Wednesday, April 15, 2009

Fabric Weaving Process


Fabric is manufactured in a variety of ways. The basic principle, however, is something like that of making birds nest where the straws are interconnected to make a web like structure. Fabric is also interconnection of yarns or threads that is achieved by many different processes. Weaving is one of the major processes for fabric construction where two distinct sets of yarns or threads are interlaced with each other to form a cloth. The lengthwise set of yarns running from the back to the front of a weaving loom is called warp. The crosswise yarns are filled in the warps and thus they are known as the filling or the weft.

Both, warps and wefts have to be specifically prepared before weaving is done. The preparation includes operations such as spooling, warping and slashing. In spooling, the yarn is wound on larger spools (cones) that are placed on a rack known as creel. From the creel, the yarns are wound on a warp beam, which looks like a huge spool. These yarns are unwound for slashing, or sizing which is done to prevent chafing or breaking of yarns during weaving. The sized yarns are then wound on a final warp beam and are ready for the loom. The weft yarns have to be spun into desired size by giving them the right amount of twist needed for the type of fabric they will make. Weaving essentially includes four major operations that are performed in sequence and are continuously repeated. These operations are shedding; picking; beating up; and taking up &letting off.

Shedding involves raising up of alternate warp yarns in order to insert the filling yarn into the warp to form a shed. Shedding is automatically performed by the harness on the modern weaving looms. In picking, when the warp yarns are raised through shedding, the weft yarn is inserted through the shed with the help of a carrier device. A single crossing of the filling from one side of the loom to the other is called a pick. Various methods are adopted for carrying the filling yarn through the shed in different kinds of looms. A shuttle loom uses a shuttle which contains a bobbin of filling yarn. It leaves a trail of the filling at the rate of about 110 to 225 picks per minute (ppm).

As the shuttle looms are very slow and noisy, many shuttle less looms have been developed which include projectile loom; rapier loom; water jet loom; air jet loom etc. In projectile loom, the picking action is done by a series of small bullet like projectiles. Rapier looms have one or two rapier devices that travel along the width of the loom to carry the weft from one side to the other. Water jet and air jet looms, as the names suggest, use a jet of water and air respectively to carry the weft yarn across the loom. All these shuttle less looms have speeds ranging from 200 to 600 ppm. There are circular looms also that are mainly used for making tubular fabrics with the help of a shuttle device that circulates the weft in a shed formed around the machine.

Beating up, also called battening, beats each weft yarn against the portion of the fabric that has already been formed which results in a firm and compact fabric construction. As the shedding, picking and battening processes are being done, the new fabric is wound on the cloth beam, which is known as 'taking up'. At the same time, the warp yarns are released from the warp beam which is known as 'letting off'.
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