Patent GB-599367-A (GB)
Title: Improvements relating to devices for obtaining electromagnetic fields of high frequency and great intensity and to apparatuses embodying such devices
IPC: H05B6/36
Filed: 1942-08-26
Abstract: 599,367. Heating by electromagnetic induction. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Aug. 26, 1942, No. 12053. Convention date, April 22, 1941. [Class 39 (iii)] [Also in Groups II and XXXV] A device for obtaining an intense high-frequency electromagnetic field for heat treatment of metal articles comprises a transformer with a secondary in the form of a cylinder b with a longitudinal slit connected by leads to an inductor work coil d of smaller diameter than that of the secondary; and the work coil d is integral with the periphery of a heat dissipating surface, preferably the small end of a frustum h of a cone or pyramid, the transverse sections of which, in planes parallel to that of the work coil, form contours closed except where interrupted by a slot g, the edges of which serve to convey current to the work coil d. The primary coil a is placed within or around the cylinder b, and the frustum h is joined, Fig. 3, directly to the cylinder b with the slots in alignment to convey current to the work coil d. The slots and work coil form current paths of minimum impedance. Supplementary longitudinal slits v are formed in the frustum and end short of the periphery d to avoid parasitic currents in the frustum external to the work coil and to assist cooling. The frustum may be of prismatic form and the cylinder may be replaced by a body of rectangular section. The device may be cooled by circulation of water or compressed gas, and by cooling fins. The cylinder, (Fig. 5, not shown), may be surmounted by a slit dome supporting a terminal cap for the primary coil. Water is supplied to pipes or passages in the parts extending adjacent the slits and passing into the interior to cool the coil a, leaving at p. A long metal article to be heated may be placed in the cylinder b and extend through the work coil. Two heaters may be placed with their peripheries d adjacent to increase the field, or two inductors may be combined, Fig. 7, on a single cylinder b slit at g. A second cylinder b may be placed within the coil a and carry a frustum with its periphery d adjacent that of the outer frustum or joined thereto. In Fig. 8a, parallel closely spaced plates u separated by mica supply two inductors h from a single cylinder. A gear wheel may be hardened by placing it within a periphery d and is tempered by air cooling, by passage of the heat backward into the mass of the metal or by quenching it with water from an adjacent hollow ring cut by an insulating sleeve and actuated by an automatic valve operating when the current is cut off. Pinions x may be spaced by ruigs r on a rod q and passed between two inductors d, water being sprayed from a ring y. In Fig. 12b the inductor d is rectangular, has cooling fins l and internal partitions k forming recesses into which project teeth x of a large pinion, slits z being arranged so that the current follows the contour of the teeth. The inductor d may be moved vertically and the pinion rotated so as to introduce fresh teeth. For hardening a wheel flange the inductor forms a hollow prism, Fig. 13b, with an open face A,B,C,D, fitting into the flange, which may be rotated. The edges AB, CD are arranged away from the flange to prevent local over-heating. In Fig. 14a (not shown), the edge of the prism is recessed to fit over a rail to be hardened. The rail or flange may be tempered by air or liquid. Ball bearings may be hardened by passage through an inclined quartz tube between two prismatic inductors, the balls then dropping into a bath. A heating device may comprise a chain of inductors d coupled to a single primary a, Fig. 18, arranged outside the cylinders b, the frustum h being replaced by a flat slotted surface d<1>. Ball bearings pass through an inclined ceramic tube i arranged centrally through the inductors d, the tube having a helicoidal groove or being rotated to rotate the balls, which fall into a tempering bath w. The device may be used for welding tubes end-on or at an angle, continuous longitudinal welding of an open cylinder to form a tube, welding two metal plates continuously, or welding glass and metal for electron tubes.