Tappet Shedding Advantages and Common Defects in Loom

Introduction

The article discusses the advantages and disadvantages of tappet shedding. It also discusses some common defects associated with tappet shedding. As general terms, tappet, cam, and wiper refer to irregular pieces of machinery that are rotated to create reciprocating motion in rods and levers through sliding contact.   A tappet shed motion is characterized by a tappet impinging on an anti-friction roller or bowl, which is supported by a treadle, with the heald-shaft being directly or indirectly connected to the treadle.

Types of Shedding Tappet

Several types of shedding tappets are used in the weaving industry. They are constructed based on two principles.

1. Negative Shedding Tappet
2. Positive shedding Tappet

1. Negative Shedding Tappet

The negative shedding tappet requires a mechanism (pulleys, stocks, bowls, springs, or dead weights) to reverse the direction of movement in healds. The negative shedding tappets are:

• The ordinary plain and twill weave shedding tappets.
• Jamieson’s tappet
• The barrel tappet.

2. Positive shedding Tappet

In the case of the positive shedding tappets, healds have automatic upward and downward movements without the need for an additional mechanism. The positive shedding tappets are as follows:

• Woodcroft’s section tappet
• Oscillating or rocking tappet
• Nuttall’s chain tappet
• Scroll tappets

Shedding Tappet Fixation

The shedding tappets may be fixed in different parts of a loom, namely,-

• Under and over the centre of the head-shafts
• Under and over one end of the heald-shafts
• Outside the loom framing.

Tappet Shedding Advantages

• Among all shedding motions, it is the simplest and cheapest.
• Within its capability, it provides the best result when used conveniently.
• The machine is designed to lift lay weights with less wear and tear than other shedding machines.
• To weave different fabrics and structures, it can move healds at high speed and increase or decrease their dwell time.
• In this way, the warp threads are put under less strain.
• A smaller amount of power is consumed and a greater amount of output is achieved.
• The fabric is less likely to be damaged by it than by other shedding devices, such as jacquards and dobbies.

Disadvantages

• It takes time and increases setup work to change tappets and gears when the weave design changes.
• Tappets can only produce simple patterns. They cannot handle complex weaves.
• There are a limited number of tappets in a loom. Usually there are 8 to 10 tappets.
• Shedding too much puts extra strain on warp yarns, resulting in yarn breakage.
• A small shed is created by under shedding. The shuttle cannot pass smoothly through the shed.
• Warp tension may be uneven if one side of the shaft lifts more than the other.
• The shed may not form correctly during operation, which affects the quality of the fabric.
• In some cases, the dwell period may not be suitable, which affects the formation of sheds and their timing.
• It is possible for the mechanism to produce jerky motion, leading to an increase in vibration and a reduction in smooth operation of the loom.

Tappet shedding defects

• There are a number of patterns that can be produced with tappets, including plains, twills, satins, and other standard weaves. There are also defects associated with tappet shedding, such as over, under, unequal shedding, and that in which the healds move as the shuttole passes through the shed, as well as that in which they move unsteadily.
• Over-shedding strains and breaks warp threads.
• As a result of undershedding, the warp is not sufficiently divided to allow the shuttle to pass through. As a result, the shuttle crosses over threads it should cross over, or breaks them, and a stronger pick is required.
• Unequal shedding occurs when one end of the shaft is lifted more than the other, causing the shuttle to pass over the threads at one end, causing wrong design and stitching defects.
• If the shedding is mistimed, the warp will be opened or closed without considering the sley’s motion, leading to faulty cloth.
• If the dwell of the tappet is not suitable for the fabric, the shuttle passes through the wrong shed and breaks the warp threads.
• It can cause a jerky movement in the heald, causing breakages of the warp threads if the tappet is defective in form.
• There is only about half a rotation of the tappet between the treadle bowl and the tappet on most cotton looms, therefore, a severe blow is inflicted upon the bowl as the tappet turns into the treading position, which leads to vibrations being transmitted from the warp and healds, resulting in thread breakage.

Conclusion

Tappet is generally used for heald shedding. Tappet is the simplest and the cheapest of all shedding motions. But, it is difficult to produce complex fabric by using tappet. However, this article tried to present tappet shedding advantages and disadvantages of tappet shedding.

References

• Arora, J. (2011). Modern Weaving Technology. Delhi: Abhishek Publications Chandigarh.
• Fox, T. W. (1992). The Mechanism of Weaving. Bombay : Universal Publishing Corporation .
• Murphy, W. (2009). Handbook of Weaving. Delhi: Abhishek Publicaitons Chandigarh.
• V. Gordeev, P. V. (1982). Cotton Weaving. Russia: Mir Publishers Moscow.