The open hearth furnace consists of a big brick room with a low arched roof. It is charged with pig iron and scrap through doors in the side walls.
FIG. 1.—A typical Bessemer converter.
Through openings at one end of the furnace come hot air and gas, which burn in the furnace, producing sufficient heat to melt the charge and refine it of its impurities. Lime and other nonmetallic substances are put in the furnace. These melt, forming a "slag" which floats on the metal and aids materially in the refining operations.
In the bessemer process air is forced through the metal. In the open-hearth furnace the metal is protected from the flaming gases by a slag covering. Therefore it is reasonable to suppose that the final product will not contain so much gas.
FIG. 2.—Action of Bessemer converter.
FIG. 3.—Regenerative open hearth furnace.