When producing a rare earth sintered magnet, magnetic properties such as saturation flux density and coercive force are secured by making finer the raw material powder subjected to sintering. However, making the raw material powder finer is a factor in hindering the dimensional accuracy of the compacted body and productivity.
The raw material powder constitutes the compacted body undergoing compressing in a magnetic field. In this compacting in a magnetic field, a magnetostatic field or a pulsed magnetic field is applied, whereby the particles of the raw material powder are oriented. During the compacting in a magnetic field, the finer the raw material powder is, the worse the fluidity of the powder is, so that the filling properties into the die become a problem. If the filling properties into the die worsen, since the powder cannot be sufficiently filled into the die, there are the problems that dimensional accuracy of the compacted body cannot be achieved, or that the filling into the die itself takes time, thus hindering productivity. It is especially difficult to produce thin-shaped or complex-shaped compacts precisely and efficiently.
As one means for improving the fluidity of a raw material powder, granulation of the raw material powder has been experimented with. For example, Japanese Patent Laid-Open No. 8-107034 (Patent Document 1) and Japanese Patent Laid-Open No. 8-88111 (Patent Document 2) propose granulation by adding a binder to a rare earth metal powder, and then spray drying the resulting slurry. Further, Japanese Patent Publication No. 7-6025 (Patent Document 3) proposes granulation by applying a magnetic field to a rare earth metal powder. Other proposals include a technique wherein granulation is performed by creating a flow (air flow) of a fluid in a chamber to thereby apply the kinetic energy from the flow to the raw material powder in the chamber (Patent Document 4).
Patent Document 1: Japanese Patent Laid-Open No. 8-107034
Patent Document 2: Japanese Patent Laid-Open No. 8-88111
Patent Document 3: Japanese Patent Publication No. 7-6025
Patent Document 4: Japanese Patent Laid-Open No. 2004-131815