Forging vs. Rolling
Though we have not yet considered the rolling mill or its products, we understand that, in general, only products of regular and uniform cross-section and of considerable length can conveniently be rolled. Where they can be obtained of satisfactory shape and size, steel products formed by the rolling process are highly desirable and are usually cheaper than those which are produced by the forging process. Compared with those made by the rolling process, forged products are usually quite costly in labor and time.
Rolling mills, however, cost immensely more to build and equip than do plants installing even the steam hammering outfit, so the rolling process cannot pay except for such articles as are demanded in great quantities. Articles of irregular and odd shape must, of course, be forged and here, especially for very small articles, the drop-forging process is available and highly satisfactory where enough pieces of one kind and size are wanted to pay for the requisite dies.
Forged articles have another advantage which we should not overlook. The physical properties which are imparted during forging are somewhat superior to those which the rolls bestow. The physical properties shown by the latter are very satisfactory, however.
CHAPTER XVII
THE ROLLING PROCESS
Early Rolls
After invention of the puddling furnace with its rather large yield from the standpoint of those days, Cort about 1783 found the hammering method unsatisfactory for his purposes and rolls were devised by him to facilitate working of the larger balls of iron which his furnace produced.
His rolls were provided with a series of grooves which systematically reduced the balls of iron to pieces of longer and longer length and proportionally decreasing diameters. They were power driven and served very well as long as iron and steel were made in quantities no larger than those which were produced in the puddling and crucible furnaces.
Quite naturally there was little or no change in the essentials of rolling mill design until it was forced by the invention of the Bessemer steel-making process. With that occurrence trouble began. The open-hearth process followed, and, with the increasingly large steel outputs of mills using these processes, necessity after necessity developed which resulted in the highly developed rolling mills of to-day.
