Patent ID: 6755988
Filing Date: 2004-06-29
Classification: C04B,H01F

Abstract:
Manufacturing method for permanent magnets of the ferrite type comprising a magnetoplumbite phase of formula M1âˆ’xRxFe12âˆ’yTyO19 in which M=Ba, Sr, Ca or Pb, R=Bi or other elements of the rare earths family, T=Mn, Co,Ni, Zn, with x and y comprised between 0.05 and 0.5, comprising the steps of:a1) forming in a mixing means, a pulverulent mixture MP of raw materials related to the elements M, R, Fc and T, comprising water in a predetermined quantity, a2) transforming said mixture into green granules A, with an optional addition of extra water, b) calcining said green granules in a calcination furnace (5) to form a clinker B, with a magnetoplumbite phase base of formula M1âˆ’xRxFe12âˆ’yTyO19, c) wet grinding said clinker, to obtain a homogeneous dispersion C of fine de-agglomerated particles of average particle size less than 1.2 um, d) concentrating and compressing said particles under an orienting magnetic field to form a green compact D, anisotropic, able to be manipulated and of predetermined shape, c) sintering said anisotropic green compact D to obtain a sintered element E, and f) dimensions optionally dimensioning the final size of said sintered element E, wherein: 1) at stage a1) of the method, forming said mixture MP, by introducing into said mixing means (3), a dry mixture MS of powders corresponding to said raw materials relative to the elements M and Fe, and a homogeneous fluid dispersion DF of said raw materials relative to the elements R and T; and 2) at stage b) of the method, calcining said green granules A at a chosen temperature and for a chosen length of time, in such a way as to obtain, at the exit from the calcination furnace (5) at the end of stage b), a clinker B which is both homogeneous in chemical composition and size, and of low apparent density, comprised between 2.5 and 3.5 and which can be ground easily during stage c).