Stopper systems are widely used in the Continuous Casting (CC) process to control the steel flow from the tundish to the mould during casting of high-quality grades. The flow regulation region is subjected to severe under-pressures and generation of pressure fluctuations, especially around the narrowest gap and the tip of the stopper. This can lead to issues with air infiltration through the refractory materials, adverse flow regimes or even cavitation, which can lead to inclusions and level instabilities in the mould. Acquiring knowledge of such pressure distribution requires data from measurements which are difficult to conduct in the hostile high-temperature and corrosive environment of liquid steel in the plants.

In this work, the pressure distribution is investigated in a Continuous Casting Simulator (CCS) based on a eutectic Bismuth-Tin alloy (Bi 58%-Sn 42%) with a low melting point (137 degrees C) equipped with a stainless-steel stopper rod. The pressure distribution is investigated through direct pressure measurements at two different points; a) Direct pressure measurement by sensor installed flush at the stopper-tip side and b) Indirect pressure measurements of back-pressure in the stopper argon line. The argon flow varied between 0 to 6 l/min, while casting speed varied between 0.6 to 1 m/min for a 1200 x 220 mm mould size.

Results show that considerable under-pressures take place in the flow regulation region, reaching levels as low as 6.6 and 80 mbar absolute pressure at the stopper tip side and argon line. There was a detectable difference in pressure between the direct pressure measurements and additional argon line measurements. Ultimately, it could be concluded that the argon line pressure measurements; often used as industrial standard for ensuring positive pressures in the casting system, generally overpredicts the pressure in the system. This could lead to inappropriate argon settings for a caster, generation of unwanted inclusions and mould level instabilities. It was additionally possible to acoustically detect the onset of cavitation in the liquid metal.