Application of vacuum-tube oscillators to inductive and dielectric heating in industry

THE knowledge that metals could be heated inductively and that nonconductors could be heated dielectrically dates from the earliest experiments with electricity. In the last few years inductive and dielectric losses, which have long been obstacles in the electrical industry, have been profitably employed in a new industrial tool powered by high-frequency motor-generator sets and vacuum-tube oscillators. Low-frequency inductive heating has been used in specialized melting applications for approximately 20 years and for some surface hardening work for the last ten years. However with the advent of the new equipment and knowledge of its use, it is no longer a highly restricted application but is ready to handle thousands of heating processes throughout the industry. Hence, it is felt that a short review of the theory of inductive and dielectric heating, together with a description of the vacuum-tube circuits used and some of their applications, would be of value at this time.