SMELTING ORES BY ELECTRICITY 



blast-furnace, impairing its operation and endangering the 

 lives of the attendants, and the furnace as well. 



This "scaffold," as it is called, is formed of metal, 

 which on account of some cause, sucli as failure of the 

 draft through the tU3'ers, becomes chilled and adheres to 

 the sides of the furnace. This " scaffold " forms a projec- 

 tion from the side of the furnace above the reducing zone, 

 where it is verj' difficult to be reached b}^ heat, and where 

 it cannot be removed b}^ the ordinary operation of the 

 furnace. 



On the contrar}^, when once started, the " scaffold " 

 tends to increase b}' the adhesion of other molten matter 

 becomirig cliilled on its surface. If this continues, the 

 "scaffold" becomes a support to the whole charge above, 

 with the result that it finally gives way, allowing the mass 

 of the charge above to drop through the base of the fur- 

 nace and probably killing the attendants. This accident is 

 very dangerous, comparative!}^ frequent, arid costly, especi- 

 ally to water- jacketed apparatus. 



The means v/hich have been most successfulh' em- 

 ployed to prevent the above danger, is that of using the 

 electric arc to fuse the chilled adhesions which can be 

 reached without interfering with the regular operation of 

 the furnace. For this service either D.C. or A.C. can be 

 used at a potential at from 75-50 volts and 500-1,000 am- 

 Deres, 



X 



With A.C, the proper voltage can be readily obtained 

 by a transformer situated raear the blast-furnace. With 

 D.C, from a standard 125-volt supply by meariS of a water 

 rlieostat in the circuit. One side of the circuit is clamped 

 to the outer casing of the blast-furnace and the other to a 

 long carbon i^i Indies in diameter, made for the purpose 

 by the National Carbon Co., or the International Acheson 

 Graphite Co. This electrode is supported in any con- 

 venient way for handling, for example, by a long pipe, etc., 



