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.

1 . A sintered ring magnet comprising a plurality of radially oriented ring-shaped powder compacts which are stacked one on top of another in an axial direction thereof and joined together by sintering, wherein one of a protruding part and a recessed part is formed on at least one of longitudinal end surfaces of said sintered ring magnet.  
   
   
       2 . A method of manufacturing sintered ring magnets comprising the steps of: 
 stacking a plurality of radially oriented ring-shaped powder compacts thereof in an axial direction to produce a ring-shaped powder compact rod;    sintering the ring-shaped powder compact rod to produce a sintered ring-shaped powder compact rod in which the ring-shaped powder compacts are joined together as a result of sintering operation; and    dividing the sintered ring-shaped powder compact rod;    wherein the ring-shaped powder compacts are joined to one another with a reduced joint strength at specific boundary regions than at the other boundary regions when sintered, and said sintered ring magnets are obtained by dividing the sintered ring-shaped powder compact rod at said specific boundary regions having the reduced joint strength.    
   
   
       3 . The method of manufacturing the sintered ring magnets according to  claim 2 , wherein the ring-shaped powder compacts are stacked on top of a dummy ring-shaped powder compact such that the dummy ring-shaped powder compact is located in a lowermost layer of the ring-shaped powder compact rod, wherein the dummy ring-shaped powder compact is joined to the ring-shaped powder compact stacked immediately above with a reduced joint strength at a boundary region therebetween as a result of the sintering operation, and wherein said sintered ring magnets are obtained by dividing the sintered ring-shaped powder compact rod after the sintering operation at said specific boundary regions having the reduced joint strength.  
   
   
       4 . The method of manufacturing the sintered ring magnets according to  claim 2 , wherein one of a protruding part and a recessed part is formed on at least one of longitudinal end surfaces of each ring-shaped powder compact facing one of said specific boundary regions, and said sintered ring magnets are obtained by dividing the sintered ring-shaped powder compact rod at each of said specific boundary regions where one of the protruding part and the recessed part is formed after the sintering operation.  
   
   
       5 . The method of manufacturing the sintered ring magnets according to  claim 2 , wherein ceramic powder having a particle size between 1 micrometer and 100 micrometers is dusted to a thickness between 1 micrometer and 100 micrometers at each of said specific boundary regions, and said sintered ring magnets are obtained by dividing the sintered ring-shaped powder compact rod at said specific boundary regions after the sintering operation.  
   
   
       6 . The method of manufacturing the sintered ring magnets according to  claim 2 , wherein burrs formed on surfaces of the ring-shaped powder compacts in a pressing process or excess magnetic powder which adheres to the surfaces of the ring-shaped powder compacts in a die release process is left unremoved from said specific boundary regions of the ring-shaped powder compacts, the ring-shaped powder compact rod is produced by using the ring-shaped powder compacts thus prepared, and said sintered ring magnets are obtained by dividing the sintered ring-shaped powder compact rod at said specific boundary regions after the sintering operation.  
   
   
       7 . The method of manufacturing the sintered ring magnets according to  claim 2 , wherein the sintered ring-shaped powder compact rod is divided at said specific boundary regions having the reduced joint strength after at least one of a curved inner surface and a curved outer surface of the sintered ring-shaped powder compact rod, in which the ring-shaped powder compacts are joined into a single structure by sintering, is finished by machining.  
   
   
       8 . The method of manufacturing the sintered ring magnets according to  claim 7 , wherein the sintered ring-shaped powder compact rod is divided at said specific boundary regions having the reduced joint strength after the sintered ring-shaped powder compact rod of which at least one of the curved inner surface and the curved outer surface has been machined is subjected to an anticorrosion surface treatment.