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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application is a continuation-in-part of U.S. patent application Ser. No. 11 / 829,115 which claims priority from U.S. Provisional Patent Application Ser. No. 60 / 839,776, entitled “EGAL” and filed 23 Aug. 2006.BACKGROUND[0002]1. Field[0003]This invention relates to the minimizing of contamination of molten metal during processing.[0004]2. Related Art[0005]In the metal casting industry, metals (ferrous or non-ferrous) are melted in a furnace, and then poured into molds to solidify into castings. In the foundry melting operations, metals are commonly melted in electric induction furnaces. Due to the induced electric current, molten metal in electric induction melting furnaces will typically circulate from the bottom upwards, in the center of the furnace, and circulate downwards along the sidewalls of the furnace, forming a molten metal meniscus with raised center and lower edges. Due to this circulation, molten metal is continuall...

AI Technical Summary

Benefits of technology

"The patent describes a system and method for providing an inert blanket over a metal surface in a container, such as an induction furnace or tundish, to prevent oxidation of the metal. The system includes a container with a metal surface, a delivery system for delivering a biphasic inert cryogen consisting of a liquid and vaporous flow components, and a hood to direct the flow of the inert cryogen towards the metal surface. The inert cryogen is generated and directed towards the metal surface to form an expanding gas with a controlled rate of expansion, while the vaporous cryogen inhibits the rate of expansion of the gas. The system can be used in various metal processing operations to improve efficiency and prevent oxidation."

Problems solved by technology

But in order to form this molten metal vortex, a considerable amount of molten aluminum is continually exposed to the atmosphere.

This aluminum oxide (dross) floats to the surface in the adjoining float-out well, and is subsequently skimmed, adding to the overall system melt loss.

So, in various types of melt furnaces (for example electric induction, or gas-fired reverb with vortex charge well), or in other types of molten metal holding or transfer vessels such as tundishes or launders, the molten metal can be exposed to atmospheric air contamination.

It is often advantageous to melt and transport the metals without exposure to atmospheric air to minimize oxidation of the metal (including its alloying components), which not only increases yield and alloy recovery efficiency, but also reduces formation of metallic oxides, which can cause casting defects (inclusions), reducing the quality of the finished product.

Molten metal, moreover, has a tendency to absorb gases (chiefly oxygen and hydrogen) from the atmosphere (ambient air), which cause gas-related casting defects such as porosity.

This process, however, requires a special vacuum furnace and is generally only suitable for small batch processes.

In addition, the use of a vacuum furnace also results in the need for a substantially long cooling period, which lowers plant productivity.

This process, however, requires an extraordinarily large volume of gas to be used during the process, even with a substantially fluid-tight chamber.

The process, moreover, fails to keep the concentration of residual oxygen low enough to prevent the formation of an oxide layer on most metal products.

Because of these effects, it is difficult, if not impossible, for gas inerting techniques to provide a true inert (0% O2) atmosphere directly at the surface of the metal.

One drawback of liquid inerting is the difficulty of efficiently delivering the liquid cryogen to the furnace interior in a liquid state.

This vapor must be vented before the liquid is injected into the chamber, otherwise flow sputtering and surging results (caused by the tendency of the gas to choke the flow of liquid in the delivery pipes).

As a result, a significant portion of the cryogen supply is lost due to boiling.

Images