Vertical twin-roll caster : metal-mould heat transfer, solidification and product characterization

Near-net-shape casting technology is an important research area in the iron and steel industry today. Various processes for near-net-shape casting of steel are currently being developed around the world. of these processes, twin-roll casting represents a major area of concentration. The main issues concerning design and operation of twin-roll casters are the metal-mould heat transfer, the metal delivery system and their possible effects in the homogeneity of solid shell formation and characteristics of the strips.In the present work, interfacial heat fluxes between the roll and the solidifying metal have been evaluated in a pilot twin-roll caster used in the production of strips of low-carbon steel. This evaluation was based on an inverse heat transfer analysis and on readings of thermocouples inserted at different positions of the roll sleeve.The variation of the roll-melt interfacial heat fluxes with time exhibited two different patterns, with single and double peaks, depending on the casting conditions. These interfacial heat fluxes were not uniform across the roll width. This result was consistent with predictions of a fluid flow, heat transfer and solidification model.Computational fluid dynamics has been used to study different metal delivery systems for twin-roll casting. The in-house METFLO code has been adapted to simulate three-dimensional turbulent fluid flow, heat transfer and solidification in this type of process. The enthalpy-porosity technique was used to couple fluid flow and solidification phenomena. Different configurations for metal delivery systems have been studied.This study has been applied to a pilot caster with a roll radius of 0.30 m, producing steel strips with thicknesses ranging from 4 to 7 mm, at relatively low casting speeds in the range of 4 to 12 m/min. The numerical predictions indicated that an extended nozzle, covering the full width of the caster and with horizontal inlets in the direction of the rolls surfaces, seems to be the best alternative for delivering liquid steel into twin-roll casters.The solidification structures of strips produced in the pilot caster have also been studied. Their characteristics were analysed in terms of fluid flow and heat transfer inside the caster