Hitachi Metals, Ltd.

Shuichi Shiina

Yasunobu Ogata

Takashi Takami

Yutaka Kubota

Shigeho Tanigawa

Kimio Uchida

A ferrite powder for bonded magnets having a substantially magnetoplumbite-type crystal structure and an average diameter of 0.9-2 &mgr;m, the ferrite powder having a basic composition represented by the following general formula: (A R )O.n&lsqb;(Fe M ) O &rsqb; by atomic ratio, wherein A is Sr and/or Ba; R is at least one of rare earth elements including Y, La being indispensable; M is at least one element selected from the group consisting of Co, Mn, Ni and Zn; and x, y and n are numbers meeting the conditions of 0.01&lE;x&lE;0.4, &lsqb;x/(2.6n)&rsqb;&lE;y&lE;&lsqb;x/(1.6n)&rsqb;, and 5&lE;n&lE;6, (Si&plus;Ca) being 0.2 weight % or less, and (Al&plus;Cr) being 0.13 weight % or less, can be produced by mixing iron oxide containing 0.06 weight % or less of (Si&plus;Ca) and 0.1 weight % or less of (Al&plus;Cr) with compounds of A, R and M elements, calcining the resultant mixture for ferritization, pulverizing the resultant magnetically isotropic ferrite and then heat-treating the pulverized ferrite at 750-950&deg; C. for 0.5-3 hours in the air.

Bonded magnet, magnet roll, a ferrite powder used therefor and method for producing same

A ferrite powder for bonded magnets having a substantially magnetoplumbite-type crystal structure and an average diameter of 0.9-2 &mgr;m, the ferrite powder having a basic composition represented by the following general formula: (A,R,O.n&lsqb;Fe,M,),O,&rsqb; by atomic ratio, wherein A is Sr and/or Ba; R is at least one of rare earth elements including Y, La being indispensable; M is at least one element selected from the group consisting of Co, Mn, Ni and Zn; and x, y and n are numbers meeting the conditions of 0.01&lE;x&lE;0.4, &lsqb;x/(2.6n)&rsqb;&lE;y&lE;&lsqb;x/(1.6n)&rsqb;, and 5&lE;n&lE;6, (Si&plus;Ca) being 0.2 weight % or less, and (Al&plus;Cr) being 0.13 weight % or less, can be produced by mixing iron oxide containing 0.06 weight % or less of (Si&plus;Ca) and 0.1 weight % or less of (Al&plus;Cr) with compounds of A, R and M elements, calcining the resultant mixture for ferritization, pulverizing the resultant magnetically isotropic ferrite and then heat-treating the pulverized ferrite at 750-950&deg; C. for 0.5-3 hours in the air.

A mold for producing an anisotropic magnet from a composition essentially consisting of magnetic powder and a binder, a mold body, a cavity for molding the composition in the presence of an anisotropically oriented magnetic field produced by a plurality of first magnets for providing magnetic fluxes for the magnetic field in the cavity, yokes, each provided between the cavity and the first magnets, and second magnets provided on both circumferential sides of the yokes for preventing the leakage of the magnetic fluxes. The first and second magnets are made of permanent magnets such as rare earth cobalt magnets. The mold may be provided at both ends with third magnets for preventing the axial leakage of the magnetic flux from the axial ends of the yokes. Two or more molds may be combined in a single molding apparatus while sharing the first magnets. This mold is suitable for the injection, extrusion or insert molding of bonded magnet rolls, motor rotors, etc.

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Saitama-ken, Japan

Shuichi Shiina