Patent GB-569718-A (GB)
Title: Improvements in or relating to the manufacture of permanent magnet material
IPC: H01F1/04
Filed: 1940-09-30
Abstract: 569,718. Heat - treating magnetic alloys ; obtaining coherent masses from powdered metals. SWIFT, LEVICK, & SONS, Ltd., HORSBURGH, G. D. L., and TETLEY, F. W. Sept. 30, 1940, No. 14698. [Classes 72 and 82 (i)] In the manufacture of permanent anestropic magnetic material, finely ground iron, aluminium, nickel and cobalt are intimately mixed, pressed in a mould and sintered at a temperature above 1150‹ C., but below the melting point of the mixture, the sintered product being then subjected to the action of a magnetic field whilst cooling, preferably from the sintering operation, from an elevated temperature above the Curie point down to a temperature at least 100‹ C. below that point. The ingredients may be mixed in the proportions of 5-11 per cent of aluminium, 7-22 of nickel, 12-30 of cobalt and the rest of iron, and the mixture may include other finely-powdered ingredients such as copper up to 10 per cent; titanium, preferably in the form of a ferrotitanium alloy, up to 5 per cent and one or more of chromium, manganese, molybdenum, silicon, uranium, vanadium, tungsten or zirconium up to a total amount of 5 per cent. Part of the iron, copper and cobalt may be used in the form of an intermediate ferro-cobalt-copper alloy produced in the refining of copper cobalt ore as described in Specification 450,431 and part of the aluminium may be added in the form of a powdered iron aluminium alloy containing from 45 to 55 per cent of aluminium. A proportion of the ingredients may consist of finely-divided waste or scrap magnet alloy containing iron, aluminium, nickel and cobalt, preferably in the proportion of 15-80 per cent of the whole, powdered iron-aluminium alloy and such other ingredients as will give a finelydivided mixture of like composition to that of the magnet alloy. The cooling of the sintered product in the magnetic field may be at a rate not exceeding 10‹ C. per second and preferably 1-5‹ C. per second. After cooling in the magnetic field, the alloy may be reheated to 500-700‹ C. for 1-24 hours and re-magnetized in the direction in which the other magnetic field was applied. The moulded alloy was sintered in the tubular passage 3 extending through a furnace to provide a sintering chamber 4, the furnace being heated by a coil 6 wound round a refractory tube 7 supported in a casing 8 containing heat insulating material. Purified and dried hydrogen is supplied to the passage 3 by a pipe 23 and also by a pipe 13 to an annular space between the passage 3 and tube 7 where it is burnt at the open end 10. One end of the passage 3 is closed by a door and on the other side of the furnace the passage 3 passes through a gap between polepiece 12 of a circuit generated by coils 14 wound round cores 15 connected together by a base 16 and is then surrounded by a water jacket formed by non-magnetic walls 18, 19, 20 and fed by water through a pipe 21. To prevent admission of air to the passage 3 when the door 11 is opened, a hydrogen burner 26 is mounted below and a similar burner may be mounted below the door 17 at the other end of the passage. Specifications 519,183 and 522,731 also are referred to.