Induction Furnace: Ironless 540-Cycle Brass Melter, 600 lb, 80 kW (Northrup, US 1,694,792, 1928)

A coreless induction furnace: one layer of flattened, water-cooled copper tube wound edgewise round a crucible. A 540-cycle current in the coil induces currents in the metal charge itself, which heat and melt it. Condensers in series with the generator correct the coil's low power factor. Result: a furnace that melts brass, bronze and also ferrous metal in about 600 lb lots at 80 kW, with an electrical efficiency of 0.94. Source: E. F. Northrup, US 1,694,792 (1928). Unknown: the crucible, the housing and the tilting gear. Picture: the patent drawing, Fig. 5.