Electric furnace

“ We still use the old familiar purifying agents, iron oxide, lime and nascent calcium. The electricity is solely a source of heat, free from the faults of the older sources which for certain purposes it now replaces. The electric furnaces are likely to displace the crucible furnaces completely, because they work both more cheaply and better. They are not likely to displace either the open-hearth furnace or the Bessemer converter, because their normal work is only to improve the product of these older furnaces. ”

“ An alternating current of 4000 amperes at 110 volts is used for a 3-ton furnace, and the intensity of the current passing through the bath is regulated by raising or lowering the electrodes.
The effect of the European War has been enormous on the development of the electric furnace in this country, for prior to the war in 1914, although the use of the electric furnace for steel-making was increasing, there were only 5 furnaces in operation in Sheffield, and two or three more in other parts of the country, producing in all about 15,000 tons per annum. ”

“ Again, the construction of electric furnaces may often be exceedingly crude and simple; in the carborundum furnace, for example, the outer walls are of loosely piled bricks, and in one type of furnace the charge is simply heaped on the ground around the carbon resistance used for heating, without containing-walls of any kind. ”

“ In general, electric furnaces have more or less round steel shells with shallow brick, magnesite or sand-lined hearths, and sidewalls and removable roofs of brick. Heat, of course, is furnished electrically. In most of them long carbon electrodes are lowered through holes in the roof 228until the lower ends strike an arc with the metal on the hearth. The number of carbons may be from one to four or more depending upon the style and size of the furnace and the manner in which electrical connections are made. ”

“ To-day all kinds of combinations of Bessemer, open-hearth, and electric furnace are being projected and it is difficult and likely impossible for any one to predict the future of any of the processes. ”

“ The older method of creating air currents was by means of furnaces, but this method, while very effective, is expensive and dangerous. In using this system a furnace is built near the outlet of the air shaft, the combustion of the fuel creating the necessary draught. But in the nature of things this furnace is a constant menace to the mine, besides being an extremely wasteful [253] expenditure of energy. The modern method of ventilating is by means of rotary fans, the electric fan having practically solved the problem. ”

“ Inasmuch as this substance can at present only be made on a commercial scale in the electric furnace--and so far as may be foreseen will never be made on a large scale except by means of electricity--inasmuch as an electric furnace can only be worked remuneratively in large factories supplied with cheap coal or water power ”

“ Walther process, which does not use electricity but depends on the intense heat generated by burning acetylene under pressure. In electric furnaces the formation of carbide depends simply on the heat of the arc, which fuses the mixture of lime and coke. The latest improvements on the first very simple forms of furnace have secured continuity of work and economy of electric energy. In the United States carbide is made exclusively in the Horry furnace. This furnace consists of a huge short cylinder or hollow wheel, mounted to revolve slowly on a horizontal shaft. ”

“ For warming buildings, the furnace would become an electric generator, from which wires, instead of pipes for steam or hot air, would lead to the rooms to be heated, when, by interposing a suitable resistance, the energy of the current would be converted into heat. The probability of being able to convert the energy due to combustion of fuel into electric instead of heat energy may be very small ”

“ Many furnaces are coal-fired, and although greater care is Page 98 required in maintaining a uniform temperature good results have been obtained. The use of electricity as a means of reaching the requisite temperature is receiving some attention, and no doubt it would make the control of temperature comparatively simple. However, the cost when applied to large quantities of work will, for the present at least, prevent this method from becoming popular. It is believed that the results obtainable \with the electric furnace would surpass any others ”

“ The most important ones are either “arc” furnaces, i.e. those heated by electric arcs, or “induction” ones, i.e. those in which the metal under treatment is heated by its own resistance to a current of electricity induced in it from without. The Heroult furnace, the best known in the arc class, and the Kjellin and Roechling-Rodenhauser furnaces, the best known of the induction class, will serve as examples.
The Heroult furnace (fig. 23) is practically a large closed crucible, ABCA, with two carbon electrodes, E and F, “in series” with the bath, H, of molten steel. ”

“ A good many people are puzzled by the fact that an electric current, which yields a perfect light at a reasonable price, should in the sister task of heating fail in rivalry with a common stove or furnace. To solve this puzzle let us place our hands above a cluster of 15 Edison incandescent lamps, each of 16 candle power, representing one horse power, yet emitting no more heat than if three ounces of coal were slowly burning away in the course of an hour. This electricity may cost us ten cents an hour, the coal costs but the fifteenth part of one cent. ”

“ Turning from the employment of the expensive reducing agents to the simple and sole application of heat, we are unwilling to believe that we do not here possess in eminence both the mineral and the medium of its reduction. Whether the electric or the reverberatory or the converter furnace system be employed, it is surely possible to produce the result. ”

“ Generally speaking, the electric heating may be done in a tenth of the time required by the forge or furnace, and the power required is between three and four horse power per cubic inch of metal heated. The feature of electric heating already noticed of a bar becoming more highly heated at the center than at the surface when exposed freely to the air, is shown in a very convincing manner at this exhibit by fusing the core of an inch bar without it losing its shape. ”

“ Heaters designed to take the place of the hot-air furnace are constructed in the same general manner as those for car use. The plan is to place a large primary heater in the cold-air box of the ordinary furnace, and then subsidiary heaters just inside the grating of registers, by means of which additional heat may be obtained when the main heater is insufficient. All classes of apparatus are made to be used with either an alternating or continuous currrent, and adapted to be attached directly to the ordinary electric supply circuits. ”

