Solenoidal Bi-2223/Ag induction heater for aluminum and copper billets

Induction heating is widely used to heat up aluminum and copper billets before extrusion. Resistive induction heating systems, which typically have the total efficiency of 50-60%, are generally used with ac current. By utilizing superconductivity, the total efficiency of induction heating system can be increased to approximately 90%. If the heating power of conventional induction heaters can be reached with a superconducting device, resistive systems could be replaced by superconducting ones, and remarkable savings would develop in the long run. In this paper the feasibility of Bi-2223/Ag induction heater is studied. A solenoidal magnet for induction heating of aluminum and copper billets is designed. Ac losses are a considerable problem in Bi-2223/Ag magnets. Thus, dc current is utilized and the eddy currents are generated by rotating the billets. Coil design aimed to maximize the heating power by maximizing the radial gradient of the magnetic flux density in the heating area. In the design procedure the optimization algorithm Sequential Quadratic Programming was coupled with electromagnetic field computation by means of Finite Element Method. The quench current of the coil was determined based on the stability analysis of conduction-cooled Bi-2223/Ag magnets.