The blooms from either the open-hearth or puddling process are treated similarly in what is termed the forge; this includes hammering, rolling, and shingling.
Fig. 151.—Rolling Tool Steel.
Squeezers or hammers are used for forming the bloom and expelling the inclosed slag. The bloom is then put through the largest groove of the roughing rolls and passed back through the next smaller, and so on until it is rolled down to the desired size. Figure [151] shows 14-inch rolls in use which, although somewhat similar to those employed for rolling iron, are larger and generally made with more rolls.
The product of this first rolling is not usually considered of superior quality, so, in order to refine it more thoroughly, the bars are cut up into short lengths, piled into bundles, reheated, and again welded. This process is called shingling and is done two or three times, depending upon the desired quality of iron. This shingling produces the laminæ of the iron referred to in section [60]. For ordinary bar iron the piles are made about 2 feet long by 4 inches square, and for larger sizes they may be made 5 or 6 feet long by 10 or 12 inches square.
The rolls are of various kinds. All shapes and sizes of bar iron used in blacksmithing may be produced in this manner. Rolling machines are known as two, three, and four high, meaning that they are provided with that number of rolls, one above the other. Universal rolling machines have two pairs of rolls in one machine; one pair runs on horizontal axes and the other on vertical axes. Each pair can be opened or closed independently, thus giving the machine a wide range.
181. Steel.—The word “steel” means very little to those who are uninformed as to its different qualities and the causes of the distinctions between them. People are generally familiar with the various purposes for which steel is used, but know very little about its nature. There are, however, great differences in the qualities, and definite reasons for them.
Formerly any combination of iron and carbon that would harden by sudden cooling or quenching was considered steel. But since modern methods of manufacturing have been adopted, tons of metal, which would have been classed as iron if judged by the cooling test, are at present known as mild or soft steel.
Steel may properly be defined as an alloy of iron with carbon, the latter not exceeding 1.8 per cent; the materials are completely fused and poured into molds, allowed to cool, and then rolled into shape. In the processes of making wrought iron the materials are only partly fused and are not cast into molds, but are taken out of the furnace in a soft, pasty condition suitable for immediate working.