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;   (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 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 0.002 lb/in 2  to about 0.005 lb/in 2 , based upon the surface area of the molten metal. 
     
     
         5 . The method of  claim 1 , wherein the molten metal possesses a generally meniscoid shape with a raised center meniscus portion and a lower edge meniscus portion, and (c) comprises (c.1) directing the liquid flow component into contact with the lower meniscoid portion. 
     
     
         6 . 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. 
     
     
         7 . The method of  claim 1 , wherein:
 the container comprises:
 a bottom wall, 
 a side wall, and 
 an opening; and 
   (c) 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.   
     
     
         8 . The method of  claim 7 , 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. 
     
     
         9 . The method of  claim 8 , wherein the flow rate is in the range of about 0.002 lb/in 2  to about 0.005 lb/in 2 , based upon the surface area of the molten metal. 
     
     
         10 . The method of  claim 1 , wherein:
 the container comprises a side wall;   the molten metal possesses a generally meniscoid shape with a raised center meniscus portion and a lower edge meniscus portion located proximate the 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 meniscoid portion to form a volume of vaporizing liquid cryogen localized within the lower meniscus edge portion.   
     
     
         11 . 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. 
     
     
         12 . A heating system comprising:
 a open vessel for containing molten metal, the vessel including a bottom wall, a side wall, and an opening;   an inert cryogen source, the inert cryogen including a liquid flow component and a vaporous flow component;   a delivery system disposed proximate the opening, the delivery system comprising:
 a lance including an inlet and a outlet, wherein the inlet is connected to the inert cryogen source; 
 a hood coupled to the outlet of the lance, wherein the hood directs the components of the inert cryogen toward the molten metal, 
   wherein the hood is configured to direct the liquid component of the inert cryogen toward the bottom wall of the vessel such that the liquid component contacts the molten metal to form an expanding volume of gas having a rate of expansion, and   wherein the hood is further configured to direct the vaporous component toward the molten metal to inhibit the rate of expansion of the expanding volume of gas.   
     
     
         13 . The heating system of  claim 12 , wherein the hood comprises a curved housing including an inlet and an outlet located downstream from the inlet. 
     
     
         14 . The heating system of  claim 13 , wherein the hood possesses a degree of curvature of about 0° to about 90°. 
     
     
         15 . The heating system of  claim 12 , wherein the hood comprises an outlet oriented such that it is generally coplanar with the opening of the vessel. 
     
     
         16 . The heating system of  claim 12 , wherein the hood comprises outlet oriented within the vessel at a point slightly below the opening of the vessel. 
     
     
         17 . The heating system of  claim 12 , wherein the delivery system is operable to generate a flow rate of inert cryogen the range of about 0.002 lb/in 2  to about 0.005 lb/in 2 , based upon the surface area of the molten metal. 
     
     
         18 . The heating system of  claim 12 , wherein the hood is oriented proximate the side wall of the vessel. 
     
     
         19 . The heating system of  claim 12 , wherein the delivery system further comprises a diffuser disposed at the outlet of the lance and housed within the hood, the diffuser operable to separate the liquid flow component from the vaporous flow component. 
     
     
         20 . The heating system of  claim 12 , wherein:
 the hood comprises a curved housing including an inlet and an outlet located downstream from the inlet;   the outlet of the hood is either generally coplanar with the opening of the vessel or disposed below the opening of the vessel; and   the delivery system is operable to generate a flow rate of inert cryogen in a range of about 0.002 lb/in 2  to about 0.005 lb/in 2 , based upon the total surface area of the molten metal.   
     
     
         21 . The heating system of  claim 20 , wherein the outlet of the hood is oriented proximate the side wall of the vessel. 
     
     
         22 . A heating system comprising:
 an open vessel for containing molten metal, the vessel including a bottom wall, a side wall, and an opening;   a source of inert cryogen, the inert cryogen including a liquid flow component and a vaporous flow component;   a delivery system disposed proximate the opening, the delivery system comprising:
 a lance including an inlet and a outlet, the inlet being connected to the inert cryogen source; 
 a means for receiving the inert cryogen from the lance and for directing the liquid component of the inert cryogen toward the bottom wall of the vessel such that the liquid component contacts the molten metal to form an expanding volume of gas having a rate of expansion, wherein the means for receiving inert cryogen is further configured to direct the vaporous component toward the molten metal to inhibit the rate of expansion of the expanding volume of gas. 
   
     
     
         23 . The heating system of  claim 22 , wherein the delivery system is operable to generate a flow rate of inert cryogen the range of about 0.002 lb/in 2  to about 0.005 lb/in 2 , based upon the surface area of the molten metal. 
     
     
         24 . The heating system of  claim 22 , wherein the means for receiving the inert cryogen is oriented proximate the side wall of the vessel.