Aluminium degassing device can remove impurities in the melt to provide cleaner and better quality metal. It is one of the most common and effective cleaning methods in foundry.
There are two main impurities in molten aluminum: dissolved hydrogen and solid.
Non metallic inclusions. As the metal cools, dissolved hydrogen escapes from the solution and forms harmful pores. The porosity and non-metallic solid inclusions reduce the strength and adversely affect the final properties of aluminum castings. During the melting process, oxide scales are formed on the surface of the molten metal, and any subsequent transfer of the molten metal is carried out. The resulting oxides are trapped in most of the molten material and then transferred to the finished casting.
Other nonmetallic inclusions, such as carbides, nitrides or borides, can come from sources such as crucible materials or other refractory materials.
Therefore, it is necessary to remove the dissolved hydrogen and non-metallic inclusions from molten aluminum by using aluminium degassing device before casting, so as to achieve the best quality.
Processes developed for cleaning metals are physical processes involving the use of inert gas fluxes. The hydrogen dissolved in the molten material diffuses into the rising bubbles of the flux gas and is transported to the surface of the molten material. This process depends on two main steps:
- The rate at which hydrogen diffuses into inert bubbles through the diffusion boundary layer
- Hydrogen concentration in inert bubbles
Diffusion is the determining stage of degassing rate. Therefore, in order to obtain the best degassing efficiency, the following requirements must be met:
The bubble of inert gas is smaller and the residence time in molten metal is longer. This ensures a large surface contact area between the inert bubbles and the molten metal, thus ensuring a higher mass transfer coefficient relative to the diffusion layer. The distribution of inert bubbles in the whole cross section of molten metal is very wide. The full velocity motion of molten material accelerates the hydrogen transport to inert bubbles. Melt the material on the static surface of the molten pool to avoid reacting with the atmosphere to absorb fresh hydrogen.