Prediction and control of powder entrapping at meniscus of molten steel in a continuous casting mold

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First, we have analyzed the flow field of molten steel in a continuous casting mold, focusing upon the unsteady behavior of the free surface profile and velocity. The computation has been performed using the MAC-type solution method to a finite differencing approximation of the three-dimensional Navier-Stokes equations for incompressible fluid flow. Here, the non-steady body-fitted coordinate system has been used. According to the numerical results, the effects of the casting speed and the kind of nozzle on the flow structure of molten steel have been found to be remarkable. Also, the experiment has been undertaken to measure the surface velocity distribution, using water instead of molten steel. It has been confirmed that the numerical results are in good agreement with the experimental data.Next, we have numerically analyzed the influence of the free surface fluctuation on the movement of hypothetical spherical materials (instead of melted powder) which are placed just below meniscus. The numerical model for liquid-particles two-phase flow has been built up by incorporating the particle trajectory method into the system of equations on the basis of the two-fluid model. According to the numerical results, the large particles whose diameter are of the order of 1mm rise to the liquid surface in a short time owing to the buoyancy force. On the other hand, motion of smaller particles follows the liquid flow. The flow field is changeable depending on the outflow angle of immersion nozzle as well as the casting speed. Also, it has been found that the powder entrapping occurs owing to the shear stress on condition that two vortical structures are formed near the free surface.