The hearth of the furnace (1) is made circular, or, preferably, elliptical. The lining of the hearth conforms to the shape of the shell.
The single flues in natural-gas furnaces at either end of the melting chamber are 5 ft. wide, and are simply large passages inclined down toward the bath at a pitch of about 4 in. to the foot. to give the flame a strong guide downward upon the metal. In order to provide a firm support for the arched roofs of the melting chamber and flues leading into it, a water bosh, made of fin...thick steel plate, is put in the form of a keystone in the arch of each roof. Natural gas is led into the sloping flues by wrought-iron pipes (10-17), and being much lighter than the air, mixes with it in its downward rush into the furnace. The stack (21) is placed in such a manner that the flues leading from each end of the hearth which have checker-work in them, alternately act as regenerators to preheat the air before it enters the furnace. The lower end of the stack is connected by a short flue (24) with a four way chamber (25), to which the flues from each end of the furnaca converge, and to which the air duct (26) delivers. This air duct (26) leads out from the ladle pit (27), and passes directly under the hearth. in this way not only heating the air, but giving a free cir culation under the hearth. and preventing an excessive heating of the bottom. Along the mid dle of the flues leading from the central four-way chamber (25) to the opposite ends of the furnace, is placed checker-work of lire-brick, supported on tiles (28), so that the bottoms of the flues are clear openings, giving a stronger draught ; but as there is constant tend ency of the heated air to ascend, there is a thoroughly uniform heating of the air entering the furnace by this arrangement. The front portions of the flues arc provided with a series of double arches. The four-way chamber (45) has the air duct (26) leading into it permanently open. and is fitted with a three-way valve (33), alternately connecting the flues lead ing to each end of the furnace with the chimney (21) and with the air chamber (25), in this way reversing the furnace on the well-known Siemens principle. This three-way valve (33) is hollow, and is kept cold by a stream of water running through it, preventing the warp ing or burning out of the valve, or with the Siemens gas furnace, the direct loss of fuel by leakage to the chimney. The tap-hole of the melting furnace is at about the ground level, and the metal is conducted, through an inclined spout some 10 ft. in length.
to the ladle pit Pi). The Lash furnaces have all the ordinary and important operations around the furnace on One ground level, the three doors on the back side of the furnace and the two on the front or tapping side being accessible for charging or for repairs to the furnace. A record of 5110 consecutive heats, of 50.000 lbs. of stock each, shows that these were charged in an average of 24 minutes per charge, 12 men, or all hands about the furnace, doing the charging from all five doors, which are balanced and arranged to open by levers in the pulpit under the control of the crane boy.
71e Rath() Furnace is represented in Pigs. 4 to 7. It consists of five separate wrought-iron cases, all on one level, lin ed with fire-brick, which form the outside walls of the four regener ators and of the melting chamber. The regener ators are connected to the melting chamber over head bynicansof wrought iron pipes, running almost horizontally, which are lined with refractory ma terial. The melting ves sel is lined with basic ma terial and covered with a roof of silica brick, en closed in a strong skew back ring of iron. The gas ports are in the side walls of the melting chamber and the air is carried in through a port in the roof directly over the gas entrance, the air port having a very steep pitch into the furnace of at least 8 in. in every foot. This arrangement guides the flame downward right on the hearth, and does away with much of the sharp cutting action of the flame on the roof, which thus has to stand the reflected and radiated heat only. The basic lining is separated from the acid by to in. only of neutral material in the form of bon brick or chrome ore. The upper 18 in. of the lining walls of the melting chamber are of silica brick. The Batho furnace is well adapted for the basic process on account of the facility of getting at • and replacing the linings. (See " Recent Improvements in Open hearth Steel Furnaces," by A. E. Hunt, Trans. Am. Inst. Mining Engrs., Vol. XVI ) Practice in F. Lynwood Garrison, in his report on the metallurgical arts, at the Paris Exhibition (Journal of Franklin Institute, 1890), says : Since the time of the introduction by Messrs. Martin of the new process in the Sireuil works, the size of the open-hearth furnace has always been increasing. Instead of the 3 to 4-ton furnaces first used, 10-ton furnaces, 20-ton furnaces, and even, as in some steel works of the Loire district, 35-ton furnaces can now be found.