Pig and scrap iron for castings are generally melted in a cupola, although a reverberatory furnace may be used. Fig. 133 shows a typical cupola in cross-section. A cast-iron or cast-steel base ring B is supported about 3 feet from the ground by four iron posts C. This ring carries a shell D of steel plates lined inside with refractory bricks. The top of the cupola acts as a chimney, although the two or more cupolas necessary in a foundry may lead into a common chimney.

Under the base ring are hinged two iron doors, FF, held up by an iron prop when the cupola is in use. About 12 inches above the sand bed is the slag hole, and about 8 inches further up are the tuyere holes. The tuyeres are merely pieces of iron pipe extending through the cupola shell and brick lining. The tuyere holes are encircled by the blast or wind box which receives ordinary air at a low pressure from a blower and delivers it through the tuyeres when the cupola is in operation. The blast box has a small mica peep door opposite each tuyere to enable the melter to see the surface of the molten iron. The cupola is charged from the charging platform through the charging door about 9 feet above the bottom. The lining bricks are supported at intervals by angle iron lining-shelves as shown.

Cast iron melts at about 2200° F. If the cupola blower breaks down, a jet of steam in the base of the cupola chimney will induce a draft sufficient at least for slow melting.