Engineering Wonders of the World
Volume III

REMARKABLE MACHINERY. 265 The Open Hearth Process. Bessemer’s steel converter. A, vertical section through trunnions; B, plan of bottom; C, section of tuyére; D, plan of do., showing air-holes. The second important steel-making process is the open hearth, introduced several years after the Bessemer. Its name signifies that the steel is pro- duced in a furnace, the metal bath of which is exposed to heated gases. To produce the high tem- perature—3,000°Fahrenheit—required, the furnaces are made regenerative— that is, the burnt gas is led, on its way to the chimney, through brick- work stoves which heat the fresh air and gas entering the furnace. There are two stoves—one for air, and one for gas—at each end of the furnace, and the two sets are brought into use alternately by the operation of valves. Within certain limits each reversal produces an increase in the temperature of the gases burning in the hearth. The usual temperature of the stoves at the finish is about 1,800° Fahrenheit. The ordinary type of open hearth furnace is stationary, built up of brick, strengthened, where necessary; with metal-work. To draw off the molten metal, a hole is knocked in the bottom at one side, and the charge is run off through a spout into a large ladle. The hole is then plugged with refractory material pre- paratory to introducing a fresh charge. This type has little interest for the engineer. For special purposes, however, the furnace is made to roll or tilt, so that the metal may be poured out as required. These tilting furnaces, which are constructed to hold up to 250 tons of molten steel—and, in a modi- fied form as metal-mixers, up to 750 tons— are fine examples of the mechanical engineer’s skill in overcoming difficulties caused by great weight and heat. Such a furnace consists of a large rec- tangular steel casing reinforced with heavy steel girders and lined with refractory brickwork. It is _ 1 in^ Furnaces, mounted upon rockers or rollers, whichever may be more suitable, and at each end has openings by which the gases DIAGRAMMATIC SECTION OF AN OPEN HEARTH REGENERATIVE FURNACE. A. A', stores for air ; G, G', stoves for gas. Air enters by passages 1 and 3 alternately; gas through passages 2 and 4 alternately. pass in and out, and movable burners which can be drawn back to allow the furnace body to roll easily. Doors are fitted at one side for introducing metal—either molten or in the “ pig ” state—steel scrap, and limestone ; at the other is a spout through which the finished steel can be poured, in any quantity desired, by tilting the furnace body. Tilting is usually effected by hydraulic cylinders ; in some cases electrical power is used. The doors and port-