Insight into droplet formation in electroslag remelting process by numerical simulation

•Droplet formation in ESR process is simulated with adaptive mesh refinement.•Characteristics obtained in large size ESR process is different from the small size.•The droplets formed in two stages: primary droplets and satellite droplets.•The process of bifurcation breakup due to Lorentz force dragging was analysed.•As surface tension increases, the number of droplets decreases but size increases. In this paper, a transient three-dimensional (3D) model is proposed to study the formation of metal droplets during electroslag remelting (ESR) process. The solution of the mass, momentum and energy conservation equations are simultaneously implemented with fully coupling electromagnetic field based on the finite volume method. The volume of fluid (VOF) model is used to capture the interface between slag and metal implicitly. Furthermore, the adaptive mesh refinement is adopted to improve the computational accuracy and efficiency. The model is firstly validated and then applied to industrial scale ESR process. Moreover, the simulation results illustrate that a two-stage process of the droplet formation occurs during the ESR process: the primary droplet formation and the satellite droplet formation. The primary droplet is formed by the gravity stretch, the pinch-off effect of the Lorentz force and surface tension. The formation process of the satellite droplet can be divided into two types: the tip pinch-off of the ligament controlled by the surface tension and the bifurcation of the ligament controlled by the Lorentz force. In addition, the effect of the metal-slag interface tension on the droplet formation is analyzed. The development of the model supports further understanding of the metallurgical reaction and non-metallic inclusion movement during ESR process.