According to the molten aluminum filtration method, the molten aluminum is passed through a ceramic foam filter to remove inclusions therein. The ceramic foam filter used to melt Al can remove fine inclusion particles of about 10 to 25 μm, which account for most of the inclusions, thereby obtaining high-quality aluminum alloy. At the same time, the ceramic foam filter can also reduce the fluctuation of molten aluminum.
Recycled aluminum scrap can save a lot of energy and bring huge advantages. However, aluminum shavings usually contain high concentrations of various impurities. Therefore, the molten aluminum obtained by remelting these aluminum scraps may contain various inclusions, including various non-metallic inclusions. The non-metallic inclusions are, for example, oxides initially contained in aluminum scrap to be used as a molten raw material, or oxides generated due to the reaction of impurities contained therein. During the remelting process, the aluminum sheet is filled with oxygen in the atmosphere. Compared with the use of aluminum, the problem of oxide inclusions in ores with aluminum scraps as raw materials is more serious.
Therefore, when using scrap aluminum alloy products as part or all of the raw materials, at least the inclusions must be removed to obtain pure aluminum materials. In addition to using flux to refine the molten Al, a further online method must be used to degas and filter the impurities of the molten Al.
According to the reactive gas method, an inert gas or halogen gas is introduced into molten Al to generate bubbles. The inclusions are attached to the bubbles and float together in the molten aluminum to separate the inclusions from the molten aluminum. This method is particularly advantageous for removing gases such as hydrogen. However, the rising bubbles violently wave the surface of the molten Al, thereby stirring the molten Al. This causes another problem that the alumina film formed on the surface of the molten aluminum is likely to be mixed back into the molten aluminum, resulting in an increase in the number of alumina inclusions.
The ceramic foam filter for molten Al includes a refractory aggregate mesh member coated with a compound that can soften or adhere at the temperature of the molten aluminum alloy. With this molten aluminum filtration method, inclusion particles can be absorbed by the coating compound to be removed from the molten Al.