Care Required in Finishing
The finishing of elastic fabrics is a process which demands great care, and has to be taken into calculation from the beginning of the web construction. Calculations must always be made as to what effect heat, moisture and sizing will have upon the covered up elastic threads, confined as they are in a multiple of small cavities and under high tension. As soon as the softening influence of heat and steam operate upon the covering of cotton yarn which confines these threads, the rubber strands begin to assert themselves and contraction at once takes place. To what extent this can go must be predetermined in fixing values, and a certain degree of uniformity of contraction arranged for.
Webs which are perfectly flat and straight when taken from the looms are liable to be transformed into unshapely products and completely ruined by unsuitable finishing. For instance, take a web with a twill center and a plain border which is apparently flat and satisfactory at the loom. The effect of heat and steam upon such a web will be to contract the soft woven center more than the harder woven plain border, which will cause the web to be long-sided and curl. Such a condition must be anticipated in the construction of the web and provision made to offset its occurrence. Sometimes it must be met by a change in the size of some of the yarns used, or number of threads employed at given points, or perhaps added gut threads must be introduced to stop contraction in certain places. It must always be remembered that we are dealing with a very much alive element when we are finishing rubber goods, and that unexpected results may at any time arise.