Method of manufacturing bismuth shot

Abstract

A molten metal alloy, such as bismuth and tin, is injected into a die block to form a tightly packed rectangular array of shot pellets. The ratio of waste sprue to shot pellets is minimized and the shot pellet yield per casting is maximized by allowing the shot pellets in the rectangular shot array to touch other shot pellets in adjoining rows and columns through small interconnecting vias. The interconnecting vias allows the molten metal to flow between shot pellets, as well as from the sprue into the shot pellets. This allows the molten metal to bypass blockages that reduce the shot pellet count per casting. The flow of the molten metal through the die block is also improved by machining away a small amount of metal from the face of the die in order to form a flashing between the shot pellets.

What is claimed is:  
     
         1 . A method for producing shot pellets, said method comprising: 
 casting an array of shot pellets from a shot pellet alloy material, wherein each shot pellet of said array of shot pellets is connected to at least two other shot pellets of said array of shot pellets by said shot pellet alloy material;    tumbling said array of shot pellets with a tumbling media, wherein said tumbling breaks up said shot pellet array into individual shot pellets and causes connecting portions of said shot pellet alloy material to be removed from surfaces of said shot pellets, and wherein said tumbling media deforms improperly cast shot pellets of said array of shot pellets for separation from properly cast shot pellets of said array of shot pellets.    
     
     
         2 . The method    claim 1   , wherein said pellet alloy material expands when transitioning from the liquid to the solid state.  
     
     
         3 . The method of    claim 2   , wherein said shot pellet alloy material is a bismuth alloy.  
     
     
         4 . The method of    claim 3   , wherein said bismuth alloy includes tin.  
     
     
         5 . The method of    claim 1   , wherein said tumbling media includes ball bearings.  
     
     
         6 . The method of    claim 1   , wherein said tumbling is continued for a time in the range of from 10 to 30 minutes.  
     
     
         7 . The method of    claim 1   , further comprising: 
 poring the tumbled array of shot pellets through a sifter to separate the individual shot pellets from said tumbling media.    
     
     
         8 . The method of    claim 7   , further comprising: 
 separating the properly cast shot pellets from the improperly cast shot pellets using a classifier.    
     
     
         9 . The method of    claim 8   , wherein said classifier rolls the shot pellets down a series of steps set at varying angles for varying shot sizes to thereby automatically discard all less-than-round shot pellets including said improperly cast shot pellets.  
     
     
         10 . A system for producing shot pellets, said system comprising: 
 means for casting an array of shot pellets from a shot pellet alloy material, wherein each shot pellet of said array of shot pellets is connected to at least two other shot pellets of said array of shot pellets by said shot pellet alloy material;    means for tumbling said array of shot pellets with a tumbling media, wherein said tumbling breaks up said shot pellet array into individual shot pellets and causes connecting portions of said shot pellet alloy material to be removed from surfaces of said shot pellets, and wherein said tumbling media deforms improperly cast shot pellets of said array of shot pellets for separation from properly cast shot pellets of said array of shot pellets.    
     
     
         11 . The system    claim 1   O, wherein said pellet alloy material expands when transitioning from the liquid to the solid state.  
     
     
         12 . The system of    claim 11   , wherein said shot pellet alloy material is a bismuth alloy.  
     
     
         13 . The system of    claim 12   , wherein said bismuth alloy includes tin.  
     
     
         14 . The system of    claim 10   , wherein said tumbling media includes ball bearings.  
     
     
         15 . The system of    claim 10   , wherein said tumbling is continued for a time in the range of from 10 to 30 minutes.  
     
     
         16 . The system of    claim 10   , further comprising: 
 means for sifting the tumbled array of shot pellets to separate the individual shot pellets from said tumbling media.    
     
     
         17 . The system of    claim 16   , further comprising: 
 means for classifying the properly cast shot pellets from the improperly cast shot pellets.    
     
     
         18 . The system of    claim 17   , wherein a classifier of said means for classifying rolls the shot pellets down a series of steps set at varying angles for varying shot sizes to thereby automatically discard all less-than-round shot pellets including said improperly cast shot pellets.  
     
     
         19 . The system of    claim 10   , wherein a plurality of said shot pellets of said array of shot pellets are also connected to a sprue by said shot pellet alloy material, wherein a thickness of said shot pellet alloy material connecting said shot pellets to said sprue is larger than a thickness of said shot pellet alloy material connecting said shot pellets to said at least two other shot pellets of said shot pellet array.