At present, the on-line degassing methods commonly used in aluminum alloy casting process are: SNIF method, ALPUR method, RDU method, MINT method, etc. no matter what kind of device and method and degassing medium are adopted, the mechanism is the same, that is to realize melt degassing according to differential pressure. AdTech online degassing unit has a better degassing effect, and it is widely used in aluminum foundry.
Degassing mechanism: when the gas used for refining degassing is blown into the melt, a large number of bubbles will be produced or reacted. At the contact surface between the bubble and the metal, there is a differential pressure between the bubble and the hydrogen in the metal at the beginning. Due to the differential pressure, the hydrogen in the melt permeates into the bubble. When the bubble rises to the metal surface, the hydrogen is carried into the atmosphere to realize degassing; The impurities are also brought to the surface of the melt to purify the melt.
On-line Degassing Methods Affecting Factors
Degassing medium. The main gas in the degassing medium is H2 and ar2, which does not react with aluminum. The main active gas is C12, which reacts with aluminum to form aluminum chloride boiling gas, and reacts with hydrogen directly. The purification effect is better than that of inert gas.
Diffusion velocity. The diffusion rate of hydrogen is the key to the balance of hydrogen concentration in the bubble during degassing. Under the same parent part, the melt with less mass diffuses faster and degassing better than the melt with more impurities.
Degassing time. If the degassing time is short, the hydrogen in the bubble and melt will escape from the surface before reaching the equilibrium, and the effect is not ideal. The increase of degassing time is conducive to the further diffusion of hydrogen atoms into the bubbles, thus increasing the degassing effect. Therefore, the degassing bath should be deep
Bubble surface area. Under the same conditions, the smaller the bubble is, the larger its surface area is, and the larger the contact area between the bubble and the melt is, the better the degassing effect is. Therefore, how to obtain micro bubbles and increase the surface area of bubbles is the key to degassing.