There are 16 bottom electrodes of steel. The 12-ton furnace uses from 1,000 to 1,200 kw., supplied by a 25-cycle current at 70 to 75 volts.

The interior of the hearth of the 12-ton furnace is 4 feet square at the bottom, widening out to 10 feet at the top. The silica brick roof is set 3 feet 9 inches above the hearth of dolomite. The bottom is tamped in to a depth of 20 inches.

The furnace, with the exception that there are three charging doors at the rear instead of one, is similar to the single-phase 2.5-ton furnace. The four electrode holders are set two on a side, arranged as in the smaller furnaces.

The metallic parts of a 10 to 12.5 ton three-phase Girod furnace, including regulators for the electrodes, measuring instruments, tilting mechanism, and conductors from the furnace to a dynamo or transformer near the furnace room, but not transforming or generating machinery and license fee, cost about $6,000. A plant with one 12-ton furnace in reserve, including building, but without dynamo or transformer, is estimated to cost, license fee excluded, about $60,000 to $100,000.

THE STASSANO FURNACE.

The Stassano a electric steel furnace differs from other electric steel furnaces in that the electrical current does not pass through the metal or slag. All heating is by radiation from three horizontal arcs. The power consumption of the Stassano furnace is somewhat higher than that of some others, so that its use is limited to furnaces having a capacity of not more than 2 tons for making highgrade small steel castings. At present there are 16 Stassano furnaces in operation in sizes up to 2 tons capacity and one is in course of construction.

The Stassano furnace (figs. 19 and 20) has a circular hearth with a cylindrical melting chamber above. In the 1-ton furnace (figs. 19 and 20) the hearth is about 3 feet in diameter, with the roof 3 feet 6 inches above it. The furnace is incased in a steel shell with one door opposite the pouring spout. There are also openings for the three electrodes which project toward the center of the melting chamber. The movement of each electrode is controlled by a hydraulic piston. The source of power is connected by a rod with the end of each electrode, each of which is connected to a phase of a three-phase system. Each electrode holder and electrode are surrounded by a water jacket. In the 2-ton furnace carbon electrodes 3 inches in diameter and 4 or 5 feet long are used. The lining of the hearth is dolomite and tar, but the roof and sides are magnesite

a Stassano, E., The application of the electric furnace to siderurgy: Trans. Am. Electrochem. Soc., vol. 15, 1909, p. 63.

brick. The external dimensions of the 1-ton furnace are about 10 feet by 8 feet; the 2-ton furnace is 10 feet high and 10 feet in diameter. The early type of Stassano furnace had a chamber beneath it (fig. 19) which contained a rotating mechanism for agitating the steel bath. This feature has not proved of great value, and is now abandoned in the more recent furnaces, which, like the Girod furnace, are set on rollers. Some furnaces recently erected at Newcastle. on Tyne, England, by the Electroflex Steel Co. have a combination of the rotating and tilting motion.

A 1-ton Stassano furnace requires 200 kw. supplied by a 3-phase at 110 volts, having a frequency of 25 cycles. A 2-ton furnace uses about 400 kw. at 120 volts.

a

THE KELLER FURNACE.

The Keller furnace (fig. 23) is very similar to the Girod furnace, as it has a conducting hearth of iron rods embedded in a refractory material. This type of furnace was the first to be used as a superrefining agent for steel that had been made by the old-established methods. There are in Europe three Keller furnaces, the capacities of which are 1 to 8 tons.

The Keller furnace consists of a conducting hearth surrounded by a steel water jacket, with a silica brick roof. The conducting hearth consists of iron bars 1 to 1 inches diameter, set vertically 1 inch apart in an iron plate. These bars are surrounded by a mixture of magnesite and tar rammed in while hot. The bars are good conductors of electricity when the furnace is cold, and the magnesite also becomes a conductor when hot. The small furnaces have one carbon electrode and the larger ones have four electrodes. In both types the connections are similar to those of the Girod furnace. A feature of the Keller furnace plant, devised before the day of continuous feeding of electrodes, is the revolving arms, with extra electrodes for quick charging (fig. 23). An 8-ton Keller furnace is operated with 750 kw.

