Patent ID: 7201809
Filing Date: 2007-04-10
Classification: H01F,H02K

Abstract:
1. A method of manufacturing radially anisotropic ring magnets in which a magnet powder packed into a cavity in a cylindrical magnet-forming mold having a core composed at least in part of a ferromagnetic material with a saturation magnetic flux density of at least 5 kG is pressed under the application of an orienting magnetic field by a horizontal magnetic field vertical compacting process; the method comprising the steps of: carrying out at least one of the following operations (i) to (v) so as to apply to the magnet powder a magnetic field from a plurality of direction rather than one direction; (i) rotate the magnet powder a given angle in the circumferential direction of the mold during application of the magnetic field, (ii) rotate the magnet powder a given angle in the circumferential direction of the mold following application of the magnetic field, then again apply a magnetic field, (iii) rotate a magnetic field-generating coil a given angle in the circumferential direction of the mold with respect to the magnet powder during application of the magnetic field, (iv) rotate a magnetic field-generating coil a given angle in the circumferential direction of the mold with respect to the magnet powder following application of the magnetic field, then again apply a magnetic field, and (v) use a plurality of coil pairs to first apply a magnetic field with one coil pair, then apply a magnetic field with the other coil pair, after applying a magnetic field one or more times, rotating the magnet powder at 60 to 120°+n×180° (where n is an integer≧0) under an application of a coil-generated magnetic field of at least 0 but less than 0.5 kOe, the latter magnetic field being from 1/20 to ⅓ as large as the magnetic field previously applied; pressing the magnetic powder during or after the application of the latter magnetic field; and obtaining a radically anisotropic ring magnet having throughout the magnet an angle of 80 to 100° between a center axis thereof and a radial anisotropy imparting direction.