Sintered bearing and manufacturing process therefor

Abstract

A sintered bearing ( 1 ) contains as main components iron, copper, a metal having a lower melting point than copper, and a solid lubricant. The sintered bearing ( 1 ) includes a surface layer (S 1 ) and a base part (S 2 ). The surface layer (S 1 ) is formed mainly of flat copper powder arranged so as to be thinned in a thickness direction. In the base part (S 2 ), an iron structure ( 33 ) and a copper structure ( 31 c ) brought into contact with the iron structure are formed of partially diffusion-alloyed powder in which copper powder is partially diffused in iron powder. Thus, a sintered bearing which achieves a balance between wear resistance of a bearing surface and strength of the bearing, and realizes low cost can be provided.

1 . A sintered bearing, which contains as main components iron, copper, a metal having a lower melting point than copper, and a solid lubricant,
 the sintered bearing comprising:
 a base part containing an iron structure and a copper structure; and 
 a surface layer covering a surface of the base part, 
   wherein:   the surface layer is formed mainly of flat copper powder arranged so as to be thinned in a thickness direction; and   at least part of the iron structure and the copper structure in the base part is formed of partially diffusion-alloyed powder in which copper powder is partially diffused in iron powder.   
     
     
         2 . The sintered bearing according to  claim 1 , wherein the copper structure is formed in a surface of the surface layer at an area ratio of 60% or more. 
     
     
         3 . The sintered bearing according to  claim 1 , wherein the iron structure and the copper structure in the base part are entirely formed of the partially diffusion-alloyed powder. 
     
     
         4 . The sintered bearing according to  claim 1 , wherein the iron structure and the copper structure in the base part are formed of: the partially diffusion-alloyed powder; and any one or both of elemental iron powder and elemental copper powder. 
     
     
         5 . The sintered bearing according to  claim 1 , wherein, in the base part, the copper structure brought into contact with the iron structure comprises a structure in which the low-melting point metal is diffused in the copper powder. 
     
     
         6 . The sintered bearing according to  claim 1 , wherein the sintered bearing contains the low-melting point metal at a weight ratio of 10 wt % or more and 30 wt % or less with respect to the flat copper powder. 
     
     
         7 . The sintered bearing according to  claim 1 , wherein the solid lubricant comprises graphite. 
     
     
         8 . The sintered bearing according to  claim 1 , wherein the iron structure is formed of a ferrite phase. 
     
     
         9 . The sintered bearing according to  claim 1 , wherein the iron structure is formed of a ferrite phase and a pearlite phase that is present at a grain boundary of the ferrite phase. 
     
     
         10 . The sintered bearing according to  claim 1 , wherein the partially diffusion-alloyed powder has a ratio of copper of 10 wt % or more and 30 wt % or less. 
     
     
         11 . The sintered bearing according to  claim 1 , wherein the sintered bearing is impregnated with a lubricating oil having a kinematic viscosity of 30 mm 2 /sec or more and 200 mm 2 /sec or less. 
     
     
         12 . The sintered bearing according to  claim 1 , wherein the sintered bearing is used for a starter configured to activate an engine. 
     
     
         13 . The sintered bearing according to  claim 1 , wherein the sintered bearing is used for a vibration motor. 
     
     
         14 . A method of manufacturing a sintered bearing, the method comprising:
 mixing partially diffusion-alloyed powder in which copper powder is partially diffused in iron powder, flat copper powder, metal powder having a lower melting point than copper, and solid lubricant powder;   forming a green compact with the resultant mixed powder; and   sintering the green compact at a temperature lower than a melting point of copper.   
     
     
         15 . The sintered bearing according to  claim 2 , wherein the iron structure and the copper structure in the base part are entirely formed of the partially diffusion-alloyed powder. 
     
     
         16 . The sintered bearing according to  claim 2 , wherein the iron structure and the copper structure in the base part are formed of: the partially diffusion-alloyed powder; and any one or both of elemental iron powder and elemental copper powder. 
     
     
         17 . The sintered bearing according to  claim 2 , wherein, in the base part, the copper structure brought into contact with the iron structure comprises a structure in which the low-melting point metal is diffused in the copper powder. 
     
     
         18 . The sintered bearing according to  claim 3 , wherein, in the base part, the copper structure brought into contact with the iron structure comprises a structure in which the low-melting point metal is diffused in the copper powder. 
     
     
         19 . The sintered bearing according to  claim 4 , wherein, in the base part, the copper structure brought into contact with the iron structure comprises a structure in which the low-melting point metal is diffused in the copper powder. 
     
     
         20 . The sintered bearing according to  claim 15 , wherein, in the base part, the copper structure brought into contact with the iron structure comprises a structure in which the low-melting point metal is diffused in the copper powder.