Design of induction heating coils for cylindrical magnetic loads

Equations are presented whereby the authors´ previous paper¹ is extended to the design of coils for heating magnetic loads, where the load remains in a fixed position relative to the coil during the heat. In heating magnetic materials, there is considerable variation in impedance of the coil circuit as the load temperature changes. The present paper first develops certain general principles by which a variable impedance circuit may be designed to absorb a predetermined maximum power, on the basis of constants determining the maximum and minimum impedance. Methods then are given by which these constants may be calculated for carbon steel loads of types SAE 1015 to SAE 1045, or their equivalent. In practice, these methods apply to most through heating and some surface heating applications. The accuracy of calculations is substantiated experimentally.