Development of advanced methods for the control of ladle stirring process : final report ; contract no 7210-PR/330, 1 July 2002 to 30 June 2005

The objective of this research project, involving Arcelor Research, MEFOS, BFI, Aceralia, Saarstahl AG and Sidenor is to develop advanced methods and systems for online control of gas-stirred ladle treatment in order to improve refining reactions, removal of inclusions and homogenisation during alloying and to minimise slag entrapment and reoxidation. Activities were driven in accordance with the planning. Developments led to a much clearer understanding of gas-stirred ladle treatments. A correlation giving the open-eye area as a function of a slag Froude number fits well with all data obtained on water-scale models, in lab-scale hot metal experiments, with numerical simulations and with industrial data. Image analysis procedures have been developed for automatic threshold and elimination of noised images. The implementation in plant of a video camera proved to be more difficult than expected. The ladle vibration increases with the Froude number. This is true for a wide range of experiments driven on both pilot-scale steel ladle and water scale models and also for industrial plants. We can evidence resonance related to gravity mode. Finally a high vibration level corresponds to a risk of open-eye. Contact and contact-less sensors give similar results. Their advantages and drawbacks are clarified. The analysis of inclusion population during cleanliness bubbling in the plants made it possible to recommend: - applying a soft bubbling, avoiding open-eye thanks to image analysis and/or based on low vibration; - generating a minimum stirring to get effective inclusion removal, by aiming at a given vibration.