GB821626A - Induction heating systems - Google Patents

Abstract

821,626. Heating by induction. MAGNETHERMIC CORPORATION. Jan. 26, 1956 [Jan. 27, 1955], No. 2604/56. Class 39(3) [Also in Group XXXV] An induction heater for metal workpieces comprises a liquid-cooled inductor winding 5 having taps for connection of the secondary windings of three singlephase transformers fed from a delta connected three-phase supply. A metal tube 6 which may be double walled, is of non- magnetic and high-temperature resistant material, e.g. stainless steel, and carries the winding 5, one or more longitudinally extending non-conductive seams 7 preventing flow of current circumferentially of the tube. The connections to the primary winding of the intermediate transformer 23 are transposed and the conductors of each of two pairs of connections a2, b1; b2, c1, between the inductor taps and the transformer secondary windings are also transposed thus forming "phase overlap" zones h1, h2 between the main zones L, M, N of the inductor winding. Fig. 2 shows how the vector of the flux B produced by the current in transformer 23 is rotated through 180 degrees by the transposition of the connections of the primary winding of the transformer 23. The vectors A, BX representing the flux in main zones N, M differ by 60 degrees, and the vector ABX representing the flux resulting from flux A and flux B differs by 30 degrees from A and BX. Similarly, flux CBX produced by flux C and flux BX is 30 degrees removed from flux C and flux BX. The small displacement between successive phases, i.e. 30 degrees, results in substantially uniform heating at a uniform rate of the workpieces. Further, the resulting reduced voltage between adjacent convolutions of the inductor winding avoids the necessity of providing annular spacers of insulating material.