At present, using N2 and Ar gas as a carrier, adding a small amount of pollution-free refining agent, using a single tube, porous or rotary degassing machines to purify aluminum liquid, is an advanced refining technology, which has been widely used in industrialized countries.
According to the dynamic theory, there is a certain relationship between the air permeability pore size, the bubble frequency and the blowing rate. The greater the bubble frequency, the smaller and more bubbles, the better the dehydrogenation effect, but after the critical frequency is exceeded, the bubble phenomenon will occur and the dehydrogenation effect will decrease. The dehydrogenation kinetic conditions can be summarized into two: the void ratio in the molten aluminum and the gas-liquid two-phase contact area. If the void ratio and the gas-liquid contact area are larger, the dehydrogenation kinetic conditions are better.
At present, the commonly used rotary degassing machines in production include partial injection (N2, Ar single pipe or multi-hole blowing head) and spray with shear field (N2, Ar rotating nozzle). According to the gas-liquid two-phase theory, the local injection causes a large circular convection of the aluminum liquid up and down. The bubble plume is a positive cone, the cone angle increases with the gas flow, and the center of the liquid surface protrudes, which is disturbed as each bubble escapes. It is easy to cause the oxidation of the liquid on the center surface-suction, and the purification effect is worse than that of rotating spray.
The use of rotary degassing machines to process molten aluminum is currently the world’s most advanced patented technology for purifying molten aluminum. N2 or Ar is introduced into the aluminum liquid with extremely small bubbles through the high-speed rotating nozzle, and through high-speed rotation, the small bubbles are highly dispersed and distributed in the aluminum liquid, the porosity is large, and the gas-liquid contact surface is large, and a large amount of dispersion The floating of the distributed bubbles brings hydrogen and inclusions to the surface of the molten aluminum, without disturbing the liquid surface much, and oxidizing and inhaling less, so the purification effect is obviously improved.
At present, the graphite nozzle of degassing unit produces relatively fine bubbles without rotating to achieve a better refining effect. There is also a casing blowing head. The molten aluminum circulates inside and outside the casing according to the principle of a gas lift pump, and then enters the casing for dehydrogenation treatment, and reciprocates to achieve the purpose of hydrogen removal purification.