The goods first pass through a pair of independently driven circular brushes, fixed at the feed end of the machine, to clear them from lint and dirt before being steamed and dried. They next pass between two pairs of nip rolls between which are fixed the steaming and sizing attachments. The goods pass through dry high pressure steam which is confined in a steam chest. They pass into and out of this chest through slots underneath the cover. A trough carries the condensed steam away from the goods and prevents dripping, otherwise they would be spotted.
Fig. 3.—Narrow Fabric Finishing Machine
The steam pressure must be carefully controlled so as to get uniform shrinkage of the goods. The steaming process softens the cotton, and the rubber threads, which are under considerable tension, gradually creep up and contract the goods. The steaming also makes the web more absorbent and thus prepares it for the size bath, through which it is passed under submerged brass rollers. The size is kept at a uniform heat by steam heated copper coils. The web then passes through the second pair of nip rolls, which are worked under pressure so as to squeeze out the size before the web reaches the drying cans.
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.