6. Dyeing
Wool and Piece and Double Dyeing
Some yarns are dyed after they have been spun. In most cases, however, woolen yarns receive their color after the wool is scoured and before it goes into the carding machine. In worsted manufacture the common procedure is to dye the top after it has been combed. In this way a uniform color is obtained, whereas it is exceedingly difficult to obtain the same color from two vats in piece-dyeing. Some materials are both wool and piece-dyed, the second dye being given to the cloth. This is done in cases where a peculiarly fast color is desired, or where the cloth contains separate materials such as wool and cotton.
The operation of the loom has already been described in connection with the manufacture of cotton, but the preparatory processes, although somewhat similar, vary considerably because of the difference in the nature of the materials. In worsted manufacture the work which has to be done before the loom can begin to operate is usually referred to as loom-mounting, and consists of five stages.
Warping
1. Warping is the arranging of the warp threads in the order necessary to produce the desired cloth. This was formerly, and still is to a great extent, done entirely by hand on a sort of rack known as the woof. In the larger mills, however, warping is now done either on a sectional warping machine or on the warping mill. Both these devices are only partly automatic, and require highly-skilled labor.
Sizing
2. The mechanical structure of woolen or worsted yarns necessitates the application of some glutinous substance to their surfaces before subjecting them to the weaving process. No matter how even the worsted yarn, a microscopic examination would show certain fibres protruding from the surface. Sizing has the effect of smoothing the surface of the yarn, and at the same time distributing more evenly the strain of weaving. The sizing machine is rather like the back-washer used in the manufacturing of worsted yarn. The warp is run through the sizing bath and then compressed between rollers, after which it is dried by steam or fan.
Beaming
3. Beaming is the term applied to winding the warp upon the beam of the loom. (The beam is the roller from which the warp threads are unwound as the weaving progresses.) In order to keep the threads in their proper position an instrument known as a raddle is employed, and the raddling process is one which requires considerable care.
Drawing in the warp threads
Healding
4. The next step, healding, is the same as that described on page [34] and enables the warp threads to be lifted in sections in order that the shuttle may pass under some and over others. From the original weave of lifting alternate threads, a great many complicated designs have been evolved, which necessitate the lifting of the warp threads in many small series. In the elementary weave where there are only two groups, this work is done by heald-wires which raise the odd and depress the even threads, thus forming a V, known as the shed, through which the shuttle may pass. As the design becomes more intricate the healding process becomes more complicated, and the number of heald shafts increases.
Sleying
5. Sleying, or reeding, is the final preparatory process, and has the object of keeping the warp threads the proper distance apart during weaving. The sley is really nothing more than a fine comb with a strip across the ends of the teeth. The warp threads are passed between the wires (reeds) of the sley and are so compelled to keep their proper position.
Weaving
The sley is attached to the batten, or fly, and as in the cotton loom performs the additional function of driving home each weft thread after the shuttle has passed.
The Power Loom
Once these processes have been completed the remainder is almost entirely automatic. The shuttle flies back and forth without aid. The proper warp threads are raised and lowered to let it pass, and after each traverse, or pick, the batten automatically drives home the weft thread, into the growing stretch of cloth that is winding itself up on to the beam at one end, while the beam at the other end delivers the parallel warp threads. The average worsted loom makes about 100 picks per minute, which is only about half as fast as the calico loom, the reason being the lower tensile strength of the yarn.