GB917698A - - Google Patents

Abstract

917,698. Magnetic compositions. INDIANA GENERAL CORPORATION. Feb. 9, 1961, No. 4874/61. Class 38 (2). [Also in Group V] A method for the production of hard magnetic moulded bodies, e.g. of ferrites of the composition MO.6Fe 2 O 3 , where M is Ba, Sr, or Pb, or mixtures thereof, comprises providing the ferrite as a finely-divided dry powder (particle size between 0.2 and 1 micron), subjecting the powder to an attenuating current field, e.g. 50-60 c/s. to prevent agglomeration of the powder, and transferring the powder to a mould cavity 15 in which the particles of the powder are aligned by application of a direct current field, compressing the powder (9000 p.s.i.) while the particles are aligned and firing the pressed article, e.g. at 1200‹ to 1280‹ C. The powder 10 is contained in a hopper 1 and is fed to a filling shoe 3 through a flexible pipe 2. The hopper and the tube are preferably made of plastics and the shoe 3 may be made of any non- magnetic material. Coils 4, 14 and 24 are wound round the hopper, pipe and shoe, respectively, and an A.C. voltage may be applied separately to each of these coils or to the coils in series to give an A.C. field of 1000- 3000 oersted. However, the coil 24 is preferably fed with a pulsating direct current to give a maximum field strength of about 10,000 oersted. This aligns the particles as they pass into the mould cavity 15. This cavity is formed in a cylinder 16, e.g. of copper or steel fitted into a table 20 which is adapted to shield the cavity 15. A plunger 17 forms the base of the cavity. A coil 5 is supplied with a steady direct current to give a field (1500-3000 oersted) in the same direction as that of the coil 24, when the pulsating direct current is used in this coil. The filling shoe 3 is slidable on the table 20 to fill the mould cavity after which the mould is removed and a male mould member (not shown) is used to compress the powder in the cavity 15.