Study On Numerical Simulation Of Multi-physical Field In Electromagnetic Soft Contact Continuous Casting Mold

In the continuous casting process of molten steel, it is well known there are some nonideal solidification phenomena which have harmful to product quality. Now an effective technique of electromagnetic soft contact continuous casting has been introduced to eliminating surface defects for non-cracks and no-oscillation marks billets, which have been proved by many physical experiments and numerical simulations. However, the soft-contact continuous casting of steel has still been a developing question.To determine the reasonable operation parameters, and provide the fundamental theories of optimal design for soft-contact mould and rich the contents of soft-contact technique, a three dimensional finite element model of electromagnetic field was developed to investigate the distribution of magnetic flux density and heat generation and electromagnetic volum force, which can represent the casting action of electromagnetic field. Then a three dimensional coupled mathematical model of electromagnetic field and flow field had been founded to simulate the fluid flow behaviors of molten steel under typical simulation parameters. At last, a coupled two dimensional finite element model had been established, for the effective calculations of electromagnetic field, fluid flow, heat transfer, and stress distribution under complex conditions of soft contact. By using this model, the effects of high frequency electromagnetic field on temperature and thermo-mechanical behaviors of steel and mould had also been studied.Based on the Maxwell equations of basic equations for electromagnetic field, a three dimensional finite element model of electromagnetic field was developed to investigate the distribution of electromagnetic field in the mold under typical simulation parameters. And the effects of frequencies and currents on the distributions of magnetic flux density and electromagnetic force density and heat generation ratio had been emphasized. The results showed the magnetic flux density distributed unevenly in space. The joule heat indicated the character of periodic symmetry of uneven distribution to result in the uneven thickness of shell in EMC mold, which had been approved by experiment. The electromagnetic force circumferential component indicates periodical antisymmetric distribution at the center of slit and segment to make the jostling or drawing function in EMC mold, which would affect the flow pattern of liquid steel.From the Bennon's continuum model, a three dimensional coupled mathematical model of electromagnetic field and flow field had been founded to simulate the fluid flow behaviors of molten steel under typical simulation parameters. And the effects of frequencies and currents on flow velocity and turbulence kinetic energy had been compared and analyzed. The results showed high frequency electromagnetic field mainly had effects on billet in meniscus zone, and the bottom of it was not worked on. In the process of EMC, flow velocities were periodical antisymmetric distribution at the center of slit and segment to result in the concavo-convex deformation at free surface, which had been made sure by experiment. So it was necessary for choices of EMC parameters to considerate this phonomena. There were two vortexes forming in longitudinal section, and the center of upper recirculation moved towards free surface, and circulation zone extended, and flow velocities increased, compared with continuous casing. The flow velocity increased when the currents enhanced, but the flow patterns nearly remain unchanged. When frequencies changed, the magnitude and direction of fluid velocity vector also altered, and the higher frequency electromagnetic field can retrain the fluctuation of free surface of liquid steel.By reasonable simplification of mold's configuration, a coupled two dimensional finite element model had been founded, for the effective calculations of electromagnetic field, fluid flow, heat transfer, and stress distribution under complex conditions. Moreover, the intermittent contact behaviors between the shell and the mold were considered. And the effects of frequencies and currents on temperature and stress for both billet and mold had been discussed and analyzed. The results of temperature field showed with the high frequency electromagnetic field, the solidification start point moved downwards and initial shell thickness got thinner, but the shell thickness increased at the outlet of mold. The temperature and its gradient of EMC mold also enhanced, and the temperature of outer wall was beyond the boiloff temperature of cooling water. It mean the flux of cooling water must be increased in EMC process. The results of stress showed the equivalent stress of initial solidification shell both at its outer and inner surface decreased, but at the bottom the equivalent stress of two sides of shell both increased. The high-stress zone and the high-deformation zone of EMC mold extended, and the negative taper added. Under the high frequency electromagnetic field, the gap size reduced at the initial solidification zone and then grew at the lower position.