SHEDDING
Object of Shedding Mechanism
A shedding mechanism separates the warp threads into two layers or divisions to form a tunnel known as “shed”. The shed provides room for passage of the shuttle. A shed may be formed by means of tappets, cams, etc.
Types of Tappet Shedding Mechanism
Generally there are two types of shedding:
1. Negative shedding
2. Positive shedding
In plain looms, tappets are used to for m sheds.
Generally there are two types of shedding:
1. Negative shedding
2. Positive shedding
In plain looms, tappets are used to for m sheds.
Negative Tappet Shedding
In a tappet shedding mechanism, if the tappet controls only one movement, either an upward or downward movement of the heald shafts, then the shedding is known as “negative tappet shedding”. The heald shafts are returned by some external devices like springs, dead weights, rollers, etc.
Positive Tappet Shedding
In a tappet shedding mechanism, if the tappet controls both upward and downward movements of the heald shafts, then the shedding is known as positive tappet shedding.
Examples :
1. Jamieson’s tappet
2. Barrel tappet and
3. Ordinary tappet
Tappets and Cams
These are irregular metallic pieces used to produce an up-and-down motion in followers and levers. The up-and-down motion is obtained by giving rotary motion to these pieces. If the follower and lever are required to get a continuous up-and-down movement, a cam or wiper is used. If the follower and lever are required to produce up-and-down movement with regular intervals of rest, tappets are used. Figure 1 shows a pair of tappets and a cam. There are specific portions in tappets that correspond to “dwell” periods, i.e. regular intervals of rest for the major parts involved in the motion.
A pair of tappets Cam
Figure 1: Tappets and Cam
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