Sintered ring magnet and method of manufacturing the same

Abstract

A ring magnet manufacturing method includes the steps of stacking a plurality of radially oriented ring-shaped powder compacts (102) in an axial direction thereof to produce a ring-shaped powder compact rod, sintering the ring-shaped powder compact rod to produce a sintered ring-shaped powder compact rod (300) in which the ring-shaped powder compacts (102) are joined together, and dividing the sintered ring-shaped powder compact rod (300). In this ring magnet manufacturing method, protruding parts (103) are formed on upper end surfaces of the ring-shaped powder compacts (102) which will be located in uppermost layers of individual sintered ring magnets (100), for example, such that the ring-shaped powder compacts (102) are joined with a reduced joint strength at specific boundary regions of the sintered ring-shaped powder compact rod (300) where the protruding parts (103) are located than at the other boundary regions. The sintered ring magnets (100) are obtained by dividing the sintered ring-shaped powder compact rod (300) at the specific boundary regions having the reduced joint strength.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a radially oriented sintered ring magnet used in compact motors, for instance, and a method of manufacturing the radially oriented sintered ring magnet. [0003] 2. Description of the Background Art [0004] A radially oriented anisotropic ring magnet is often used in permanent magnet motors. It is common practice to use an axially elongate ring magnet when manufacturing a compact high-power motor having a small inertia. [0005] A problem encountered when pressing magnetic powder in a magnetic field for producing an axially elongate ring magnet is that a sufficient field strength of alignment field is not obtained, resulting in a reduction in alignment coefficient of the magnetic powder and an inability to achieve a high magnetic property. [0006] When a ring magnet is radially oriented magnetically, a magnetic flux passing through a core of a metal die unit for pressing magnetic powder in...

AI Technical Summary

Benefits of technology

[0017] According to this ring magnet manufacturing method of the invention, several ring magnets joined into a single structure, or the sintered ring-shaped powder compact rod, by the sintering operation are handled together in subsequent processes. This approach of the invention produces the following advantageous effects. Specifically, since several sintered ring magnets are handled as a single structure, the sintered ring magnets can be transferred together from one process to next with high efficiency. Since curved inner surfaces and outer surfaces of several sintered ring magnets can be machined together in the form of the sintered ring-shaped powder compact rod, it is possible to achieve improved machining efficiency. Since several sintered ring magnets can be subjected together to an anticorrosion surface treatment in the form of the sintered ring-shaped powder compact rod, it is possible to achieve improved treatment efficiency. Additionally, it is possible to produce the sintered ring-shaped powder compact rod with a high degree of shape accuracy.

Problems solved by technology

A problem encountered when pressing magnetic powder in a magnetic field for producing an axially elongate ring magnet is that a sufficient field strength of alignment field is not obtained, resulting in a reduction in alignment coefficient of the magnetic powder and an inability to achieve a high magnetic property.

It is commonly known that a problem occurs due to deterioration of a property of magnetic alignment when pressing a ring magnet in a magnetic field if the ring magnet has an axial length larger than a value of H given by equation (2) above.

A chronic problem encountered in the manufacture of a sintered ring magnet is that the powder compact does not shrink uniformly but becomes deformed as a result of shrinkage during sintering operation.

Since a ring magnet is produced by making multiple layers of powder compacts by carrying out these sequential steps, the method of Japanese Patent Application Publication No. 1990-281721 leads to low manufacturing productivity.

Also, since all these steps are performed in the pressing machine, there exist various limitations in operation in the individual steps.

Furthermore, the powder compacts in lower layers are pressurized more times than those in upper layers, magnetic alignment is disturbed in the lower-layer powder compacts, inevitably causing deterioration of magnetic properties.

Moreover, this ring magnet manufacturing method is associated with a problem that the magnetic properties deteriorate at each boundary region between the adjacent powder compacts due to the influence of the powder compact in a lower layer.

The aforementioned method of Japanese Patent Application Publication No. 2001-335808 has a problem that the compact restraining jig is a consumable and it is necessary to set the compact restraining jig with a central axis thereof precisely aligned with a central axis of the ring-shaped powder compact, resulting in low manufacturing productivity.

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