Billet Heating with the Homopolar Generator
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Forging billets are presently brought from room temperature to forging temperature using one of three heating methods -- indirect heating in a furnace, either fuel-fired or electric; direct electric resistance heating; or induction heating. Homopolar generators, operating in the pulsed mode, offer a fourth possible billet heating method. Although basically a direct resistance heating method, the homopolar generator type of power supply has several advantages over a conventional transfonner-type supply. First, homopolar generators can be designed to deliver energy at much higher power levels than transformers, resulting in very much shorter heating times than are required using conventional direct resistance heating systems. The shorter heating times minimize oxide scale formation on the billets. Second, pulsed homopolar generators, because they do not impose an increased load on the power mains during delivery of pulses, permit power averaging and minimize demand charges. When compared with slot furnaces, homopolar generator billet heating systems offer increased operating efficiency as well as the advantages of ease of maintenance and freedom from the necessity of maintaining temperature under no-load conditions in addition to the much reduced scale formation.