MHD STIRRING OF LIQUID METAL IN CRUCIBLES WITH CIRCULAR AND SQUARE CROSS SECTIONS UNDER ROTATING MAGNETIC FIELD

摘要

Manufacturing of aluminum-based alloys and composites by MHD stirring of the solidifying melt is commonly used in industry. Solidification takes place in a stationary crucible or in a hot-top mold of the continuous casting machine for the production of cylindrical ingots. The stirring of melt flows in the crystallization zone affects the crystalline structure of ingots. It is evident that the flow topology and intensity in the liquid phase will have an effect on the processes occurring at crystallization. Continuous casting machines are currently equipped with MHD stirrers generating azimuthal motion in the mold with the hot top of circular cross-section exposed to a rotating magnetic field. The flow pattern is similar, in this case, to solid rotation, and the most intensive transfer processes occur in the near-wall region and near the ingot solidification front, where shear stresses are high. In this paper, the possibility of intensifying transfer processes in the entire volume of the stirred metal is investigated by giving a square shape to the hot top of the mold. Simulations show that the total kinetic energy of toroidal flow in the crucible of square cross-section is almost twice as low as that of the flow in the crucible of circular cross-section (the inductor is the same in both cases). Turbulent pulsations in these crucibles are mainly concentrated in the near-wall region. The toroidal flow pulsation energy is lower in the square crucible, but the stirring of passive impurity into the metal in the square crucible proceeds faster than in the circular crucible. If the total kinetic energy of toroidal flow in crucibles with circular and square cross-sections is the same, the energy of turbulent pulsations in the crucible with square cross-section is somewhat higher, and these pulsations are distributed in the larger volume compared to the crucible with circular cross-section. Hence, it can be concluded that the efficiency of MHD stirring in the crucible of square cross-section is relatively higher than in that with circular cross-section.