Monday, March 15, 2021

Tappet shedding mechanism ( Negative shedding)

 Tappet shedding mechanism ( Negative shedding).  

The shedding motion is the first primary loom motion. " The process of diving the warp sheet into two layers by the manual or mechanical process is called shedding motion. The layers are formed by heald shafts. Since we know that the ends get drawn through the eyes of heald wires and when some of the heald shafts get raised and the rest of the heald shafts get lowered, a V - shape passage in front of the reed for weft insertion is formed. This V-shaped passage for weft insertion is called a shed.

Structure of negative tappet shedding mechanism:

In this negative tappet shedding mechanism, two tappets are used. The tappets are mounted on a countershaft. 

This countershaft receives rotatory motion from the bottom shaft through spur gears.  

The countershaft makes one revolution when the bottom shaft rotates for one revolution for a plain tappet shedding mechanism. 

Two treadle levers are used. The anti-friction bowls are also mounted on these treadle levers. 

Each tappet touches to respective anti-friction bowl. The tappets are mounted in such a way that the lifting position of both tappets is kept just opposite to each other. 

The treadle levers are connected to the healed shafts with the help of jack bars. 

The top side of each healed shaft is connected to the reversing roller with the help of a leather strap. 

Two leather straps are used for each head shaft. The method of connection between the healed shaft and reversing roller through leather straps is shown in the below figure.

Working principle of negative tappet shedding mechanism:

The rotating bottom shaft transmits motion to the countershaft through spur gearing. 

As the countershaft rotates the tappets fastened on the countershaft begin to rotate in the same direction.

The rotating tappet presses to the anti-friction bowl. 

Since the anti-friction bowl gets mounted on the treadle lever so that the treadle lever goes to the down position. 

Since the rear end of the treadle lever gets connected to the jack bar so that the heald shaft connected with this treadle lever comes in a down position and the other heald shaft goes to up position because the downward movement of the front heald shaft imparts the partial rotatory motion to the reversing roller.

The position of the tappets gets changed after the half revolution of the countershaft. 

Now the other tappet presses the bowl mounted on the respective treadle lever. 

The back heald shaft goes to a down position. 

The front heald shaft lifts up by the reversing roller which receives reverse movement through the leather straps connected with the back heald shaft. 

In this way, the position of front and back heald shafts change regularly.


You may also be interested in the following articles:

Let - off motion, secondary loom motion

Take - up motion, a secondary loom motion

Shedding motion, a primary loom motion

Picking motion, a primary loom motion

Beating motion, a primary loom motion

Schematic diagram of loom

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