ECCC-24MD中SEN吐出孔的优化设计

Flow control in the tundish, mold and strand Session 10 1 Düsseldorf, 27 June – 1 July 2011 1. Title of the paper The port design development of submerged entry shroud（SES）for the optimum flow in the mould 2. Author(s) name(s) and affiliation(s) Erwin den Nijs Krosaki Harima Corporation Dutch Office Rooswijkweg 84, 1951 MJ Velsen-Noord The Netherlands Garry Coombes Tata Steel Strip Products UK, Port Talbot Takahiro Kuroda Flow Control Refractories Division, Krosaki Harima Corporation 1-1,Higashihama-machi, Yahatanishi-ku, Kitakyushu City, Fukuoka, 806-8586, Japan 3. Contact data for questions Erwin den Nijs Krosaki Harima Corporation Dutch Office Rooswijkweg 84, 1951 MJ Velsen-Noord The Netherlands Tel +31251228030 Fax +31251227106 Email dennijs@krosaki.nl 4. Key Words SES improved port design mould fluctuation Port Talbot 5. Abstract In accordance with the recent requirement for the optimum flow in the mould of continuous casting process in steel mills all over the world, improvements of steel flow with the port design of SES have been achieved to some extent. Nowadays, it has been getting more and more important to produce high-quality steel and realize high productivity in continuous casting operation. When high productivity is being considered, in general, it is necessary to increase the inner diameter and the port size of SES, which lead to higher casting speed, in order to achieve effective throughput. However, when the port size is increased, uneven steel flow occurs in the mould due to the imbalanced flow distribution from the port, and it results in mould fluctuation and inclusion of the mould powder. This leads to reduction in steel quality and also becomes one of the causes of break-out failure. In this presentation, further development of the port design for the Tata Steel Strip Products UK, Port Talbot Works Continuous Caster 3 (CC3) is reported. This improved port design for CC3 is developed to optimize the steel flow in the mould and minimize mould powder inclusion by reducing the mould fluctuation with optimum flow from the port of the SES. In addition, the actual casting of the improved SES was executed, and the improvements of flow in the mould and steel quality were investigated and evaluated with Tata Steel Strip Products UK, Port Talbot Works. The goal of this presentation is to show the efforts done by Tata Steel Strip Products UK, Port Talbot Works to improve the steel flow in the CC3 mould by using an improved Krosaki Harima SES. 6. Introduction (a brief overview of any preconditions, procedures and problems) The improved port design is based on the general two ports design SES for normal slab continuous caster. Flow control in the tundish, mold and strand Session 10 2 Düsseldorf, 27 June – 1 July 2011 The improved port design have been developed by computer fluid dynamics (CFD) and water modeling (1/1 scale) compared with conventional design as first step to optimize the flow in the mould, after that the improved SES have been used in actual casting compared with conventional SES. The related parameters in continuous casting and steel quality and yields have been investigated and evaluated. 7. Text, Tables and Figures Improvement of SES port design The consideration of the flow from the port in general SES port design (rectangular or oval) for normal slab continuous caster, when the port cross section is divided to three portions (upper, middle and lower), the main flow is observed at lower portion of port with large flux. This large flux hit to mould narrow face and brings on the mould fluctuation and mould powder inclusion caused by large reversed flow. Therefore it is important to get the equalized flow from both ports and homogeneous flow in whole portion of the port in order to optimize the flow in the mould. In this development of the flow optimization in the mould, it is applied the small steps to both inner port wall as the improved port design shown in Figure 1. With the improved port design the flow from the port is observed not only at lower portion of the port but also at upper and middle portions of the port. As the result it is verified the reduction of the mould fluctuation by decreased reversed flow. The comparison of the port design between current and improved is shown in Figure 1. Figure 1 Comparison of SES port design Evaluation of the flow in the mould by computer fluid dynamics (CFD) The CFD analysis is introduced and done to find the applicable port design which can optimize the flow in the mould as first step. The example of CFD comparison is shown in Figure 2 with the CFD condition (through put corresponding the molten steel 3.0 ton/min, mould size 234mm thickness * 1,500mm width). It is verified that the improved design shows optimized flow in the mould (Double roll) and also slower flow velocity at meniscus compared to current design. Flow control in the tundish, mold and strand Session 10 3 Düsseldorf, 27 June – 1 July 2011 Current design Improved design Front view Near ports Top view Velocity distribution Figure 2 Comparison of computer fluid dynamics (CFD) Flow control in the tundish, mold and strand Session 10 4 Düsseldorf, 27 June – 1 July 2011 Evaluation of the flow in the mould by water modeling As the flow evaluation for improved port design, the water modeling (scale 1/1) is used. The port velocities (measurement the average velocities on each portion within 1 minute by pitoh tube velocity meter) and meniscus velocities (measurement at both (left and right) center position between mould and SES in 3 minutes by propeller current-meter) are measured and evaluated. The details of the velocities measurement positions are shown in Figure 3 and 4. Figure 3 Measurement of flow velocities at both ports Figure 4 Measurement of flow velocities at meniscus Evaluation result by water modeling (Flow velocity distributions at both ports) As the example of comparison of flow velocity at both ports, the measurement result with the water modeling