Vapor-reinforced expanding volume of gas to minimize the contamination of products treated in a melting furnace

Abstract

Systems and corresponding methods are described herein that provide an effective inert blanket over a metal surface (hot solid (charge) metal or molten metal) in a container such as an induction furnace. The system includes a container of metal and a system configured to delivery biphasic inert cryogen toward the metal. The delivery system may include a lance disposed at the top of the container. The lance has a hood that directs both a flow of liquid cryogen and a flow of vaporous gas toward the metal surface. The liquid cryogen contacts the metal surface, generating a volume of expanding gas over the metal surface, The vaporous cryogen creates a reinforcing vapor that slows the expansion rate of the expanding gas, localizing the expanding gas over the metal surface.

1 . A method for reducing the oxidation of molten metal, the method comprising:
 (a) forming molten metal within a container, the molten metal having an exposed surface defining a surface area and possessing a generally meniscoid shape with a lowered center meniscus portion and a upper edge meniscus portion;   (b) generating a biphasic inert cryogen comprising a liquid flow component and a vaporous flow component;   (c) directing the liquid flow component into contact with the upper edge meniscoid portion of the molten metal to generate an expanding gaseous volume having a rate of expansion; and   (d) directing the vaporous flow component into the container to inhibit the rate of expansion of the gaseous volume.   
     
     
         2 . The method of  claim 1 , wherein (b) comprises (b.1) directing a flow of biphasic inert cryogen at a flow rate effective to generate the expanding gaseous volume that is substantially coextensive with the exposed surface of the molten metal. 
     
     
         3 . The method of  claim 2 , wherein the flow rate is dependent upon the surface area of the molten metal. 
     
     
         4 . The method of  claim 2 , wherein the flow rate is in the range of about 0.001 lb/in 2 /min. to about 0.005 lb/in 2 /min., based upon the surface area of the molten metal. 
     
     
         5 . The method of  claim 1 , further comprising (e) maintaining the flow rate to localize the liquid flow component within a portion of the molten metal exposed surface. 
     
     
         6 . The method of  claim 1 , wherein the container comprises:
 a bottom wall,   a side wall, and   an opening; and   
       further comprises directing the liquid flow component proximate the side wall such that the liquid flow component contacts the molten metal at a point proximate the side wall. 
     
     
         7 . The method of  claim 6 , wherein the flow rate of the inert cryogen is maintained such that liquid flow is localized within an area smaller than the total surface area of the molten metal exposed surface. 
     
     
         8 . The method of  claim 7 , wherein the flow rate is in the range of about 0.001 lb/in 2 /min. to about 0.005 lb/in 2  min., based upon the surface area of the molten metal. 
     
     
         9 . The method of  claim 1 , wherein;
 (a) the container comprises a side wall;   (b) generating the biphasic inert cryogen comprises (b.1) directing a liquid inert cryogen from a source through a diffuser to separate the liquid flow component from the vaporous flow component; and   (c) directing the liquid flow component comprises (c.1) directing the liquid flow component along the side wall such that it contacts the upper edge meniscoid portion to form a volume of vaporizing liquid cryogen localized within the upper edge meniscus edge portion.   
     
     
         10 . The method of  claim 1 , wherein (b) generating the biphasic inert cryogen comprises (b.1) directing a liquid inert cryogen from a source through a diffuser to separate the liquid flow component from the vaporous flow component. 
     
     
         11 . The method of  claim 1 , wherein:
 (a) the container comprises a side wall;   (b) generating the biphasic inert cryogen comprises (b.1) directing a liquid inert cryogen from a source through a diffuser to separate the liquid flow component from the vaporous flow component; and   (c) directing the liquid flow component comprises (c.1) directing the liquid flow component along the side wall such that it contacts the lower centered meniscoid portion to form a volume of vaporizing liquid cryogen localized within the lower meniscus edge portion.   
     
     
         12 . A method for reducing the oxidation of molten metal, the method comprising:
 (a) forming molten metal within a container, the molten metal having an exposed surface defining a surface area and possessing a generally flattened surface shape;   (b) generating a biphasic inert cryogen comprising a liquid flow component and a vaporous flow component;   (c) directing the liquid flow component into contact with a confined area on the surface of the molten metal to generate an expanding gaseous volume having a rate of expansion; and   (d) directing the vaporous flow component into the container to inhibit the rate of expansion of the gaseous volume.   
     
     
         13 . The method of  claim 12 , wherein (b) comprises (b.1) directing a flow of biphasic inert cryogen at a flow rate effective to generate the expanding gaseous volume that is substantially coextensive with the exposed surface of the molten metal. 
     
     
         14 . The method of  claim 13 , wherein the flow rate is dependent upon the surface area of the molten metal. 
     
     
         15 . The method of  claim 13 , wherein the flow rate is in the range of about 0.001 lb/in 2 /min. to about 0.005 lb/in 2 /min., based upon the surface area of the molten metal. 
     
     
         16 . The method of  claim 15 , further comprising (e) maintaining the flow rate to localize the liquid flow component within a portion of the molten metal exposed surface. 
     
     
         17 . The method of  claim 12 , wherein the container comprises:
 a bottom wall,   a side wall, and   an opening; and   
       further comprises directing the liquid flow component proximate the side wall such that the liquid flow component contacts the molten metal at a point proximate the side wall. 
     
     
         18 . The method of  claim 17 , wherein the flow rate of the inert cryogen is maintained such that liquid flow is localized within an area smaller than the total surface area of the molten metal exposed surface. 
     
     
         19 . The method of  claim 18 , wherein the flow rate is in the range of about 0.001 lb/in 2 /min. to about 0.005 lb/in 2  min., based upon the surface area of the molten metal.