Air jet weaving knowledge

optimize loom process to reduce weft stop and improve efficiency of air jet loom  

For certain varieties, the weaving efficiency of air-jet loom is decided by the production of high and low, and production of high and low depends on the loom speed and efficiency, and the methods to improve the speed of increase production alone is one-sided, so, when the loom speed increased to a certain level, loom efficiency is decided the main factors of weaving loom production and benefit.  The main factors affecting the efficiency of loom are: the time occupied by loom warp and weft stop, variety change and equipment maintenance, among which the time occupied by variety change and equipment maintenance changes little in the dynamic production process, and is basically constant under certain conditions.  Therefore, how to reduce the warp/weft stop is an important factor to improve the efficiency of air jet loom, increase the output and benefit.  The weft insertion mode of air jet loom depends on the air flow with certain pressure and speed injected by the nozzle, and the weft stop times are higher than the warp stop times under this air flow insertion condition.  When weaving staple yarn fabrics, weft stops account for about 70% of the total stops, up to 80%.  The weft stop of processing filament is almost 100%.  With the increase of speed and width of air jet loom, weft insertion rate increases, and weft stop tends to increase correspondingly.  Therefore, it is of great practical significance to further improve the efficiency of air-jet loom to study and reduce the zonal stop rate.

air jet loom

 There are many factors causing weft stop of air jet loom, which can be summarized into three categories:

• One is that the weft yarn breaks after filling insertion.
• The second is the weft insertion failure caused by the blocking of the weft in the weft mouth.
• The third type is the stop where the weft ends are blown open due to the improper airflow configuration of the main and auxiliary nozzles and the nature of the yarn.
• The reasons of weft stop can be further summarized into two aspects: the quality characteristics of the original yarn and the characteristics of the weaving process.
• Weft stop caused by weft break during filling insertion

The speed of air-jet loom is very high. The weft insertion rate is 1500 ~ 2000 m/min, and even higher, 2500 m/min. If the weft insertion rate is 2000 m/min, the speed of the weft is about 120 km/h, which is equivalent to the speed of a car on the highway. The time of filling in and out of the weft is only about 0.05 seconds, and the initial speed of filling in is 35 ~ 40 m/s. When the filling insertion is completed, the stopper of the filling feeder immediately stops feeding, while the airflow from the main and auxiliary nozzles will not stop immediately, so that the filling yarn is suddenly subjected to a great impact load when it reaches the other side of the cloth, resulting in the maximum tension value of filling insertion, also known as the tension peak. If the weft breaking strength is too much lower than the peak weft insertion tension, it may break and cause stoppage. It is very important to configure the weaving technology correctly and choose the weft of good quality.

Effect of yarn strength on weft breaking in air jet Loom

•  A large number of experimental studies on the problems affecting the breaking strength of yarn have been carried out abroad by using the mixing tester of single yarn strength and yarn strip. It is found that about 61% of the reasons for yarn breaking are caused by yarn details, and 39% are caused by yarn weak twist, thick knot, joint and other problems. Therefore, reducing yarn details is the key to reduce weft break and stop and improve loom efficiency.
• The ratio of peak tension to weft strength should be controlled below 55% in order to maintain the break rate of 3-4 weft / 100,000 weft on the air jet loom, and the weft strength should reach the following level: Single yarn strength of 12cN/ Tex or above, single strength unevenness rate of 9% ~ 10%, elongation rate of 2% or more, the minimum weft strength of not less than 7cN/ Tex weaving, the minimum strength number should be reduced.
• At the end of the 20th century, due to the perfect combination of computer technology, sensing technology, frequency conversion speed regulation technology and spinning technology, spinning machinery at home and abroad has made remarkable progress, greatly improving the spinning quality, making the yarn quality level of production high, providing good raw yarn conditions for air jet loom.

The peak tension of weft yarn in flight caused by the air pressure of the main and auxiliary nozzles is another main factor causing weft yarn breakage. Therefore, in addition to the quality of the original yarn, the air pressure of the main and auxiliary nozzles and the matching condition of the process which cause weft yarn tension load are very important.

