Modelling molten flux layer thickness profiles in compact strip process moulds for continuous thin slab casting

Abstract

The important functions promoted by powdered flux added over the liquid steel surface in continuous casting moulds are strongly affected by the thickness of the liquid layer that forms as a result of the heat absorbed. The present work discusses the results of a three-dimensional steady state model, developed to represent the coupled fluid flow and heat transfer phenomena that determine thickness profiles of the liquid flux layer. Since the laminar flow of the liquid slag layer depends on the shearing imposed on it by the turbulent motion of the liquid steel beneath it, and since additionally this motion is strongly influenced by the flow characteristics of the steel stream poured into the mould through the submerged entry nozzle (SEN), separate turbulent flow models for the liquid steel in the SEN and the mould were also developed. The consistency among the models and their accuracy was judged by comparing thickness and temperature flux profiles measured in plant against predicted ones; the comparison showed good agreement. The effects of casting speed, mould width, and flux viscosity and heat of melting on the liquid layer thickness were investigated. The last variable was found to exert the most marked influence. Different from conventional casting moulds, where the liquid layer thickness increases with increasing casting speed, in compact strip process moulds the thickness remains almost constant with increasing casting speed. This difference is well accounted for by the model, which suggests that this behaviour stems from the different slag flow patterns generated in straight, wide moulds and in thin moulds having a central upper funnel shaped section.