The hydrogen removal degassing purification is mainly using an inert gas (N2, Ar) to purge the aluminum melt, which can effectively remove the hydrogen and oxide inclusions in the melt.
The principle of hydrogen removal degassing purification: Since the initial hydrogen partial pressure in the N2 bubble is zero, there is a pressure difference at the interface between the bubble and the molten aluminum, so that the hydrogen melted in the molten metal is continuously sucked into the bubble. This suction process will not stop until the partial pressure of hydrogen in the bubble is equal to the partial pressure of hydrogen in the molten aluminum. After the bubble rises to the surface, the H in the bubble escapes and enters the atmosphere. Therefore, during the rising process of the bubble, both oxidized inclusions and hydrogen are brought out, so that the aluminum liquid can be purified.
According to the principle of hydrogen removal purification, we know that there are three main ways to improve the speed and efficiency of hydrogen removal:
1. Increase the number of purification bubbles as much as possible to increase the effective contact surface area between the aluminum liquid and the bubbles.
2. Reduce the diameter of the purification bubbles as much as possible, and try to increase the movement speed of the purification bubbles in the molten aluminum without causing splashes of the liquid surface, that is, increase the agitation intensity, strengthen the renewal of the gas-liquid surface, and improve its mass transfer Ability.
3. Extend the floating distance of the purification bubbles in the molten aluminum as much as possible, that is, increase the time for the bubbles to process the molten aluminum, thereby improving the efficiency of hydrogen removal.
With the improvement of the requirements for the purity of the melt, the hydrogen removal technology is also continuously improved and developed. It has developed from the original single-pipe injection to the porous blowing head to the current rotating nozzle. Since the 1980s, the use of rotary nozzle air blowing treatment methods has become the main development trend of advanced foreign aluminum liquid purification technology.
The rotary degassing equipment is equipped with a graphite-made gas rotating nozzle, and the gas passes through the rotor of the nozzle to form fine and dispersed small bubbles. Melt agitated by the rotor. The bubbles are evenly dispersed in the entire melt, increasing the gas-liquid contact area, extending the movement distance and residence time of the bubbles in the aluminum liquid, increasing the gas volume, and the bubbles adsorbing the gas and oxidized inclusions in the melt. The bubbles float to the surface of the melt, thereby producing the purification effect of degassing and discharging impurities.