When an ingot has reached the temperature for rolling, it is lifted from the pit and carried by the crane to the ingot buggy, where it rests until a lever is released to dump it on the roller table. The greater the reduction in size to be made in the ingot, the hotter it needs to be, because of the longer time required for rolling. It is best, when possible, to roll the ingot to the finished shape in a single heat, as a second heating adds to the cost of the finished materials. An ingot, for example, may be rolled into a length of five railroad rails of 33 feet each, making 165 feet in one piece, and this length could not be reheated without cutting it into pieces and much handling.

Fig. 40 shows the first stages in the process of rolling a large ingot. The mill in this view is known as a reversible blooming mill. This mill has too heavy rolls, the upper of which is shown at E. These rolls revolve in opposite directions and are driven by a large reversible engine or by a motor. The function of a blooming mill is usually merely to reduce the cross section of the ingot to a convenient size for finishing in smaller rolls to the exact cross section desired. The ingot A rests on the ingot buggy B, awaiting the breaking down of the ingot C.

The roller table consists of a succession of horizontal rollers TT driven in unison by the cogged bevel wheels DD from a single shaft running the length of the table. This table extends out from both sides of the mill, and conveys the ingot back and forth into contact with the mill rolls, which engage it and send it through, reducing its vertical dimension a given amount at each pass. When the ingot has passed through the rolls, it is turned on its side by a device called the manipulator. The motion of the table rollers and of the mill rolls is then reversed, and the ingot passes back between the rolls. After each pass, the upper roll, R, is let down a given amount by heavy screws which control its ends in the mill housings, and which are operated by the mechanism seen on top of the mill, under control of the man in charge. The roller table is driven by a reversible motor G.

After a few passes through the rolls, the ingot - or bloom, as it may now be called - is conveyed along the roller table to a heavy hydraulic-shearing machine which cuts off the discard from the bloom. The hydraulic shears are so mounted that the roller table conveys material to and from them in the same way that it is conveyed to the rolls, and these shears are powerful enough to do their work instantly, without loss of time.

After the crop ends are sheared off, the bloom, still red hot, is conveyed back to the mill. Its passage back and forth between the rolls is repeated, and it is shifted by the manipulator from side to side of the roller table to direct it into the different sections or passes along the rolls until it is reduced to the size desired. It is then either cut into bloom length of 6 feet, more or less, by the hydraulic shears, or is conveyed by the roller table to another mill which rolls it in one length into railroad rails or other shapes of about the same cross-sectional area. However, a blooming mill may be fitted with rolls not only to do the work of breaking ingots down into blooms, but to do certain classes of finishing, as in rolling large billets or large structural shapes.

Fig. 40. - Starting an Ingot through the Blooming Rolls.

Throughout the rolling, the material is at a red heat.