中间包水口处环形气幕与钢液旋流耦合作用下夹杂物的迁移行为

In order to improve the cleanliness of molten steel, the annular gas curtain at the tundish nozzle could be used to remove small inclusions in the molten steel by the use of argon bubbles during continuous casting. Moreover, the clogging of tundish nozzle could be prevented by the entering argon bubbles. The technology of swirling flow of liquid steel in tundish upper nozzle can promote the collision and growth of small bubbles and inclusions of the molten steel in tundish nozzle. When the coupled technologies of the annular gas curtain and the swirling flow of liquid steel at the tundish nozzle are used, the content of small-sized inclusions in the molten steel could be further reduced and the subsurface defects of strand caused by the fine bubbles could be eliminated. However, when the technologies of annular gas curtain and swirling flow of molten steel at tundish nozzle are adopted synchronously, what is the distribution and the migration behavior of argon bubbles in the tundish and nozzle? How does it relate to the migration behavior of inclusions? How does the swirling intensity of liquid steel affect the collision and growth of small bubbles and inclusions? These problems have been previous studies less, which need to be further explored. In order to solve these problems, this project aims to measure the collision and growth behavior of small argon bubbles and small inclusions by using high-speed camera. The migration behavior of inclusions is measured by the aid of the water model and thermal simulation experiments. Then, combining with theoretical analysis and mathematical modelling, the migration mechanism of inclusions in the molten steel is clarified under the coupling effect of annular gas curtain and swirling flow of liquid steel. Based on the above results, the coupling control method of annular gas curtain and swirling flow of liquid steel at tundish nozzle will be presented in this project, which will provide a theoretical basis and practical suggestions for the production of high quality continuous casting strand.

为提高钢液洁净度，中间包水口处采用环形气幕技术，利用氩气泡去除钢液内小粒径夹杂物，随钢液进入水口内的氩气泡可以防止水口堵塞。采用上水口钢液旋流技术可以促进水口内小气泡和夹杂物的碰撞长大，与环形气幕技术耦合使用，可以进一步降低钢液内小粒径夹杂物含量，并消除小气泡带来的铸坯皮下缺陷问题。水口处环形气幕与钢液旋流技术耦合作用下，中间包和水口内氩气泡分布状态、迁移行为是什么？其与夹杂物迁移行为有何关联？钢液旋流强度对小气泡和夹杂物碰撞长大行为如何影响？这些问题，前人研究较少，需要进一步探索。本申请项目以解决这些问题为目标，利用高速相机测量氩气泡和夹杂物碰撞长大行为；利用水模型及热模拟实验测量夹杂物的迁移行为；结合理论分析和数学模型，从根本上明确水口处环形气幕与钢液旋流耦合作用下钢液内夹杂物的迁移机制。基于这些研究，提出水口处环形气幕与钢液旋流耦合调控方法，为生产高质量连铸坯提供理论依据和操作指导。

向中间包内吹入氩气，形成的氩气泡可有效去除钢液中的夹杂物；利用旋流水口技术可促进夹杂物的碰撞长大，是去除钢液内小粒径夹杂物的另一有效途径。基于上水口环形吹氩与旋流水口的冶金效果，本项目研究了中间包上水口环形吹氩及钢液旋流耦合作用下气液两相流及夹杂物迁移行为。上水口用弥散型透气砖的气泡生成行为结果表明，弥散型透气砖形成气泡尺寸大小不一；增大吹氩量，气泡尺寸范围明显增大，且呈现正态分布；透气砖内部尺寸分布是影响气泡尺寸分布和平均尺寸的关键参数。上水口环形吹氩中间包内形成以塞棒为中心的圆柱状气泡羽流，增大吹氩量，环形气泡羽流中气泡数目明显增多；增大拉坯速度，环形气泡羽流的宽度和气泡数量减小；增大透气环距水口中心距离，环形气泡羽流宽度随之增大；增大吹氩量和拉坯速度、减小透气环距水口中心距离，进入结晶器气泡数量和尺寸逐渐增大。吹氩量过大时，中间包液面形成以塞棒为中心的圆环状渣眼，发生钢液卷渣的位置可能是距离塞棒较远的钢渣界面或者是渣眼边缘；增大吹氩量，渣眼面积和卷渣深度逐渐增大，本项目研究条件下临界吹氩量为4.2 L·min-1。环形吹氩和旋流水口耦合下，部分气泡进入水口及结晶器内，进入水口内的氩气泡在钢液旋流作用下逐渐向水口中心汇集；增大吹氩量、拉坯速度和旋流槽高度、增加旋流槽数目，水口内钢液切向速度增大，进入到结晶器的气量和气泡平均尺寸均呈现逐渐增大趋势。在旋流上水口作用下，进入水口内的夹杂物颗粒随钢液旋转流动，促进低密度夹杂物向水口中心迁移；增大拉坯速度，壁面夹杂物沉积数目先增大后减小，夹杂物沉积率逐渐减小；增大吹氩量，夹杂物在中间包内停留时间呈现明显减小趋势。增大环形透气砖内外径，中间包挡墙右侧夹杂物运动轨迹范围明显增加；工业试验表明，与不吹氩条件相比，吹氩后钢中夹杂物数目均明显减少，不同种类夹杂物的最大尺寸呈下降趋势。研究结果可为生产高质量连铸坯提供理论依据和操作指导。