Auxiliary nozzle
On special-shaped reed air-jet looms, the weft yarn flying through the shed relies on the correct delivery of the main nozzle to the special-shaped reed groove, and then is sent through the shed through relay transmission by dozens of auxiliary nozzles installed at a certain distance. 1. The function of the auxiliary nozzle (1) Transport the weft yarn through the shed. (2) Use the stretching nozzle (also called the tail nozzle) to straighten the weft yarn and improve the quality of weft insertion. (3) Work with the main nozzle to optimize the weft insertion parameters to achieve the goals of improving weft insertion quality and saving gas and energy. Production practice shows that during normal operation, the total air consumption of the auxiliary nozzles accounts for about 75% of the entire machine’s air consumption. Therefore, whether the air-jet loom can further increase the speed and be widely adopted depends on whether it can further increase the weft yarn flying speed (the key is to improve the quality of air flow synthesis) and further reduce the air consumption, so as to achieve the purpose of saving gas and energy and reducing production costs. 2. Type of auxiliary nozzle The auxiliary nozzle consists of a pipe base 1, a pipe sleeve 2 and a nozzle 3. The head end of the nozzle is flattened and formed, and the position of the nozzle hole is on the slope at an angle α to the pipe body, α is called the injection angle; the nozzle and the pipe sleeve are generally fixed with resin glue, and the two are positioned at a certain angle β. It is called the spray direction angle, as shown in Figure 16-1. The shape and size of the auxiliary nozzle vary depending on the machine model, reed seat structure and the shape of the special-shaped reed groove. Therefore, the classification of auxiliary nozzles is generally divided into two categories: circular 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, nineteen holes, twenty-one holes, etc.; non-circular holes can be divided into rectangular holes, starfish-shaped holes, etc. From the perspective of production practice, the airflow performance of various hole-shaped auxiliary nozzles has its own merits, but there are indeed differences; it shows that various air-jet loom manufacturers in the world have different applications of air-jet weft insertion technology, reflecting their own value . For example, air-jet looms produced in Asia often use single-hole or double-hole auxiliary nozzles; while air-jet looms produced in Europe often use multi-hole or non-circular hole auxiliary nozzles. The values obtained from surveying and mapping of several common auxiliary nozzles are shown in Table 16-1 for reference.
3. Adjustment of auxiliary nozzles The auxiliary nozzles jointly play the role of relay weft insertion under “group” conditions. Therefore, in addition to requiring that the relevant parameters of the individual auxiliary nozzles be strictly consistent when manufacturing them, they are also required to have more stringent and consistent requirements on the spray direction angle after installation to obtain the best synthetic air flow. This is more important for the installation and debugging of single and double hole auxiliary nozzles. It can be seen that it is particularly necessary to understand and grasp in advance the changes in the size and orientation of the γ angle caused by changes in the air supply pressure of single and double hole auxiliary nozzles. Therefore, it is believed that the practice of not adjusting the spray direction angle due to obvious changes in the air supply pressure after the machine is put on is difficult to achieve the effects of saving energy and energy and optimizing the weft insertion conditions. 4. Several functional auxiliary nozzles are based on years of practice. The currently used auxiliary nozzles have various impacts on air-jet looms. More than 90% of auxiliary nozzles are scrapped due to wear and tear. The energy consumption of auxiliary nozzles accounts for about 10% of the energy consumption of the entire machine. More than 70%, etc. In view of the energy consumption and efficiency issues of air-jet weaving, here is a brief introduction to the design key points and usage effects of functional auxiliary nozzles such as anti-friction, energy-saving and speed-increasing types that have obtained national patents. (1) Functional auxiliary nozzle 1. Anti-friction auxiliary nozzle The reason for the wear of the auxiliary nozzle is the distance between the auxiliary nozzle and the weaving edge when it is inserted into the warp yarn. The spray direction angle β of the existing method makes the auxiliary nozzle enter and exit the shed sideways. The main cause of wear and tear. Due to the β angle of the existing method, the auxiliary nozzle enters and exits the shed sideways, resulting in a thickness increment ΔB in the direction of thickness B, as shown in Figure 16-2. In order to make the auxiliary nozzle still have its original thickness B parallel to the warp yarn entry and exit shed, the anti-friction auxiliary nozzle moves the β angle upward to the head end of the nozzle body and presses it at once. This not only ensures the β angle of consistent size necessary for the process, but also avoids the errors caused by β1 and β1 on the original nozzle during assembly. Figure 16-3 shows the working status of the anti-friction auxiliary nozzle. At this time, it can enter and exit the shed with thickness B, thus reducing the mutual friction between the auxiliary nozzle and the warp yarn. At the same time, the β angle can be adjusted through the adjusting screw according to the process requirements. 2. Speed-increasing auxiliary nozzle Test results show that the structural dimensions of the nozzle seat and nozzle body are closely related to the speed of the auxiliary jet flow. According to the basic principles of fluid mechanics, if the gas flow in the nozzle is isentropic flow, the relationship between the velocity change rate of the flow in the pipe and the pipe cross-sectional area change rate is:
From the above It can be seen from the formula that when flowing at subsonic speed (Ma<1), the airflow speed increases faster than the density decreases, so the nozzle cross section shrinks (tapering can accelerate the airflow), and the gas has a speed-increasing effect in the tapering nozzle. Based on the basic principles of the continuity equation of fluid mechanics mentioned above, the channel of the auxiliary jet flow was optimized and designed. Figure 16-4 shows the structural diagram of the speed-increasing auxiliary nozzle. The ratio of the inner diameters of the large and small ends of the tapered airflow channel ranges from D/d=1.02 to 3.0.
3. Energy-saving auxiliary nozzle The air jet weft insertion process requires that the air flow for weft insertion must have a certain speed and flow rate. Therefore, the air flow injected into the reed groove by the auxiliary nozzle must also have a certain speed and flow rate. When the auxiliary nozzle is set, the speed and flow rate of the air flow injected for each weft insertion are proportional to its air supply pressure. In the same supplyUnder the condition of high pressure, differences in factors such as the number of nozzles, hole size, shape and finishing accuracy of the auxiliary nozzle will affect the speed and flow rate of the jet. After analyzing the air flow performance of various auxiliary nozzles, it is known that energy saving can be achieved by reducing the air supply pressure and saving flow rate (Figure 16-5). Therefore, the key point of the design of the energy-saving auxiliary nozzle is to reduce the air consumption of each weft insertion, adopt a multi-hole design with different diameters, improve its clustering ability, and easily converge with the main jet flow, so as to reduce the air flow attenuation rate and reduce clogging. the goal of. The energy-saving auxiliary nozzle is characterized by multiple holes with different diameters, that is, a large hole in the middle
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