Reasonable filling insertion time and arrival time are the conditions to reduce the peak weft tension. Weft insertion time refers to the loom spindle Angle corresponding to the weft entering the opening. Arrival time is the spindle Angle corresponding to the arrival of the weft opening to the opposite side of the cloth. The difference between the two is the filling Angle of flight. The larger the flight Angle is, the longer the time the filling yarn flies in the shed, the lower the flight speed and the lower the peak filling tension. Therefore, increasing the flight Angle of the weft as much as possible is beneficial to reducing the ratio of peak tension to weft strength so as to reduce breakage. However, too early filling insertion will stop the increase of weft because the opening height is not enough (generally the opening height is 2 ~ 3 mm in the initial stage of filling insertion), and the weft yarn flying is not smooth due to warp and weft yarn hairiness, other defects and oil stains in the reed. On the contrary, the later the filling insertion time, the smaller the flight Angle and the less the flight time of the filling yarn in the yarn passage, the flight speed is bound to increase, the air pressure of the main and auxiliary nozzles must increase, so that the weft tension increases correspondingly, the ratio of the peak weft tension to the yarn strength increases, and the chance of weft break increases. Therefore, the correct choice of weft insertion time is an important factor to reduce zonal stop.

• Flight Angle varies from machine to machine. For example, The flight Angle of Japan’s Tsudakoma air jet loom is 160°(80° ~ 120°), and that of Bejano air jet loom is 220°(70° ~ 290°).
• When the auxiliary nozzle pressure has different configuration due to different flight Angle, the main and auxiliary injection time is also different.
•  In addition to the pressure of the main and auxiliary nozzles and the flight Angle of the weft, the time of jet air acting on the weft and the brake time of the weft have an effect on the flight speed of the weft.
• The weft tension load can be reduced by strictly controlling the weft braking time and the jet time of the main nozzle. The earlier the solenoid valve of the main nozzle closes, the lower the weft arrival speed and the weft tension load will be.
• The maximum tension load is closely related to filling insertion Angle and filling insertion time. The experiment shows that when filling insertion time increases by 12 ms, the filling tension load can be reduced by 30%.In a word, when the unevenness ratio of single strength is between 9% and 10%, the ratio of peak tension load to single strength of weft is kept below 55%, which can keep broken weft at 3 ~ 4 times / 100,000 weft. This is the objective and principle of rational filling insertion process.
• From the perspective of machine parameter setting, a large number of stops in this situation are affected by the main nozzle injection pressure and injection time. On the one hand, increasing the jet pressure of the main nozzle will produce relatively high air velocity, and the weft yarn will be seriously untwisted in the main nozzle area, thus increasing the possibility of the weft yarn being blown disorderly. On the other hand, the starting time of the main nozzle will also affect the number of weft blowing disorder. Theoretically, the starting time of the main nozzle should be at the same time when the weft yarn is stopped by the weft storage. If the weft yarn is still controlled by the weft storage, the main nozzle will start spraying, and the weft yarn located at the main nozzle will be subjected to unnecessary tension load. If the main nozzle spraying time is longer than the stop filling release time, filling insertion will fail.
• In fact, when the solenoid valve of the main nozzle is opened at the moment, the air pressure of the main nozzle can not be established immediately and needs to be delayed for a few milliseconds. Therefore, if the main nozzle starts to spray after stopping the filling release, the pressure of the main nozzle cannot reach the normal level immediately, which will affect the flight of the filling yarn at the main nozzle. Therefore, a compromise should be taken when choosing the starting time of the main nozzle, neither too early to cause the weft to be blown out of order, nor too late to affect the flight of the weft.
• Only from the perspective of reducing yarn tension load, the main nozzle injection time at 100° seems to be the most appropriate, because there is no peak tension at the beginning of filling insertion. However, in order to achieve the necessary filling insertion time, on the one hand, the injection pressure of the main nozzle must be kept within 0.5Pa, because too much injection pressure is detrimental to the filling load; On the other hand, the spray time of the main nozzle is between 80° and 92°, and there is no significant difference in the main nozzle pressure. Therefore, considering the low yarn load and the main nozzle pressure, the best time for the main nozzle to start spraying is about 92°.
• The actual production interruption mostly occurs between the weft holder and the main nozzle, and there are also cases where the peak tension caused by the auxiliary nozzle meets the weak ring of the weft yarn in the weaving mouth, so that the weft breaking occurs in the weaving mouth.