“ Electric steel-making processes, or more accurately processes in which electrically heated furnaces are used, have developed very rapidly. In steel-making, electric furnaces are used for two distinct purposes, first for making steel sufficiently better than Bessemer and open-hearth steels to replace these for certain important purposes, and second for replacing the very expensive crucible process for making the very best steel. ”

“ Heavy copper wires carrying a current of 2,200 volts lead from the power-house to Mr. Acheson's furnaces, where the electrical energy is transformed into heat.
There are ten furnaces in all, built loosely of fire-brick, and fitted at each end with electrical connections. And strange they look to one who is familiar with the ordinary fuel furnace, for they have no chimneys, no doors, no drafts, no ash-pits, no blinding glow of heat and light. The room in which they stand is comfortably cool. Each time a furnace is charged it is built up anew ”

“ In these furnaces, the regenerator chambers themselves are generally placed underneath the melting furnace, and they are built of fire-brick and filled with loosely-stacked fire-bricks, whose function it is to absorb or deliver the heat. In the most modern type of furnaces of this class, the gas-regenerators are omitted entirely, the air only being pre-heated by means of regenerators, while the gas enters the furnace direct from the producer, thus carrying with it the heat generated in the producer during the gasification of the fuel. ”

“ It has been attempted to overcome this difficulty by putting the hot ingots under shields or hoods, lined with non-heat-conducting material, and to bury them in non-heat-conducting material in a pulverized state, for the purpose of retaining and equalizing the heat; but all these attempts have proved futile in practice, and the fact remains, that the universal practice in steel works at the present day all over the world is to employ a heating furnace of some description requiring fuel. ”

“ In houses heated by furnaces or other modern systems, lack of a damper in the fireplace flue may interfere with uniform heating, particularly in very cold windy weather, whether or not there is a fire on the hearth. When air heated by the furnace is carried up the chimney there is a waste of the furnace fuel, but a damper partially open serves a slow fire of hardwood without smoking the room or wasting heated air from the main heating system. ”

“ Their efforts met with little practical success until they finally hit on the very simple idea of applying the principle of the condenser to furnaces, an idea which was embodied in a patent taken out by Frederick in 1856. The products of combustion from the furnace, instead of passing direct to the chimney, were led through a chamber filled with refractory brickwork, to which they gave up their heat. As soon as the chamber was sufficiently hot, the current was shut off, and the air-supply of the furnace led through it. ”

“ It is the least expensive plant to be used for general heating. Indirect radiation from hot water or steam is to be preferred to a furnace. A combination of a hot-air furnace with hot water, or steam, is used with fair success. In this case, a hot-water coil is placed in an ordinary furnace, which connects with hot-water radiators in a conservatory or other room for the purpose of contributing a uniform degree of heat to that room. The water supply is a tank, located well above the level of the radiators, and connecting through an inlet pipe with the coil in the furnace. ”

“ His efforts to procure a means of making his fire burn under his little dump of ore led him first into the science which has attained a new importance in very recent times, pneumatics. The first American furnaces were blown by the ordinary leather bellows, or by a contrivance they had which was called a "blowing tub," or by a very ancient machine known as a "trompe" in which water running through a wooden pipe was very ingeniously made to furnish air to a furnace. It is when the means are small that ingenuity is actually shown. ”

“ As a matter of fact, several small furnaces will cost considerably more than one large furnace, and the saving in original furnace cost by such an installation, taken in conjunction with the added efficiency of the larger furnace over the small, will probably more than offset the cost of additional boiler units for spares.
The essential features in furnace design for this class of fuel are ample combustion space and a length of gas travel sufficient to enable the gases to be completely burned before the boiler heating surfaces are encountered. ”

“ In porcelain kilns, the potters, after hours of firing, have been able to produce a cumulative temperature of as much as 3,300 degrees Fahrenheit; and this, with the oxy-hydrogen flame (in which hydrogen gas is spurred to greater heat by an excess of oxygen) , is the very extreme of heat obtainable by any artificial means except by the electrical furnace. Thus the electrical furnace has fully doubled the practical possibilities in the artificial production of heat. ”

“ There appears to be no mechanical device for removing the ashes out of the cellar. So, if the householder puts in a coal burning steam or hot water plant as a matter of economy, and then in a few years covets an oil burner, it is perfectly practical and possible to have one installed in his furnace. Whatever the fuel, make sure enough radiation is provided with steam or hot water plants to heat the house evenly and adequately in the coldest weather according to your ideas rather than the plumber's. He is usually a hardy individual who considers 68 degrees warm enough for any one. ”

“ For large furnaces, blowing machines of various kinds are used, generally consisting of a pair of large cylinders having pistons worked in them by steam power, and pumping air into a large air-chamber, from which it proceeds in three or four pipes to the furnace, or sometimes to numerous furnaces, each having a tube and stop-cock by which the “blast” may be turned on, similarly to gas or water, the air-chamber being always kept filled at a great pressure by the cylinders, and furnished with a safety-valve to prevent the pressure bursting it. ”

“ Hot-air furnaces are made with cold-air pipes. The fresh air from outdoors comes through these cold-air pipes and, after being heated, is driven into the rooms of the house. Some people think they will save coal by closing these drafts. Not only do they not save coal (for the furnace does not give as much heat when this draft is closed) , but they kill their body cells by refusing to give them oxygen. The cold-air pipe in a hot-air furnace should always be kept wide open. ”