Flux for Molten Aluminum to Remove Alkali Metal Elements

In order to remove the alkali metal elements (ie Na, Ca, K, Li), the use of a chlorine-containing reactive flux gas is a recognized method for processing molten aluminum. Under equilibrium conditions, the chlorides of each of these elements are produced as reaction products. Except for LiCl, all these halide salts are pure species and are solid at normal processing temperature, so they are easily separated to the surface of the melt in the form of surface and removed by skimming.

Alkali metal elements are usually present in melt concentrations below 500 ppm. According to the law of mass action (the reaction rate is approximately proportional to the concentration of the reactant), non-equilibrium metastable salts such as AlCl3 and MgCl2 (if Mg is present) are formed. These halides are undesirable because they greatly affect the airborne emissions in the process. In addition, MgCl 2 melts at 1306°F, and usually melts at normal melt processing temperatures. Molten salt is very undesirable because it is difficult to remove the surface for skimming. Therefore, it is highly desirable to react or complex alkali elements to produce a higher melting point salt, which is more effectively separated into a solid form by flotation to the surface.

Flux for Molten Aluminum

In the existing method of dispersing the flux gas in, for example, an aluminum melt, the flux for molten aluminum is introduced into the main body downward in the axial direction, and dispersed by a rotating impeller mounted on the shaft. However, this method is not unlimited. The rotating impeller produces a vortex around the shaft, which indicates that most of the molten metal rotates or circulates around the impeller shaft at a rate close to the speed of the impeller. The refining flux added to the molten metal tends to circulate with the molten metal with minimal dispersion.

In addition, the vortex has the effect of increasing the surface area of ​​the melt exposed to air. The increased exposure of molten metal to the air leads to increased slag formation, subsequent entrainment of slag and its harmful side effects. When the flux is a gas, the vortex can cause problems in another way. The melt gas moves toward the center of the vortex by physical separation, and as a result, other parts of the melt are not sufficiently processed by the melt gas. Therefore, the effectiveness of the method is reduced because part of the melt is not processed by the flux. In addition, the flux gas entrained in the molten metal flow pattern tends to coalesce, resulting in the formation of larger flux gas bubbles in the melt. Larger bubbles will reduce the efficiency of the flux, because less molten metal is processed.

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