Tappet Shedding Mechanism

Scope Of Tappet Shedding :

A. suitable for weaving plain, twill designs.

B. comparatively economical mechanism.

Motion transfer Of Tappet :

Motor -> Motor pulley -> Machine pulley-> Crankshaft ->Bottom shaft -> Tappet shaft

Types of tappet: 
Various kinds of shedding tappets are used in industries. They are of two main types:

  • Negative shedding tappet
  • Positive shedding tappet

Negative shedding tappet

In this mechanism, lifting is done mechanically, and lowering is and lowering is done by spring. That means the Negative tappet needs an extra arrangement of pulley, bowl, spring and dead weight to reverse the direction of healds. This belt pulley either raises or lower the head.
Example: Shuttle loom.

Positive shedding tappet

In this mechanism, both lifting and lowering motions are done mechanically. This means this mechanism provides both upward and downward movement of heald without the help of an additional mechanism.
Example: Rapier loom.

Construction of negative shedding mechanism:

The figure shows a negative tappet shedding mechanism. A pair of tappets A and B are fixed to the bottom shaft C at 180 degrees to each other. Two treadle levers D and E are connected to the loom back-rail by a bracket or fulcrum F.

The bracket acts as a fulcrum for the levers. The two treadles have teeth to carry the lamb rods G and H respectively. Two heald shafts J and K are connected to the lamb rods. A top reversing roller shaft Q carries two rollers of different diameters. The roller of small diameter N is connected to a leather strap L to which the front heald shaft J is connected. The roller P of large diameter is connected to a leather strap M to which the back heald shaft K is connected. The tappets A and B touch the anti-friction bowls or followers R and S respectively, which are fixed to the treadle levers.

The heald shafts have heald eyes T and U through which the war p threads pass X is the war p sheet and Y is the cloth. The odd ends are passed through one heald shaft while the even ends are passed through the other heald shaft.

Working Procedure of negative tappet shedding:

When the bottom shaft is rotated in the clockwise direction as shown in the figure, the tappets are also rotated. The tappet will depress the anti-friction bowl and the treadle. Being fulcrumed at one end, the front portion of the treadle moves down. This action is transferred to the lamb rod, the heald shaft and the leather strap. So, one heald shaft is lowered and the threads connected to this heald shaft are lowered and form the bottom layer of the shed.

The leather straps attached to the reversing rollers are connected in opposite directions, i.e. when leather strap is pulled down, it is unwound from its roller. The shaft therefore rotates in the clockwise direction and the other leather strap is wound on to its roller. The heald shaft is raised and therefore the lamb rod and treadle lever are also raised. The threads connected to the heald shaft are also raised and form the top layer of the shed.

For the next shed, the other tappet works with the other set of bowl, treadle, lamb rod, heald shaft, strap and roller and the other heald shaft is lowered. The first heald shaft is raised by the top reversing rollers, and the positions of the healds shafts are thus interchanged. Thus, for one rotation of the bottom shaft, two sheds are formed.

In this type of tappet shedding therefore, one tappet depresses the concerned treadle and the corresponding heald shaft is lowered. But the other heald shaft is raised by means of the top reversing rollers. So, this type of shedding mechanism is known as “negative tappet shedding mechanism

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