Patent ID: 6811718
Filing Date: 2004-11-02
Classification: C01G,C01P,C04B,H01F

Abstract:
A method for manufacturing ferrite type permanent magnets comprising a magnetoplumbite phase of the formula M1-xRxFe12-yTyO19 wherein Fe and M=Ba, Sr, Ca, Pb represent the main elements, and R and T are substitute elements where R=Bi or rare earth elements, and T=Mn, Co, Ni, Zn, where x and y are between 0.05 and 0.5, comprising the steps of:a) forming a mixture of particles of raw materials M, Fe, R and T defined respectively as PM, PF, PR and PT, said particles having, respectively, a surface area GM, GF, GR and GT, at least one of GR and GT being selected according to GF and according to weight % S of substitute raw material particles PS=PR+PT with respect to PF, so as to obtain a mixture comprising, statistically and ideally a pre-determined proportion of particles PR or PT with reference to the particles PF; b) roasting said mixture to form a clinker B of a magnetoplumbite phase according to a formula M1-xRxF12-yTyO19; c) wet grinding said clinker to obtain a homogeneous dispersion of separated fine particles of average particle size of less than 1.2 &mgr;m; d) concentrating and compressing said separated fine particles in an orientation magnetic field to form an anisotropic green compact of a predetermined shape; e) sintering said anisotropic green compact to obtain a sintered element; f) optionally, performing a final shaping of said sintered element; wherein GS is selected according to a theoretical grain size GSTH=K.GF, the constant K is equal to (100/% S)1/3. (dF/dS)2/3, where dF and dS are respectively specific mass of PF and specific mass of Ps, and GS of is at least equal to 0.7. GSTH.