MHD acoustics and its application to solidification control by continuous casting

V. V. Buryak¹ - A. A. Kolesnichenko¹ - A. F. Kolesnichenko²

¹ Net Shape Cast (Ukraine), 87, 18/1 Rusanivska Naberezhna, Kiev, 02147, Ukraine
² Net Shape Cast, Inc.11643 Anhinga, Venice, Fl, 34292, USA

Abstract
The MHD acoustic phenomenon always appears when an electrically conductive liquid is exposed to non-stationary electromagnetic fields. Magnetic pressure generates pressure waves, which propagate through the liquid. Spreading of the pressure waves creates a non-stationary flow. If the liquid is confined inside a vessel with walls, mass- and heat transfer develops in both hydrodynamic and heat boundary layers. The MHD acoustic phenomenon can be implemented in continuous casting steel, e.g., billets, blooms and slabs. In case of solidifying ingot, the wall is the boundary, where the liquid phase transforms into the solid phase. Solidification means creation of a crystallite structure and production of a solid material. The future physical and mechanical properties of a cast ingot are directly determined by its crystallite structure, which, due to the controlled mass- and heat transfer in the boundary layer, can be controlled by the MHD acoustic phenomenon as well. Due to the spreading of pressure waves throughout the liquid part of the ingot, the solidification is controlled in the whole ingot from the meniscus to the final point of solidification, in contrast to the well-known electromagnetic stirring, which only partially (locally) influences the structure of the solidifying ingot. Electromagnetic generators of acoustic waves, which cause a periodic motion of metal as a result of pressure wave propagation, are described. The intensity of this motion has been determined. It is shown that the velocity of the pressure wave propagation is equal to a group velocity by complete (group) waves of electromagnetic pressure. The wave group velocity differs from the sound velocity and depends on the frequency spectrum components of the electromagnetic field, which the liquid metal is subject to. To illustrate MHD acoustics practical applications, a system for solidification control by continuous steel casting is described. The new system for solidification control is very similar to conventional Electromagnetic Stirrings (EMS) and could be applied to continuous steel casting of all kind of ingots (billet, bloom, thick and thin slab). Figs 11, Refs 7.