SEPARATION OF NONMETALLIC PARTICLES IN TUNDISHES

The separation of nonmetallic particles by buoyancy in tundishes is in vestigated theoretically. It is shown, that the best possible separati on is achieved if the projection of the region through which flow from the inlet to the outlet mainly occurs, covers as large a part of the surface as possible. In contrast, the volume of this region, its dista nce from the surface and the mean retention time do not influence sepa ration directly. Numerical calculations of the flow fields and particl e separation in two different tundish geometries with and without a ba ffle predict no significant differences in the capability of separatin g nonmetallic particles. This surprising result may be explained by th e principle stated above. In contrast to these findings, observations made during production provide indirect evidence that the insertion of a baffle reduces the concentration of Al2O3 at the outlet of the tund ish significantly. This would mean that besides buoyancy, another proc ess contributes significantly to the separation of nonmetallics. Such a process is not identified in this paper, but it is shown that turbul ent diffusion and inertial impaction are not likely candidates.