Fig. 145.—Running Metal from the Blast Furnace to Ladles for Transporting to either the Open Hearth Furnace or the Pig Molder.
169. The Reduction or Blast Furnace.—[Fig. 145]. The reduction or blast furnace is almost universally used for the reduction of iron ore. It is a large barrel-shaped structure, the exterior of which is formed of iron plates about 1⁄2 inch thick, bent and riveted together like the outer shell of a boiler. This is lined with brickwork or masonry, the inner portion being made of fire brick to protect the furnace from the intense heat. Figure [146] shows a sectional view of a furnace of this kind.
Fig. 146.—Sectional View of a Blast Furnace.
The stack D is supported on a cast-iron ring, which rests on iron pillars. The hearth K and the boshes E are beneath the stack and are built independent of it, usually after the stack has been erected. This is done so that the hearth can be repaired or relined whenever it becomes injured. The hearth is also perforated for the introduction of the tuyères t, through which the blast enters the furnace from the blast main B. The opening to the downcomer or pipe leading to the stoves is shown at A.
Figure [147] shows the mechanical arrangement at the top of the furnace, called the bell and hopper, for receiving and admitting the ore flux and fuel. By lowering the bell C the material is allowed to drop into the furnace.
Fig. 147.—Sectional View of the Bell and Hopper.
The fuel, ore, and flux are charged into the furnace at the top in alternate layers, as previously explained; the iron settles down through the boshes, is melted, and drops to the bottom or hearth. The slag is drawn off at the cinder notch c, [Fig. 146], after which the iron is tapped off at the iron notch g. Hollow plates p for water circulation are inserted in the boshes to protect the lining from burning out too rapidly.
The melted iron runs from the tapping notch into a large groove made in sand. This groove is called the “sow.” It is connected with smaller grooves called the “pigs.” Into these the metal runs and forms pig iron. Considerable sand adheres to pigs thus formed, and as the sand is objectionable for foundry, Bessemer, and open-hearth purposes, and as an enormous amount of hand labor is required in breaking up and removing it, pig molding machines are used. Figure [148] shows one of these machines with a ladle pouring the metal into it.