Mixed powder for powder metallurgy and manufacturing method thereof

Abstract

This mixed powder for powder metallurgy, the powder having excellent fluidity and minimal graphite powder scattering, can be obtained relatively conveniently by mixing fine graphite having an average grain diameter of 4 μm or less with an iron based powder. The process is performed without the addition of a binder and while shearing force is applied. It is preferable that the fine graphite have an average grain diameter of 2.4 μm or less and be wet-milled. A portion of the fine graphite is preferably added in place of at least one constituent selected from the group consisting of carbon black, fullerene, carbon compounds carbonized by baking, and graphite having an average grain diameter of 5 μm or more.

1 . A mixed powder, obtained by a process comprising mixing a fine graphite having a mean particle size of 4 μm or less with an iron based powder without adding a binder while applying a shear force. 
     
     
         2 . The mixed powder according to  claim 1 , wherein the mean particle size of the fine graphite is 2.4 μm or less. 
     
     
         3 . The mixed powder according to  claim 1 , wherein the fine graphite is obtained by wet crushing. 
     
     
         4 . The mixed powder according to  claim 1 , wherein the fine graphite is partially replaced with at least one selected from the group consisting of carbon black, fullerene, a carbon compound to be carbonized by burning, and a graphite having a mean particle size of 5 μm or more, to be added. 
     
     
         5 . The mixed powder according to  claim 4 , wherein a ratio of the fine graphite to a total amount of the fine graphite, the graphite, the carbon black, the fullerene, and the carbon compound is 15 mass % or more. 
     
     
         6 . The mixed powder according to  claim 5 , wherein the total amount of the fine graphite, the graphite, the carbon black, the fullerene, and the carbon compound is from 0.1 part to 3 parts by mass per 100 parts by mass of the iron based powder. 
     
     
         7 . The mixed powder according to  claim 1 , comprising at least one selected from the group consisting of a lubricant, a strength improver, an abrasion resistance improver, and a machinability improver. 
     
     
         8 . A mixed powder obtained by a process comprising mixing a fine graphite having a mean particle size of 4 μm or less with an iron based powder with an addition of a binder in a ratio of 0.1 part by mass or less per 100 parts by mass of the iron based powder while applying a shear force. 
     
     
         9 . A method for manufacturing a mixed powder for powder metallurgy, comprising:
 preparing a fine graphite having a mean particle size of 4 μm or less, and   mixing the fine graphite with an iron based powder without adding a binder while applying a shear force.   
     
     
         10 . A method for manufacturing a mixed powder, the method comprising:
 preparing a fine graphite having a mean particle size of 4 μm or less,   adding a binder to the fine graphite in a ratio of 0.1 part by mass or less per 100 parts by mass of an iron based powder, thereby obtaining a mixture of the fine graphite and the binder and   mixing the mixture with the iron based powder while applying a shear force.   
     
     
         11 . The method according to  claim 9 ,
 wherein the mixing is with a mixer comprising moving stirring vanes.   
     
     
         12 . The method according to  claim 10 , wherein the mixing is with a mixer comprising moving stirring vanes. 
     
     
         13 . The mixed power according to  claim 2 , wherein the mean particle size of the fine graphite is 2.0 μm or less. 
     
     
         14 . The mixed powder according to  claim 5 , wherein the ratio of the fine graphite to the total amount of the fine graphite, the graphite, the carbon black, the fullerene, and the carbon compound is 25 mass % or more. 
     
     
         15 . The mixed powder according to  claim 6 , wherein the total amount of the fine graphite, the graphite, the carbon black, the fullerene, and the carbon compound is from 0.3 part to 2.0 parts by mass per 100 parts by mass of the iron based powder. 
     
     
         16 . The method according to  claim 10 , wherein, in the adding, the binder is added in the ratio of 0.05 part by mass or less per 100 parts by mass of the iron based powder.