Separation of nonmetallic particles in tundishes

The Separation of nonmetallic particles by buoyancy in tundishes is investigated theoretically. It is shown, that the best possible separation is achieved it 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 distance from the surface and the mean retention time do not influence separation directly. Numerical calculations of the flow fields and particle separation in two different tundish geometries with and without a baffle predict no significant differences in the capability of separating nonmetallic particles. This surprising result may be explained by the 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 Al 2 O 3 at the outlet of the tundish significantly. This would mean that besides buoyancy, another process contributes significantly to the separation of nonmetallics. Such a process is not identified in this paper, but it is shown that turbulent diffusion and inertial impaction are not likely candidates.