4. Converting and Finishing
Old-Fashioned Bleaching
Cotton cloth as it comes from the loom has a gray or yellowish appearance due to the impurities it contains. The old-fashioned method of removing these consists in simply spreading the cloth in the sun for a few days until it is bleached white. Most cloth mills dispose of their goods in the gray and allow the finishing to be done by a separate establishment, although the large manufacturers of “fancies” sometimes do their own finishing.
Sewing Together
The first step in the finishing plant is to inspect the cloth and then to sew the ends of many pieces together into long strips. This greatly facilitates subsequent operations, because the cloth can now be run through various processes as a single unit.
Brushing
In order to obtain a smooth surface for later processes, the cloth is first run through a machine which brushes up the fibres and loose ends, much as a carpet-sweeper picks up the fibres of a carpet. Sometimes a bladed roller like a lawn-mower is used.
Singeing
Removing the raised lint is a dangerous operation because it might easily damage the cloth, and this is usually done by the process of singeing. The cloth is run rapidly through gas flames or over hot plates and is quickly cooled. In this way the fuzz is burned off without injuring the cloth.
Inspecting
Sewing Ends Together
Napping
The next step is usually the bleaching process, except where the cloth is to be finished as a corduroy, velvet, or flannel. In the latter case it is first run through the napper, a machine which brushes up the fibre with wire teeth in such a way as to leave a raised face or nap.
Singeing
Bleaching Process
Bleaching is accomplished by boiling the cloth for several hours in large iron tanks known as kiers, which contain a solution of caustic soda. Next it is washed and scoured in dilute acid for several hours with the object of removing iron stains. Then it is again washed, boiled a second time, washed, run through a chemical solution of bleaching powder, and allowed to steep. After a last washing the cloth is dried by running over copper drums filled with steam, and is then rolled up in bundles about the size of a barrel.
White Goods
If the cloth is to be finished as plain white goods it is next starched and ironed (calendared), inspected, and put up in bolts for shipment.
Mercerization
If, however, it is desired either to dye or print the cloth with various colors and designs, it still has several treatments to pass through. White goods are sometimes mercerized, but more commonly this process is employed with cloth that is to be dyed. Mercerization is the treating of cotton yarn or cloth to the action of caustic soda dissolved in water, the remaining soda being removed by a wash of dilute sulphuric acid. The result is an increased strength of fibre, loss of elasticity, silky appearance, and an affinity for certain dyes and mordants.
Napping
Dyeing
The subject of dyeing is one of intense interest and wide scope, but it is unfortunately beyond the field of this brief survey. Suffice it to say that various chemical processes and mechanical devices are employed to give a permanent color to the cloth. (Yarn and raw stock dyeing are less commonly employed in the cotton than in the woolen and worsted industries.)
Resist and Discharge Printing
Some cotton cloth is simply dyed with a solid color and finished, but frequently it is first dyed with one color and then printed with others, or with a chemical which will discharge the dye and leave white figures wherever it touches the cloth. In contrast to this discharge method, where it is desired to obtain white figures on a colored back-ground, it is also possible first to print the figures with a chemical that will resist the subsequent action of the dye-stuff. Where a white ground is used and it is not essential that the colors and design appear on both sides of the cloth it is not necessary to dye at all.
Bleaching Kiers
Printing Process
The printing process is a very old one, and was employed centuries ago in China and India, where natives used to impregnate cloth with colored designs by pounding small wooden blocks carved and filled with color on its surface. The modern printing machine has a series of copper rollers in which the design to be printed is etched or sunk. Under each roller where it is fixed in the printing press is a trough filled with the particular coloring matter which that roller is to print on the cloth. As the mechanism revolves the roller is constantly supplied with new color, which is scraped off its surface except where the sunken design holds it, by a knife, called the doctor. If the design calls for six colors there will be six rollers at work, and so on up to fourteen colors at a single run through the press.
Engraving
An infinite number of designs are printed, and the method of getting them etched on the copper roller is a fascinating one. A zinc plate is carved by hand on a greatly enlarged scale from the original sketch, and from this plate the girls who operate the pantograph machines transfer the outlines of each color on to the copper rollers.
Printing Machine
The Pantograph
When the roller is placed in the pantograph it is coated with varnish. As the girl traces the outlines of the design on her zinc plate with a little pointer, she presses a treddle which brings a number of little diamond points in contact with the roller. Each one of these points cuts through the varnish, reproducing the design in its original size. There will be as many points as the number of times the design is repeated across the roller. When the roller is finished it is given a bath in nitric acid which will eat into the copper where the varnish has been cut away, thus sinking the design so that it will hold color.
A Battery of Forty-eight
Aging and Washing
There remain now only the finishing operations before the cloth is ready to be packed for the market. Usually, after printing, the cloth is steamed, or aged, to make the colors fast. Then it is fixed and soaped thoroughly, after which it is run through the drier.
Starching
The Tenter
In order to give the cloth the proper “feel” an operation is next performed which closely resembles warp sizing. A certain amount of hot starch is pressed into the cloth, after which it is drawn through the tenter frames and not only dried but stretched back to its normal width. The tenter frame is about one hundred feet long and contains long lines of steam pipes. On each side an endless chain with clips grips the cloth and moving gradually further apart, these chains stretch the cloth, delivering it dry and of even width. (Some goods, notably those made for Asiatic consumption in England, are not only starched but filled with China clay, which adds over 100% to their weight.)
Engraving Plate
As it comes off the tenter the cloth goes through steel rollers and is pressed smooth, after which it is automatically folded and made ready for ticketing and packing.