Sheet iron (as it is commonly known) is made by rolling sheet-bar into thin sheets, as was stated in Par. 154.

At the sheet mill, the operation of rolling sheets is as follows: The 30-foot sheet-bars are cut into short lengths, heated in a reheating furnace, and run through the rolls sidewise, as the width of the bar is stretched out to form the length of the sheet. Polling stretches metal in the direction of its travel through the rolls and very little if at all in the direction of the axes of the rolls, hence bars are cut into lengths but slightly longer than the width of the sheets to be rolled from them. A mill similar to that for rolling sheet brass and sheet copper is used for this work.

After about the first five passes through the roughing rolls the bar has stretched out greatly, is very thin, and wobbly while hot, hence, for easy handling it is folded double, and two thicknesses of metal pass through the rolls at once. The sheets are not hot enough to weld, and their scale keeps them from sticking together. This doubling is called "matching." This doubled sheet is then reheated with three other matches, and all are given one pass through the smoothing rolls together, thus making six thicknesses of metal in one pass. These six sheets are allowed to cool and are then sheared along the ends and the edges, after which they are "opened" or taken apart.

The sheets then go to the cold rolls through which they are passed singly one or more times to give density and smoothness, after which they are piled about one hundred in a pile for annealing. Fig. 58 shows a heavy tray C on which sheets are piled for annealing. The cover T is placed over the pile and sand is placed all around the lower edge of the cover to exclude air. The cover and tray are lined with fire bricks and suitable lugs are fitted for handling by the crane.

Fig. 58. - Annealing Tray for Sheet Iron.

Annealing requires about 12 hours. When cold, the cover is lifted and the sheets are stripped apart by hand. After inspection, they may be bundled for market as "dead soft" sheets, or may be sent to other departments to be corrugated, tinned, galvanized or planished.

If hard sheets are required they are selected from the cold rolled stock before annealing.