Positive tappet shedding mechanism:-

Positive tappet shedding mechanism:-

In this type of shedding, the heald shaft is raised and lowered by the tappet.

Construction:-

The tappet shaft carries another tappet which has a groves or track in which a bowl is placed . The bowl is connected to in turn to a tappet lever with link rods, links J and a heald shaft . Each tappet is separately connected to a heald shaft through link rods and tappet lever. These are two fulcrums for tappet lever and links.

Working principle:-

When the tappet is rotated , the bowl is also rotated. According to the shape of the groove, the bowl is moved up or down or is still. If the bowl is moved up , the tappet lever move to the right through the links and the heald shaft is lowered. If the bowl is moved down , the tappet lever moves to the left and the heald shaft is raised. Since the heald shaft is raised and lowered by means of the mechanism, this tappet shedding is known as positive tappet shedding mechanism when the bowl stands still, the heald shafts in the dwell stage.

Image of positive tappet shedding.

A positive shedding tappet, and the one most generally employed , is known as the wood craft tappet.

This style of tappet self contained and is now made in different forms , according to the class of fabrics which it is to adopted.

This style of tappet self contained and is now made in different forms , according to the class of fabrics which it is to adopted.

The treadles are fulcrummed on the shaft and are provided at with knuckle , on which the anti-friction pulley is pivoted . The pulleys are specially tempered or made of steel in order to better resist the friction to which they are subjected. The movement of this pulley is determined by the shape and the arrangement of the section plate 1 to 12 . In this type of tappet only two different section plates are used.

That shown at it is employed to raise the treadle; that is to depress the treadle. The pulley is actuated by the projecting rims, of metal cast on the side of the plates with which it is constant contact. The healds are connected to jack leavers placed above and below the heald; the levers extend outside the loom frame, and in turn are attached to the end of the treadle by means of a connector. When the treadle is forced upward by means of a section plate the heald shaft is drawn down and vice versa, with the section plate.

These tappets are made to work with from 8 to 12 treadles , and can be constructed for weave containing upto 24 picks to the round. A tappet contains 12 sections or pick in one repeat. The tappet shaft is supported in open bearing in the frame work and secured to this shaft, the tappet wheel contains a minimum number of teeth (in this 180) which is multiple of the weaves for which the tappet may be required. The wheel is also fitted width a number of standard bolt holes , in order to accommodate section plates of the different sizes, such as are required for weave containing a varying number of picks to the round.

Advantages of tappet shedding:-

1) It is robust , simple, and cheap.

2) It is capable of lifting a heavy weight with less wear and tear than other shedding mechanism.

3) It can move heald shaft at great speed.

4) It puts less strain upon the warp.

5) It consumes less power and gives great output.

6) It requires less maitainance.

Disadvantages:-

1) If the weave is changed , it will be necessary to change the tappet and the change gear wheel in the counter shaft arrangement. So work involved in changing the weave is more.

2) The capacity of tappet to produce a pattern/weave is very much limited. A maximum of 8 to 10 tappets only can be used.

Faults that may occur in tappet shedding mechanism:-

(1) If tappet is faulty, it imparts a jerky movement to the heald shaft.

(2) The tappet should always touch the bowls. Otherwise a severe bowl is applied to the bowl and vibration is transmitted to the heald shaft. End breakages may occur ad a result of this.

(3)  Over shedding : If the depth of a shed is too much , strain on the warp will more and breakages occur.

(4) Under shedding: If the depth of shed is too low the shuttle will not reach to other end and may be trapped in the shed or may fly out. Hence end breakages will occur.

(5) Uneven shedding: Uneven shedding is caused by lifting one end of the heald shafts more than the other. So the shuttle will move over same warp threads and fly out or get trapped in shed.

(6) If the shedding is mistimed then the other motion like picking and beat-up can not be done smoothly and end breakages may occur.

Comments:-

Tappet shedding mechanism produce the shed by using the reciprocating motion of the tappet. Some faults are involved in this mechanism. If this faults are removed , we can get good result from the tappet shedding mechanism.

Ref:-https://textileleaner.net