VSEh Institute of Industrial Researches (Düsseldorf, Germany):

Rödl S., Mag. Eng., Head of Department, e-mail: sigurd.roedl@bfi.de
Kleimt B., Dr. Eng., Head of Department
Köchner H., Dr. Eng., Head of Department

Deutsche Edelstahlwerke GmbH (Siegen, Germany):
Jung H.-P., Mag. Eng., Head of Department of Technological Innovations STS-P
Klung S., Mag. Eng., Head of Project

Steel is subjected to purging by inert gas at the final stage of ladle treatment to provide high degree of steel purity and intensify removal of non-metallic inclusions. This work was aimed on development of the optimal purging procedure and optimization of its control remedies. At first the criterion of cleanness depending on operating parameters of ladle treatment has been determined. Then this process was simulated to obtain optimal technological parameters. For a process route with EAF, LF, RH degassing, final treatment station and a six-strand billet caster a prediction model for a cleanliness indicator was developed via a multi-linear regression analysis of relevant operational parameters. By mathematical and physical modelling, information on the separation behaviour of nonmetallic inclusions was obtained. The influence of inclusion properties like diameter, density and morphology as well as of different boundary conditions was investigated. Information on optimum gas flow rate and stirring time could be provided with regard to an operational window for the soft bubbling stirring process. An image-based on-line monitoring system was installed and adjusted to the process for direct control of the stirring intensity. With this system also the result of the on-line prediction model for steel cleanliness is displayed. It provides the operator with information on the required stirring intensity and stirring duration, to achieve an improved cleanliness. As an overall result an optimum adjustment of the final stirring treatment in the ladle with regard to steel cleanliness can be achieved, leading to an increased product quality and yield.

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