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Shedding | Tappet Shedding | Positive Tappet Shedding | Negative Tappet Shedding

Updated: Jan 28, 2021

Shedding is a process by which warp sheet is divided into two which will facilitate the passage of weft yarn from one end to another end of the loom.

There are mainly three types of shedding namely.

  1. Tappet Shedding.

  2. Dobby Shedding.

  3. Jacquard Shedding.

Tappet Shedding:

In this method shedding is done by the Shedding cams or tappets mounted on the bottom shaft. This motion used only for weave repeating on two picks like Plain weave, Weft-rib, or hair cord weave.

Principle of Tappet Shedding:

The principle of tappet shedding consists in using a tappet which impinges upon an Anti-friction roller or bowl, supported in a treadle, the heald shaft being directly or indirectly connected to the treadle from which it is operated.

Scope of Tappet Shedding:

  1. The control of Up and Down moment of heald shafts is done by used of Tappet or Cam in case of Tappet Shedding.

  2. It is the simplest shedding mechanism.

  3. By use of Tappet shedding 8 heald shafts can be controlled at once.

  4. Weaves like Plain, Twill, Satin, and Sateen can be produced by use of Tappet Shedding.

  5. Tappet Shedding is the least versatile Shedding mechanism.

Types of Tappet Shedding:

There are two types of Tappet shedding namely,

  • Positive Shedding

  • Negative Shedding

Positive Shedding:

In case of Positive Shedding both lifting and lowering of Heald Shaft is done by use of Tappet or Cam.

Construction of Positive Tappet Shedding:

The Cam or Tappet is mounted on a shaft and has a track on which a bowl is placed. The bowl is connected to a tappet lever with link rods, links, and a heald shaft.

Each Tappet is Separately connected to a heald shaft through link rods and tappet lever. These are fulcrumed for tappet lever and links.

Working of Positive Tappet:

As the tappet is rotating bowl will also rotate. As per the Cam / Tappet profile the bowl moves up and down. If the bowl moves up the tappet lever moves to the right and the Heald shaft is lowered. If the bowl moves down the tappet lever moves to the left and the heald shaft is raised.

As the heald shaft is moves up and down the tappet that is why this motion is called as positive tappet shedding mechanism.

Negative Tappet Shedding:

In Negative Tappet Shedding either Raising or Lowering of Heald shafts is done by the moment of Tappet and the other motion (raising or lowering) is carryout by some other mechanism like reversing spring or dead weights etc.

Construction of negative Tappet Shedding:

A pair of tappets A&B are mounted on a Bottom Shaft C. These two Tappets are placed at 180o to each other. Two treadle levers D and E are connected to the R, loom by a bracket F. These two treadles have teeth which carries the lamb rods G and H, respectively. Two heald shafts J and K are Connected to the lamb rods. A top roller reversing shaft Q carry two rollers of different dia.

The roller of small diameter N is connected to leather strap L to which the front heald shaft J is connected. The roller P of large diameter is connected to the leather strap M to which the back heald shaft k is connected.

The tappet A and B touch the anti-friction bowls R and S, respectively. The heald shafts have heald eyes T and U through which the warp threads pass X is the warp sheet and y the cloth.

Working of Negative tappet shedding: -

As the bottom shaft rotates in the clockwise direction the tappets are also rotates. The tappet will press the anti-friction bowl and the treadle. This motion will be transferred to the lamb rod. From lamb to heald shafts and leather strap. So, one heald shaft is lowered and it forms the bottom layer of the shed. The other heald shaft is raised up by the roller reversing motion. It forms the top layer of shed. So, for one rotation of bottom shaft two sheds are formed. For the next shed the other set of bowls and treadle works.

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