Comparison between axial and radial melt stirring on purification of industrial aluminum during Ohno Continuous Casting

Abstract

With the purpose of enhancing the purity of a dilute industrial aluminum alloy during Ohno Continuous Casting (OCC) process, the melt mechanical stirring direction which can effectively and uniformly transport the accumulated solute rich liquid ahead of the solid-liquid interface into the bulk melt was numerically determined. Steady axial and transverse convective velocity cells were induced into the melt through mechanical stirring (at the same intensity) to produce rotational convective flow fields near the solid-liquid interface and their effect on solute transport were compared. For the same mechanical stirring intensity, axial stirring produced stronger melt velocity flow magnitudes than transverse stirring and these convective axial cells deeply penetrated the solute boundary layer. Due to the concave shape of the interface, axial stirring cells non-uniformly thinned the solute boundary layer producing a deep depression at the centre of the solute boundary layer whereas transverse stirring uniformly and weakly thinned the solute boundary layer. It was concluded that, with concave interfaces, the use of transverse stirring with higher velocity magnitudes in the melt is effective in uniformly thinning the solute boundary layer to produce pure, uniform and unidirectional ingots. For more flat interfaces, axial stirring was found to be a better method of uniformly thinning the solute boundary layer to produce uniform and ultrapure ingots without destabilizing the interface.