condition (through put corresponding the molten steel 3.7ton/min, mould size 234mm thickness * 1,500mm width) is shown in Figure 5. It is verified that the improved design has the flow velocities at upper and middle portions of port compared to current design. Flow control in the tundish, mold and strand Session 10 5 Düsseldorf, 27 June – 1 July 2011 Figure 5 Comparison of flow velocity at both ports Evaluation result by water modeling (Flow velocity distributions at meniscus) As the example of comparison of flow velocity at meniscus, the measurement result in 3 minutes with the water modeling condition (through put corresponding the molten steel 3.7ton/min, mould size 234mm thickness * 1,500mm width) is shown in Figure 6. It is verified that the improved design shows less velocity variations and stable flow velocity in 3 minutes compared to current design. And the comparison of average meniscus velocity between left and right and variation of flow velocity are shown in Figure 7. It is verified that the improved design shows slower average flow velocity at meniscus and stable flow velocity compared to current design. Figure 6 Comparison of flow velocity variations at meniscus in 3 minutes Flow control in the tundish, mold and strand Session 10 6 Düsseldorf, 27 June – 1 July 2011 Figure 7 Comparison of average flow velocity and standard deviation for flow velocity at meniscus Evaluation result by water modeling (Relationship between through put and flow velocity at meniscus) The relationships between through put and flow velocity at meniscus in several different conditions (mould width and through put) and flow velocity variations are shown in Figure 8 and Figure 9. It is verified that the current design shows the increasing of the flow velocity and velocity variation at meniscus with an increase the through put. On the other hand, it is verified that the improved design shows the reduction for increasing of the flow velocity and velocity variation at meniscus with an increase the through put compared to current design. 0 10 20 30 40 50 0 1 2 3 4 5 Flo w v elo city (c m/s ec) Through put (ton/min) Relationship between through put and flow velocity at meniscus ●：Current ●：Improved Figure 8 Relationship between through put and flow velocity at meniscus Flow control in the tundish, mold and strand Session 10 7 Düsseldorf, 27 June – 1 July 2011 0 5 10 15 20 0 1 2 3 4 5 Sta nda rd dev iat ion σ (cm /se c) Through put (ton/min) Relationship between through put and Standard deviation for flow velocity at meniscus ●：Current ●：Improved Figure 9 Relationship between through put and standard deviation for flow velocity at meniscus Evaluation in actual casting (Comparison of SES service life) The actual casting with SES improved port design is carried in slab continuous caster in order to evaluate and investigate the related parameters in continuous casting and steel quality and yields compared with current design SES. The comparison of SES service life between current and improved is shown in Table 1. It is verified that the improved SES shows almost same service life time as current SES. Table 1 Comparison of SES service life Evaluation in actual casting (Evaluation of the flow in the mould) As the evaluation of the flow in the mould, the thermal distribution in the mould which is provided by thermocouple where is located around the mould is applied. As the evaluation of the mould fluctuation, the amount of mould fluctuation during the casting is applied. Evaluation in actual casting (Thermal distribution in the mould) The example of comparison of thermal distribution in the mould between current and improved is shown in Figure 10. These SES is used in same time for 80 minutes. It is verified that the improved design showed less variation of thermal distribution between mould loose and fixed faces compared to current design. Flow control in the tundish, mold and strand Session 10 8 Düsseldorf, 27 June – 1 July 2011 Figure 10 Comparison of thermal distributions in the mould Evaluation in actual casting (Mould fluctuation) The example of comparison of the amount of mould fluctuation during the casting between current and improved is shown in Figure 11. These SES is used in same time for 275 minutes. It is verified that the improved design showed small amount of mould fluctuation in whole casting speeds compared to current design. Figure 11 Comparison of the amount of mould fluctuation Furthermore as the evaluation of mould fluctuation for specific steel grades C,D,E and F, the comparison of average mould level change during the casting is shown in Figure 12 and 13. It is verified that the improved design shows better mould level change (at least same) on different casting strand compared to current design. Figure 12 Comparison of average mould level change (Improved design on strand A) Flow control in the tundish, mold and strand Session 10 9 Düsseldorf, 27 June – 1 July 2011 Figure 12 Comparison of average mould level change (Improved design on strand B) 8. Conclusion As the conclusion for the development of SES port design for optimizing the flow in the mould, it is considered that the following points have been achieved. The flow optimization in the mould is achieved with improved port design by getting the equalized flow from both ports and homogeneous flow in whole portion of the port. The flow stabilization of mould fluctuation is achieved with improved port design in case of increasing the through put (increasing the casting speed). This will also contribute to reduce the mould powder inclusion. In the results, it is verified that the steel yield for specific steel grades improve 18.5% and 16.7% (on each strand) with improved design compared to current design directly. This result could have a large financial benefit. Finally the slabs casted with the equalizer SES showed fewer laminations and a decrease in slab rejections. 9. Abbreviations SES: Submerged Entry Shroud CFD: Computer Fluid Dynamics 10. Acknowledgements (optional)