Tuesday, May 18, 2021

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

 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 air-jet loom. High loom efficiency also achieves in air-jet loom. Main disadvantage of air-jet loom is high power consumption and extra cost of 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 gets increased when more than one type of weft counts are 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, weft yarn enters into the main nozzle and rests there.

Air- jet loom weft insertion cycle:

When the reed moves toward the back dead center position and the dwell period of the sley gets begins, the weft insertion cycle begins. First of all, the weft brake of weft accumulator gets opened. Now the air supply of main nozzle gets switched on. The compressed air stream emerging from main nozzle drags the weft yarn into the shed. The weft yarn travels trough fixed weft passage. A profile reed is used for this purpose as shown in the below schematic diagram. Now the relay nozzles actuates one by one after a fraction of 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 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 at 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 be 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 impart fixed and safe passage of the weft toward the weft accumulator. Since the weft yarn gets unwound very quickly during weft insertion, so that 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 depend upon the number of colours getting used in the fabric. This accumulator ensures continuous supply of weft yarn at constant yarn tension during weft insertion process. Accumulator also decide the required pick length in the air-jet loom. First of all, used reed space is measured. Now the perimeter of accumulator drum is calculated. The number of weft coils is calculated with the help of 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 whole number is find. 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 send a command to actuate the weft brake immediately. This weft brake stops the weft supply till 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 main nozzle gets controlled by control computer through magnetic valve. An air pressure regulator valve regulates the air pressure of 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 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 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 out side of the shed, the weft brake gets closed and the stretch nozzle sucks the the tail of 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 center position and beats the last inserted pick. As reed starts to move toward the back dead center position, the filling cutter cuts the weft yarn.

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