基于新型中间包设计的连铸旋流浇铸技术的基础研究

It has been found from steel industrial trials that a swirling steel flow in the Submerge Entry Nozzle can effectively improve the steel product quality. Currently, there are mainly two methods to produce a swirling flow in the SEN, namely the swirl blade method and the electromagnetic stirring method. However, the short lifespan of the swirl blade and the non-metallic inclusion deposition on its surface restrict its usage in a steel production. The electromagnetic stirring method does not have the above limitations, while it increases the cost of steel production due to an investment in equipment as well as in supply of electricity. Therefore, a new reliable and cost-saving swirling flow casting technology was proposed in this proposal. The new swirling flow casting system will be studied both by numerical simulation and by physical experiments, based on the theory of similarity criterion, computational fluid dynamics knowledge and advanced measurement tools like PIV. Specifically, a numerical model validated by water model experiment will be built up to describe the swirling steel flow in the continuous casting process. The characteristics of the swirling steel flow in the new system will be investigated, with the aim to know the formation mechanism of swirling flow, the decisive factor of swirling flow intensity, the distributions of velocity, turbulence properties and the wall shear stress, steel/slag interface phenomena, and the change of flow properties during steel flowing towards the SEN outlet. The dependence of the swirling steel flow on the casting speed and the tundish design parameters will be revealed. In addition, non-metallic inclusions behaviors in the swirling flow system will be investigated to understand some phenomena, like deposition on the wall, separation towards the swirling flow center, and its float up and removal by the top slag. The effect of swirling flow on inclusion behavior will be revealed. This systematical study will build up a strong basis for the development and future application of the new swirling flow casting technology in continuous casting process.

工业试验已证明旋流水口能有效提高铸坯质量，针对现有叶片旋流水口存在着叶片寿命短、易堵塞和电磁旋流水口设备投资大、需要消耗电能等问题，本项目提出了基于新型中间包设计的连铸旋流浇铸技术。借助物理模拟和数值模拟的手段，基于相似原理和流体力学的基本理论，建立能准确描述旋流流场的数值模型，系统研究新型中间包旋流浇铸过程中钢水旋流的发生机理，旋流流场的特点及分布规律，旋流强度大小的决定性因素及其变化规律，渣金界面行为，以及壁面剪切力的分布规律等，揭示浇铸速度及新型中间包几何参数设计对钢水旋流流场的影响规律。研究非金属夹杂物在新型旋流浇铸流场中的运动行为，如壁面沉积行为、向心分离行为，以及上浮去除行为等，揭示旋流对夹杂物行为的影响机制。通过系统的数值模拟与物理模拟研究，为开发应用具备自主知识产权的新型旋流浇铸技术打下坚实的基础。

我国是连铸工业大国，高效连铸技术的创新发展将进一步提升我国钢铁工业的国际竞争力，为我国经济发展提供高品质原材料支撑。本项目基于中间包设计的连铸旋流浇铸技术的基础研究，致力于发展具备我国自主知识产权的旋流连铸新技术，为我国连铸工业创新升级提供可靠技术支撑。.本项目利用水模型实验和数值模拟手段，系统研究了基于新型中间包设计的旋流连铸过程中的多相流动行为及控制机制，明确了中间包、浸入式水口和结晶器内钢水的流动行为、分布规律、渣/金界面行为、传热行为、夹杂物行为等特征，掌握了旋流强度的关键影响因素。研究结果表明，利用新型中间包或柱状旋流装置的新设计，可以在浸入式水口内产生高强度旋流，钢水旋转速度可达到3.0 m/s左右，其大小主要受旋流装置切线入口钢水流速的影响。水平方向上，钢水旋转速度自水口中心到水口壁面先增大后减小；竖直方向上，旋流强度随水口入口距离的增大而呈线性减小。受旋流影响，水口内壁面处压力高于大气压，可避免连铸过程中的水口吸气及钢水二次氧化。此外，水口壁面剪切力分布均匀、数值增大，对水口内壁面的冲刷作用有利于抑制夹杂物沉积，从而减缓水口堵塞。在旋流钢水中，低密度的夹杂物存在向心分离行为，这增加了夹杂物的碰撞长大概率，本项目提出了描述夹杂物在旋流中向心分离行为的无量纲数，Separation Number，用来描述不同旋流中不同密度和大小的夹杂物的向心分离能力。在结晶器内，钢水自水口出口以360°方向均匀的流向凝固前沿，结晶器内钢水的冲击流消失、过热消除较快、温度场分布更均匀，弯月面处流动增大、传热更活跃，通过调整水口的浸入深度和出口形状可以进一步改变弯月面处的流动行为。通过本项目研究，明确了旋流连铸新技术的多相流动特征、分布规律及调控机制，为旋流连铸技术工业化奠定了坚实的基础。