A rolling mill in its simplest form consists of a pair of rolls (never called rollers in the iron and steel industry) mounted one above the other in a strong framework. Their surfaces may be flat, for rolling strip, plates or sheets; or they may have grooves cut in them to shape the iron or steel into, say, a round bar, railway rail or girder. Only a limited amount of shaping can be done in a single passage through the rolls; the metal must be passed through several times. This was done by men with tongs holding the red-hot metal, hard but skilled work. With the Bessemer and Siemens processes steel could be made not only quicker but in bigger individual pieces. Molten steel was cast into rectangular blocks, or ingots, which were rolled to the required shape. As ingots became bigger, men could not handle them and machinery had to take over.
Sir John Alleyne, of Butterley in Derbyshire, patented a mechanical device for moving ingots in 1861. He also devised a rolling mill which could rotate the rolls in either direction, enabling the metal to be passed back and forth, some rolling being carried out at each movement, until it was of the required size and shape. These two devices saved time and took over work which was too heavy for men to do. Alleyne’s mill was improved upon by John Ramsbottom, of Crewe railway works, who made the first really successful reversing mill in 1866 by coupling the engine of a railway locomotive to a rolling mill. A railway engine, of course, has to be capable of running in either direction, so it could just as easily rotate the rolls either way; all the man in charge had to do was to pull a lever.
These inventions were the basis on which many modern rolling mills operate today. There were several other changes in steel rolling, some of them matters of detail, but all adding up to a general improvement. One development, however, was a completely new idea. This was the continuous rolling mill invented by George Bedson, of Manchester, in 1862. Bedson built a mill, for rolling small iron rods for making into wire, with sets of rolls in a long straight line, so that the metal being rolled came out of one pair of rolls, passed immediately to the next pair and so on down the line until the finished size and shape were achieved. It saved time, needed fewer men and made a better product. The first Bedson mill had sixteen pairs of rolls so the metal was rolled sixteen times before it came to the end of the line. Later mills had even more pairs of rolls and could produce rods at very high speed. The principle was adapted to roll other steel products besides rods, and it is the basis of many modern mills.
By the end of the nineteenth century iron- and steelmaking were very much more mechanized, but the source of power was still steam. Electricity had appeared in the iron- and steelworks, but at first only for lighting: some works had electric light in the 1880s. Today it is the source of power in every works and the steam engines survive only in museums.
Electricity is also used today in steelworks as a direct source of heat, and its beginnings for this purpose go back a long way. If an electric arc is struck very intense heat is generated; Siemens suggested that it could be used for steelmaking in 1878, but nothing came of it at the time. Nor was there much interest in the arc furnace designed by the Frenchman Paul Héroult in 1886, though he used it himself for making aluminium (see p. 109), and in 1900 actually made steel in it. The electric furnace was ahead of its time, and it was a national emergency which really started it going. In the First World War, munition manufacture produced quite large quantities of small shreds and scraps of metal called swarf, which was very valuable raw material for steelmaking if it could be melted. Neither the Bessemer converter nor the Siemens open-hearth furnace would do this adequately, but the electric furnace would.
Alloy Steels
