Two stage melting and casting system and method

Abstract

A system for two stage casting of a metal alloy is disclosed that dispenses multiple feedstock metals into an arc melting crucible via a pressurized inert gas or metal vapor chamber to lower the volatilization rate of metals in an arc melting crucible at a rate proportional to the composition of the final desired alloy. The melt from the melting crucible enters a second stage cold wall crucible through a passage, where the melt cools and solidifies. A casting piston is used to slowly and progressively withdraw the solidified alloy from the cold wall crucible as it cools.

What is claimed is: 
     
         1 . A system for two stage casting of a metal alloy, comprising:
 a first stage comprising a first crucible, a pressurized inert gas or metal vapor chamber connected to the first crucible to adjust a volatilization rate of feedstock metals in the first crucible such that all metals introduced into the first crucible are retained in a liquid state in the first crucible, and a feedstock control system to dispense feedstock metals into the chamber and into the first crucible, wherein the feedstock metals are dispensed at a rate sufficient to achieve a target composition of a final metal alloy;   wherein at least one of the feedstock metals is in the form of an electrode, wherein the system is operable to supply electrical current to the electrode; and   a second stage comprising a second cooling crucible connected to the first crucible via a passageway.   
     
     
         2 . The system according to  claim 1  further comprising a layer of metal salt/slag on the first crucible, the layer of metal salt/slag having an upper surface. 
     
     
         3 . The system according to  claim 2  wherein the electrode has a tip submerged below the upper surface of the layer of metal salt/slag. 
     
     
         4 . The system according to  claim 3  further comprising one or more secondary feedstock elements fed into the metal salt/slag via a feedstock control system. 
     
     
         5 . A two stage method of producing a metal alloy comprising;
 placing a metal salt layer in a first crucible, wherein the first crucible is connected to a second crucible via a passageway;   introducing a first electrode into the metal salt layer;   passing an electrical current through the first electrode to produce a slag layer in the first crucible from the metal salt layer via resistance heating;   pushing the electrode into the slag layer so that a tip of the electrode begins to melt into a molten composition below the slag layer in the first crucible;   introducing secondary feedstock elements into the slag layer to melt the secondary feedstock elements into the molten composition in the first crucible;   continuing to melt the electrode and the secondary feedstock elements into the composition until a desired volume of composition is reached;   once the desired volume of molten composition is achieved, opening the passageway to the second crucible such that the molten composition flows into the second crucible; and   cooling the composition in the second crucible to a solid state.   
     
     
         6 . The method of  claim 5  wherein cooling the composition comprises progressively lowering a piston attached to a bottom of the second crucible as the molten composition solidifies bottom up in the second crucible. 
     
     
         7 . The method of  claim 5  wherein the electrode is a metal having a highest melting point of any of the elements to be introduced into the first crucible. 
     
     
         8 . The method of  claim 5  wherein the electrode is a hollow tube. 
     
     
         9 . The method of  claim 5  wherein the electrode is titanium or a titanium alloy. 
     
     
         10 . The method of  claim 5  wherein the resistive heating of the metal salt by the first electrode heats the slag layer to a temperature above a secondary element melting point. 
     
     
         11 . The method of  claim 5  wherein as a bottom portion of the composition in the secondary crucible solidifies the secondary crucible is withdrawn such that the bottom portion is progressively lowered relative to a top of the secondary crucible. 
     
     
         12 . A system for two stage casting of a metal alloy, comprising:
 a first stage comprising a first crucible, a pressurized inert gas or metal vapor chamber connected to the first crucible to adjust a volatilization rate of feedstock metals in the first crucible such that all metals introduced into the first crucible are retained in a liquid state in the first crucible, and a feedstock control system to dispense feedstock metals through the chamber and into the first crucible, wherein the feedstock metals are dispensed at a rate sufficient to achieve a molten composition of a final metal alloy;   wherein at least one of the feedstock metals is in the form of an electrode, wherein the system is operable to supply electrical current to the electrode;   an electromagnetic stirring mechanism operable to stir the molten composition in the first crucible; and   a second stage comprising a second cooling crucible connected to the first crucible via a passageway.   
     
     
         13 . The system according to  claim 12  further comprising a layer of metal salt/slag on the first crucible, the layer of metal salt/slag having an upper surface. 
     
     
         14 . The system according to  claim 13  wherein the electrode has a tip submerged below the upper surface of the layer of metal salt/slag. 
     
     
         15 . The system according to  claim 14  further comprising one or more secondary feedstock elements fed into the metal salt/slag via a feedstock control system. 
     
     
         16 . The system according to  claim 15  wherein the secondary feedstock elements are high density materials that sit below the upper surface of the slag layer. 
     
     
         17 . The system according to  claim 15  wherein one of the electrode and the secondary elements include one or more hollow elements extending below the upper surface of the slag layer. 
     
     
         18 . The system according to  claim 13  wherein the slag layer is a metal salt/slag layer having an increasing temperature gradient from the upper surface to a bottom of the layer. 
     
     
         19 . The system according to  claim 15  wherein the secondary elements extend below the upper surface of the slag layer. 
     
     
         20 . The system according to  claim 15  wherein the layer has a thickness sufficient to achieve a first temperature associated with its upper surface, and a second temperature associated with its lower surface, wherein the first temperature is lower than the melting point of the electrode and wherein the second temperature is higher than the melting point of the electrode.