Weft insertion mechanism
7. Air flow control valve The air flow control valve used in air-jet looms has two forms: mechanical and electromagnetic. It is an actuator that controls the injection timing of the main and auxiliary nozzles. It is required to have high switching frequency and high-speed response characteristics.
(1) Mechanical air flow control valve [Figure 2-11(a)]: The air flow control valve used early on air jet looms is a mechanical valve, which relies on a cam to open and close the air flow control valve and has no self-adjusting function. , it is inconvenient to adjust, easy to wear, and has a short lifespan. It is now rarely used on air-jet looms. (2) Electromagnetic air flow control valve [Figure 2-11(b)]: Because the electromagnetic air flow control valve has the advantages of better controllability, sensitive action, simple adjustment, and long service life, it has been widely used on air-jet looms. application. The opening time of the solenoid valve is (8.8±0.4)ms, the reset time is (22±1.2)ms, the frequency should be no less than 20Hz, and the service life should be more than 1×109 times to ensure adaptability to different loom speeds. When the loom is running, the action of the air jets from the main and auxiliary nozzles is controlled by the solenoid valve, and the action of the solenoid valve is controlled by the weft insertion circuit. (3) The control characteristics of the solenoid valve: the injection timing of the main and auxiliary nozzles (i.e. the action timing of the solenoid valve) can be set and adjusted by the keyboard, which is particularly simple. On the operation keyboard, the set timing can be displayed digitally. Timing is set according to the crankshaft angle. Even when the rotation speed is changed, the timing remains unchanged, so there is generally no need to readjust it. The main nozzle injection timing can be delayed when the loom is started and weft insertion to prevent missing and loose wefts. When the loom is stopped, no matter where the crankshaft is, the nozzles will not emit air, thus avoiding waste of compressed air. When the loom is stopped, use the test button to open and close all the solenoid valves at specified time intervals to confirm whether the nozzles and piping are normal and whether the solenoid valves operate correctly. It has a slow weft insertion function, which can insert a single weft yarn during inching operation, which facilitates the work of the machine axis. The new weft insertion method is characterized by closed-loop control. Closed-loop control means that the information of whether the weft yarn detected by the detection system arrives on time is transmitted to the computer. After comparison and inference by the computer, the injection time and air pressure of the next weft are given, so as to facilitate automatic adjustment of weft insertion parameters, stabilize the weft yarn flight, and improve Fabric quality. 8. Weft feeder Since the air-jet loom uses a package with a particularly large package volume to supply the weft, the weft yarn is prone to breakage when unwinding on the package at high speed, which affects the efficiency of the loom; at the same time, the unwinding tension of the weft yarn changes with the diameter of the package. , will affect the fabric quality. The adoption of a weft feeder can eliminate changes in weft yarn tension caused by changes in weft yarn diameter, reduce the weft yarn breakage rate, and achieve the purpose of improving fabric quality and loom operation efficiency. Therefore, in order to achieve high weft insertion rate and ensure product quality, air-jet looms must be equipped with weft feeders with excellent performance. When the projectile and rapier looms insert weft, the front end of the weft is forced to be pulled, and the length of the weft insertion is determined by the leisure distance of the projectile or rapier. Therefore, the weft feeder used in the projectile and rapier looms does not require a fixed-length device. ; However, air-jet looms use free-end weft insertion, and the weft insertion length cannot be controlled with fluid. Therefore, the weft feeder used in air-jet looms must have a length-fixing device to effectively control the weft insertion length. There are various forms of weft feeders, and different companies have different forms, but they can be roughly divided into two types: trough airflow weft storage and drum-type weft storage. Among them, the airflow trough type weft feeder has the advantages of simple structure and low price. However, due to the weak control force of the airflow on the weft yarn, the shape of the weft storage is unstable and easy to entangle, loop, blow, etc., so it is not suitable for multiple sprays and has been used. disuse. Drum-type weft feeders are divided into two types: mechanical and electronic. The electronic disc-type weft feeder has uniform withdrawal and tension, can meet the requirements of high-speed weft insertion, and can realize automatic control, so it is widely adopted (Figure 2-12). The number of weft feeders on the loom is the same as the number of main nozzles. Single color, two colors, four colors, six colors or eight colors can be selected according to the requirements of the fabric on the number of weft types. Double-jet mixed weft technology can be applied to single-color fabrics to improve fabric quality and adapt to high-speed weft insertion. 9. Electronic drum length measuring and weft storage device (1) The electronic drum type weft storage method uses yarn wound on the drum for weft insertion, which can reduce the unwinding resistance during weft insertion. Due to the reduction in resistance, the corresponding Reduce the weft insertion air pressure. Compared with the air flow method and mechanical drum weft storage, it consumes less compressed air; the number of weft breaks is fewer, which can improve operating efficiency and product quality; the weft insertion length error is small, which can reduce the consumption of weft yarn.
(2) To control the number of winding turns on the drum, some use electric sensors, and some use electric encoders. The speed ratio between the weft feeder and the loom is fixed, so when the loom starts accelerating or stops decelerating, it can be synchronized with the loom, and it can truly wind according to the required number of turns, with a constant winding amount. (3) Taking the set time for the weft yarn to reach the specified position as the benchmark, the time error of each time the weft yarn reaches the specified position is compensated by the change in the action timing of the yarn stop pin and the main nozzle. (4) Weft insertion is prone to errors when the loom is started, and the injection time of the main nozzle and the release time of the yarn stop pin are delayed to control. (5) When stopped, the electric energy in the inverter capacitor can immediately stop the weft storage motor, so when it is turned on again, it can be turned on directly without any processing, simplifying the operation and reducing the waste of spinning yarn. 10. The weft brake is used to reduce the tension peak in the weft when the yarn stop pin acts, reduce the weft breakage rate, and improve the operating efficiency of the loom and the quality of the fabric. The application effect is obvious when the weft yarn has low holding yarn, uneven evenness, weak spinning yarn strength, wide reed width or high loom speed, but has no obvious effect on other occasions.
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