Magnesium die casting system

Abstract

An improved magnesium die casting system incorporates filling of the shot sleeve from the underside and/or in-line re-melting of scrap magnesium using a re-melt furnace. A pump is used to transfer molten magnesium from a casting furnace to the shot sleeve through an underflow filling tube. The shot sleeve is filled in a laminar manner, minimizing entrapped gases. The in-line re-melt system allows recycling of scrap in-house and reduces energy cost associated with heating and re-heating scrap. The improved system increases casting quality and reduces scrap rates and recycling costs.

1 . A magnesium die casting system comprising: a casting furnace for producing molten magnesium alloy, a pump for transferring the molten magnesium alloy, and a die casting machine having a shot sleeve for receiving the molten magnesium alloy, the shot sleeve adapted for filling from the underside thereof.  
   
   
       2 . The magnesium die casting system of  claim 1 , wherein the shot sleeve includes sealing means between the shot sleeve and an underflow filling tube.  
   
   
       3 . The magnesium die casting system of  claim 1 , wherein the molten magnesium is transferred at a flow rate and wherein the flow rate is modulated according to an algorithm.  
   
   
       4 . The magnesium die casting system of  claim 1 , wherein the shot sleeve is heated.  
   
   
       5 . The magnesium die casting system of  claim 1 , wherein the shot sleeve comprises gas flow ports.  
   
   
       6 . A magnesium die casting system comprising: 
 a) a casting furnace containing molten magnesium alloy;    b) a die casting machine comprising a die for creating magnesium die castings and a shot sleeve sized to receive a charge of molten magnesium corresponding to a volume of the die, the shot sleeve comprising a plunger means for periodically transferring the charge to the die at a pre-determined cycle time;    c) a filling port for filling the shot sleeve with the charge of molten magnesium, the filling port located on an underside of the shot sleeve;    d) a filling tube connected to the filling port and in fluid communication with the casting furnace; and,    e) a positive displacement pump in the casting furnace in fluid communication with the filling tube for delivering the charge of molten magnesium to the shot sleeve through the filling port on the underside thereof at a flow rate corresponding to the pre-determined cycle time, the flow rate selected to provide laminar filling of the shot sleeve.    
   
   
       7 . A magnesium die casting system according to  claim 6 , wherein the shot sleeve further comprises a gas port, the gas port being open during filling of the shot sleeve and permitting any gases within the shot sleeve to be displaced upwardly through the gas port as the level of molten metal rises in the shot sleeve during filling.  
   
   
       8 . A magnesium die casting system according to  claim 7 , wherein the gas port is located on an upper portion of the shot sleeve.  
   
   
       9 . A magnesium die casting system according to  claim 6 , wherein the shot sleeve further comprises gas ports for evacuating the shot sleeve independently of any evacuation of the die.  
   
   
       10 . A magnesium die casting system according to  claim 9 , wherein the shot sleeve is evacuated while the die is closed during formation of the casting.  
   
   
       11 . A magnesium die casting system according to  claim 9 , wherein the shot sleeve is evacuated with an applied vacuum from 0.1 to 2 psi.  
   
   
       12 . A magnesium die casting system according to  claim 6 , wherein the pre-determined cycle time is less than six seconds.  
   
   
       13 . A magnesium die casting system according to  claim 6 , wherein the pre-determined cycle time is about four seconds.  
   
   
       14 . A magnesium die casting system according to  claim 6 , wherein the filling tube comprises a heated portion to maintain a desired molten metal temperature.  
   
   
       15 . A magnesium die casting system according to  claim 6 , wherein the molten magnesium is transferred to the shot sleeve at about the temperature of the molten metal in the casting furnace.  
   
   
       16 . A magnesium die casting system according to  claim 6 , wherein the flow rate is modulated during the filling operation according to an algorithm.  
   
   
       17 . A magnesium die casting system comprising: 
 a) a casting furnace containing molten magnesium alloy;    b) a die casting machine comprising a die for creating magnesium die castings and a shot sleeve sized to receive a charge of molten magnesium corresponding to a volume of the die, the shot sleeve comprising a plunger means for periodically transferring the charge to the die at a pre-determined cycle time;    c) a filling port for filling the shot sleeve with the charge of molten magnesium, the filling port located on an underside of the shot sleeve;    d) a filling tube connected to the filling port and in fluid communication with the casting furnace;    e) a positive displacement pump in the casting furnace in fluid communication with the filling tube for delivering the charge of molten magnesium to the shot sleeve through the filling port on the underside thereof at a flow rate corresponding to the pre-determined cycle time; and,    f) a gas port located on the shot sleeve, the gas port being open during filling of the shot sleeve and permitting any gases within the shot sleeve to be displaced upwardly through the gas port as the level of molten metal rises in the shot sleeve during filling.    
   
   
       18 . A magnesium die casting system according to  claim 17 , wherein the shot sleeve is horizontal.  
   
   
       19 . A magnesium die casting system according to  claim 18 , wherein the gas port is located on an upper portion of the shot sleeve.  
   
   
       20 . A magnesium die casting system according to  claim 19 , wherein the flow rate is selected to provide laminar filling of the shot sleeve from the underside thereof.