Structure and working principle of air-jet loom weft insertion system

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एयर-जेट लूम वेफ्ट इंसर्शन सिस्टम की संरचना और कार्य सिद्धांत

 Air-jet loom weft insertion system:

The weft insertion is carried out with the help of a stream of compressed air in the air-jet loom. This weft insertion method enables to achieve very high loom speed and good fabric quality. There very lowest maintenance cost appears in the air-jet loom. High loom efficiency is also achieved in the air-jet loom. The main disadvantage of the air-jet loom is high power consumption and extra cost of the compressor and its maintenance. The number of weft colours is limited. Mainly tappet shedding motion is used in the air jet loom. When we use dobby or jacquard shedding, the loom speed gets decreased.  You can see in the below picture:

Weft yarn passage in air jet weft insertion system:

The weft yarn package is mounted on the creel. The number of weft packages depends upon the number of weft colours getting used in the fabric. The yarn packages also get increased when more than one type of weft count is used in the fabric. 

Next, the weft yarn passes through the weft accumulator which ensures regular weft supply at constant tension during weft insertion. 

Finally, the weft yarn enters into the main nozzle and rests there.

Air-jet loom weft insertion cycle:

When the reed moves toward the back dead centre position and the dwell period of the sley gets begins, the weft insertion cycle begins. First of all, the weft brake of the weft accumulator gets opened. Now the air supply of the main nozzle gets switched on. The compressed air stream emerging from the main nozzle drags the weft yarn into the shed. The weft yarn travels through a fixed weft passage. A profile reed is used for this purpose as shown in the below schematic diagram. Now the relay nozzles actuate one by one after a fraction of a second. As the weft journey gets completed, the weft brake gets closed immediately and the air stretch nozzle sucks the tail of the weft yarn. Next, the reed starts to move toward the fell of the cloth and beats the last inserted pick. As the reed starts to move away from the fell of the cloth, the filling cutter cuts the filling yarn. This cycle is repeated continuously. You can understand the weft insertion cycle by the below picture:

Structure and working principle of air-jet weft insertion system:

The working principle of the air-jet loom is very simple. compressed air is used to insert the thread into the shed. The main weft insertion mechanism is generally mounted on the left side in most of the loom.
The weft yarn package is mounted on the creel. There may be four packages mounted on the creel. This number may also vary according to loom specification. A weft tensioner and thread guide are mounted on the weft creel for each weft yarn package. The thread guide imparts fixed and safe passage of the weft toward the weft accumulator. Since the weft yarn gets unwound very quickly during weft insertion, so a balloon separator is also used for each weft yarn package.
The weft accumulator comes in the next. It is mounted on the square and round pipes frame. The accumulator is fastened on this frame. The number of weft accumulators depends upon the number of colours getting used in the fabric. This accumulator ensures a continuous supply of weft yarn at constant yarn tension during the weft insertion process. Accumulator also decides the required pick length in the air-jet loom. First of all, used reed space is measured. Now the perimeter of the accumulator drum is calculated. The number of weft coils is calculated with the help of the above two parameters. This number of coils is entered into the control computer. The number of coils should be a whole number. If our calculated number of weft coils required is not a whole number, the diameter of the accumulator drum is adjusted and the whole number is found. A weft brake is also mounted over the accumulator drum. When the weft insertion takes place, the control computer counts the number of weft coils getting inserted into the shed. As the number of coils getting inserted reaches the preset value, the control computer sends a command to actuate the weft brake immediately. This weft brake stops the weft supply till the next command. The weft brake timing is also entered into the control computer.

The main nozzle comes in the next. This main nozzle is connected to the compressed air supply. The air supply of the main nozzle gets controlled by the control computer through the magnetic valve. An air pressure regulator valve regulates the air pressure of the main nozzle. The weft yarn rests inside the main nozzle. When the control computer sends a command to the magnetic valve, the air supply of the main nozzle gets switched on. the compressed air carries the weft yarn into the shed. 

The main nozzle alone can not insert the weft yarn from one selvedge to another selvedge. So many relay nozzles are mounted on the sley. These relay nozzles are connected to the compressed air supply and are individually controlled by magnetic valves. These relay nozzles are not activated together. When the main nozzle propels the weft yarn into the shed, The relay nozzles situated near the main nozzle actuates first. As the journey of weft yarn progresses, the next nozzles actuate and help to accelerate the journey of weft yarn toward the opposite side selvedge. When the weft yarn reaches the outside of the shed, the weft brake gets closed and the stretch nozzle sucks the tail of the weft yarn.

A filling detector is mounted at the stretch nozzle side on the reed. It detects the presence of weft regularly. If weft yarn insertion falls short or gets failed, the filling detector stops the loom immediately.
When the weft insertion gets completed, the reed starts to move toward the front dead centre position and beats the last inserted pick. As the reed starts to move toward the back dead centre position, the filling cutter cuts the weft yarn.

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