CRUCIBLE FLUXING OF POTROOM METAL IN A NORSK HYDRO CAST SHOP EFFECT ON DROSS REDUCTION AND INCREASED METAL RECOVERY

摘要

Potroom metal Hydro Aluminum Sunndal contains approximately 50 ppm sodium (Na) as it enters the cast house. New equipment for fluxing the potroom metal with AlF_3 and Argon directly in the tapping crucible was installed in October 1998. In the crucible fluxing process, a half-life period for Na of 2 minutes is obtained. The Na content is reduced to typically 1-5 ppm before the metal is charged into the casting furnace. The process has caused 23 pct reduction in the amount of dross in the cast house. Today, the dross amounts to less than 1 pct of the metal flow. In addition, the metal recovery form dross has increased from 61 to 73 pct. The net metal loss is reduced from approximately 0,25 to 0,135 pct of the total metal production. The reduction in metal loss (i.e. burn up) may be explained by removal of Na as a catalyst in the oxidizing process.