Allowance for Contraction
The first of the dry cans is usually covered with cloth, so as to absorb any size which may remain on the surface of the goods and allow it to penetrate by further softening. As the goods continue to pass over the hot cans a gradual process of contraction takes place. This contraction is provided for by a corresponding regulation of the speed of the cans. Intermediate expansion pulleys are provided for this purpose, so that the speed adjustments can readily be made to meet the requirements of different kinds of web.
The two pairs of front rubber nip rolls are likewise independently driven, so as to provide for the shrinkage which takes place at the steam box and size bath. At the delivery end of the machine the goods pass through a set of nip rolls which are belt-driven from cone pulleys, so as to be able to deliver the goods at the speed they leave the last drying cans. From these last nip rolls, which are fixed quite high, they drop into receiving cans or boxes.
Ten to twenty-five strips running side by side are finished at one time. Adjustable guides are provided at different places on the machines to keep the goods running in proper position. The speed of the machine is usually governed by a Reeves transmission, and the delivery of the goods ranges from 10 to 15 yards per minute, according to the requirements of finishing. Three inches per yard is generally allowed for shrinkage, but this again is determined by the goods. Neglect at any point in this process may so interfere with the calculated shrinkage that values and costs are materially changed.
New patterns and grades should be tested for shrinkage as soon as the goods come from the loom, as short lengths made in sample looms are not at all times reliable. Frequent tests are also advisable to see that original conditions are maintained, as changes made by heat, steam and speed are always liable to occur.
The immersing process is used mostly for single cloth garter webs. Double cloth webs having a warp pile on the face are sized on the back only. Exceptions are made on double cloth white webs used for the corset trade, which are bathed with a very light size and often tinted in this bathing process to the desired tone of white to match the cloths they are to be associated with. Where the goods are sized on the back only the effect of this has to be considered when they are constructed, and provision made to maintain a proper balance under such conditions.
In frilled webs the elastic portion only is sized, so as not to interfere in any way with the soft flutings of the frill. This is done by guiding each strip over narrow pulleys which are run through the size bath. The size accumulated on these pulleys is absorbed by the web passing over them.