Stirring velocity effectiveness of two- and three-phase EMS for small to medium cross section billets and blooms

摘要

Purpose - To use an experimentally calibrated turbulent flow model to determine whether two- and three-phase electromagnetic stirrers provide equivalent stirring when continuously casting steel billets and blooms. Design/methodology/approach - The results obtained in this paper were obtained by using a 3D quasistatic electromagnetic model to obtain the Lorentz forces that act on the liquid steel. A computationally efficient method was used to account for the effect of the conducting fluid motion on the forces. A 3D turbulent flow model that incorporated Reynolds stresses and high order upwinding was used to predict the fluid flow. The model has been calibrated using the experimental data. Findings - The paper shows that for square and rectangular cross section casting moulds, having inside dimensions of 140 X 140mm and 140 X 196 mm, respectively, a two-phase electromagnetic stirrer consistently produces stirring velocities that are 12-15 percent below those produced by an equivalent three-phase design. Research limitations/implications - The impact on the fluid entering the casting mould through the submerged nozzle has been neglected. The model should be furtha-developed to consider this important factor. Practical implications - A two-phase stirrer is much more compact than the equivalent three-phase design, and since space is at a premium in the vicinity of the casting mould, being able to use a compact design is desirable. The two-phase design was long believed to produce inferior stirring due to the negative impact of electromagnetic space harmonics. This paper shows that for the range of mould dimensions considered in the paper, there is a good trade-off between the compact two-phase design and the slightly lower stirring velocities that result. Originality/value - The paper presents the first quantitative comparison between two- and three-phase electromagnetic stirrers that illustrates, in a practical sense, the stirring effectiveness of each approach. The paper will be of value to users of this equipment.