中间包水口吹氩过程壁面氩气膜的形成与迁移行为研究

Due to the inclusions of high-melting point such as aluminium oxide adhering on the inner surface of nozzle, the clogging of tundish nozzle frequently occurs during continuous casting of steel. It seriously disturbs the production rhythm and degrades the steel quality. Generally, the argon blowing in tundish nozzle was employed in the actual production, aiming to effectively prevent the clogging of nozzle by means of the stable and continuous argon film on inner surface of nozzle. However, how do the argon blowing parameters, the permeability parameters of upper nozzle, the flow rate of molten steel near the inner surface of nozzle, and the opening degree of sliding nozzle relate to the formation and stability behaviors of argon film on inner surface of nozzle? How do the thickness of argon film, the heat transfer behavior and mechanical behavior of argon film affect on the stability of argon film? How do above influence factors affect the behaviors of downward migration and rupture of argon film along nozzle surface? How do the distribution of argon bubbles in molten steel after rupture of argon film affect on the entrapment and attachment of inclusions to argon bubbles? In order to solve these problems that were rarely reported in the previous studies, the water model experiments, the thermal simulation experiments of low-melting point metal, and the theoretical calculation and numerical simulation analysis of argon blowing in tundish nozzle will be studied in this project. Then, the stability mechanism and influence factors of argon film on inner surface of nozzle will be clarified clearly, which can provide theoretical and technology basis to the parameter optimization of the blowing argon parameters and permeability of upper nozzle in order to prevent the clogging of tundish nozzle and improve strand quality of steel.

连铸中因氧化铝等高熔点夹杂物粘附在水口内壁，导致中间包水口出现堵塞现象，严重扰乱生产节奏并恶化铸坯质量。生产中常采用水口吹氩操作，若在水口壁面形成稳定、连续的氩气膜，则可有效防止水口堵塞。然而，吹氩参数、上水口透气性参数、水口内壁附近钢液流动状态、滑动水口开口度等因素与水口壁面氩气膜形成和稳定行为之间有何关联？水口壁面氩气膜的厚度、传热和受力行为对其稳定性有何影响？氩气膜沿水口内壁向下迁移、破裂行为与各影响因素之间有何关系？气膜破裂后进入水口内部氩气泡的分布状态对夹杂物的捕捉和粘附行为有何影响？这些问题前人研究很少，本项目将以解决这些问题为目标，通过中间包水口吹氩水模型实验和低熔点金属热态模拟实验的研究方法，结合理论计算和数值模拟分析，明确水口吹氩条件下水口壁面形成稳定、连续氩气膜的调控机制，为最终优化水口吹氩工艺参数及上水口透气性参数，防止水口堵塞和提高铸坯质量提供理论基础和技术依据。

铝镇静钢连铸中特别容易发生水口堵塞，严重恶化铸坯质量。采取连铸中间包水口吹氩技术可在水口壁面与钢液界面间形成一层气膜，可以有效防止水口堵塞。然而，前人对水口壁面上气膜的形成机制和影响因素研究较少。.基于气泡的受力变化，理论分析了中间包上水口吹氩过程壁面气泡的形成行为。结果表明，随吹氩量和壁面倾角的增大、透气孔直径和有效透气孔数量的减小，脱离水口内壁的氩气泡临界直径减小。在给定条件下，水口壁面越往下气泡离壁面的距离越来越近；气泡离壁面的距离随着吹氩量的增加而逐渐减小；气泡离壁面的距离随着拉速的增加而逐渐减小。.采用局部相似比为1:1的中间包水口水模型，研究了工艺参数和水口参数对水口壁面上气泡形成和运动行为的影响。结果表明，开始吹氩时，上水口壁面最顶部气孔出现一个个慢慢长大的气泡；上水口壁面上部气孔出现一条条气泡链。吹气量一定时，随着水流量的增加，气泡链离壁面的平均距离逐渐减少；水流量一定时，随着吹气量的增加，气泡链离壁面的平均距离逐渐增大。气泡链离壁面的平均距离越小，气泡链越容易叠加，越容易形成连续气幕。.数值模拟结果表明，当水口壁面上氩气泡临界直径越大、拉速越大、吹氩量越小，水口壁面附近气相浓度较高的区域范围越小。当水口壁面吹出的氩气泡临界直径越大、拉速越小、吹氩量越小，气泡越早脱离壁面，氩气膜覆盖水口壁面的长度越短。水口内部气泡往中心卷动的位置随拉速增加、吹氩量减小而逐渐降低。不吹氩时，上水口底部壁面附近和SEN出口处上方的流速极低，这两个部位是水口容易堵塞的部位。上水口底部区域壁面附近的钢液流速随拉速的增加而增加，随着吹氩量的增加而减少。SEN出口处上方区域壁面附近的钢液流速随拉速的增加而增加，随吹氩量增加而增大。.在保证足够多数量的气泡链前提下，吹气量和拉速配合合适时能得到更大范围的连续气膜，为最终优化水口吹氩工艺参数及上水口透气性参数，防止水口堵塞和提高铸坯质量提供理论基础和技术依据。