Wednesday, May 12, 2021

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

 Rapier weft transfer process:

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

Types of rapier weft transfer:

There are 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 weft tension and gripping pressure of both grippers. The gripping pressure of receiving gripper is kept little bit higher than insert gripper. The weft tension is also maintained according to gripping pressure of 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 to flying out of gripper from the passage. Receiving gripper B reaches the sley center first and gets ready to receive the weft yarn from insert gripper. This receiving gripper rest in its dwell period. The insert gripper A loaded with weft yarn  reaches the sley center position. When insert gripper reaches the weft transfer position C, the yarn carried by insert gripper crosses the tip of gripper hook E. As the dwell period of 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 soffisticated . 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 gripping jaws of the both grippers are carried out with the help of 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 extra mechanism during complete weft insertion cycle. The empty receiving gripper starts to move toward the sley  center position first. 

As the weft insertion cycle gets begun, the the weft selection finger falls as per weft pattern feed in program computer. Now the insert gripper starts to move toward the sley center. The gripping jaws of  insert gripper are opened with the help of a gripper opener. As the insert gripper moves slightly toward the sley center, 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 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 fraction of second. The yarn gripped by inseert gripper gets entered between opened gripping jaws of receiving gripper. Next, the gripping jaws of receiving gripper get closed by mechanism. The receiving gripper grips the weft yarn firmly. 

Now the inseert gripper opener opens the gripping jaws of insert gripper and weft yarn gets released from 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 fraction of second.  

When the receiving gripper reaches near the selvedge, the other gripper opener opens the gripping jaws of receiving gripper and weft yarn gets released. The catch selvedge hold the weft yarn and prevents slackened it. 

This cycle is repeated continuously. The schematic diagram of positive weft transfer process is given below.








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