Shape and stability of the slag/melt interface in a small dc ESR process

The electro-slag remelting (ESR) process has been used effectively to produce large ingots of high quality based on the controlled solidification that can be achieved. Despite numerous simulations, it is still challenging to predict important operating details of the process, such as the effect of the electrode immersion and, more importantly, the results of instabilities in the melting system (electrode, slag, pool). In order to have a better understanding of the process, the present work aims to verify the validity of two assumptions which were widely used in previous simulations. First is the flatness of the slag/steel interface, and second concerns the verticality and the stationarity of the density of the electric current over the entire domain. In the present paper, a mathematical model of the magneto-hydrodynamic (MHD) phenomena occurring during ESR, modelling more rigorously the closure of the electric current at the mould is presented. At the present stage, the model does not include any buoyancy or solidification effects. The multiphase aspect of the problem is solved by using a VOF model, the domain is divided in two sub-domains (steel and slag) separated by a free interface. The effect of the imposed dc current and the mould diameter on the initial interface was investigated. We show that except if the mould is insulating, the interface is never flat. In some cases the interface even becomes unstable leading to an electric shortcut.