42 



NATURE 



[May 13, 1897 



THE MANUFACTURE OF CARBORUNDUM 

 AT NIAGARA FALLS} 



'T'HE first carborundum furnace consisted of an iron bowl 

 ^ lined with carbon, and a carbon rod ; a mixture of clay 

 and carbon was introduced into the bowl, and the rod placed in 

 the mixture. A current sufficient to fuse the mixture, or at 

 least to brinp it to a very high temperature, was now passed 

 through the furnace, the iron bowl and carbon rod serving as 

 terminals or electrodes. When the current was cut off, and the 

 furnace had cooled down, it was opened, with the result that a 

 few bright blue crystals were found surrounding the carbon rod. 

 The furnaces constructed after this first experiment approached 

 more nearly in form the furnaces in use to-day. They were 

 built of brick, their internal dimensions being 10 inches in 

 length, 4 inches in width, and 4 inches in depth. The terminals 

 were a pair of carbons, which could be mcjved longitudinally, 

 thus permitting the distance between them to be altered at 

 pleasure. These were essentially arc furnaces ; that is to say, 

 the idea was to form an arc between the terminals, and to bring 

 about the necessary chemical changes by the high temperature 

 thus produced. It was soon found, however, that this method 

 of working was not satisfactory, and the incandescent furnace, 

 which is the kind that is now adopted, was therefore constructed. 



iidum furnace ready for operation. 



Into furnaces of this kind a core consisting of granulated coke, 

 which forms a continuous electrical connection between the 

 carbon terminals, is introduced. By adjusting the diameter of 

 the core to the proper size, it is heated to a sufficiently high 

 temperature, by the passage of the current, to convert the sur- 

 rounding mixture into carborundum. 



It was at first supposed that the crystals formed in the furnaces 

 were a compound of aluminium and carbon, but it was soon 

 found that the amount and quality of the carborundum depended 

 on the amount of silica present in the mixture. A good glass 

 sand was, therefore, substituted for the clay in the mixture. It 

 was also found that the addition of a little .salt to the mixture 

 facilitated the running of the furnaces. Some trouble was ex- 

 perienced from the gases formed during the running of a furnace, 

 and to lessen this, sawdust was added to the mixture to render it 

 porous, and to allow the free escape of the gas. The output of 

 the.se small furnaces amounted to about a quarter of a pound a day. 

 The crude materials for the manufacture of carborundum at 

 Niagara Falls are sand, coke, sawdust, and salt. These are 

 ready for immediate use, with the exception of the coke, which 

 must be reduced to kernels of a certain size, to be used as 



.\bridged from a paper by Mr. Francis A. P'itzgerald, in the Journal of 

 Mit ' ■ 



the Franklin Institute, February 1897, 



NO. 1437, VOL. 56] 



' ' core," and ground to a fine powder, to be used in making the 

 mixture or charge for the furnaces. The furnaces are built of 

 brick, and have the form of an oblong box, the internal dimen- 

 sions being, approximately, 16 feet in length, 5 feet in width, 

 and 5 feet in depth (Fig. i). The ends are built up very solidly, 

 with a thickness of about 2 feet. In the centre of either end are 

 the terminals, consisting of sixty carbon rods 30 inches long and 

 3 inches in diameter. The outer ends of the carbons are 

 enclosed in a square iron frame, to which is screwed a stout 

 plate, bored with sixty holes corresponding to the ends of the 

 carbons. Through each of these holes is passed a short piece of 

 jl-inch copper rod, fitting tightly in a hole drilled in the carbon. 

 Finally, all the free space between the inside of the plate and 

 the ends of the carbons is tightly packed with graphite. Each 

 plate is provided with four projections, to which the cables con- 

 veying the current may be bolted. These ends are the only per- 

 manent parts of the furnace ; the remainder is built up every 

 time the furnace is operated. 



The side walls of the furnace are first built up to a height ot 

 about 4 feet. Pieces of sheet iron are then placed at a distance 

 of about 4 inches from the inner ends of the carbon terminals in 

 such a way as to keep the mixture from coming in contact with 

 the latter. The mixture is then thrown into the furnace until 

 it is rather more than half full. A seniicircular trench, having 

 a radius of \o\ inches, and 

 extending from end to end 

 of the furnace, is now formed, 

 the bottom of the trench 

 being a little above the level 

 of the bottom row of carbons. 

 Into this trench is introduced 

 the core, which has been 

 carefully weighed, so that 

 the amount required to make 

 the core of the right size is 

 used. All the core having 

 been emptied into the trench, 

 the top is 'rounded oft" neatly 

 by hand, so that, when 

 fini.shed, we have a solid 

 cylinder 21 inches in diam- 

 eter and about 14 feet long, 

 composed of small pieces of 

 coke, and extending from 

 the sheet iron plates at 

 either end of the furnace. 



The next operation is to 

 make the connections be- 

 tween the core and the ter- 

 minals. This is done by 

 ]3acking finely-ground coke 

 into the spaces between the 

 ends of the carbons and the 

 pieces of sheet iron, after 

 which the walls are built 

 up to a height of about 

 5 feet, the pieces of sheet 

 iron removed, and more mixture thrown in and heaped up to 

 a height of about 8 feet. 



All that is required now to make carborundum is the electric 

 current. The current as supplied from the Niagara Falls 

 Power Company has an electromotive force or pressure of 2200 

 volts, so that in order to use it in the furnaces it must be trans- 

 formed to a lower voltage. The transformer at the Carborun- 

 dum Works has a maximum capacity of 830 kilowatts, or about 

 1 100 horse-power, and transforms the 2200-volt current into one 

 of only 185 volts. Associated with the transformer is a regu- 

 lator, by means of which the current from the former can be 

 raised to 250, or lowered to 100 volts. 



After the circuit has been closed in the transformer-room, no 

 apparent change occurs in the furnace for about half an hour. 

 Then a peculiar odour is perceived, due to escaping gases, and 

 when a lighted match is held near the furnace walls the gas 

 ignites with a slight explosion. When the current has been on 

 for three or four hours, the side walls and top of the furnace are 

 completely enveloped by the lambent blue flame of carbon 

 monoxide gas, formed by the combination of the carbon of the 

 coke with the oxygen of the sand. During the run of a single 

 furnace 5^ tons of this gas are given off. At the end of four or 

 five hours the top of the furnace begins to subside gradually. 



