GB302529A - Improvements in or relating to apparatus for heating rods, tubes and the like by electricity - Google Patents

Abstract

302,529. Northrup, E. F. March 21, 1928. Heating by electricity.-In induction heating apparatus wherein. the rods, tubes, or the like to be heated are inserted into or passed through coils spaced apart, one or more of the coils in the later portion of the path of the rods is energized by currents of higher frequency than that applied to the other coils. Eddy currents are induced in the rods themselves or in conducting casings surrounding them. In Fig. 1 the coils B<1>, B<2> are connected in series with the generator G, and the coil B<3> is connected up in a circuit employing a spark gap D and condensers C', C<2> so as to operate at a higher frequency. In a modification the voltage of the higher-frequency circuit is raised by a transformer. In a further modification the coil B<3> is fed by a separate generator of higher frequency than the generator G. In Fig. 3 all the coils are in series and a higher frequency is imposed on the coil B<3>. In the three-phase arrangement of Fig. 4, coils H, I, K are connected directly to the supply, and coils H', I<1>, K<1> are fed by a higher frequency, and preferably higher voltage, generator G<1> driven by a synchronous motor Sm connected to the supply. A similar arrangement may be employed for two-phase working.