Method for producing high-strength sintered compact and high-strength sintered compact production system

Abstract

A method for producing a high-strength sintered compact includes a press molding step and a sintering step, the press molding step including a first press molding step and a second press molding step, a heating step being provided between the first press molding step and the second press molding step, the first press molding step applying a first pressure to the mixed powder in a first die at room temperature that is less than a melting point of the lubricant powder to form a primary green compact, the heating step heating the primary green compact to the melting point of the lubricant powder, and the second press molding step applying a second pressure to the primary green compact in a second die at the melting point of the lubricant powder to form a densified secondary green compact, the second die being pre-heated to the melting point of the lubricant powder.

1 . A method for producing a high-strength sintered compact comprising:
 a press molding step that applies pressure to a mixed powder to form a green compact, the mixed powder being a mixture of a basic metal powder and a lubricant powder; and   a sintering step that sinters the green compact to form a sintered compact that exhibits improved mechanical strength,   the press molding step including a first press molding step and a second press molding step, a heating step being provided between the first press molding step and the second press molding step,   the first press molding step applying a first pressure to the mixed powder in a first die at room temperature that is less than a melting point of the lubricant powder to form a primary green compact,   the heating step heating the primary green compact to the melting point of the lubricant powder, and   the second press molding step applying a second pressure to the primary green compact in a second die at the melting point of the lubricant powder to form a densified secondary green compact, the second die being heated to the melting point of the lubricant powder.   
     
     
         2 . The method for producing a high-strength sintered compact as defined in  claim 1 , wherein the lubricant powder has a low melting point within a range of 90 to 190° C. 
     
     
         3 . The method for producing a high-strength sintered compact as defined in  claim 1 , wherein the mixed powder is prepared by mixing a pure iron powder as the basic metal powder with 0.03 to 0.10 wt % of a zinc stearate powder as the lubricant powder, the first pressure is selected to compress the mixed powder so that the primary green compact has a density of 7.0 to 7.5 g/cm 3 , and the second pressure is selected to compress the primary green compact so that the secondary green compact has a density of 7.75 g/cm 3 . 
     
     
         4 . The method for producing a high-strength sintered compact as defined in  claim 1 , wherein the mixed powder is prepared by mixing an Fe—Si alloy powder as the basic metal powder with 0.03 to 0.10 wt % of a zinc stearate powder as the lubricant powder, the first pressure is selected to compress the mixed powder so that the primary green compact has a true density ratio of 70 to 85%, and the second pressure is selected to compress the primary green compact so that the secondary green compact has a true density ratio of 85 to 95%. 
     
     
         5 . The method for producing a high-strength sintered compact as defined in  claim 1 , wherein the second pressure is selected to be equal to the first pressure. 
     
     
         6 . A high-strength sintered compact production system comprising:
 a mixed powder feeding device that can externally supply a mixed powder that is a mixture of a basic metal powder and a lubricant powder that has a low melting point;   a first press molding device that applies a first pressure to the mixed powder in a first die to form a primary green compact, the first die being filled with the mixed powder using the mixed powder feeding device;   a heating device that heats the primary green compact removed from the first die to the melting point of the lubricant powder;   a second press molding device that includes a second die that can be pre-heated to the melting point of the lubricant powder in advance, and applies a second pressure to the primary green compact that has been heated and is placed in the pre-heated second die to form a densified secondary green compact; and   a sintering device that sinters the secondary green compact to form a sintered compact that exhibits improved mechanical strength.   
     
     
         7 . The high-strength sintered compact production system as defined in  claim 6 , wherein the heating device and the second press molding device are formed by a heating/press molding device having a function of the heating device and a function of the second press molding device, the heating/press molding device includes a plurality of heating/press molding sub-devices, and each of the plurality of heating/press molding sub-devices can be selectively and sequentially operated in each cycle. 
     
     
         8 . The method for producing a high-strength sintered compact as defined in  claim 2 , wherein the mixed powder is prepared by mixing a pure iron powder as the basic metal powder with 0.03 to 0.10 wt % of a zinc stearate powder as the lubricant powder, the first pressure is selected to compress the mixed powder so that the primary green compact has a density of 7.0 to 7.5 g/cm 3 , and the second pressure is selected to compress the primary green compact so that the secondary green compact has a density of 7.75 g/cm 3 . 
     
     
         9 . The method for producing a high-strength sintered compact as defined in  claim 2 , wherein the mixed powder is prepared by mixing an Fe—Si alloy powder as the basic metal powder with 0.03 to 0.10 wt % of a zinc stearate powder as the lubricant powder, the first pressure is selected to compress the mixed powder so that the primary green compact has a true density ratio of 70 to 85%, and the second pressure is selected to compress the primary green compact so that the secondary green compact has a true density ratio of 85 to 95%. 
     
     
         10 . The method for producing a high-strength sintered compact as defined in  claim 2 , wherein the second pressure is selected to be equal to the first pressure.