Air aspiration is an important cause of nozzle clogging and inclusions in final products of continuous casting of steel due to the presence of metal oxides (such as alumina) which occur through the reoxidation of molten steel. This problem is most likely to occur when the flow control system (slide-gate or stopper rod) causes the pressure inside the nozzle to drop below atmospheric pressure, drawing gas into the system through possible cracks or gaps in the refractory walls. In this work, a 1-D pressure-energy model of the complete metal delivery system from the tundish to the mold is developed to predict the pressure distribution and throughput under dynamic operating conditions and varying clogging conditions. The energy balance approach includes pressure losses in the slide-gate, wall friction, and nozzle geometry variations, including the effects of multiphase flow due to argon gas injection. The model also predicts air aspiration, oxide inclusion formation, and the time for clogging shutdown. The predicted pressure distribution is verified with a three-dimensional numerical simulation of multiphase turbulent flow, and is validated with plant measurements. Parametric studies with different submerged entry nozzle (SEN) designs revealed that a smaller SEN diameter may lessen negative pressure by redistributing the pressure loss from the slide-gate to the entire nozzle through increased friction losses. Under negative pressure, a submillimeter-thin gap was shown to cause considerable air aspiration. Clogging shutdown times were evaluated for several scenarios under static and dynamic operating conditions.

A 1D analytical model for slag infiltration during continuous casting of steel is developed to investigate the slag behavior in the mold–strand gap. The superposition principle and Fourier expansion are applied to obtain the analytical solution for transient slag flow under arbitrary mold oscillation including non-sinusoidal oscillation mode. The validated model using literature data partially explains several controversies such as slope of slag film channel, mechanism of non-sinusoidal mold oscillation, and timing of slag infiltration. The model shows that a converging slag film into the casting direction is required to open the mold–strand gap if compression is applied in between. Also, model calculations imply that higher slag consumption is achievable from non-sinusoidal mold oscillation by means of the increase of film thickness through longer positive pressure with higher peak pressure. The model demonstrates a time difference between slag flow and pressure near the meniscus and the discrepancy in timing of infiltration between previous works is attributed to the mismatch. The model provides a concise but reliable tool to understand slag infiltration behavior and design mold oscillation settings.

The pressure and flow rate of an argon line embedded within a stopper rod serve as useful industrial indicators and control factors for mitigating air aspiration into the Submerged Entry Nozzle (SEN) during the continuous casting of steel. This manuscript investigates several challenges associated with interpreting monitored argon line pressures and gas flow rates, including variations in gas pressure during delivery, actual volumes of gas entering the nozzle, argon leakage, and air aspiration. To address these issues, a new one-dimensional (1D) analytical model of compressible argon flow in the stopper rod was developed, incorporating gas dynamics and heat transfer. This concise 1D model was validated using data from a continuous casting simulator (CCS) employing a low-melting-point Bi-Sn alloy (melting point 137 °C). Pilot trials were conducted to replicate various industrial casting scenarios, generating datasets for model validation and demonstration of real-time operation. The 1D model predictions were compared with those from a CFD-based compressible flow model under CCS operating conditions. Following validation, parametric studies were conducted to explore realistic industrial scenarios (e.g., gas flow rate < 5 SLPM, nozzle diameter < 5 mm), including extreme conditions such as air aspiration and choking: a critical nozzle diameter (1.223 mm) corresponds to choked flow, limiting the maximum achievable gas flow rate to 5 SLPM. Additionally, the real-time prediction capabilities of the model were demonstrated using measured argon line pressures and flow rates from CCS trials. The proposed 1D model thus provides a practical tool for accurately interpreting SEN flow conditions from monitored argon pressures and effectively estimating argon bubble injection by clarifying actual gas pressures and flow rates at the stopper injection point.