Aluminium degassing and cleaning using an impeller station

Aluminium degassing and cleaning using an impeller station 

The degassing of aluminium is needed to remove hydrogen from the melt. The removal or reduction of small amounts of undesirable elements and impurities necessitates treatment of the melt with halogens, such as chlorine, fluorine or bromine. This treatment is referred to as cleaning, and is usually combined with the degassing treatment. 

Adequate degassing with physically operating treatment processes does not achieve sufficient cleaning in most aluminium castings. Vacuiun degassing achieves a very low hydrogen content in the melt but, at the same time, the lower munber of nuclei means that crystallisation is less effective. 

In some isolated cases, an Ar/SFe-mixture has been used. The latter is a greenhouse gas with a high global warming potential, which falls under the Kyoto protocol, (see also Section 4.2.7.1) 

The use of an impeller with Ar/CU or N2/CI2 avoids the use of hexachloroethane in the cleaning treatment of aluminium. The use of hexachloroethane was banned from 30 June 2003 in the EU. 

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