Multipolar cylindrical permanent magnet - comprises sintered rare-earth iron-boride with optimised thickness for highest flux density and cracking resistance

摘要

The material used contains R, Fe, B, in which R represents at least one Rare Earth element from the group Nd, Pr, Dy, Ho and Tb, as well as at least One of the elements from the group La, Ce, Sm, Gd, Er, Eu, Tm, Yb and Y. The magnet, made of this material shows at the surface, inner or outer surface depending on its use, multiple magnetic anisotropy, the proportions of R, Fe and B used are resp. 10-30 at. %, 65-80 at.% and 2-28 at.%. The magnet is made in the shape of a hollow cylinder with an inner dia. D1, outer dia. D2 and a number of magnetic poles P, with the relationships: if P = 4 then D1/D2 is 0.35-0.85, if P = 6 then D1/D2 is 0.45-0.85 and if P = 8 then D1/D2 is 0.55-0.85. The magnetic poles are pref. slightly tilted in relation to the cylinder-axis, i.e. at least 5% when P is 4-8. For a value of P from 10-48 the ratio of D1/D2 is given by: D1/D2 = 1-k.(pi/P), in which k is a constant of at least 1.0. Inside the magnet a bush may be placed, of pref. a ferromagnetic material, if the magnetic poles are on the outside of the ring and vice-versa. Also claimed is the construction of a DC-motor for driving hard disks using a magnet as described with 4-12 poles. Also claimed is the construction of a motor for a tape-streamer and an inner hub spindle motor for driving hard disks using a magnet as described A mfg. method for the cylindrical magnet is also claimed. USE/ADVANTAGE - The magnet claimed has a high magnetic flux density and no danger of cracks developing which is a weakness of current ring-magnets. The motors claimed have optimised properties due to optimised magnet properties, weight and size of the magnets.