Abstract: This invention concerns a process for the reliable avoidance of slag contamination of the converter tapping steel by flush slag. In accordance with the invention a plastic, workable stopper made of fire-proof material containing silicic and oxidic components as well as suitable binding agents is used for this purpose. The stopper is introduced so far into the tapping channel with the help of a setting device that its front surface, terminated with a funnel-shaped compression plate, almost aligns flushly with the interior side of the converter, and it fills in the diameter of the tapping channel as a result of being compressed, creating such a plane that the flush slag occurring during tipping of the converter is reliably directed past the tapping channel. Stopper systems used up to now had the disadvantage that age-dependent enlargements of the tapping channel had a detrimental effect on the functioning of the stopper.