Introduction
The cleanliness of molten steel is a critical factor in ensuring the quality of high-performance steel products, particularly in industries such as automotive, aerospace, and construction. To meet these stringent purity requirements, the tundish, a vessel used to transfer molten steel from the ladle to the continuous casting machine, plays a pivotal role in removing impurities. Traditionally, tundishes have relied on elements like slag dams and weirs to filter out impurities from molten steel. However, these conventional devices have limitations in terms of efficiency and impurity removal capability.
In recent years, advanced ceramic filters have been proposed as a more effective alternative. These filters, made from materials that resemble the impurities present in molten steel, can trap and remove inclusions more effectively. However, while ceramic filters have been shown to enhance impurity removal, the design of the filter and the flow characteristics within the tundish significantly affect their performance. This study focuses on optimizing the filter's design by adjusting the elevation angle of its pores, aiming to improve both the flow distribution and the impurity removal rate of molten steel.
Tundish Filter Design and Experimentation
In this study, tundish filters with pores at different elevation angles (20°, 25°, 30°, 35°, and 40°) were tested to determine how these angles influence the removal of impurities in molten steel. The filters' effects on the molten steel's flow field and impurity removal efficiency were evaluated through numerical simulations using the Discrete Phase Model, a computational method that tracks the motion of particles (impurities) within the molten steel.
The filter design, characterized by various elevation angles, alters the way molten steel flows through the tundish, impacting the contact rate between the steel and the covering agent, which helps trap impurities. By adjusting the elevation angle of the filter pores, the flow of molten steel can be controlled, improving the efficiency of impurity removal.
Results and Discussion
Impurity Removal Efficiency
The primary finding of the study is that the elevation angle of the tundish filter significantly affects the impurity removal rate. Among the various angles tested, the filter with a 40° elevation angle achieved the highest impurity removal rate, reaching 74.05%. This is a substantial improvement over the removal rates associated with lower elevation angles.
At the 40° angle, the filter caused the molten steel flow density to decrease before the filter inlet, leading to a more stable flow after passing through the filter. This stabilization is crucial because it increases the contact rate between the impurities and the tundish covering agent, which facilitates the capture of smaller inclusions. The higher contact rate results in a more efficient impurity removal process, ultimately enhancing the cleanliness of the molten steel.
Flow Field Distribution
In addition to impurity removal, the flow field within the tundish is also influenced by the elevation angle of the filter. The results showed that increasing the elevation angle to 40° made the flow field more stable. A stable flow field is important because it allows the impurities to remain in contact with the filter and the covering agent for a longer duration, improving the chances of successful removal.
The flow pattern created by the 40° filter angle also contributes to the uniform distribution of molten steel within the tundish, reducing turbulence and ensuring that impurities are evenly dispersed. This leads to more efficient filtration and a higher removal rate of both fine and large-sized inclusions.
Mechanism of Impurity Removal
The study also explored the mechanisms that contribute to the enhanced impurity removal efficiency at the 40° filter angle. The key mechanism lies in the regulation of flow direction and velocity. By adjusting the angle of the filter pores, the molten steel's flow is directed in such a way that impurities have a greater chance of colliding with the covering agent, which helps agglomerate the smaller particles into larger ones. These larger particles are more easily removed by the tundish covering agent or float to the surface due to their increased size.
Furthermore, the increased stability in the flow field ensures that the molten steel's impurities remain in contact with the covering agent for a longer period, increasing the likelihood of successful impurity absorption.
Comparative Study on Different Filter Angles
The study's comparative analysis revealed that the filter with a 40° elevation angle was the most effective in terms of impurity removal efficiency, outperforming filters with angles of 20°, 25°, 30°, and 35°. While filters with lower elevation angles still contributed to impurity removal, their efficiency was not as high as the 40° filter. These results provide compelling evidence that adjusting the elevation angle of the filter plays a crucial role in optimizing impurity removal rates.
Model Description
The numerical simulations were conducted using the Discrete Phase Model, which is widely used to model particle behavior in fluid flow. DPM tracks the movement of particles, in this case, impurities, as they interact with the molten steel flow. By using this model, the study was able to simulate the effects of different filter elevation angles on both the flow distribution and impurity removal efficiency.
The model incorporates parameters such as particle size, velocity, and contact time with the covering agent, providing a detailed understanding of how different filter designs impact impurity removal. The results from the simulations were validated through a comparison with experimental data, ensuring the reliability of the findings.
Conclusion
This study offers valuable insights into the role of tundish filter elevation angles in enhancing impurity removal from molten steel. By systematically varying the elevation angle of the filter pores and simulating their effects on molten steel flow and impurity capture, the study demonstrates that a 40° elevation angle significantly improves impurity removal efficiency. These findings provide a foundation for further optimization of tundish filter designs, offering a pathway to producing cleaner molten steel and, by extension, higher-quality steel products. The research also highlights the importance of understanding the flow field dynamics within the tundish and how design adjustments can lead to more effective impurity filtration.
