This article was originally published in Electrochemical and Metallurgical Industry Publication of July 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.
In numerous articles in this journal details of construction of the Heroult electric furnace have been given, so that our readers are perfectly familiar with them. We are glad to reproduce herewith a number of views of one of the largest plants now in operation in this country using the Heroult process for the production of steel of highest quality.
The steel is made in an open-hearth furnace of the familiar Wellman type and is then refined in a Heroult electric steel furnace. The daily output is 60 tons. The capacity of the open-hearth furnace is 25 tons, that of the electric furnace is 4 tons. The open-hearth furnace works continuously. When 4 tons of molten metal are taken from the open hearth and supplied to the electric furnace, another 4 tons of scrap, etc. are charged into the open-hearth furnace. The treatment of 4 tons in the electric furnace is completed in 1 ½ hours.
From very exact tests made by Professor Eichhoff, he states that 200 kilowatt hours are sufficient for treating a charge of 5 tons if the overoxidized metal is supplied directly from the open-hearth furnace in molten condition to the electric furnace. If the price of the kilowatt-hour is assumed to be one-half cent—which is possible if cheap electric power is available at the steel works, for instance, from gas engines operated with blast-furnace gases—the total electrical energy necessary for the treatment of 5 tons in the electric furnace does not cost more than $1.00, or the cost of power in the electric-furnace treatment of 1 ton is not more than 20 cents.
If the charge would be supplied into the electric furnace in cold condition considerably more energy would be required, according to Eichhoff about 750 to 870 kw-hours. It is for this reason that the metal taken out from the open-hearth furnace should be furnished directly into the electric furnace with as little loss of heat as possible.
Since in the Heroult furnace the current passes from one electrode into the slag on top of the metal, through the slag and out of it into the second electrode, it is important that the arcs between the end of each electrode and the slag are playing properly. If a rod of steel in contact with the molten mass (provided in the bottom of the furnace) is connected to two outside circuits, either of which leads to one electrode and contains one voltmeter, then each voltmeter is in shunt with its electrode, the arc and the fused metal and indicates whether there is the proper tension between the electrode and the metal. In other words, it indicates whether the arc is established in the proper way.
The indication of the voltmeter may, of course, be directly applied to automatic regulation of the position of the electrodes by electromagnetic means. Although so much has been written concerning the electrical features of construction of the Heroult furnace it seems that the essential metallurgical features of Dr. Heroult's method of working are not yet thoroughly understood.