Experimental Research Of Slit Manners Influence On Distribution Of Magnetic Field And Temperature Field In The Mold

As the development of continues casting towards near-net shape and no defects, the requirements on the billet surface quality are more severe. Oscillation marks in billet associated with surface cracks and other defects such as curved hooks, entrap mold flux, floating inclusions and bubbles that ultimately form surface defects after rolling and annealing. In the past several decades, it has received much attention from researchers about how to minimize oscillation marks. With the development of electromagnetic theory in the continuous casting technology, a new type of efficient continuous casting technology was developed, i.e. electromagnetic soft-contact continuous casting technology. The technology can significantly improve the surface quality of billet. After the electromagnetic soft-contact mold technology for round billet has been successfully developed, the development of billet electromagnetic soft-contact mold becomes a focus research.In the study, a compound mold with two corner slits was used to investigate the effect of slit form on the distribution of magnetic field and surface behavior in the mold. The distribution of magnetic field along the casting direction as well as along the circumferential direction in the mold was measured using electromagnetic induction method under different electrical power. Then, the height of the liquid Sn-Pb-Bi alloy was measured under different electrical power using the dip-coating method. Finally, we use a high-speed camera to record the fluid flow of liquid Sn-Pb-Bi alloy imposed high frequency electromagnetic field.Through the above experiments, we can draw the following conclusion.(1) When there is no corner slit in the mold, the magnetic flux density in the corner is14%smaller than that in other region which means the distribution of magnetic field along the circumferential direction is uneven. However, when the mold corner is divided into two parts by a slit, the magnetic flux density in the corner is7%smaller than that in other region which means the distribution of magnetic field along the circumferential direction is improved a lot.Magnetic flux density increases with the electric power increases, and electric power is proportional to the square of the magnetic flux density.(2) The liquid metal in the liquid pool deforms prominently under the high frequency electromagnetic field. The whole process is composed by three stages, i.e. initial deformation of the meniscus, the separation of the meniscus from the mold wall and the vibration of the melt surface in the center of liquid pool.(3) When the mold corner is divided into two parts by a slit, the contact angle between the meniscus and the mold decreases, accompanying the triple point moves downwards. The height of meniscus is increased from8.8mm to11.2mm under high frequency electromagnetic field when electric power comes to54kW. There is a significant temperature gradient in the liquid metal pool. The temperature of liquid metal near the mold wall is lower than the bath center; temperature peak is away from the mold wall of8mm.(4) The temperature in the same position increases linearly with time, the heating rate of the different regions is significantly different. The heating rate of liquid metal in the edge of liquid metal pool is higher than those in the pool center.(5) The heating rate of liquid metal pool increases with the number of slit increases. The liquid metal temperature near the slit is higher than those near the segment center, the temperature gradient is1.8℃when the electric power comes to8kW.