WOOLLEN GOODS The finishing of woollen goods requires in general plant and processes entirely different from those described in connection with cotton. The methods employed naturally vary with the nature of the fabric: for example, worsted fabrics (woven from yarns produced from the longest staple fibre, and containing the maximum of parallelism between the fibres) require in general a "clearer" finish than woollen fabrics woven from yarns composed of interlaced fibres of all lengths, which lend themselves to milling and raising. In the former case, the characteristics of the fabric structure dependent upon the nature of the weave are largely retained, and even developed, whilst in the latter case the thready appearance of the loom state fabric often gives way to a felted effect in which the individual warp and weft threads are no longer discernible, the change being usually accompanied by an increase in density and a corresponding decrease in width and length of the fabric. In wool goods, "finishing" covers all the processes undergone by the fabric after leaving the loom. There are certain preliminary operations to which the piece is subjected before the finishing process proper, which are intended to correct weaving faults and yarn defects. The pieces are "perched" over a bar or roller usually in a north light and examined by the eye and by hand feeling. "Knotting" consists in removing knots from warp or weft by first drawing these through to the back of the cloth, of ter which they are cut away. "Mending" or "darning" is the process of correcting defects such as holes and missing yarn (short ends and picks) by inserting new threads correctly inter laced in accordance with the weave structure. The finishing proc esses proper divide themselves into the two groups of wet and dry operations.
Crabbing. The object of this process is to "set" the fabric, i.e., to obviate the risk of distortion in subsequent processes. The piece is tightly wound in a stretched condition over a perforated roller, on which allow steam or hot water or both to be forced through the piece. The combined effect of moisture and heat is to render the wool fibre plastic, and in this condition the internal strains in the fabric which might produce cockling in a subsequent wet process are released, and on cooling the fabric assumes a more or less permanent "set." Scouring. This process is intended to remove grease and oil and mechanically adhering dirt from the wool goods. The deter gents used are either soaps or alkalis depending upon the amount and character of the oil present in the wool. Some fabrics are conveniently scoured in the rope-form, whilst others—e.g., those liable to crease, are best scoured in the open width.
Milling. This process makes use of a special property of the \ ove fibre of "felting." The woollen cloth is impregnated with a solution of soap (more rarely of acid) and subjected to pressure between rotating rollers in the milling machine, or by the action of fallers in the stilling stocks. As a result of this action, the fibres become matted or felted if the milling is carried far enough, the warp and weft threads appear to lose their identity, and the woven structure of the cloth is entirely hidden. The cloth often gains strength as a result of milling, whilst the density is increased at the expense of the width and length, the whole fabric being rendered more consistent.
Tentering. After the scouring process, the pieces may be dried by first removing the excess of water by hydro-extracting or by passing through the wringer; and afterwards subjecting to the drying action of warm air whilst stretched out between the lists or edges. In addition to drying the pieces, this operation straight ens and "sets" the cloth.
Carbonizing. Some kinds of wool fabrics, e.g., velours, may be produced from low quality wools containing vegetable matter. This impurity may be removed by soaking the fabric after scour ing in a solution of sulphuric or other acid, drying, and raising to a temperature of about ioo° C, when the vegetable matter is disintegrated and may be removed by a slight beating and air draught.
Cutting. This operation formerly performed by hand with large shears is now carried out on a suitable machine. It consists in removing the pile of the fabric beyond a certain length, this length varying greatly with the class of fabric. For example, worsted cloths are cut close to the surface in order to enhance the effects of weave and colour. Woollen fabrics only receive as a rule a cutting sufficient to level up the projecting fibres.
Blowing consists in subjecting the pieces wound in the open width on a perforated beam to the action of steam. There is some resemblance to the crabbing process already described, and the object is again to "set" the fabric permanently, though other advantages are also usually obtained, such as increase in the lustre of the fabric.
Steaming differs from the blowing process in that the fabric is drawn from one roller to another over a box with perforated top from which steam issues. The object is to raise the fibre somewhat, and thus destroy any glaze, and to soften the feel or handle as a result of the conditioning effect of the steam, i.e., by the absorption of moisture.
Raising. This is a mechanical operation in which fibres are lifted from the yarns in the cloth, or from the surface to pro duce a pile or nap. The raising process was formerly effected by the use of teazles (Dipsacus fullonum) applied by hand; and teazles are still used, mounted on cylinders and operated by power. In addition, cord-wire raising is now largely practised; in this form a number of raising rollers are covered with cord clothing, and revolve against the cloth which is made to pass over them by an independent motion.
Pressing is an important operation in the finishing of wool goods; it may be carried out with the object of smoothing the surface of the fibre and imparting an appearance of uniformity, or by prolonged treatment the lustre of the fabric may be greatly increased. The fabric, charged with a sufficient amount of mois ture, is subjected to the combined action of (usually) heat and hydraulic pressure. Three different systems are used, (a) the vertical hydraulic press, (b) the intermittent hydraulic press, (c) the rotary press.
Shrinking. The tendency of wool garments to contract in wear is well-known. The object of the shrinking process is to bring out this contraction in dimensions before the garment is made up. It is usually effected by thoroughly wetting the material, and redyeing it at a low temperature, after which a mild pressing treat ment is applied to remove creases, etc. There are many names for varieties of this "shrunk finish" ; perhaps the best known being "the London-shrunk finish." Not all the above processes are utilized in finishing a particular class of wool fabric. Worsted cloths in the main undergo the series of operations known as the clear-cut finish. These cloths include fancy vestings and suitings, striped trouserings, costume cloths and dress fabrics, fancy worsteds, etc. A finishing routine for the latter involves knotting and mending, crabbing, scouring. tentering, brushing and steaming, cutting, blowing and pressing.