THE GRÖNWALL FURNACE.

In general external appearance the Grönwall or Electro-Metals furnace (figs. 24 and 25) resembles the single-phase Héroult furnace. However, it uses two-phase current and has a conducting hearth. A noteworthy feature of this design is the steadiness of the load on the power line when cold scrap is worked, as the arcs are not connected in series. There are four Grönwall furnaces in operation.

a Keller, C. A., A contribution to the study of electric furnaces as applied to the manufacture of iron and steel: Trans. Am. Electrochem. Soc., vol. 15, 1909, p. 87.

Robertson, T. D., The Grönwall steel refining furnace: Metall. Chem. Eng., vol. 9, 1911, p. 573,

The current may be directly supplied as two-phase or transformed from three-phase to two-phase by the Scott connection of transformers. In the Electro-Metals furnace at Sheffield there are two 12-inch carbon electrodes projecting into the furnace through the roof, each of which is connected to a phase, the conducting hearth forming the neutral of the system. This conducting hearth consists of carbon paste rammed on the steel bottom of the furnace to a depth of 4 inches, over which is placed a mixture of dolomite and tar to a depth of 10 inches. In figures 24 and 25 the neutral point is a carbon block, but, as stated above, this has been recently changed at the Sheffield furnace. By this connection half of the power goes through one electrode and half through the other, each being independent of the other.

The furnace proper is rectangular in shape, like the Héroult furnace, the exterior being 6 feet 6 inches wide by 8 feet 10 inches long by 4 feet 11 inches high. There are two doors at the sides and pouring spout, with the electrode holders, at the rear. The holders are of manganese steel, held tightly around the electrodes by wedges. At first, as shown in figure 25, current was led to the electrodes through these holders, but at present the electrodes are electrically connected with cables and two copper plates, inch thick and 6 inches wide, shaped so as to pass around the electrode. The furnace is tilted by hand by means of a screw device. Electrodes are adjusted by hand, although there is no technical reason why an automatic regulator should not be used. The lining of the sides is magnesite brick and the roof is silica brick. The use of water jackets around the electrodes has been discontinued. As now operated there is no water cooling of any part of the furnace. The furnace is set upon a concrete foundation, being tilted on the usual curved bars. The power required is 500 kw., the frequency of the current being 25 cycles; the voltage of the two carbon electrodes is 105, while between each electrode and the neutral point, the hearth, the voltage is about 75.

THE NATHUSIUS FURNACE.

The Nathusius a furnace (fig. 26) is three-phase and combines heating from above by arcs with resistance heating from below in the steel bath for the purpose of decreasing local heating by the arcs. The furnace is circular in form and is incased in a steel shell. There are three water-cooled carbon electrodes which project through the roof into the furnace above the surface of the charge, and three or a multiple of three water-cooled bottom electrodes of mild steel set in the hearth. Both upper and lower electrodes are arranged in a

a

Nathusius, H., The refining of steel in the Nathusius electric furnace: Jour. Iron and Steel Inst., vol. 85, 1912, No. 1, p. 51.

triangle (p. 76). The electric connections are shown in figure 26. The electrodes are suspended by cables from overhead runways and are adjusted either automatically or by hand. On tilting, these electrodes are raised out of the furnace. The tilting mechanism is operated by an electric motor. Furnaces under 6-ton capacity are on trunnions, but with the larger sizes rollers are used. The 5-ton furnace at Friedenshütte, Germany, is normally operated with about 600 kw. Sixty-cycle current is used. The voltage between the upper electrodes is 110 volts, between the lower electrodes 10 volts, and between the upper and lower electrodes 61 volts. In addition to this 5-ton furnace the same company operates a 2 to 3 ton furnace for melting ferro-alloys.

