Process for refining molten metal

A process for refining a molten metal selected from the group consisting of magnesium, copper, zinc, tin, and lead comprising the steps of:

• a. providing a refining vessel for containing molten metal, said vessel containing at least one refining zone;
• b. feeding molten metal into the refining vessel;
• c. maintaining a protective atmosphere above the surface of the molten metal at a greater than atmospheric pressure, thereby preventing contact of the molten metal with air or atmosphere moisture;
• d. providing at least one gas injection device in said refining vessel submerged in said molten metal comprising (i) a shaft fixedly attached to a vaned rotor at its lower end, (ii) a stationary sleeve surrounding said shaft, and (iii) a passageway for conveying and discharging refining gas into molten metal running the length of said gas injection device;
• e. introducing refining gas into the upper end of said passageway under sufficient pressure to be injected into the melt, the flow rate of said gas being defined by the following formula:
• V = W C/N
• where:
• V = flow rate of gas through each injection device, normal cu.ft./min.
• W = the feed rate of molten metal into said refining vessel, lbs/min.
• C = the specific refining gas requirement in normal cubin feet/pound metal
• N = the number of gas injection devices in said refining vessel;
• f. sub-dividing the refining gas into discrete gas bubbles by rotating said vaned rotor at a speed sufficient to create a circulation pattern in the molten metal such that the gas bubbles are transported substantially radially outward with a downward component relative to their points of entry into the melt, resulting in the removal of dissolved gases and substantially all non-metallic impurities from the aluminum melt;
• g. withdrawing the spent refining gas and the dissolved gases released by the metal while collecting other non-metallic impurities in a slag layer on the surface of the molten metal;
• and
• h. withdrawing the refined molten metal from said refining vessel.

A process for refining molten metal selected from the group consisting of magnesium, copper, zinc, tin, and lead comprising the steps of:

• a. feeding molten metal into a refining zone;
• b. maintaining a protective atmosphere above the surface of said molten metal at a greater than atmospheric pressure, thereby preventing contact of the melt with air or atmospheric moisture;
• c. introducing a refining gas into said melt beneath the surface thereof;
• d. preheating said refining gas before being sub-divided into gas bubbles by expanding the gas to the point where thermal growth of said bubbles in the melt is substantially prevented;
• e. sub-dividing the refining gas into discrete gas bubbles;
• f. creating a circulation pattern in the molten metal such that the bubbles of said refining gas are transported substantially radially outward with a downward component relative to their points of entry into the melt, whereby said gas bubbles come into intimate contact with substantially the entire mass of molten metal in said refining zone, resulting in the removal of dissolved gases and substantially all nonmetallic impurities from said melt;
• g. withdrawing the spent refining gas containing the dissolved gases released by the metal, while collecting other non-metallic impurities in a slag layer on the surface of the molten metal;
• and
• h. withdrawing the refined molten metal from said refining zone.