One end is inserted into the nozzle body and connected to the throat. The other end extends into the atmosphere and is aligned with the reed groove. The head end of the nozzle core A is cylindrical and extends into the yarn guide tube. The cavity forms an annular slit with the inner wall of the yarn guide tube. When the airflow flows out from the outlet h, the speed is close to the speed of sound so that a powerful injection zone can be formed in the weft yarn injection zone i to introduce the weft yarn into the nozzle. The long yarn guide tube C fully acts on the weft yarn so that the weft yarn can fly into the shed at a high enough speed. Be very careful when installing the main nozzle. If the installation position is inappropriate, it will seriously affect the flying state of the weft yarn. The main nozzle should be as close to the edge of the fabric as possible, and its axis should be aligned with the center line of the special-shaped reed groove. 6. Auxiliary nozzle, also called relay nozzle, referred to as auxiliary nozzle, it sprays airflow diagonally upward in the direction of weft yarn travel. The structure diagram of the auxiliary nozzle is shown in Figure 2-6.
(1) The function of the auxiliary nozzle: spray before the arrival of the weft yarn, drive the air in front of the weft yarn to relax, reduce the resistance of the air to the weft yarn; generate a relative negative pressure at the front end of the weft yarn, which has an attraction effect on the weft yarn; supplement the energy of the main jet flow , keep the weft insertion airflow at a certain speed, and send the weft yarn through the shed in a relay manner; overcome the gravity of the weft yarn and make it fly slightly above the center of the reed groove. During normal operation, the total air consumption of the auxiliary nozzle is related to the air pressure and the reed width on the machine. The performance and appearance quality of the auxiliary nozzle directly affect the loom speed, weaving efficiency, energy consumption and fabric quality. Therefore, the performance of the auxiliary nozzle has the following requirements: The wind speed at the nozzle outlet is high, and the consistency of the wind speed between nozzles is good; the air flow is well focused, and the range is as far as possible; there is a precise injection angle; the inner cavity and surface are completely smooth. (2) Type of auxiliary nozzle: The shape and size of the auxiliary nozzle vary depending on the machine model and fabric variety. The classification of auxiliary nozzles is generally divided into two categories: circular holes and non-circular holes according to the number and shape of their nozzles. Circular holes can be divided into single holes, double holes, five holes, seven holes, ten holes, nineteen holes and twenty-one holes, etc.; non-circular holes can be divided into rectangular holes, starfish-shaped holes, etc. Since various auxiliary nozzles have differences in pipe diameter, pipe length, flattened shape, number of holes, and hole diameter at the air flow inlet, under the same air supply pressure, the outlet wind speeds of various auxiliary nozzles are not exactly the same. . In production, both single holes and multiple holes are widely used. Japan’s Tsudakoma series uses single-hole auxiliary nozzles, Toyota JA uses double-holes, and European countries mostly use multi-hole auxiliary nozzles. The schematic diagram of the auxiliary nozzle nozzle hole is shown in Figure 2-7.
The distribution of auxiliary nozzles on the reed base is shown in Figure 2-8. Generally, the auxiliary nozzles are in groups of 5, and there are also groups of 2, 3 or 4, and each group of nozzles is controlled on a solenoid valve. Therefore, the opening and closing times of several auxiliary nozzles in the same group are the same. The number of auxiliary nozzles is related to the reed width. The injection time of each group of nozzles is connected to each other. The distance between each nozzle is usually 60~80mm, and the standard setting is 80mm.
In order to avoid the speed reduction and fluttering of the weft yarn head end caused by the influence of spinning yarn quality when the weft yarn flies close to the exit side, the spacing of the auxiliary nozzles on the exit side can be reduced to ensure that the weft yarn head end maintains high-speed flight and Straighten. (3) Adjustment of the auxiliary nozzle: After using the electric stroboscope, observe the flying status of the weft yarn. Adjust the auxiliary nozzle according to different conditions of weft yarn flight. The ideal flying attitude of the weft yarn is shown in Figure 2-9(a). It is ideal for the large “wavy” weft yarn to fly above the center of the reed groove.
As shown in Figure 2-9(b), when the small “wavy” weft is irregular, the auxiliary nozzle should be adjusted as follows: the installation angle becomes smaller; the installation height is increased; the air pressure is increased; the reed is cleaned.
When the entire weft yarn flies below the center of the reed groove, the auxiliary nozzle should be adjusted as follows: increase the installation angle; shorten the installation distance. (4) Extension nozzle: The extension nozzle is also called the draft nozzle. It is installed after the last auxiliary nozzle and is located outside the fabric width. The structure of the extension nozzle is similar to that of the auxiliary nozzle. It has a long air supply time and can pull the weft yarn to straighten. When the main and auxiliary nozzles are closed successively, the extension nozzle continues to ensure spraying to prevent the weft yarn from rebounding before hedging. It is used to prevent weft yarn rebound and shrinkage, etc. It is mostly used when the weft yarn is strongly twisted filament or core-spun yarn. Adopting higher air pressure will increaseAir consumption of the machine (Figure 2-10).
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