Vergleich des induktiven Erwärmungsverhaltens von Eisen- und Nichteisenmetallen mit einem Royer-Converter

This master's thesis involved developing an induction heater based on a Royer converter to systematically investigate the inductive heating behavior of ferrous and non-ferrous metals. The focus of the investigation was the influence of material properties, as well as the influence of coil geometry and frequency on heating.
The developed circuit is based on a Royer converter with MOSFET ZVS (self-oscillating) technology and modularly adjustable resonant capacitance. The circuit was designed for a base frequency of 100 kHz and allowed for additional tests at 50 kHz and 150 kHz. To analyze the coil influence, three coil types were developed and manufactured: a twisted stranded wire coil, a high-frequency optimized fine wire coil (HF coil), and a copper tube coil.
The heating tests were conducted under controlled electrical conditions. Temperature measurements were taken using an infrared thermometer. Current and voltage curves were recorded. The aim of the analysis was to determine the skin effect, frequency dependence, and interactions between the coil and the workpiece.
Nine material variants were investigated: Grade 2 titanium, V2A stainless steel, copper, brass, aluminum, and ferritic steel in four surface states (bare, galvanized, rusted, black coated). The selection covered a broad spectrum of electrical, thermal, and magnetic properties.
The results show significant differences in heating behavior depending on the material, coil type, and frequency. As expected, the ferritic steel proved to be the most efficient to heat. While copper and aluminum exhibited significantly lower heating performance due to their high conductivity. The HF coil showed 150 kHz achieved the best results for non-ferrous metals, while the tubular coil proved to be the least efficient, yet still stable in operation.
This work contributes to a better understanding of the influencing factors in the inductive heating of metallic materials in the high-frequency range. It also demonstrates the possibilities, as well as the limitations, of a system based on the Royer converter without control electronics.