Visualization of liquid metal bubbly flows using the X-ray radioscopy

The quality of continuous cast steel is significantly affected by the flow pattern in the mould and submerged entry nozzle (SEN). The flow in continuous casting machines is often a two-phase one because argon is injected to avoid clogging inside the casting nozzle. Moreover, the argon bubbles are supposed to drag alumina particles and transport them towards the slag layer at the free surface. On the other hand, the gas injection leads to highly turbulent and complex two-phase flows, which are difficult to predict by numerical simulations. The injected bubbles have a distinct influence on the flow pattern and may trigger instabilities in the mold, for instance, observations made on real casters showed correlations between gas pressure variations in the SEN and mould meniscus perturbations.

Despite of the considerable number of previous studies mainly performed as numerical simulations and water models the understanding of liquid metal two phase flows remains fragmentary. Many open questions require further investigations, as concerns the formation process of gas bubbles, their distribution and flow regime in the SEN, the size of bubbles entering the mould, the flotation of the gas in the mould, the gas entrapment in the solidifying strand, etc. This situation motivated us to construct a specific model experiment where liquid metal two-phase flows can be investigated under flow conditions which are similar to those in the real continuous casting process.

We present an experimental study in a mockup of the continuous casting process. The two-phase flows in the mould and the SEN were visualized by means of X-ray radioscopy. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously with the low melting, eutectic alloy GaInSn under isothermal conditions. Experimental results will be presented and discussed accompanied by statistical analysis.