Sintered bearing and method of manufacturing same

Abstract

Provided is a sintered bearing formed mainly of an iron structure ( 33 ) and a copper structure ( 31 ) which are formed of a partially diffusion-alloyed powder ( 11 ) of an iron powder ( 12 ) and a copper powder ( 13 ). The sintered bearing includes a copper structure ( 31 d ) formed of a granular elemental copper powder ( 13 ′) having a grain diameter of 45 μm or less, the ratio of the copper structure ( 31 d ) being 10 mass % or less. With this, a further increase in strength of the sintered bearing can be realized.

1 . A sintered bearing, which is formed mainly of an iron structure and a copper structure which are formed of partially diffusion-alloyed powder of iron powder and copper powder,
 the sintered bearing comprising a copper structure formed of granular elemental copper powder having a grain diameter of 45 μm or less, a ratio of the copper structure formed of the elemental copper powder being 10 mass % or less.   
     
     
         2 . The sintered bearing according to  claim 1 , wherein the partially diffusion-alloyed powder contains 30 mass % or more of powder having a grain diameter of more than 106 μm. 
     
     
         3 . The sintered bearing according to  claim 1 , wherein the sintered bearing has a density of 7.0 g/cm 3  or more. 
     
     
         4 . The sintered bearing according to  claim 1 , further comprising 2 mass % to 3 mass % of a low-melting point substance having a melting point lower than that of copper. 
     
     
         5 . The sintered bearing according to  claim 1 , further comprising a surface layer formed mainly of flat copper powder arranged substantially parallel to a surface of the sintered bearing. 
     
     
         6 . The sintered bearing according to  claim 1 , wherein the partially diffusion-alloyed powder has a grain diameter equal to or less than ½ of a minimum thickness of the sintered bearing. 
     
     
         7 . The sintered bearing according to  claim 1 , wherein the sintered bearing is used for a vibration motor. 
     
     
         8 . A method of manufacturing a sintered bearing, comprising the steps of:
 classifying partially diffusion-alloyed powder of iron powder and copper powder by passage through a sieve;   compression-molding raw material powders containing the classified partially diffusion-alloyed powder to form a green compact; and   sintering the green compact to form a sintered compact,   the raw material powders containing, at a ratio of 10 mass % or less, elemental copper powder that has escaped from the partially diffusion-alloyed powder as a result of the classifying.   
     
     
         9 . The method of manufacturing a sintered bearing according to  claim 8 , wherein the classifying partial diffusion alloy is performed using a sieve having an opening of 125 μm or more. 
     
     
         10 . The sintered bearing according to  claim 1 , further comprising:
 a sintered compact; and   a grease impregnated into the sintered compact,   wherein the grease contains a thickener, and a base oil having a kinematic viscosity at 40° C. of 40 mm 2 /s or more and 60 mm 2 /s or less, and a kinematic viscosity at 100° C. of 5 mm 2 /s or more and 10 mm 2 /s or less according to a kinematic viscosity measurement method based on JIS K 2283, and a concentration of the thickener in the grease is from 0.1 wt % to 3 wt %.   
     
     
         11 . The sintered bearing according to  claim 10 , wherein the base oil to be used comprises a poly-α-olefin-based synthetic lubricating oil. 
     
     
         12 . The sintered bearing according to  claim 10 , wherein the base oil to be used comprises a poly-α-olefin-based synthetic lubricating oil and an ester-based synthetic lubricating oil. 
     
     
         13 . The sintered bearing according to  claim 10 , wherein the thickener to be used comprises a lithium soap. 
     
     
         14 . The sintered bearing according to  claim 10 , wherein the sintered bearing is incorporated into a device to be reflow-soldered onto a circuit board. 
     
     
         15 . A device to be soldered onto a circuit board through use of a reflow solder, the device comprising the sintered bearing of  claim 10 . 
     
     
         16 . The sintered bearing according to  claim 2 , wherein the sintered bearing has a density of 7.0 g/cm 3  or more. 
     
     
         17 . The sintered bearing according to  claim 2 , further comprising 2 mass % to 3 mass % of a low-melting point substance having a melting point lower than that of copper. 
     
     
         18 . The sintered bearing according to  claim 3 , further comprising 2 mass % to 3 mass % of a low-melting point substance having a melting point lower than that of copper. 
     
     
         19 . The sintered bearing according to  claim 16 , further comprising 2 mass % to 3 mass % of a low-melting point substance having a melting point lower than that of copper. 
     
     
         20 . The sintered bearing according to  claim 2 , further comprising a surface layer formed mainly of flat copper powder arranged substantially parallel to a surface of the sintered bearing.