When processing molten metal such as aluminum, dissolved gases including hydrogen are removed through degassing techniques. Metals including magnesium are removed from the molten metal through demagging techniques. Gases commonly used for degassing are nitrogen and argon while gas commonly used for demagging is chlorine.
When processing molten aluminum, a bath of the molten aluminum is contained within a vessel such as a furnace. A layer of dross is formed at the surface of the molten metal bath composed of various chemical compounds such as aluminum oxide, magnesium compounds, flux and refractory particles. Some particles formed of magnesium compounds are too small to float to the surface of the bath. Chlorine gas released into the molten aluminum bath bonds with such magnesium compounds forming magnesium chloride, which can be removed from the surface of the bath. Solid fluxes of various compositions can be added to the molten metal to remove magnesium or other impurities. For example, U.S. Pat. No. 3,650,730 discloses adding solid flux containing chlorine salt instead of using chlorine gas. Adding solid flux to molten metal is dangerous because workers are near the molten metal when the flux is added. Chlorine gas is extremely toxic and chlorine gas that does not react with magnesium in the bath may enter the surrounding area creating a hazardous workplace.
The processing of molten metal commonly employs pumps that include various components depending on the application, including circulation, transfer and gas purification pumps. A gas purification pump disclosed in U.S. Pat. No. 5,993,728 to Vild, is used for injecting chlorine gas into molten metal to react with magnesium such as from aluminum can scrap. The pump includes a submerged base having an inlet opening leading to an interior impeller chamber. A discharge passageway leads from the impeller chamber to an exterior of the pump. An impeller is rotated in the impeller chamber, which draws molten metal through the inlet into the impeller chamber and out the discharge passageway. The chlorine gas is injected into the discharge passageway.
In conventional practice as shown by U.S. Pat. No. 4,052,199 to Vild, solid flux can be manually added to molten aluminum in another chamber downstream of the pump to remove magnesium prevalent in aluminum can scrap.
U.S. Pat. No. 6,589,313 discloses a hollow shaft on the end of which is an impeller. The shaft and impeller are rotated and positioned at an angle relative to the bath by a complex apparatus. Solid flux and gas is added to the rotating shaft and dispersed in the molten metal.
A device for degassing molten metal without pumping includes a motor powered vertical shaft and rotor on the end positioned in a well or location of a furnace. A source of pressurized gas is connected to the shaft. The shaft and rotor include a passageway for the gas. The spinning of the rotor disperses the gas in the molten metal.
An improved device for injecting gas into a pump for pumping molten metal is disclosed in published U.S. patent application Pub. No. 2006/0180962.
An improvement disclosed in U.S. patent application Ser. No. 11/691,664, filed Mar. 27, 2007, entitled “FLUX INJECTION WITH PUMP FOR PUMPING MOLTEN METAL,” features a machine for feeding solid flux into a gas vortex for entraining the solid with the gas and directing it into molten metal discharged from a pump.