The basic materials used for the manufacture of pig iron are iron ore, coal coke, and limestone. A typical blast furnace consists of a cylindrical steel shell lined with a nonmetallic substance such as firebrick. The molten pig iron flows out through a hole near the bottom when the furnace is tapped. Above this hole, but below the tuyeres, is another hole for draining the slag. The top contains vents for the escaping gases.
Blast furnaces operate continuously.
The iron itself is drawn off or tapped about five times a day. The air used to supply the blast in a blast furnace is preheated. Although almost all the iron and steel manufactured in the world is produced by blast furnaces, other methods have been practiced to a limited extent. The so-called direct method produces iron and steel from iron ore and coke mixed in a revolving kiln and heated. The kiln produces so-called sponge iron of much higher purity than pig iron.