In the aluminum melt, hydrogen not only exists in the atomic state, but also exists in the melt in combination with various inclusions. AdTech offers online degassing unit for hydrogen removal. Because the rotating nozzle has a “flotation” function while removing hydrogen, a considerable amount of insoluble inclusions can be removed, and the purpose of hydrogen removal is also achieved.
In addition, adding a small amount of Cl2 to Ar is very helpful to remove hydrogen and various insoluble inclusions in the melt. This is mainly due to:
The reaction of chlorine and aluminum produces AlCl3, which reduces the interfacial tension between the bubbles and the melt, thereby making the refined bubbles smaller. As we all know, this is beneficial to the removal of hydrogen.
Since the formation of AlCl3 is accompanied by a violent exothermic effect, hydrogen removal is a diffusion mass transfer process at the gas-liquid interface. The increase in heat melting during the mass transfer process is conducive to improving the mass transfer conditions, thereby increasing the efficiency of hydrogen removal.
The AlCl3 in the bubble also reduces the interfacial tension between the bubble and various insoluble inclusions, making it easier to adhere to the bubble, not only removing the oxidized inclusions, but also the combined with the oxidized inclusions hydrogen.
Main Ways to Prevent Recontamination
- Keep the metal liquid level in the launder system and mold stable during the casting process, and ensure that the oxide film on the surface of the melt is not damaged as much as possible. Take chemical analysis samples and online hydrogen measurement to destroy the oxide film on the melt surface. It should be done before the melt filtration.
- The surface of the refractory material in contact with the melt should be smooth, not easy to be wetted by molten aluminum, and the properties of the material should be stable.
- Use as little or no water-containing paint as possible.