Process of producing metal powders

Abstract

The invention provides an industrially efficient, low-cost, mass-production system for the process of producing fine solder powders using an in-oil atomization method wherein solder is melted in a heated dispersion medium for fine granulation. Molten solder melted in a solder melting tank and a mixture of a particle dispersion medium and a particle coalescence-preventing agent, prepared in a dispersion medium heating tank, are fed to a fine-granulation machine, in which dispersion energy is applied to obtain a dispersion of molten solder particles. The dispersion is processed in a solidifier-by-cooling to obtain a dispersion of solid solder particles, which is processed in a solid-liquid separator to separate the solid solder particles. The solid solder particles are washed and dried to obtain fine powders. The respective devices at these steps are connected together by way of piping, so that fine solder powders can continuously be produced.

What is claimed is:  
     
         1 . A process of producing metal powders, comprising steps of: 
 (a) melting a raw low-melting metal to obtain a metal melt,    (b) mixing a particle dispersion medium and a particle coalescence-preventing agent to obtain a dispersion medium that may or may not be heated,    (c) supplying the melt of said low-melting metal from said step (a) and supplying said dispersion medium from said step (b) with application of dispersion energy that disperses the melt of said low-melting metal in the form of fine particles, thereby obtaining a molten metal particle dispersion wherein molten metal particles are dispersed in said dispersion medium,    (d) cooling said molten metal particle dispersion to solidify said molten metal particles into solid metal particles,    (e) separating said solid metal particles from a liquid residue,    (f) washing said separated solid metal particles with a detergent to remove depositions to said solid metal particles, and    (g) drying said washed metal particles, wherein: 
 in said step (c), said particle coalescence-preventing agent adsorbs to and/or reacts with said molten metal particles to prevent coalescence of at least said molten metal particles so that said solid metal particles can be finely granulated in said steps (c) to (g), and said steps (a) to (g) are controlled in the form of a series of mutually correlative steps.  
   
     
     
         2 . The process of  claim 1 , wherein there is provided a dispersion medium recycle step in which the liquid residue separated in said step (e) is directly used as a part or the whole of the dispersion medium in said step (b) or a dispersion medium regenerated from said liquid residue in a dispersion medium regeneration step (h) is recycled as a part or the whole of the dispersion in said step (b), wherein said dispersion medium recycle step is continuously controlled in correlation to said step (b).  
     
     
         3 . The process of  claim 1 , wherein there is provided a detergent recycle step in which a spent detergent that may contain the depositions removed in said step (f) is directly used as a part or the whole of the detergent used in said step (f) or a detergent regenerated from said spent detergent in a detergent regeneration step (i) is recycled as a part or the whole of the detergent used in said step (f), wherein said detergent recycle step is continuously controlled in correlation to said step (f).  
     
     
         4 . The process of  claim 2 , wherein there is provided a detergent recycle step in which a spent detergent that may contain the depositions removed in said step (f) is directly used as a part or the whole of the detergent used in said step (f) or a detergent regenerated from said spent detergent in a detergent regeneration step (i) is recycled as a part or the whole of the detergent used in said step (f), wherein said detergent recycle step is continuously controlled in correlation to said step (f).  
     
     
         5 . The process of  claim 1 , wherein the detergent used in said step (f) has a vapor pressure of at least 15 kPa at 40° C. and a latent heat of vaporization of at most 100 kJ/kg.  
     
     
         6 . The process of  claim 2 , wherein the detergent used in said step (f) has a vapor pressure of at least 15 kPa at 40° C. and a latent heat of vaporization of at most 100 kJ/kg.  
     
     
         7 . The process of  claim 3 , wherein the detergent used in said step (f) has a vapor pressure of at least 15 kPa at 40° C. and a latent heat of vaporization of at most 100 kJ/kg.  
     
     
         8 . The process of  claim 4 , wherein the detergent used in said step (f) has a vapor pressure of at least 15 kPa at 40° C. and a latent heat of vaporization of at most 100 kJ/kg.  
     
     
         9 . The process of  claim 1 , wherein in said step (g), said washed solid metal particles are dried such that the liquid residue deposited to said solid metal particles accounts for 0.01 to 1% of said solid metal particles, thereby reducing oxidization and dusting of powders of said solid metal particles.  
     
     
         10 . The process of  claim 2 , wherein in said step (g), said washed solid metal particles are dried such that the liquid residue deposited to said solid metal particles accounts for 0.01 to 1% of said solid metal particles, thereby reducing oxidization and dusting of powders of said solid metal particles.  
     
     
         11 . The process of  claim 3 , wherein in said step (g), said washed solid metal particles are dried such that the liquid residue deposited to said solid metal particles accounts for 0.01 to 1% of said solid metal particles, thereby reducing oxidization and dusting of powders of said solid metal particles.  
     
     
         12 . The process of  claim 4 , wherein in said step (g), said washed solid metal particles are dried such that the liquid residue deposited to said solid metal particles accounts for 0.01 to 1% of said solid metal particles, thereby reducing oxidization and dusting of powders of said solid metal particles.  
     
     
         13 . The process of  claim 1 , wherein said step (d) of cooling the molten metal particle dispersion to solidify said molten metal particles into solid metal particles is carried out while said molten metal particles dispersion is passed through an inner pipe of a double pipe structure and a coolant is passed through an outer pipe of the double pipe structure.  
     
     
         14 . The process of  claim 2 , wherein said step (d) of cooling the molten metal particle dispersion to solidify said molten metal particles into solid metal particles is carried out while said molten metal particles dispersion is passed through an inner pipe of a double pipe structure and a coolant is passed through an outer pipe of the double pipe structure.  
     
     
         15 . The process  claim 3 , wherein said step (d) of cooling the molten metal particle dispersion to solidify said molten metal particles into solid metal particles is carried out while said molten metal particles dispersion is passed through an inner pipe of a double pipe structure and a coolant is passed through an outer pipe of the double pipe structure.  
     
     
         16 . The process of  claim 1 , wherein said double pipe is located at an angle of 45 to 90 degrees with respect to horizontal.  
     
     
         17 . The process of  claim 2 , wherein said double pipe is located at an angle of 45 to 90 degrees with respect to horizontal.  
     
     
         18 . The process of  claim 3 , wherein said double pipe is located at an angle of 45 to 90 degrees with respect to horizontal.  
     
     
         19 . The process of  claim 1 , wherein in said step (b), the dispersion medium that is a mixture of the particle dispersion medium with the particle coalescence-preventing agent is heated in such a way that said dispersion medium is preheated in a preheating tank, and then passed through a heated delivery pipe for a residence time that does not exceed 10 minutes at most.  
     
     
         20 . The process of  claim 2 , wherein in said step (b), the dispersion medium that is a mixture of the particle dispersion medium with the particle coalescence-preventing agent is heated in such a way that said dispersion medium is preheated in a preheating tank, and then passed through a heated delivery pipe for a residence time that does not exceed 10 minutes at most.