水口碗部吹氩下结晶器内气泡分布及钢-渣两相流行为

Distribution of bubbles and two-phase flow behavior of steel-slag in mold with argon injection from bowl of nozzle

水口吹氩可减缓连铸过程中水口堵塞,但会带来铸坯皮下气泡和钢-渣界面波动加剧风险。基于水口碗部吹氩工艺,通过耦合DPM离散相模型和VOF多相流模型,建立三维中间包-水口-结晶器数学模型,并通过1∶2比例水模型对数值模拟计算得到的气泡羽流形貌和气泡尺寸分布进行验证。研究了吹氩量、拉坯速度和水口浸入深度等工艺参数对结晶器内钢液流动、不同区域气泡尺寸分布和钢-渣界面波动的影响。结果表明:低吹氩量下,出侧孔钢液形成冲击窄面的下部流股和冲击钢-渣界面的上部流股,大尺寸气泡分布于1/2和1/4宽面的水口临近区域;增大吹氩量,流股在窄面冲击点位置上移,水口临近区域出现渣眼并逐渐增大,1/2宽面大尺寸气泡数目先增大后减小,近壁面处小尺寸气泡数目大幅增加;低拉速下,结晶器内钢液流动呈单环流模式,气泡集中分布于水口临近区域并形成较大面积渣眼;增大拉速有利于气泡在结晶器内均匀分布,水口附近渣眼面积减小,但近窄面区域小气泡数目增多;低水口浸入深度,气泡易从水口临近区域上浮,增大水口浸入深度有利于降低近壁面处小气泡数目。

Argon injection in nozzle can prevent nozzle clogging during the continuous casting process,but it can also cause defects of subcutaneous bubbles in slabs and increase the risk of intensified fluctuations at the steel-slag interface.Herein,for the process of argon injection from the bowl of nozzle,a three-dimensional mathematical model of the tundish-nozzle-mold was established by coupling the DPM model and VOF model.A 1∶2 scaled water model experiment was conducted to verify the morphology of bubble plume and size distribution of bubbles in the mold.The effects of argon flow rate,casting speed,and submerged depth of nozzle on the flow field,size distribution of bubbles in varied regions and fluctuation behavior of steel-slag interface in the mold were investigated.The results show that with a low argon flow rate,the liquid steel flowing out from the nozzle ports separates into two streams:one rushes to the narrow face,and the other impacts the steel-slag interface.Large size bubbles are mainly distributed in the near-nozzle region of the 1/2 and 1/4 wide faces.With the increase in the argon flow rate,the impacting position of the stream on the narrow face move upwards,and the slag open eyes appear in the vicinity of the nozzle and gradually become larger.Moreover,the number of large size bubbles in 1/2 wide face first increases and then decreases,and the number of small size bubbles near the narrow face increases significantly.With a low casting speed,a single-roll flow pattern is formed in the mold,and the bubbles are concentrated near the wall of the nozzle with a large slag open eye generated here.An increasing casting speed is beneficial for the uniform spatial distribution of bubbles in the mold,and reduce the area of slag open eye,but will increase the number of small bubbles in the area near the narrow face.In addition,a low submerged depth is favorable for bubbles to float upwards in the near-nozzle region.Moderately increasing the submerged depth of the nozzle can decrease the number of small bubbles near the wide face.