Electrometallurgy of steel and iron

Abstract

The most modern of industries, electrometallurgy, has for its purpose the application of electricity to metallurgical processes, with a view thereby of obtaining products not capable of being produced in any other way, and also of obtaining older products either more economically, or superior in quality. Electrometallurgy has demonstrated that it can do all of these things, and therefore there can be no doubt that it is destined to play a large part in the manufacture of such products in the future. This new industry combines the principles of electricity and chemistry, and engineers to be successful in this field must have training both in electrical engineering and metallurgy. Electricity is used in the processes of metallurgy in two ways. First, electrolytically, whereby electrolysis is used for the purpose of obtaining the desired results. In this method, direct currents are used, and the output of the processes is directly proportional to the current used. Electrolytic iron, which is the purest kind of iron, can be combined in this way at a cost of refining of $10.00 per ton. In the second method, the heating effect of the electric currents is used to obtain the high temperatures necessary for metallurgical operations. This can compete with the ordinary methods notwithstanding the cost of electric power, owing to the fact that heat can so easily be applied just where it has to be used, thus resulting in economical use of power and high efficiency. Furnaces in which the current is utilized for its electrolytic action and heating effect are called electrolytical furnaces. They may use either direct or alternating current, and the output is directly proportional to the watts input, the efficiency being the proportion of the heat utilized in the metallurgical processes to the heat generated in the furnace. Electric furnaces are of two types — arc furnaces, and resistance furnaces. In arc furnaces, the substance dealt with may constitute one or both poles of the arc. It may be placed in the path of the arc between the poles, or it may be placed entirely outside, and heated by radiation from the arc. In resistance furnaces, the substance to be heated constitutes the resistance through which the current is passed; the simplest type of this consisting of a long, narrow, serpentine channel containing the material to be melted. Terminals are placed at each end, and sufficient voltage applied to force the required current through the material. In the induction type of furnace the resistance, which constitutes the material to be melted, is made the secondary of the transformer in which the heating current is induced from the primary coil. The resistance in this case is placed in an annular channel surrounding an iron core, making thereby a one-turn secondary coil. The primary coil is wound directly on the core inside the annular secondary. The greatest difficulty of this furnace is to obtain successful screening of heat from the primary coil and core, for which purpose a water jacket is used. These induction furnaces are in successful operation up to 15 tons capacity, and one of 25 tons capacity is now in course of construction. The electrometallurgy of steel was first attempted in the manufacture of ferroalloys, which previously could not be made. These alloys required for their manufacture a temperature which can only be obtained by the electric furnace. The next step was the manufacture of the highest and most expensive grade of steel; that is, crucible steel. Electric furnaces can now be utilized to manufacture exactly the same quality of steel as crucible steel, in much larger quantities, of more uniform grade, and at about one-half the former cost. There is no doubt that the old method of manufacturing crucible steel is destined to be entirely replaced by electrical methods. Where electric power is available in large quantities at small cost, electric furnaces are beginning to compete in the manufacture of steel called electric steel, which is considerably better than open hearth steel. The difficulty in the past has been that the small furnaces used, had low efficiencies, but as larger furnaces arc being built, the efficiencies arc steadily increasing, and consequently reducing the cost. At present an efficiency of 80 per cent has been obtained. At some places this steel is now being manufactured at a cost only slightly in excess of the cost of open hearth steel, and it is reasonable to assume that the future will see a still further reduction in cost of manufacture.