Different types of shedding mechanism in weaving process:-

Different types of shedding mechanism in weaving process:-

There are three main types of shedding  (opening of warp) are available for different types of fabrics they are,

Qa. Tappet shedding.

2.  Dobby shedding.

3.  Jacquard shedding.

(1) Tappet Shedding.

AQA tappet is given a rotary motion so that it depress a follower and a lever, known respectively as the friction bowl and the treadle arrangement by means of which the heald shaft is operated.

Scope of tappet shedding:-

1. Tappet shedding uses tappets and cams to control the up/down movement of shafts.

2. The bulkiness of its mechanical movement limits the loom to control upto 8 shafts (repeat not more than 8).

3. Therefore tappet shedding is the simplest and least versatile shedding motion.

4. The design is restricted to plain, twill, simple sateen or satin weave.

5. Any design more than 8 shafts required dobby loom.

Negative tappet shedding mechanism:-

Figure shows a negative shedding tappet mechanism. A pair of tappets A & B is fixed to the bottom shaft C at 180 degree to each other. Two treadle lever D & E are connected to the loom back rail by a bracket F. The bracket acts as a fulcrum for the lever S. The two healds have teeth to carry the lamb rods G & H respectively. Two heald shafts J & K are connected to the lam rods. A top reversing roller shaft Q carries two rollers of diffrent diameters. 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 leather strap M to which the back heald shaft K is connected. The A & B touch the anti-friction bowls or followers R & S respectively which are fixed to the treadle levers.

Image of negative tappet shedding mechanism.

The heald shafts have Heald eyes T & U through which the warp threads pass . X is the warp shaft and Y is the cloth. The odd ends are passed one heald shaft while the even end through the other heald shaft.

Working principle:-

When the bottom shaft is rotated in the clock wise 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. The action is transferred to the lamb rod , the heald shaft is lowered and the threads connected for this heald shafts are lowered and from the bottom layer of the shed.

Fig of dwell.

The leather strap attached to the reversing rollers are connected in opposite direction i.e. when leather strap is pulled down; it is unwound from its roller. Therefore rotates in the clockwise direction and the other leather strap is wound on to its roller. The heald shafts are also raised and therefore the lamb rod and treadle levers are also raised. The threads connected to the healds are also raised and from the top layer of the sheds. For the next shed, the other tappet works with the other set of bowl , treadle, lamb rod, heald shaft. Strap and other heald shaft is raised by the top running rollers , and the position of the heald shafts are thus interchanged. Thus, for one rotation of the bottom shaft, two sheds are formed. In this type f tappet shedding therefore, one tappet depressed 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 that this type of shedding mechanism is known as “negative tappet shedding mechanism".

Timing and setting:-

1. Turn the crank shaft to top center position.

2. Fix the anti-friction bowl to the treadle levers, they should move freely in the shaft.

3. Fix the treadle levers with thea bracket to the back rail of the loom.

4. Set the grid and grid bracket to the front rail of the loom in the slots of the grid.

5. Make sure that the tappet with lower throw is fixed to the bottom shaft at the starting handle side.

6. Fix the top reversing rollers to the top reversing roller shaft to be equidistant from the ends and at the same time ensure that the connected screw of the rollers are symmetrical about the central axis of shaft . When the heald shafts are at the same level the roller of small diameter is always connected to the front heald shaft.

7. The heald shaft are connected to the top reversing rollers by the means of cords and leather straps are connected to the rollers, such that when one of them wind on its roller the other strap unwinds from its roller and vice versa.

8. Lamb rods are connected to the heald shaft by cords.

9. Adjust the tappets on the bottom shaft and make sure of the following points,

a) The tappet with a bigger throw should be connected to the back heald shaft.

b) The bowl should have perfect contact with the surfaces.

c) The treadles should be at the same level and parallel to each other at the top center position.

Heald Shaft:-

The hook the lamb rod of the front heald shaft should be connected to the first notch of the treadle lever while that of the back heald shaft should be connected to the third notch. If the depth of shed is altered, the connections of the hooks to the treadle lever can be changed.

Point to be observed:-

1. Turn the crank shaft through two revolutions and make sure that the bowls are always in contact with the tappets.

2. The heald shaft should not touch the side frame or the slay.

3. Turn the crank shaft to the bottom center and check the size of shed . The bottom line of warp sheet or the heald eyes of the lowered heald shaft should have a clearance of 1 mm from the race board and the top.

Ref:-https://textilelearner.net