As an important part of aluminum melt treatment, online degassing has been paid more and more attention by the aluminum foundry. Degassing and filtering are important processes of aluminum melt treatment. On-line degassing itself benefits from the treatment of the aluminum melt upstream of the furnace, as well as the downstream process filtration of the online treatment. These treatment processes complement each other, and their overall effect is much better than that of a single treatment process.
Why should aluminum melt be degassed?
The main purpose of the online degassing device is to remove hydrogen from the aluminum melt. Hydrogen is the only gas that can be dissolved in the aluminum melt. The solubility of hydrogen will rapidly decrease with the solidification of molten aluminum during casting. At this time, hydrogen will escape from the melt, causing pores in aluminum casting products.
The target value of dissolved hydrogen content depends on the application of the final product, ranging from 0.20ml/100gAl for general 6000 series backlog billets to 0.10ml/100gAl for rolling billets for aerospace applications. When using inert gas bubbles to remove hydrogen from aluminum melt, argon and nitrogen are usually used. Because nitrogen has a tendency to generate aluminum nitride, which is a harmful inclusion and can generate more aluminum ash, in order to obtain the best aluminum melt quality, it is more preferred to use argon. Adding a small amount of chlorine gas when using inert gas for degassing can more effectively remove non-wetting inclusions and alkali metal impurities.
The inclusions in the aluminum water come from the electrolytic aluminum production process, from remelting in the furnace or internal additives. Inclusions can cause tearing and surface defects during sheet rolling, pinholes during aluminum foil rolling, and cause and increase die loss during aluminum extrusion. The reduction of 50% of non-wetting inclusions in the degassing system is a representative index. The additional mechanical filtration (ie, foam ceramic filter) is also a means to meet the quality index.