Tuesday, 11 August 2009

Elements of Weaving

Elements of Weaving
Weaving is carried out on a machine traditionally known as a loom.
Fig. illustrates the layout of a weaving loom in the form of a simple schematic diagram.

The sheet of warp yarns, which consists of a number of ends is carried upon the weavers beam A. The warp ends from the beam are then drawn through the healds B1 and B2, threaded through the splits of the reed C and at the point D they become interlaced with the weft supplied by the shuttle E. The cloth is formed at the fell of the cloth, marked F and is wound upon the cloth roller marked G situated at the front of the loom.
There are three types of motions identified on a loom.
PRIMARY MOTIONS
Every loom requires three primary motions to produce woven fabrics.
1. Shedding
2. Weft Insertion
3. Beating up
Shedding
It is the name given to the motion which moves the heald frames up and down in order to separate the warp sheet into two layers and create a triangle in front of the reed (referred to as the shed) through which the weft can be passed.

Weft Insertion (Picking)
It is the means by which the weft is projected through the shed. This was traditionally by shuttle, but more recently it is done by projectile, airjet or water jet.

Beating up
It is where the reed pushes the weft into the fell of he cloth to form fabric. This requires considerable force. Hence the term, beating up.

SECONDARY MOTIONS
There are three secondary motions in weaving : let off; take up and weft selection
Let off motion - It ensures that the warp ends are controlled at the optimum tension for the fabric that is being woven.
Take up motion - It withdraws cloth from the fell and stores it at the front of the loom.
Weft selection - It is necessary to change the weft being inserted.

Ancillary or Tertiary motions
These are widely used on modern weaving machines
These include
1. Warp stop motions
2. Warp protectors
3. Weft stop motions
4. Weft replenishment
Warp stop motions stop the loom at the event of the breakage of an end.

Warp Protectors- These protect the warp in the event of shuttle flying etc.
Weft stop motions halt the loom when the weft yarn break. Warp protector motions stops the loom before beat up if shuttle fails to reach the other side of the loom.
Weft replenishment assures a continuous supply of weft yarn to the loom wherever a supply package becomes exhausted.

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