What is Air-Jet Weaving Machine?
Air-jet weaving is a shuttleless weaving technique in which compressed air is used for weft insertion as a medium. Air jet weaving machine or loom has the highest weft insertion performance and it is considered as the most productive loom in the manufacturing of light to medium weight fabrics. Compressed air is blown through a nozzle along with weft yarn. Due to the frictional force between air and the yarn, compressed air jet carries the weft along with it to the other side of the machine through the shed. It has an extremely high weft insertion rate. Out of all shuttleless weft insertion techniques, air-jet weft insertion is the simplest. Relative to shuttle, projectile and rapier, the mass of insertion medium is very small in air-jet weaving. The weaving widths range generally from 190 to 400 cm. As regards the multicolor weft carrier, up to 8 different wefts can be fed.
Air jet weaving machine was invented in Czechoslovakia and later refined by the Swiss, Dutch, and Japanese were designed to retain the tensionless aspect of the picking action of the water jet while eliminating the problems caused by the use of water.
These weaving machines use a jet of air to propel the weft yarn through the shed at rates of up to 600 ppm. Data from manufacturers indicate that air-jet looms operate at speeds up to 2,200 meters of pick inserted per minute. They can weave multicolored yarns to make plaids and are available with both dobby and jacquard patterning mechanisms.
Air-jet looms require uniform weft yarns. They are more suitable for use with heavier than lighter yarns because the lighter weight yarns are more difficult to control through the shed. Yet, if the yarn is too heavy, the air jet may not be able to carry the weft across the loom. Within these restraints, the air-jet loom is effective and can produce a wide variety of fabrics. Also, the air-jet loom operates at a lower noise level than the shuttle, projectile, or rapier looms. Air-jet weaving is more popular because the machines cost less to purchase, install, operate, and maintain than rapier or projectile weaving machines, and the air-jet can be used on a broader variety of yarns than a water jet.
Principle of Air-Jet Weaving Machine:
The important components in air-jet weaving are tandem / auxiliary and main nozzles, stopper or weft brake systems, yarn feeders and air guides, such as a confusor or profile reed. Figure 1 shows the schematic of air-jet weft insertion.
Weft from supply package 1 is drawn by measuring drum 2. The amount of weft yarn for each pick is measured. When compressed air 7 is blown through tandem nozzle 5 and main nozzle 6, stopper 4 opens and releases the weft yarn. Airstream 8 carries the weft to the other side of the machine. Only a predetermined length of yarn for a pick will be released by the stopper so that extra weft yarn will not be protruding outside the selvedge. This completes one cycle of pick insertion. The tandem nozzle/auxiliary nozzle airstream pulls the yarn from the measuring drum, and the main nozzle air-stream gives the necessary initial acceleration to the weft yarn. The relay nozzles augment the main nozzle in carrying the weft across the warp shed. Figure 2 shows a main nozzle of an advanced air-jet weaving machine fitted in the sley, and Figure 3 shows an auxiliary nozzle of an advanced air-jet weaving machine fitted in the frame.
Weft Insertion Methods of Air-Jet Weaving:
Mainly three weft insertion configurations are used in air-jet weaving machines:
- Single nozzle with confusor guides and suction
- Multiple nozzles with guides
- Multiple nozzles with profile reed
1. Single Nozzle with Confusor Guides and Suction
In this system, a single nozzle is used to insert the weft. The air speed falls rapidly beyond a short distance from the nozzle due to the expansion of the air-stream in a parabolic form. The acceleration of the yarn also falls more rapidly. To overcome this effect, a multi-ring constrictor known as a confusor is mounted on the sley over the entire width of the machine. The confusor forms an orifice and guides the airstream without loss of velocity. The confusor goes below the warp during beat-up. To augment the air velocity at the off end of the machine, suction is provided. Figure 4 shows a single nozzle and confusor guide system. Because the confusor lamellae have to be placed closely and have to get in and out of the warp shed for every pick, they place a large amount of stress on warp yarns. Because the air velocity drops after a distance, loom width is a limitation in this system.
2. Multiple Nozzles with Guides
The disadvantage of the single nozzle system is the drop in velocity after a certain distance. In a multiple nozzle system, this has been overcome by providing auxiliary nozzles across the loom at certain intervals. Air will be injected through them in groups sequentially in the direction of the yarn movement. Suction is dispensed with in this system. Figure 5 shows multiple nozzles with a guide system.
3. Multiple Nozzles with a Profile Reed
In this system, the air guides are built in the reed itself as an integral part, and this type of reed is called a profile reed. The profile reed system eliminates the entrance and exit of the confusor air guides in and out of the shed for every pick. The auxiliary nozzles, also called relay nozzles, are fixed across the machine on the sley. Figure 6 shows multiple nozzles with a profile reed system. Figure 7 shows a profile reed and relay nozzles.
Timing Diagram of Air Jet Weaving Machine
The typical sequence of different operations of an air-jet weaving machine with multi-nozzles and profile reed is given in Figure 8. The main nozzle is on at point 1, around 45°, and first relay nozzle group is opened at point 2 around 60°.
Thereafter, the yarn is released at point 3, around 80°, and weft insertion starts. At point 4, around 120°, the main nozzle is stopped. At point 5, around 230°, the yarn clamp closes, and further release of weft is stopped. The last group of relay nozzles are closed at point 6, around 260°. Thereafter, beat-up takes place. This completes one cycle of operation.
