Saturday, May 15, 2021

Structure and working principle of projectile loom weft insertion system

Projectile loom weft insertion system:

A projectile loom weft insertion system is another type of non-conventional weft insertion system. The projectile loom is only the loom in the non-conventional loom category which weaves the fabric at zero percent selvedge waste during fabric weaving.

Weft passage of projectile loom weft insertion system:
The weft package is mounted on the weft creel. First of all, the weft yarn passes through the weft accumulator. This weft accumulator ensures the regular weft yarn supply at constant filling tension.  This accumulator mounted after the weft package. Next, the weft yarn passes through the filling brake and then it passes through the filling tensioner. Now the weft yarn passes through the returner. finally, the weft yarn is gripped firmly by the projectile feeder.
Weft insertion cycle of projectile loom weft insertion:
First of all, the conveyor chain pushes the projectile over the projectile lifter. The projectile opener opens the gripper. Next, the projectile lifter lifts up the projectile and brings it in the required position. 
Now, the weft brake gets opened and the projectile feeder moves toward the projectile. This projectile feeder feeds the weft yarn between the opened grippers of the projectile. As the weft feeding process completed, the projectile opener comes out of the projectile and the grippers of the projectile get closed. The projectile feeder releases the weft yarn when the grippers of the projectile catch the weft yarn firmly.
The projectile brake remains opened during the propulsion of the projectile into the shed. Next, the picking shoe mounted on the picking arm hits the projectile hardly from the picking side to the receiving side. The weft brake remains opened during weft insertion. As the projectile reaches the receiving side, the projectile brake breaks the momentum of this projectile. The projectile brake gets closed now. The weft brake is also closed at this time. 
When the momentum of the projectile gets broken completely, the projectile brake gets opened again. Now the returner comes into the action and brings the projectile back to its proper position. 
The grippers mounted at both sides of the fabric selvedge catch the yarn firmly. Now the projectile feeder grips the weft yarn again at the picking side. The projectile opener releases the weft yarn from the projectile at receiving side now and the filling cutter cuts the weft yarn at receiving side. This weft insertion cycle is repeated continuously. You can also see the complete weft insertion cycle in the below schematic diagram:

Some important parts of the projectile loom weft insertion system.
The important part of  projectile loom weft insertion system are given below:
Projectile:
Its length is 90 mm approximately. It has a 40 - 60 grams weight range. The body of the projectile is made of steel. The grippers are fitted inside it. A hole is made at the gripper side to open the gripper's jaws as per the requirement with the help of a projectile opener. It is projected into a projectile guide at the speed of 28 - 30 feet per second. An actual picture of a projectile is given below.

Guide teeth and projectile guide:
The projectile guide is constructed by arranging many guide teeth in one straight line. These guide teeth are mounted on the sley in a straight line. Proper alignment of guide teeth is carried out with the help of an alignment gauge. The projectile travels through this projectile guide. Weft gets released in the projectile guide but during beating motion, the weft yarn comes out of the projectile guide through the open space( slot) present in each guide tooth.  A real picture of guide teeth is given below:

Conveyor chain ( projectile transport system):
The projectile is propelled in the loom from the picking side only. The number of projectiles being used on the loom depends upon the reed space used. These projectiles are transported from receiving side to the picking side with the help of a conveyor chain. It is a simplex chain. The projections are mounted on the conveyor chain at regular intervals of distance. There is 10 inches distance kept between two adjacent projections mounted on the chain. The projectile falls upon the travelling path and the conveyor chain moves over this travelling path. This conveyor chain rotates in the anti-clockwise direction. When rotating projection passes over the travelling path, it pushes the projectile and carries it to the projectile lifter.

Picking mechanism of Sulzer projectile weft insertion system:
The picking shoe or metal picker 2 is mounted on the picking arm 3. The fixed end 12 of the torsion bar 11 is fastened on the side frame of the loom. The other end of the torsion bar passes through sleeve 10 and is connected to the picking arm 3. The torsion bar 11 is also connected with cam follower 5 with the help of toggle forming arms 8,9 and arm 13. Cam 4 touches the cam follower 5. The cam 4 is fastened on the camshaft. A bevel gear is mounted at the outer end of this camshaft. This bevel gear gets engaged with another bevel gear mounted on the drive shaft.
When the drive shaft rotates, the camshaft is also rotated. the cam presses the cam follower. Since one end of the torsion bar gets fixed so the other end of the torsion bar gets twisted and energy is stored in it. As the cam further moves, the torsion bar comes very fast in its original position. When the torsion bar returns to its original position, the picking shoe or metal picker mounted on the picking arm hits the projectile hardly and the projectile gets propelled from the picking side to receiving side. 


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