PREPARATORY PROCESSES

The yarn from the spinning frame is not necessarily in a fit state for the manufacture of fabric. some of it will require winding into suitable forms for weaving or for knitting, some of the singles yarns have to be doubled to strengthen them or folded to make fancy yarns, some yarns have to be dyed or bleached for certain special purposes. For use as warps in woven cloth, yarn has to be sized so as to withstand the friction of the loom, an oiling process is desirable. Some lace yarns are waxed after doubling.

Apart from the colouration of yarns for coloured woven fabrics, the chief preparatory processes are: winding, warping and sizing of yarns for woven fabrics.

Winding: Spun yarn is the raw material for fabric manufacturer and it is submitted to certain processes preliminary to weaving or knitting.

Winding is an important preliminary to cloth manufacture. Winding is to obtain longer lengths of yarn. Winding is necessary because bobbins from spinning frames, and the cops from mules can only carry a relatively short length of yarn. [One aspect of winding is to wind the yarn on large bobbins known as warpers’ bobbins from which a warp will be prepared later. Care should be taken to adjust the tension and remove any slubs and other thick places in the yarn.]

The bleached or dyed yarn is wound into hanks. Yarns may be wound into special packages such as cheeses and cones. Cheese form for many purposes, and the cone form is suited to soft-spun yarns for hosiery manufacture.

Weft yarns like silk and rayon yarns are wound on paper tubes, linen weft on wooden pirns, cotton weft are cop-wound, woollen yarns onto solid cops without spindles.

[Pirn winding is different from the winding of warp yarns in that the yarn is generally wound from long lengths into shorter lengths; the winding may take place from bobbins, cheeses, or cones.]

Warping: Woven fabrics consist of two sets of interlacing threads, warp and weft; the former pass along the length the fabric, and latter interlace with them at right angles crossing from side to side. It follows therefore that for the weaving of long lengths of fabric, a long warp must be prepared.

The principle of warping is to construct a sheet of parallel yarns from the various supply packages which may be bobbins, cones, cheeses etc; the yarns must also be evenly spaced. With cotton fabric from 400 to 600 of the packages [or bobbins .are placed in a creel which is formed of a series of vertical bars]. Wonted beaming may accommodate 800 to 1,000 packages of yarn.

Beam warping or beaming is perhaps the simplest method of making a warp; it is suited to cotton, linen, worsted and rayon. Ball warping is probably the oldest method of preparing warps and it is still used where bleached or dyed state is required. Section warping is utilised for coloured yarns where a number of threads are wound on to a wooden block, and later the blocks are placed side by side to make the required width of warp.

It is important to note that a good warp is a sound foundation for a satisfactory woven fabric.

Sizing: During weaving process the warp threads are subjected to friction when the shuttle passes. Hence it is essential to reinforce and lubricate the warp before it goes into loom. This process is known as sizing.

As the fibres have to be bound together to form a compact thread without projecting hairs, and also as the resulting thread must possess a smooth and lubricated surface, the sizing material must be an adhesive substance, preferably with film-forming properties. The chief adhesive substances are gums, starches and glues. The softening and lubricating material is generally an oily or fatty substance such as glycerol, olive oil etc., which helps to keep the yarn supple and prevent the starch from flaking; deliquescent substances such as calcium chloride may also be added to counteract any tendency to undue dryness of the sized yarns. Finally an antiseptic substance like zinc chloride or phenol is added to prevent mildew formation during storage. (British Cotton Industry uses Shirlan is salicylanilide). 

Care must be taken so that the sizing agents can readily be removed before the bleaching and dyeing of the cloth.