The filling is blocked in the yarn passage

Zonal stop with incomplete filling insertion

• On the one hand, the air pressure of the main and auxiliary nozzles gives insufficient tension to the speed of the weft. On the other hand, the weft was stopped by warp defects, hairiness and side yarn organization.The modern automatic winding machine has the function of automatic yarn cleaning, automatic detection and removal of all kinds of defects, realizing the joint of air twisting, so that the yarn has no joint. It improves the external and internal quality of yarn and creates a good condition for the use of air jet loom.
• According to statistics, among the factors causing weft stop of air jet loom due to incomplete filling insertion, yarn hairiness will affect the unclear opening and hinder the normal flight of weft yarn in the process of air jet loom, resulting in weft stop.Take the 30-count yarn for example, if the hair length is 3 mm, the diameter of the yarn is 18 times larger! According to hair distribution and actual production requirements, defined 3 mm and above hair as harmful hair. If yarns with hairiness of 3 mm are used as warp yarns, there will be resistance to the flight of weft yarns. It is difficult to insert weft because the adjacent warp yarns are entangled with each other and the opening is not clear. If the length of wool on the weft yarn is 3 mm or more, the diameter of the weft yarn will increase, and filling insertion will be difficult. Many studies show that 60% of the weft stop is directly related to yarn hairiness. The weft travels very fast in the yarn passage and enters the flying zone at an initial speed of 35 m/s driven by the main nozzle of the air jet loom. The speed of filling yarn from entering the opening to flying out of the opening is very fast, so the yarn must be smooth and without resistance to make the filling pass smoothly and complete a filling insertion. Therefore, it is the key to solve the problem of yarn hairiness and improve the efficiency of air jet loom.
• Since the 20th century, due to the rapid development of spinning technology, spinning engineering has achieved many successes in reducing yarn hairiness (as mentioned above), greatly improving yarn finish and reducing yarn hairiness, making air-jet loom high-speed and production efficiency further improved.

The warp yarn hairiness has also been significantly reduced due to the improvement of pre-weaving techniques.

• The new sizing machine is equipped with wet separating and double pulp groove, high pressure sizing. The technology of humidification before pulp, wet separating and stranding, double groove and multi groove can reduce yarn hairiness.
• In production, high pressure sizing must be adopted for coarse and high-density varieties to meet the requirements of energy saving, improve the quality of semi-products, make warp sizing even, reduce hairiness and improve loom efficiency (as mentioned above).
•  If the humidification technology before pulp, two high and low pressure sizing and the development and application of new sizing materials are combined to sizing warp yarns, more satisfactory results will be achieved in reducing yarn hairiness.

The filling is blown apart by the jet and stops

• Low twist yarns are easy to untwist during weaving, or some yarns are easy to be blown apart by air flow due to the characteristics of the yarn structure. Normal twist yarns are easier to blow apart than high twist yarns. Ring spun yarns are more suitable for weaving than rotary cup yarns and are not easy to be blown apart by air flow.
• If the nozzle pressure is too high, the possibility of blowing the filling yarn is high. In addition, the main and auxiliary nozzles spraying on the filling yarn for a long time will also cause blowing of the filling yarn and cause stop.
• The starting time of the main nozzle will affect the stop of blowing weft yarn. The spraying time of the main nozzle should be synchronized with the filling stopper releasing and stopping the filling. If the filling yarn does not stop releasing from the filling stopper when the main nozzle starts spraying, it will bring unnecessary tension load to the filling yarn at the main nozzle and be blown away, resulting in broken weft. If the filling yarn is released earlier than the main nozzle spraying time, the filling insertion time will be missed, resulting in filling insertion failure.

In the air jet loom with two nozzles, if the two nozzles are not matched properly, the back nozzles will blow the weft sprayed by the front nozzles disorderly, resulting in stop.

• to solve the problem of broken weft from reducing weft tension, improve yarn strength and irregularity of manpower, to ensure that the weft tension peak value and the ratio of the yarn strength control below 55%, single yarn strength irregularity in 9% ~ 10%, and strive to minimize due to factors such as joint, soft twist, yarn details caused by the strong weak link. Reasonable configuration of weaving process is an important technical index to reduce weft insertion tension, avoid the increase of peak tension and reduce weaving breakage. Weft stop and warp stop caused by weft insertion tension and yarn strength together account for more than 35% of all loom stops.
• to solve the problem of blocked weft insertion and weft stop, efforts should be made to reduce hairiness in all relevant processes from spinning to weaving, especially to reduce hairiness of more than 3 mm. Warp yarn opening should be clear, yarn defects should be few, reed should be kept clean, and weavers should be reasonably selected according to yarn characteristics
• Art. The weft stop caused by blocked weft insertion due to hairiness accounts for about 30% of the total weft stop of the loom.
• In the weft weaving process, due to the loom technology and the nature of the yarn, the nozzle jet air blows the weft yarn apart and causes it to stop. Although this situation is rare, attention should be paid to it. The weaving process should be reasonably selected according to the condition of the original yarn (such as low-twist ring spun yarn, rotary cup spun yarn, air-jet spun yarn and vortex spun yarn, etc.), and such weft stops account for about 2% ~ 5% of the total stops.

air jet loom

In a word, reducing weft stop is the key to improve the efficiency of air jet loom and increase the production and benefit of loom. Therefore, it is necessary to reduce weft stop by every means to achieve high efficiency, high yield, high quality and low consumption under the condition of high speed operation of air jet loom.