GB621413A - Improvements in or relating to methods of manufacturing permanent magnets - Google Patents

Abstract

621,413. Heat treating magnets; alloys. JESSOP & SONS, Ltd., W., and OLIVER, D. A. Feb. 7, 1947, No. 3626. [Classes 72 and 82(i)] In a method of manufacturing a permanent magnet of the kind employed in electric apparatus with metal vanes or drums which need damping, formed from a magnetic alloy and having a coercive force of 200 oersteds or greater, a ring casting is heated to a temperature above the Curie point and cooled to below the Curie point at a controlled rate, during which cooling two semi-circular leakage fields are applied in such manner that the path of the magnetic flux is divided between two diametrically opposite neutral points one portion passing through each semi-circular segment of the casting. As shown, the ring casting 1 may be mounted between two elliptical pole pieces 5 disposed within coils 7 and 9 and heated to a temperature of 1200‹C. by an induction coil and then cooled, the rate of cooling being controlled and a heavy direct current passed through the coils 7 and 9 so that a magnetic field passes through the casting. When the temperature has dropped to 500‹C. the coils 7 and 9 are deenergized, the casting removed and, after cooling, a radial slot may be cut in it. The casting may be heated in any type of furnace and the poles of the electromagnet may have small posts projecting upwardly between which the casting is placed. A sheet of asbestos or other insulator may be placed between casting and pole to prevent local cooling of the casting. A suitable alloy consists of carbon .06 per cent, Ni 11.5 per cent, Al 8.0 per cent, Cu 4.0 per cent, Co 21 per cent, the balance being iron and unavoidable impurities. Specification 605,113 is referred to.