Heating Characteristic and Thermal Optimization of Superconducting DC Induction Heater with Adjustable Air Gap Structure

The novel superconducting direct-current (DC) induction heater shows great advantages of high efficiency and heating quality compared to traditional alternating-current (AC) induction heater in aluminum extrusion. The efficiency of the superconducting DC induction heater can be up to 80-90%, which is much higher than the 40-50% efficiency of the AC induction heater. The uniform and gradient temperature distributions of the aluminum billet are the most significant parameters to evaluate the heating quality of this induction heater, which has a strong influence on the product quality of extrusion processing. In this paper, the superconducting magnet with adjustable air gap structure is designed to achieve controllable axial temperature uniformity and axial temperature gradient distribution. Each adjustable air-gap structure consists of 10 identical iron pieces whose position can be changed independently. Therefore, the uniformity and gradient temperature of the aluminum billet in the axial direction are controllable. The thermal optimization of the uniform and gradient temperature distributions for typical aluminum billets (Phi = 446 mm) is measured. A numerical finite-element method (FEM) model is built to analyze the heating behavior of the aluminum billet. The simulation and experimental results match well. The result of uniform and gradient axial temperatures are +/- 3 degrees C and the controllable range from 10 degrees C/m to 40 degrees C/m, respectively. The result obtained from the temperature-distribution optimization is useful for industrial applications.