Weaving

WEAVING

Weaving is the simple technique of making a fabric. The lengthwise and crosswise yarns are overlapped (interlaced) one above the other in an alternative manner. This process of interlac-ing is done on loom. Loom is a wooden / metal machine, which holds the warp yarns and facilitates the weft yarn to pass up and below the warp to form the woven structure.

The technique of fabric construc-tion by weaving was probably known as spinning during the ancient times. In the course of time, looms were made which were simple and hand operated. The fab-ric woven in these looms is called hand loom fabric. Today power loom has taken place of the hand operated loom which can weave fabric faster and with less defects in comparison to hand looms (Figure 5.1).

Looms can be classified into vari-ous categories. This classification is based upon the picking operations used by the loom. The looms which use shuttles for weft insertion are called conventional shuttle or fly shuttle looms. The fabric woven in this loom has more defects as it used large wooden shuttle which causes abrasion resulting in more broken yarns. These looms are also very noisy and PPM (Picks Per Minute) is also low.

The looms which use other devices to bring the filling yarn through the fabric are called shuttleless looms. These looms have high productivity with fewer fabric faults (Figure 5.2).

The major parts of a loom are described below:

Major Parts of a Loom:

·           Warp Beam: This is round roller/ cylinder on to which the warp/ lengthwise yarns are arranged one after another in a parallel manner (Figure 5.3).

·           Whip Roll: A small guide roller over which the warp yarns pass, as they move to the lease rod.

·           Lease Rod: Two guide rod between the whip roll and the heddles, to separate the alternative warp yarns.

·           Heddles: Small wire made out of steel. They are a set of vertical wires laid into the hardness frame. This helps in the movement of the warp yarns (Figure 5.4).

·           Harness: A wooden frame to sep-arate warp yarn such that a shed (V shaped gap) is formed, through which weft thread is passed.

·           Bobbin: Small long plastic or metal holder on to which the (filling) weft yarns are wound.

·           Shuttle: A wooden / plastic boat shaped device which hold the bob-bin with the weft yarns. This moves from right to left pulling the weft yarn in its place (Figure 5.5).

·           Reed: A vertical wooden frame with very close steel wires. Each warp yarns pass through each wire. The gap between the wires is known as dents (Figure 5.6).

·           Breast Beam: This is a bar, which guides the newly woven cloth towards the cloth beam.

·           Cloth Beam: A wood or steel roller on to which the woven cloth is wound after weaving (Figure 5.7).

Basic Weaving Operation

The yarns intended for warp must pass through some basic operations like– spooling, and warping to prepare them to withstand the strain during weaving.

Spooling

Winding of warp yarns on large spools, or cones which are placed on a rack called creel is known as spooling. These yarns are then wound on the warp beam (Figure 5.8).

Sizing

The warp yarns are unwound and dipped in a sizing bath which consists of starch. The slasher machine covers every yarn with a coating which adds strength to the warp yarns to withstand the stress, during weaving (Figure 5.9).

Warping

Warping is the process of winding the sized warp yarns on the warp beam which will be placed over the loom. The warp beam is located at the back of the loom and holds the lengthwise yarns. It controls and releases the warp yarns as the weaving process is carried on. The warp ends are threaded through the heddles held by the harness. Every basic loom has a minimum of 2 heddles. The number of heddles in a loom varies from 2 to 12 for basic weaves, but for fancy weaves the number increases upto 32. The heddles help in the movement of warp yarn to form the shed, through which the shuttle carries the filling yarns. Once the filling yarn is passed through then reed is pushed to put the filling yarn in its place (Figure 5.10).

Fabric Making

The interlacing of warp and weft yarns results in woven fabric making. This is done on a loom through four main pro-cesses. They are shedding, picking, beating up and taking up and letting off processes.

·           Shedding can be described as raising the specific warp yarns by the hard movement of the heddles; to form a ‘V’ shaped gap known as shed for the weft yarns to interlace through.

·           Picking is the processing of interlac-ing /passing the filling yarn (weft) through the shed formed from right to left (Figure5.11).

·           Beating up is also known as bat-tening. This is the process of push-ing the filling yarn (weft) firmly into its place by the movement of the reed. Beating arranges the filling yarns parallel to each other very closely to create a woven structure.

·           Taking up and letting off is the pro-cess of winding up woven cloth into the cloth beam and releasing more warp yarns from the warp beam for weaving.

Terms Used in Woven Fabrics

The common terms used while weaving are given below :

Selvedges

Selvedges are the lengthwise edges which run on both sides of the fabric. They are usually 0.5 to 1.5 cm broad. Selvedges prevent the fabric from raveling. It is strong with more number of warp yarns. There are different types of selvedges namely plain selvedge, tape selvedge, split selvedge, fringe selvedge, fused sel-vedge and adhesive finished selvedge (Figure 5.12).

Thread Count

The number of warp (ends) and weft (picks) per square inch of fabric is called thread count or fabric count. The higher the fabric count the more strong and more durable is the fabric. Fabric with higher thread count is more expensive and is denoted by X x Y. Example 30 x 50 thread count means 30 and 50 yarns in warp and weft direction for one inch. When the number of warp and weft yarns are almost equal the construction of fabric is called balanced and when the difference in warp or weft yarns is more than the other, it is called an unbalanced construction.

Factors Affecting the Durability of the Fabric

The durability of a fabric depends on various factors. The most common are listed below :

·           The kind and quality of the fibre.

·           The tensile strength of the yarn.

·           The amount of twist in the yarn.

·           The use of ply yarns as compared with singles.

·           The use of uniform yarn rather than novelty yarns and

·           The compactness of a fabric.