|The principle of induction heating
As in resistance heating, the electromagnetic induction is used here. In this heating principle, however, the heat is generated contact-free in the component. A primary coil (inductor) generates a magnetic field that induces a voltage in the secondary coil (component). The current generated by that, also called eddy current, is responsible for the heating of the component. In contrast to resistance heating, the heat is generated at the outer skin of the component and serves as a source of heat for heating the whole cross section. The higher the frequency of voltage applied to the inductor, the smaller is the depth of penetration of the eddy current into the component (skin effect). Other than by resistance heating, thin components are therefore well brazeable by induction heating.
Unlike resistance heating, electromagnetic induction is used for heating the brazing point. In this principle, heat is generated contact-free in the component. Using the knowledge of the inductivity of coils, machines were manufactured, which generated heat according to that principle. Thus, the US patent Number 422190 of 1889 shows how to heat a component by only using one coil and one ferrite core. Nowadays, heating machines consist of a frequency generator that heats the component with medium frequency (10 to 25 kHz) or high frequency (from 150 kHz) via a water-cooled coil (inductor). Modern generators have an additional hose package and coaxial transformer between inductor and generator. As such equipment makes the inductor movable it can be well integrated into a brazing machine.