The oxide film and impurity particles suspended in the aluminum liquid are difficult to be completely removed in the furnace with a wide open surface. The effect of applying flux by powder spraying machine is better, but it is still difficult to achieve the purpose of purifying aluminum liquid comprehensively. Therefore, in addition to using a flux to remove some contaminated impurities in a large-capacity furnace, the modern casting workshop also uses an on-line purification device outside the furnace to conduct a comprehensive purification treatment of the aluminum liquid flowing out of the holding furnace to completely remove the residual gas and slag in the aluminum liquid.
Principle of On-line Purification Device Outside the Furnace
The principle of the purification device outside the furnace is to allow the aluminum liquid and the emotional gas to fully contact in the small purification furnace equipped with the heater, so that the hydrogen present in the aluminum liquid diffuses into the inert bubbles with zero hydrogen partial pressure and escapes. Out of the liquid. The solid slag suspended in the liquid aluminum will also be adsorbed on the surface of the bubble and be removed together. After online purification treatment, the hydrogen content of the aluminum liquid can be reduced to half of the original value; non-metallic inclusions with a diameter of less than 50um can be removed by 50%. This is important for the production of aluminum-magnesium alloys and the direct extraction of liquid aluminum from electrolytic cells to produce aluminum.
Emotional gas can be dispersed into tiny bubbles into the aluminum liquid through the rotating nozzle, atomizing nozzle or porous ceramic plate. The purifier outside the furnace has the patent name of the inventor. In order to prevent secondary contamination of the molten aluminum in the purification furnace, some devices also cover the surface of the molten aluminum with emotional gas. The inert gas can be nitrogen or argon. Nitrogen must use high-purity nitrogen with a purity greater than 99.995%, its dew point is lower than -70℃. The purity of argon should be greater than 99.98%, and the water content and oxygen content should be less than 0.01%. The cost of argon is higher than that of nitrogen, but its advantage is that it will not react with aluminum liquid 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 0.10mL/100g (Al).
The time for the aluminum liquid to pass through the purification device is very short. After treatment, the smaller slag and inclusions in the smaller size are difficult to be separated from the aluminum liquid in such a short time. In order to ensure the cleanliness of the aluminum liquid, all external purification devices are equipped with There is a filtering device to remove suspended debris. The shape of the impurities in the aluminum liquid is a film or particles, the thickness of the film is 0.1~0.5um, and the length or width is 10~5000um; the particle diameter is 0.1~50um; the impurities include oxides such as Al2O3, SiO2, MgO, and AlF3, Al4C3, AlN and other non-oxides.
The liquid aluminum filter generally adopts foam ceramic plates. When the aluminum liquid passes through the tortuous and communicating channels in the foam ceramic, the internal debris is deposited on the channel walls under the action of hydrodynamics, inertia, interception, collision, adsorption, etc. Make the clean aluminum liquid enter the casting and rolling flow plate. The filtration efficiency of the foam ceramic plate is directly related to the diameter of the micropores, but the diameter of the debris intercepted is much smaller than the average diameter of the micropores. Foam ceramic plates are usually replaced once in a furnace to ensure the passing ability of the aluminum liquid and prevent the sundries and slag particles deposited in the pores from re-entering the aluminum liquid.