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 within a melting furnace, the method comprising:
 (a) forming molten metal within a furnace container comprising a bottom wall, a side wall and an opening, 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 down the side wall of the furnace container such that the liquid flow component comes into contact with the molten metal, forms a localized pool in the furnace container at a point proximate the side wall and generates an expanding gaseous volume having a rate of expansion; and   (d) directing the vaporous flow component into the furnace container to inhibit the rate of expansion of the gaseous volume by forming a vapor blanket over the liquid flow component;   (e) maintaining the flow rate to localize the liquid flow component within a portion of the molten metal exposed surface such that liquid flow is localized within an area smaller than the total surface area of the molten metal exposed surface.   
     
     
         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 /min. to about 0.005 lb/in 2 /min., 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.