furnace these grooves or heating channels, each of which corresponds to the annular hearth of the Kjellin furnace, open into a distinct open hearth, where all metallurgical operations, such as the addition of fluxes and alloys, take place. The grooves, which have a comparatively small cross section, form the secondary circuits in which the currents that heat the metal are induced.

Two side doors are provided in a single-phase furnace and three in a three-phase furnace. The furnace is set on rollers and is tilted by means of a hydraulic motor. One door has a spout for pouring. As the doors are slightly above the level of the bath, removing the slag is no more difficult than in the arc furnace, which is not the case with other induction furnaces.

In figure 27, HH represents the two legs of the transformer that are surrounded by primary coils A connected with the alternating-current circuit. Secondary currents are induced in the two closed circuits formed by the bath. These two circuits are connected by the hearth in the center so as to resemble the figure 8. The primary coils are so arranged that the induced currents have the same direction in the common part of the two circuits. The difference between this furnace and the ordinary induction furnace consists in the use of extra secondary coils BB surrounding the primary coils AA. The secondary coils are connected to metallic plates EE, covered by an electrically conducting mixture of lining material, G, which forms part of the lining of the furnace. The current from the secondaries passes through the plates, E, through the lining, G, and then through the main hearth, D.

This current used in combination with the current from the channels CC gives a better power factor than when the furnace is operated with the current from the channels only. Another advantage is that the magnetic leakage field surrounding the primary coils, which formerly had the effect of checking the primary current and decreasing the power factor, is now utilized for inducing currents in the extra secondaries.

The result is that the main hearth can be made of much larger cross section than before and that, nevertheless, even in big furnaces a good power factor can be maintained without the use of such a low frequency of the current as was necessary with the original induction furnace.

The single-phase furnace gives better satisfaction than the threephase furnace because it is less complicated. Also, the strong circulation of the bath in the central hearth of the three-phase furnace causes great wear on the lining.

Röchling-Rodenhauser furnaces have been built in various sizes. The 8 to 10 ton single-phase furnace at Volklingen, Germany, takes 600 kw., supplied by a current of 4,000 to 5,000 volts with a fre

quency of 25 cycles. The 2 to 3 ton 3-phase furnace at the same place takes from 200 to 250 kw., supplied by a 400-volt current with a frequency of 50 cycles. The power load of these furnaces is very steady. The 2 to 3 ton furnace recently installed at Landsdowne, Pa., requires 300 kw., furnished by a 25-cycle current at 480 volts.

OTHER INDUCTION STEEL FURNACES.

The Frick furnace is very similar to the Kjellin furnace, differing from it only in slight details of design. The primary windings are placed above and below the annular ring instead of within it. One 12-ton Frick furnace is in operation in Germany.

00

FIGURE 31.-Plan and elevation of Hering resistance furnace.

The Hiorth furnace is a further development of the Kjellin furnace, differing only in that the bath lies in two annular grooves instead of one, thus surrounding both sides of the primary coil. One tilting Hiorth furnace has been erected in Norway.

AN ELECTRICAL RESISTANCE FURNACE ADAPTABLE TO STEEL

MANUFACTURE.

A resistance furnace based upon the "pinch effect" has been designed and operated on an experimental scale by Hering." Although this furnace (fig. 31) is not in commercial operation as

a Hering, C., A new type of electric furnace: Trans. Am. Electrochem. Soc., vol. 19, 1911, p. 255.

yet for the production of steel, several are in the course of construction for this purpose, and small ones have been shown in operation. The following is a brief description of the principle on which this resistance furnace operates.

The "pinch phenomenon " is the local contraction of cross section of a liquid resistor through which electric current is passing and in which heat is being generated. In open channels this contraction or pinching often results in complete rupture, thereby limiting the temperature. This contraction is caused by an electromagnetic force that acts from the circumference to the center of the conductor and in a direction perpendicular to the axis.

If a conductor consists of a column of liquid metal in a vertical hole in a nonconducting material closed at the bottom by the electrode and opening at the top into the bath of metal in the hearth, then this force acts horizontally, and perpendicularly to the axis along the whole length, which results in an axial force that causes the liquid metal to flow out of the center of the open end. In the Hering furnace such a column is made the resistor in which the desired heat is generated by passing the current through the column by means of an electrode at the bottom. Two such resistors are placed in the bottom of a furnace of any desired shape for singlephase current and three for three-phase current. As this “pinch effect" can not now rupture the circuit, it expels the heated liquid rapidly from the holes and forces it against the blanket of slag, thereby continually renewing the surface exposed to the slag action, while the cooler liquid in the bottom of the hearth is sucked down into the hole near the circumference to be in turn heated and immediately expelled. The ejecting force increases as the square of the current and diminishes with an increase in the cross section of the conductor.

