DISCOVERY 



285 



is, in fact, only limited by the boiling-point of carbon 

 or other materials in the path of the arc, and may be 

 as high as 7,000° Fahr. A second advantage is that 

 the conditions can be adjusted to give temperatures 

 of any lower degree as desired, while the use of elec- 

 tricity enables a careful and convenient adjustment 

 of the heating to be made. 



Fig. 3 illustrates a bath of steel during the pouring 

 operation. This metal has been prepared by sub- 

 mitting a charge of cast iron with certain alloys and 

 fluxes for a few hours to the high temperature of 

 electric arcs formed between the tlirec superposed 

 carbon electrodes and the surface of the slag. 



The main incentives to the development of electric 

 furnaces in the iron and steel industry have been the 

 exacting requirements of the present-day engineer. 

 The demand for high-grade material which, on a large 

 scale, can only be met satisfactorily by electro- 

 metallurgical methods, is particularly in evidence in 

 the case of metals for cars and aircraft machinery, and 

 particularly in America, for the steel rails necessary to 

 meet the increasing weight and speed of 

 rolling stock. Apart from a field of its own 

 which electricity has established in the 

 above instances, the application of electrical 

 heating methods is gradually extending over 

 the whole field of chemical and metallur- 

 gical technology. For instance, in certain 

 countries, the electric furnace has entered 

 into successful rivalry with, and proved its 

 overall superiority to, the modern blast 

 furnace for producing cast iron, which in 

 its present-day efiiciency and economy is 

 generally put forward as the model of fuel- 

 heating processes. The electric smelting 

 of iron ores has become mainly established 

 at several centres in Sweden where cheap 

 water power is available. A typical plant 

 in use for this purpose is a modified blast 

 furnace of the ordinary type. The charge 

 is admitted down a tall shaft to the 

 melting chamber at the base, where it is 

 submitted to the heating action of arcs from 

 a number of electrodes spaced equidistantly 

 and traversing the roof of the chamber. 

 The electrodes are of moulded carbon, 2 feet 

 in diameter and 4 to 5 feet long. The gases 

 produced from the reaction, which when 

 burned give out great heat, arc led through 

 the column of descending charge and cause 

 a partial reduction and preheating of the 

 ore. The hot gases are withdrawn from 

 the top, and a portion of them is again admitted at 

 the base and thus continuously circulated, while the 

 remainder is utilised in heating steel furnaces and for 



generating power. These furnaces are now constructed 

 in larger sizes ; units to the number of about twenty, 

 each consuming 10,000 horse-power, are now in 

 operation in Sweden. 



The electric smelting of iron ores can best compete 

 with the older-established and highly-efficient blast 

 furnace in districts where suitable ore and cheap 

 power is available, but where fuel is scarce. Some 

 form of carbon is, of course, necessary for the reduction 

 of the ore even in the electrical process, but a smaller 

 amount is used in the electrical heating than where, 

 in the form of coke, it is used also to produce heat in 

 the blast furnace. Apart from the question of the 

 relative economies of coke and electrical energy, a 

 further consideration is the improved quality of 

 iron made electrically. This is due to the reduction 

 of contamination of the iron by the impurities 

 contained in the coke. The usual Swedish practice 

 is to utilise charcoal as the form of carbon, and thus 

 produce material of the special qualities of the well- 

 known Swedish charcoal-iron. This product was 



ll.i. 3.— BuoIH H.\l,l, ELECTRIC FURNACE. 

 iliy kind pcrtmsbion ol Messrs. Loiigmatis, Green &■ Co.) 



formerly produced in charcoal-heated blast furnaces, 

 and the saving of charcoal effected by the electrical 

 procedure represents the main factor in its economy. 