OTHER ELECTRIC STEEL FURNACES OF THE ARC TYPE.

Several other types of arc furnaces which have no especially novel feature are in operation at the plants where they were originally designed. The Chaplet furnace, used for the manufacture of ferroalloys, the direct production of steel from ores and scrap, is similar in principle to the Héroult furnace, but has two separate chambers with an electrode in each. Four Chaplet furnaces are in operation in France. The Anderson furnace is also similar to the Héroult furnace, but has an electromagnet beneath it for the purpose of controlling the position of the arc. Five Anderson furnaces have been built in England. The Stobie two-phase furnace is very similar to the Grönwall furnace. There has also been designed a Stobie threephase furnace. Four Stobie furnaces are being built at Newcastle, England. One three-phase Soderburg furnace, similar to the Girod furnace, is in operation. In the design of the Harden Paragon furnace the bath is heated from above by arcs, and also from the sides and bottom by side plates in the lining.

INDUCTION FURNACES.

a

THE KJELLIN FURNACE.

The Kjellin furnace, the pioneer of induction steel-furnaces, is especially adapted to the melting of fine materials to obtain a highgrade steel. At present 9 of these furnaces are in operation, but the writer does not know of any others being erected.

The Kjellin furnace (fig. 21) is in reality a transformer in which the bath of molten metal forms the secondary circuit. The magnetic

a Härdén, J., The Paragon electric furnace and recent developments in metallurgy : Met. and Chem. Eng., vol. 9, 1911, p. 595.

Kjellin, F. A., The Kjellin and Röchling-Rodenhauser electric furnaces: Trans. Am. Electrochem. Soc., vol. 15, 1909, p. 173.

circuit C is built up of laminated sheet iron like the core of a transformer. The primary circuit is a coil consisting of a number of turns of insulated copper wire or tubing surrounding the magnetic circuit. The ring-shaped crucible B, made of suitable refractory materials, also surrounds the magnetic circuit, and when filled with molten metal forms the secondary circuit of the transformer. The annular crucible is supplied with covers.

If the coil be connected with the poles of an alternating current generator, the current passing through the coil excites a variable magnetic flux in the iron core, and the variation in the magnetic flux induces a current in the closed circuit formed by the molten metal in the crucible B. The ratio between the primary and secondary current is fixed by the number of turns of the primary, and the magnitude of the current in the steel is then almost the same as the primary current multiplied by the turns of the primary coil. Thus in a small furnace of this type a current of 500 volts and 280 amperes supplied to the coil induces a current of 7 volts and 24,000 amperes in the metallic bath. Before starting the furnace an iron ring must be placed in the crucible and melted down to form a bath, or the crucible must be filled with molten metal taken from another source. On continuous work it is customary to leave enough metal in the crucible to establish the bath. Kjellin furnaces have been built in sizes up to 8.5 tons capacity, requiring 750 kw.

THE RÖCHLING-RODENHAUSER FURNACE.

The Röchling-Rodenhauser furnace is an improvement of the Kjellin induction furnace designed especially for the refining of molten basic Bessemer steel and for use with currents of frequency ordinarily used in steel plants. The Kjellin furnace of 8 tons capacity required a current of not more than 5 cycles frequency or the power factor would drop below 0.6. The Röchling-Rodenhauser furnace is so designed as to have a power factor of 0.6 when using a frequency as high as 50 cycles. The furnace is the most widely used of the induction furnaces and is especially adapted to refining molten metal. Eighteen of these furnaces are already in operation and four are in course of construction.

The Röchling-Rodenhauser furnace (fig. 27) has a hearth of very different shape from the Kjellin furnace, as it has a distinct open hearth which no other induction furnace possesses. Both single and three-phase current furnaces are constructed, the former having two grooves in which the metal is melted and the latter three. In either

a Rodenhauser, W., The electric furnace and electric process of steel making: Jour. Iron and Steel Inst., vol. 79, No. 1, 1909, p. 261.