André Larouche

The effect of water ejection and water incursion on the evolution of thermal field during the start-up phase of the direct chill casting process

Abstract A comprehensive mathematical model has been developed to describe heat transfer during the start-up phase of the direct chill casting process. The model, based on the commercial finite element package ABAQUS, includes primary cooling to the mould, secondary cooling to water and ingot base cooling. The algorithm used to account for secondary cooling to the water includes boiling curves that are a function of surface temperature, water flow rate and position relative to the point of water impingement. In addition, the secondary cooling algorithm accounts for water ejection, which can occur at low water flow rates (low heat extraction rates). The algorithm used to describe ingot base cooling, includes the drop in contact heat transfer due to base deformation (butt curl) and also the increase in heat transfer due to water incursion between the ingot base and the bottom block. The model has been verified against temperature measurements obtained from two 711×1680 mm AA5182 ingots, cast under different conditions (non-typical “cold” practice and non-typical “hot” practice). Ingot base deflection data has also been obtained for the two test castings. Comparison of the model predictions with the data collected from the embedded thermocouples indicates that a 2-D longitudinal model is capable of describing the flow of heat in the early stages of the casting process in a region close to the centre of the rolling face. A sensitivity analysis completed with the model has clearly identified the link between ingot base cooling and secondary water-cooling heat transfer during the start-up phase.

Study of Shell Zone Formation in Lithographic and Anodizing Quality Aluminum Alloys: Experimental and Numerical Approach

Shell thickness is an important quality factor for lithographic and anodizing quality aluminum alloys. Increasing pressure is placed on casting plants to produce a thinner shell zone for these alloys. This study, based on plant trials and mathematical modelling highlights the most significant parameters influencing shell zone formation. Results obtained show the importance of metal temperature and distribution and mould metal level on shell zone formation. As an answer to specific plant problems, this study led to the development of improved metal distribution systems for DC casting of litho and anodizing quality alloys.

Understanding T-Ingot Horizontal DC Casting Using Process Modelling

Horizontal continuous casting process has been successfully implemented in Alcan for the production of T-ingots of primary aluminium and foundry alloys. Ability to achieve increased productivity targets and reduce production costs relies on a fundamental understanding of key process characteristics and operating parameters. Thanks to the long-standing experience in vertical DC Casting, numerical modelling appeared as a powerful approach to understand phenomena related to metal flow, solidification and ultimately defect formation. As part of a collaborative R&D program, a global model of horizontal casting process, integrating specialized sub-models on critical aspects of the process such as meniscus dynamics, is being developed. Experimental characterization of primary and secondary cooling is performed in parallel with modelling work to provide the information necessary to properly characterize mould heat transfer. This paper will present the development of a 3D process model of T-ingot casting along with its application to solve specific process challenges that have emerged during the first years of production in the plant.