Wednesday, May 12, 2021

Types of rapier weft transfer process, Negative weft transfer and positive weft transfer

 Rapier weft transfer process:

The weft transfer process in the rapier loom is just like a batten change in a relay race. When both rapier reaches in sley centre position, the receiving gripper receives weft yarn from insert gripper. The transfer of weft yarn from the insert gripper to receiving gripper is called the weft transfer process in the rapier loom.

Types of rapier weft transfer:

There is the following kind of weft transfer methods used in the rapier weft insertion system.
1 - Negative rapier weft transfer method.

2 - Positive rapier weft transfer method.

Negative weft transfer method:

In negative weft transfer method, the opening mechanism for opening of the gripping jaws of both grippers is not used during weft transfer process. The weft transfer takes place due to the weft tension and gripping pressure of both grippers. The gripping pressure of receiving gripper is kept a little bit higher than the insert gripper. The weft tension is also maintained according to the gripping pressure of the insert gripper. 
The grippers mounted on flexible ribbons make reciprocating motion through a fixed passage made by guide teeth D. These guide teeth avail a proper and fixed passage to grippers. These guide teeth also prevent flying out of the gripper from the passage. Receiving gripper B reaches the sley centre first and gets ready to receive the weft yarn from the insert gripper. This receiving gripper rest in its dwell period. The insert gripper A loaded with weft yarn reaches the sley centre position. When the insert gripper reaches the weft transfer position C, the yarn carried by the insert gripper crosses the tip of gripper hook E. As the dwell period of the insert gripper begins, the receiving gripper starts to move toward the fabric selvedge at the same time. Since the gripping pressure of receiving gripper is kept little bit higher than the insert gripper so that it gets succeeded to catch the weft yarn between the gripping jaws H and carries the weft yarn toward the fabric selvedge. The schematic diagram of negative rapier weft transfer shown in the below picture:
Positive weft transfer method:

This weft transfer method is more reliable, efficient, and sophisticated. Very fine filament yarn to very high coarse spun yarn can be inserted successfully without any trouble.
In the positive rapier weft transfer method, the opening of the gripping jaws of both grippers is carried out with the help of a mechanical opening system. The gripping jaws of both grippers get opened and closed as per timings. 
The most efficient positive rapier weft transfer has been developed by Dornier loom manufacturer. 
In this mechanism, the grippers are mounted on rigid rapier racks. 
The gripping jaws of grippers get opened and closed mechanically with the help of an extra mechanism during the complete weft insertion cycle. The empty receiving gripper starts to move toward the sley centre position first. 
As the weft insertion cycle gets begun, the weft selection finger falls as per the weft pattern feeding program computer. Now the insert gripper starts to move toward the sley centre. The gripping jaws of the insert gripper are opened with the help of a gripper opener. As the insert gripper moves slightly toward the sley centre, the weft yarn comes between the gripping jaws. Now the gripping jaws are closed. The insertion cycle progresses and both the grippers get entered into the shed.
As the receiving gripper reaches the weft transfer position, it comes in the rest position. The gripper opener opens the gripping jaws of receiving gripper. The insert gripper loaded with weft yarn reaches the weft transfer position after a fraction of a second. The yarn gripped by the insert gripper gets entered between opened gripping jaws of receiving gripper. Next, the gripping jaws of receiving gripper get closed by the mechanism. The receiving gripper grips the weft yarn firmly. 
Now the insert gripper opener opens the gripping jaws of the insert gripper and weft yarn gets released from the insert gripper.
The receiving gripper begins to move toward the fabric selvedge now. The empty insert gripper also begins to move toward the fabric selvedge after a fraction of a second.  
When the receiving gripper reaches near the selvedge, the other gripper opener opens the gripping jaws of receiving gripper and the weft yarn gets released. The catch selvedge holds the weft yarn and prevents slackened it. 
This cycle is repeated continuously. The schematic diagram of the positive weft transfer process is given below.







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