Control of Air Blow in Main and Relay Nozzles
Air-jet weaving machines are high-speed weaving machines, and precise air blow control is very essential for efficient performance. All the relay nozzles are grouped into five or six groups. The number of groups depends on the machine’s width. Figure 9 shows the timing of air blow in main and relay nozzles.
First, the main nozzle blow air and the weft are carried forward up to relay nozzle group 1. Then relay nozzle group 1 starts blowing at the tip of the weft yarn. This carries the weft to the next stage, and this continues up to the end. Every time, air is blown only at the tip so that the yarn is pulled throughout the insertion. This prevents buckling of yarn as well as low consumption of air.
Yarn Performance in Air-Jet Insertion
Since the force required to move the yarn is exclusively provided by the frictional force between the yarn and air, yarn properties such as the structure, twist, yarn diameter and fiber surface play an important role in air-jet weft insertion. Spun and coarse yarns have higher frictional coefficients. Therefore, they perform better than fine and smooth yarns. Spun yarns having a high twist, large denier, long stable and high fibril cohesion perform better in air-jet weaving. For weaving continuous filament yarns in an air jet, more air is required than for spun yarns due to their smooth surface. Larger diameter yarns require more air pressure due to their increased mass. Higher linear density increases insertion time.
Twist plays an important role in air-jet yarn insertion. Increased twist brings the fibers closer and makes the yarn more compact. This makes the yarn smoother and reduces the diameter of the yarn, which, in turn, reduces the friction between yarn and air jet, resulting in a longer insertion time. Plied yarns have a longer insertion time than single-ply yarns due to the fact that plied yarn results in a smoother yarn surface. Textured yarns increase the frictional force between the yarn and the air jet than straight filament yarn. Therefore, textured yarns take less time for insertion.
Major Parts and Functions of Air-Jet Weaving Machine
Shedding Mechanism of Air-Jet Loom:
Air-jet weaving machines are equipped with negative cam shedding mechanisms for high-speed operations. Figure 9 shows a negative cam shedding mechanism. When non-positive cam 1 operates, it pulls heald frames 4 into a low position via cable traction 3. Once the cam operation is over, spring 5 pulls the heald frames to a high shed position. Figure 10 shows a negative cam tappet.
Yarn Feeders of Air-Jet Loom
In air-jet weaving machines, specially designed drum storage feeders are used. Figure 11 shows a yarn feeder. The rotating yarn guide draws the weft yarn from the package and winds on the measuring drum. The electronically controlled stopper pin releases the weft yarn at the time of weft insertion. In order to minimize weft waste, it is necessary to release an exact length of weft for each pick. This is done by the stopper pin.
Sley Movement of Air-Jet Loom
The sley is driven by a crank mechanism in an air-jet weaving machine with a small arm. Figure 12 shows a sley movement in an air-jet weaving machine. Crank 1 oscillates sley arm 2, which, in turn, rocks sley tube 3. The rocking of the sley tube makes beat-up. Figure 13 shows a sley arm.
Selvedge of Air-Jet Loom
Leno selvedge is mainly used in air-jet weaving machines. Tucked-in selvedge is rarely used. Fused selvedge also can be formed. Mainly high-quality selvedge is formed by using full and half leno selvedge devices. Figure 14 shows a full-cross leno device. This device binds the weft on both sides with two leno yarns. The two spool holders with special leno yarns are rotated by a gear drive. The leno yarns unwound from the spools move up and down to produce a full-cross leno weave around the weft.
Air Requirement of Air-Jet Loom
Compressed air is used in air-jet weaving. For this purpose, separate air compressors are to be installed, and pipelines have to be arranged. The quality of air is important. The air must be free from oil and moisture. Otherwise, the nozzles will be clogged.
Hence, oil filters and air driers have to be installed in the airline. Humidity in the air causes corrosion in the air pipes and may even cause corrosion in the machine itself. Maintaining these units involves additional cost. Figure 15 shows a compressed air plant system.
Developments in Air-Jet Weaving
The air-jet weaving machine continues to dominate as the machines of very high speeds. Today, practically (in Indian condition) at 1200 rpm the machine works or wider machine can attain a WIR of 2500 mpm. The system had the disadvantage of higher energy consumption due to the usage of compressed air in picking, which accounts for 60% of total energy consumption.
The machine makers claim a reduction in energy by about 10% (Sulzer, Somet) in their latest models. The developments in picking related systems have helped in expanding the horizon of weft material and count. The yarn color selection up to 6 or 8 beyond which demand is very rare. That means, the major limitations of the system are being attended and scope for applicability has been increasing.
Conclusion:
Air jet weaving machine is the easiest to be automated, as all main mechanical functions are controlled by a microprocessor. A jet of air is typically used by an air jet loom to propel the filling yarn through the weaving shed. In this article I have tried to discuss details about air jet weaving machine. If you have any query about this loom please let me know in comment section.
References:
- Fabric Manufacturing Technology: Weaving and Knitting by K. Thangamani and S. Sundaresan
- Reference Books of Weaving (ACIMIT) by Giovanni Castelli, Salvatore Maietta, Giuseppe Sigrisi, Ivo Matteo Slaviero
- Control Systems in Textile Machines by G. Nagarajan and Dr. G. Ramakrishnan
- Handbook on Fabric Manufacturing: Grey Fabrics: Preparation, Weaving to Marketing by B. Purushothama
- Mechanisms of Flat Weaving Technology By Valeriy V. Choogin, Palitha Bandara and Elena V. Chepelyuk
