Reheating furnaces are of many forms according to the fuel used, the size and shape of the material to be reheated, and the rapidity demanded in handling the heated material. The largest types of reheating furnaces are those used for heating armor and other large ingots to be shaped under the hydraulic forging press. These furnaces are heated usually by the regenerative system. The smallest types are possibly the small portable oil-burning furnaces for heating rivets, and used also for heating small material to be forged. The fuels used are long-flame coal, crude oil, or gas, and usually a smoke stack is necessary to take away the products of combustion, but many oil and gas furnaces have no smoke stacks. The reverbera-tory type of furnace, with end or side door in the fuel space, and end or side doors in the heating space, according to the convenience of each specific case, is much used for reheating.

Fig. 50. - Furnace for Reheating Billets.

Fig. 50 shows a small furnace for reheating billets. This is equipped for burning oil and has a door at each end. The flame from the oil burner (at the side) is directed into the heating space through a hole in the furnace wall.

Fig. 51. -Regenerative Reheating Furnace and Charging Crane.

A reheating-furnace bottom is usually a flat magnesite bottom, sloping slightly to one side. The soaking-pit is a reheating furnace, but it is adapted only to ingots, which can stand on end.

The continuous furnace is a type much used. This is equipped with a gravity slide or suitable mechanism for moving a continuous line of material through the furnace in a given time, and the heating is accomplished while the material is passing through.