Quality comparison between molten metal from remelted sheets; mill finish and coated

Abstract

Deterioration of metal quality caused by contamination (e.g. coatings) is an issue in remelting of aluminium scrap. Therefore molten metal quality from remelting sheet material with and without coating is compared. In the experiments the crucibles are placed inside a resistance furnace to ensure that the charges are melted under the same conditions at the same time, measuring temperature and hydrogen. The melts was subjected to (i) settling overnight (ii) blowing air through a porous plug for 2.5 min to generate oxides (iii) settle overnight and adding turnings and (iv) adding carbon. The bifilm index is used as a measure of metal quality. The results show a statistically significant difference in the quality of the samples comparing coated and non-coated for all the melt treatments (i) - (iv), even if the charge material only contained approximately 0.4 % coat.