The online purification device allows the molten aluminum fully contact the inert gas, so that the hydrogen in the molten aluminum diffuses into the inert bubbles with zero hydrogen partial pressure. The solid inclusions suspended in the aluminum liquid will also be adsorbed on the surface of the bubbles. With the small bubbles rising, the gas and inclusion are removed.
After online purification treatment for molten aluminum, the hydrogen content of molten aluminum can be reduced to half. Non-metallic inclusions with a particle diameter below 50μm can be removed by 50%, and that above 100pm can be removed by 90%. Adding Cl2 in the inert gas can increase the hydrogen removal rate from 50% to 65%, and also remove 60%-75% of Na and Li.
The inert gas can be dispersed into tiny bubbles into the aluminum liquid through the rotating nozzle. The emotional gas can be nitrogen or argon. Nitrogen must be high-purity nitrogen with a purity greater than 99.995%. The cost of argon is higher than that of nitrogen, but its advantage is that it will not react with molten aluminum to form compounds at high temperatures. After the aluminum liquid is purified online, the hydrogen content should be below 0.12mL/100g(Al). For products with strict quality requirements, the hydrogen content should be below 0.10m/100g(Al).
The time for the molten aluminum to pass through the online degassing purification device is very short. After processing, it is difficult to completely separate the smaller slag and inclusions from the molten aluminum in such a short time. In order to ensure the cleanliness of molten aluminum, all purification devices outside the furnace are equipped with filtering devices to remove suspended debris. The shape of impurities in molten aluminum is thin films or particles. There are oxides such as Al203 and SiO2, and non-oxides such as AlF3 and Al4C3.