OPEN-HEARTH METHOD
In the open-hearth method the metal from the blast-furnaces is not sent to the converter, but is poured into oven-like structures built of fire brick, and in these heated to a terrific temperature. This heat has the same effect upon the metal as the blast of air in the Bessemer converter, and this open-hearth process has become very popular for manufacturing certain kinds of steel. While in the method of application this process differs greatly from that of Bessemer, it differs largely in the fact that the oxygen necessary to burn off the carbonic oxide, silicon, etc., is made to play over the molten mass instead of passing through it.
It has been noted that the old type of blast-furnace gave off great quantities of combustible gases which became waste products. Even gases containing something like 20 or 25 per cent. of carbonic acid may be highly inflammable, and thus an enormous quantity of valuable fuel was constantly wasted. In some furnaces, to be sure, they were put to practical use for heating the blast, but as the quantities given off were greatly in excess of the amount necessary for this purpose, there was a constant loss even with such furnaces.
Quite recently it has been found that the gases can be used directly in gas engines, developing three or four times as much energy in this way as if they were used as fuel under ordinary steam boilers. These engines are now used for operating the rolling-mill machinery, and the machinery of shops adjoining the furnaces, which, however, must not be situated at any very great distances from the furnaces. This accounts partly for the grouping together of blast-furnaces, rolling mills, and machine shops, the economical feature of this arrangement being so great that segregated establishments find it next to impossible to compete in the open market with such "communities" under the conditions prevailing in the steel industry.