Document 3Nv9VnMKGBVjgj8wGNqNQG3vD

the induction stirrer HE first American electric-arc Toledo blades were made by essen Tfurnace, a tiny two-ton rectangu tially the crucible method.) Before lar unit, went into operation in 1906 in long, however, electric furnaces had the plant ofHolcomb Steel Company, supplanted the crucible process al Syracuse, New York. most entirely. In those early days, the electric The first electric furnaces produced furnace was considered merely an a few types of high-cost, high-quality improvement on the ancient crucible steels of very special compositions. process for making fine steels in small Today the electric furnace, still the batches, (The historic Damascus and predominate source of the finest quality steel, is capable of making practically all known grades, includ ing stainless steel, high-speed and other alloy tool steels, special alloy steel, and construction alloy steel. And, although steel made in electric furnaces represents only 6 to 7 per cent of our total steel production, electric furnace steel today is indis pensable to American industry. The Modern Electric Furnace Two distinct types of electric furnaces are now in common use: the induction furnace and the electricarc furnace. The former induces highfrequency current of high amperage in the furnace charge, the resulting heat melting and refining the charge. Such furnaces are comparatively small, a charge of four tons being un usual, and are used to a limited ex tent for melting high-grade alloys. The electric-arc furnace, however, is practically universally used in the quantity production of electric steel. This furnace employs the intense heat of an electric arc to melt the charge and refine the steel. Arc furnaces of 100-ton capacity are now in use. Most modem electric-arc furnaces are refinements of an early design, the Heroult furnace, which was de veloped by Dr. Paul Heroult. The modern electric-arc furnace built by American Bridge is still known as the Heroult furnace, although this type of furnace is now also made by other manufacturers. The shell of this type of furnace is usually cylindrical, lined throughout with special types of firebrick. The furnace roof is a simple flat dome, also firebrick-lined, through which three massive graphite electrodes project down into the furnace through circu lar openings spaced at the points of an equilateral triangle. Each elec trode is supported by an individual mast structure capable of being raised or lowered to provide separate move ment of any electrode. Most large furnaces are charged from above and known as the "topcharge" design. The electrodes are raised and the entire roof structure swung aside to permit loading the furnace by charging buckets from above. All furnaces of the Heroult type are designed to tilt in two direc tions, one for de-slagging and one for pouring the finished heat. The entire furnace ismounted on rugged, toothed rockers which mesh with toothed rails. Electric motors tilt the structure by means ofa crank and levermechanism. Operation of the Conventional Furnace Unlike the open-hearth furnace, the electric furnace is usually charged exclusively with scrap. The alloy con tent of the scrap must be accurately known so that best operation of elec tric furnaces demands careful selec tion of the scrap and a scientific scrap segregation or control program. After the furnace has received its