Improving Induction Crucible Furnaces

Abstract

The main deficiencies of existing induction crucible furnaces are associated with elevated wall thickness of the lined crucible, the tubular copper single-layer inductor (with internal cooling by conditioned water), and the absence or presence of surrounding vertical I-shaped composite metal rods, forming a discrete ferromagnetic screen. The first deficiency is that much of the working electromagnetic flux Φ_wo is wasted, since it passes along the crucible lining, which is not electrically conducting, rather than along the furnace charge. Only 38.5–57.0% of Φ_wo is utilized. The second deficiency is associated with the high cost and laboriousness of manufacturing the inductor turns from special copper pipe, which vibrates at double frequency. That creates noise and weakens the furnace structure. Such inductors are characterized by low electrical efficiency and high costs of preparation and cooling of the conditioned water in systems of area several times greater than the furnace itself. The consequence of the third deficiency is that much of the electromagnetic scattering flux Φ_sc is not involved in heating the batch and the melt but instead heats the electrically conducting elements of the furnace, including the magnetic rods that surround the inductor. Because of the poor utilization of the total flux Φ generated by the inductor, the efficiency is decreased practically to 19–30%, while the power factor falls to 0.03–0.10, with increase in the energy consumption. To minimize or eliminate the deficiencies, three modifications are proposed: decrease in the sleeve’s wall thickness, with simultaneous strengthening by installing a cylindrical shell between the crucible and the inductor; introduction of a magnetic ring around the inductor; and the use of a single-wire or multicore inductor, instead of a tubular inductor. The combination of a cylindrical shell, a magnetic ring, and upper and lower housing plates permits the formation of a closed annular cavity where the inductor may be placed, with cooling of the inductor and the magnetic ring by circulating fluid. On the basis of research, a new design of an induction crucible furnace with a wire inductor and a composite magnetic ring (magnetic core) has been developed at Polzunov Altai State Technical University, tested, and patented. In experiments, the efficiency of the proposed structural elements is confirmed, indicating that the design merits further study.