Development and industrial testing of a novel stopper ring filter system for steel foundry applications

In the present study, ring filters were applied directly in a steel casting ladle for the first time. The carbon-bonded alumina filter system was fitted to the existing stopper system enabling steel melt filtration directly above the shroud without risk of filter blockage. Two identical casting trials were performed, whereby one resulted in successful retrieval of the filter and one resulted in filter failure. Analysis of cast steel samples regarding their inclusion population revealed that the filter failure did not impair the steel quality. The intact filter was analyzed via digital light microscopy, SEM/EDS and XRD. Contact zones revealed location-dependent morphological and chemical differences indicating inclusion removal and limited damage by slag contact. Overall, the investigation showed that the new principle is feasible and the risk due to filter failure is limited, which makes room for future casting trials to quantify the filtration efficiency and the impact of filter geometry.