Before describing a few of the processes it may be said that in the earlier days of electric steel furnaces it was considered that they could only be installed in places most favorably lo cated for a cheap supply of power, or in places where metallurgical fuel, such as coal and coke, was extremely scarce and high priced. The earlier furnaces were all of the single-phase type, and in the case of those employing elec trodes only one or two electrodes were, used. About 10 years ago three-phase furnaces with three electrodes came into use, and since that time furnaces with from four to sik electrodes have been produced in the larger sizes. The cheapening of power costs in many localities has brought about a much more general in troduction of these furnaces than was con templated even by their inventors. Another early idea in regard to electric furnaces oper ation was that they could only be used commer cially for refining material previously melted in the open hearth or the. Bessemer. The first installation in the United States, which was made at the plant of the Halcomb Steel Company, was of this type, and the electric furnace, which was of four gross ton capacity, was used for refining material melted in a 20-ton basic open hearth furnace. This in stallation is still in use after 13 years of con tinuous service. An identical installation was started in Germany at almost the same time. To-day furnaces operated on cold charges. are much more numerous than those employing the original duplex process, and they are located in places that formerly would have been thought unsuitable for such installations.
The Stassano In the Stassano furnace the heat is radiated more pairs of large carbon electrodes placed above the charge and in the top of the furnace. The furnace is of the arc type, and, as the elec trodes are not in contact with the material that is to be melted, it is plain that no impurities are introduced into the melt from the electrodes themselves. Either iron or steel may be pro duced, depending upon the mixture used. With the earlier furnaces of this type the hearth large electrodes pass through the roof of the furnace. In the single-phase furnace, such as was first used exclusively, the current passes down one of these electrodes, crosses a narrow air gap through the slag into the melt, and is then conducted back through the slag and an other air gap to the second electrode. Alter nating current of about 100 volts is used. The rotated during the operation at a small angle to the vertical, facilitating the mixture of the ingredients and the reactions taking place in them. This process is still in use in Italy with both rotating and stationary hearths. Its use has not been adopted to any very great extent in other countries, and some of the installations that were made in this country have been aban doned. It was found that the arc, placed so high above the charge, produced an excessive heating of the refractories of the roof, and that the expense for upkeep was high. The furnace is capable, however, of producing high quality steel.
Heroult Process.— This process, as applied to the production of steel, makes use of an arc resistance tilting furnace, usually basic lined with dolomite or magnesite. Two or more width of the air gap is automatically regulated by very ingenious devices which automatically raise or lower the electrode as the resistance in the circuit varies. Tool steel, or structural materials, and especially alloy steels, can be made by this process in this furnace either from a charge of cold materials or from a liquid charge previously melted in some other fur nace. The charge may consist of miscellaneous scrap, ore and lime, and usually some fluor spar, sand and lime are used for the prepara tion of slags toward the end of the process. When it is desired to remove both sulphur and phosphorus from the charge it is custom ary to rake off the first slag formed during the melting-down period, and with it goes most of the phosphorus. The operation during this
period is oxidizing. After the phosphorus slag is. removed a second slag, usually known as a ((carbide slag,' is formed, and under reducing conditions in the furnace the sulphur is very largely eliminated. In this particular the elec tric processes of several types are far superior to any other processes for removing sulphur. When such furnaces are used in conjunction with the basic open hearth furnace, the bur den of dephosphorizing is borne by the basic open hearth and desulphurizing and deoxi dizing only are done in the electric furnace, and the operation is carried out entirely under re ducing conditions.
made by the Canadian commission, by Dr. V. Engelhardt and by the writer, during the earlier years of its operation. The furnace, as described by Dr. Haanel, constitutes a step down transformer. A primary coil of insulated wire is wound about one leg of the magnetic circuit. The secondary is formed by the charge in an annular groove, also surrounding the same leg of the magnetic circuit. In the original Kjellin furnace at Gysinge, Sweden, the primary alternating current is delivered at 90 volts and 3,000 amperes. The secondary current induced in the charge itself is of low - Colby and Kjellin Processes.— The in ventor of • the induction furnace was Mr. Ed ward A. Colby, an American. It does not appear, however, that at the time of taking out his patents in 1890 he had any idea that the process might be used on a large scale for steel melting. Ten years later Kjellin, in Sweden, employed the principle of induction to the con struction of electrical furnaces for steel melt ing, and since the results of these later experi ments have been .made public Colby has also designed a furnace for similar use. The Kjellin process was put into actual service in Sweden about 1900, producing a merchantable product, mostly tool steel, and has been made the subject of many careful investigations. This process naturally attracted the attention of makers of high-grade steels as the nearest substitute for the old. process of crucible melt ing. The furnace was studied in operation, and careful investigations of the product were potential, and the conversion of electric energy into heat takes place in the substance of the charge itself. The furnace may he either acid or basic lined, but the latter is most used, the lining constituting the annular groove or crucible, being usually made of magnesite. The furnace may be either tilting or stationary. No attempt was made at purification of the ma terials used, but carefully selected raw ma terials, well melted, gave an excellent steel, the analysis of which was nearly the mean of the constituent materials of the mixture. This, of course, is a more expensive way of producing tool steel than by refining processes, but it is the surest way, and processes depending upon refining methods can never be as certain in their results as the crucible or the induction process, in which raw materials of known impurity are employed. Larger furnaces of the induction type were later produced in Germany, in which by a special arrangement of the hearth refining was possible, but in both the simpler and these more complicated fur naces the question of repair of linings was very serious, and it can scarcely be considered that they have been a commercial success. Some very large ones were installed in this country, but it is understood that they have been abandoned as uncommercial. One elec trical disadvantage is that these furnaces for best operation require a current of unusually low frequency. The modified Kjellin furnace, adapted to refining, is known as the Rochling Rodenhauser furnace. The induction furnace can operate upon two kinds of mixtures: first, pig iron or scrap, and second, pig iron, scrap and ore briquettes.