There is an active and systematic circulation of the liquid bath, and the temperature is very evenly distributed throughout the bath. As far as is known now, there is no temperature limit except that which causes failure of the refractory lining. The electrodes may be made of metal, and no adjustment of them is necessary; they are not consumed. The hottest liquid is in the center of the resistors. The rapid flow is not along the walls of the hole but in the center. The power factor can be made very high, and ordinary frequencies may be used.

The furnace can be operated with direct or alternating current of one, two, or three phase. The transformers in the latter case are attached directly to the bottom of the furnace, as the amperage is very high.

ELECTRIC STEEL MANUFACTURING PRACTICE.

There are two courses of procedure for steel manufacture in which the electric furnace has been used: Cold scrap iron and steel of either inferior or high-grade quality is melted and refined in an electric furnace with the production of steel of the highest grade equal to the best crucible steel; and molten steel, the product of either the acid or basic converters, or of the acid or basic open-hearth furnaces, is superrefined, or made into alloy steel, in an electric furnace.

MANUFACTURE OF STEEL FROM SCRAP IRON AND STEEL IN THE ELECTRIC FURNACE.

SOCIÉTÉ ÉLECTRO-MÉTALLURGIQUE FRANÇAISE, LA PRAZ, SAVOIE, FRANCE. The plant of the Société Électro-Métallurgique Française, at La Praz, Savoy, France, has passed through many phases of the use of the electric furnace in metallurgical operations. The first product produced here by Héroult was aluminum, which was followed by calcium carbide, ferro-alloys, electrodes, and steel. To-day the plant uses 7,500 kilowatts for the production of aluminum, steel, and electrodes.

DESCRIPTION OF PLANT.

The principal products of the 2.5 to 3 ton Héroult furnace (fig. 18) in operation at La Praz are high carbon and alloy tool steels. The furnace is the original Héroult furnace examined by the Canadian commission. It differs from the furnace at Braintree in that the lining is thinner, giving a more shallow hearth. The hearth is ground dolomite and tar, the sides are magnesite brick, and the roof is silica brick. The two carbon electrodes are 14 inches square. The holders are of somewhat more simple design than those in the Braintree furnace (p. 94). They consist of two clamps of steel held together by a pin, being tightened by a wedge. Current is brought in by cables attached to pins in the ends of the electrodes and to the electrode holders. Electrodes are not threaded for continuous feeding. The holders and ports in the roof are water cooled. The electrodes may be regulated either by hand or automatically. Power is supplied by a single-phase alternator directly connected to the furnace. about 30 feet away. The power required is 300 kw., and is supplied by a 33-cycle single-phase current, at 100 to 110 volts, giving 50 to 55 volts on each electrode.

PRACTICE AT PLANT.

The furnaces are charged with low-carbon steel or wrought-iron turnings and a part of the first refining flux. As the melting proceeds, all of the first flux, consisting of iron ore and lime, is added to remove the phosphorus. When this is accomplished the slag is

completely removed from the furnace and a flux of lime added to remove the sulphur. The slag is completely deoxidized for the removal of sulphur by the addition of coke dust. The metal is finally carburized to the desired point by addition of carburite, and then poured into ingots.

The results of operations covering one week are given below. The number of heats is probably somewhat greater than the usual number, as at the time of the writer's visit the average was three in 24 hours. A noteworthy reduction of power consumption has been made over that of 1904, as the figure of December 24, 1911, was 528 kilowatt-hours per ton as compared to 840 kilowatt-hours per ton, of 1 per cent carbon steel, refined with two slags, for 1904, a reduction of 312 kilowatt-hours, or 37.1 per cent decrease. The electrode consumption of 18 kg. (39.6 pounds) in 1904 would probably approximately hold for to-day, as the methods have not been changed materially in that respect. The roof had stood 107 heats up to the week mentioned.

Results of operation of furnace for week ended Dec. 24, 1911.

Lowest power consumption, per ton, at furnace. 459.2 kilowatt-hours.

Average power for week at furnace, per ton_

Scrap, per cent_----.

Clear ingots, per cent--

528 kilowatt-hours.

3

93

Loss by oxidation, per cent_

FINAL FORM OF PRODUCT.

The ingots cast at the furnace are reheated and reduced in rolls and hammered to 1 inch to inch rods of circular or square cross section. The product is sold in this form. Samples of steels of the following composition were taken by the writer:

Tool steels produced in Héroult furnace, La Praz, France, 1912.