Study on the effect of multi area controllable electromagnetic braking on behavior of non-uniform molten steel flow and steel-slag interface in the mold
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摘要: 连铸过程中，因水口堵塞引发的结晶器内部钢液流动畸变是影响铸件质量和生产效率的关键因素之一。为解决此问题，文中提出多区域独立可控电磁制动技术，以改善钢液流态，减少水口堵塞带来的负面影响。首先，选定板坯结晶器作为研究对象，构建电磁连铸结晶器内钢液流动与渣金界面行为分析模型；其次，对比分析无电磁制动、现行全幅一段电磁制动以及多区域独立可控电磁制动作用下，结晶器内部钢液非均匀流动特性与渣金界面的演变规律。模拟结果表明，在单侧水口发生25%堵塞的情况下，相较于全幅一段电磁制动，多区域独立可控电磁制动所产生的制动效应对非堵塞侧结晶器内钢液的流动控制效果更显著。与未施加电磁制动时相比，当施加的磁场强度为0.3 T时，全幅一段电磁制动结晶器内非堵塞侧钢液表面最大流速和界面最大波高分别增加了16.7%和1.6%，而多区域独立可控电磁制动结晶器内非堵塞侧钢液表面最大流速和界面最大波高分别降低了16.7%和48.4%。可见，采用多区域独立可控电磁制动可实现分区域控制结晶器内部钢液流动，从而改善流场的对称性，并减少因水口堵塞引起的流动不对称现象。Abstract: In the process of continuous casting, the distortion of molten steel flow in mold caused by nozzle clogging is a key factor affecting the quality and production efficiency of castings. To solve this problem, a multi area controllable electromagnetic braking (MAC-EMBr) technology is proposed to improve flow state of molten steel and reduce negative impact of nozzle clogging. Firstly, a slab mold is selected as the research object to establish an analytical model of molten steel flow and steel-slag interface behavior in electromagnetic continuous casting mold. Secondly, the fluid-flow-related phenomena of three casting cases in the slab mold, i.e., No-EMBr, Ruler-EMBr, and MAC-EMBr, are further investigated numerically to evaluate the metallurgical capability of the MAC-EMBr, including the non-uniform flow characteristics of molten steel and the evolution pattern of steel-slag interface inside the mold. According to the simulation results, with a 25% blockage rate of a single-side nozzle, the braking effect of the Ruler-EMBr on the backflow in the upper region of the mold is not remarkably. In detail, when the magnetic flux density reaches 0.3 T, the maximum magnitude of the surface velocity and the maximum amplitude of the level fluctuation on non-clogging side with the Ruler-EMBr are 16.7% and 1.6% higher than those with No-EMBr, respectively. This is not conducive to the stability of steel-slag interface in the mold. However, under the same magnetic flux density as the Ruler-EMBr, the application of MAC-EMBr has great potential to suppress the upward backflow on the non-clogging side. In comparison with No-EMBr, the maximum magnitude of the surface velocity and the maximum amplitude of the level fluctuation with the MAC-EMBr are decreased by 16.7% and 48.4%, respectively. As a result, the flow of molten steel in the mold can be well controlled in different regions with the MAC-EMBr, so as to improve the symmetry of the flow field and reduce the flow asymmetry caused by nozzle clogging.
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图 2 试验测量和数值模拟结晶器内液面波动结果
(a) 试验测量结果；(b) 试验和模拟比对结果
Figure 2. Experimental measurement and numerical simulation of level fluctuation heights in the mold
图 3 多区域独立可控电磁制动结晶器内磁场强度分布
(a) 结晶器内磁场强度；(b) 沿结晶器高度方向宽面中心截面磁场强度
Figure 3. Distribution of magnetic field intensity in the mold with MAC-EMBr
图 4 多区域独立可控电磁制动结晶器宽面中心截面钢液速度分布
Figure 4. Velocity distribution in the central section of wide surface in the mold with MAC-EMBr
(a) BMAC-I=BMAC-II=0 T；(b) BMAC-I=0.1 T，BMAC-II=0.3 T；(c) BMAC-I=0.2 T，BMAC-II=0.3 T；(d) BMAC-I=BMAC-II=0.3 T
图 5 多区域独立可控电磁制动结晶器内钢液速度等直面图
Figure 5. Isosurface diagram of velocity in the mold with MAC-EMBr
(a) BMAC-I=BMAC-II=0 T；(b) BMAC-I=0.1 T，BMAC-II=0.3 T；(c) BMAC-I=0.2 T，BMAC-II=0.3 T；(d) BMAC-I=BMAC-II=0.3 T
图 6 多区域独立可控电磁制动结晶器内钢液表面速度分布云图
Figure 6. Nephogram of surface velocity in the mold with MAC-EMBr
(a) BMAC-I=BMAC-II=0 T；(b) BMAC-I=0.1 T，BMAC-II=0.3 T；(c) BMAC-I=0.2 T，BMAC-II=0.3 T；(d) BMAC-I=BMAC-II=0.3 T
图 7 多区域独立可控电磁制动结晶器内钢液表面速度分布
Figure 7. Surface velocity distribution in the mold with MAC-EMBr
图 8 多区域独立可控电磁制动结晶器内渣金界面波动云图
Figure 8. Nephogram of steel slag interface fluctuation in the mold with MAC-EMBr
(a) Bleft = Bright = 0.0 T；(b) Bleft = 0.1 T，Bright = 0.3 T；(c) Bleft = 0.2 T，Bright = 0.3 T；(d) Bleft = 0.3 T，Bright = 0.3 T
图 9 多区域独立可控电磁制动结晶器内渣金界面波动高度
Figure 9. Fluctuation height of steel slag interface in the mold with MAC-EMBr
图 10 结晶器宽面中心截面钢液速度分布
(a) 无磁场；(b) 全幅一段电磁制动；(c) 多区域独立可控电磁制动
Figure 10. Velocity distribution in the central section of wide surface in the mold under different braking conditions
图 11 结晶器内钢液速度等直面图
(a) 无磁场；(b) 全幅一段电磁制动；(c) 多区域独立可控电磁制动
Figure 11. Isosurface diagram of velocity in the mold under different braking conditions
图 12 结晶器内钢液表面速度分布云图
(a) 无磁场；(b) 全幅一段电磁制动；(c) 多区域独立可控电磁制动
Figure 12. Nephogram of surface velocity in the mold under different braking conditions
图 14 结晶器内渣金界面波动云图
(a) 无磁场；(b) 全幅一段电磁制动；(c) 多区域独立可控电磁制动
Figure 14. Nephogram of steel slag interface fluctuation in the mold under different braking conditions
表 1 板坯结晶器计算参数
Table 1. Computational parameters of slab mold
铸坯断面/（mm×mm） 结晶器长度/mm 结晶器计算域/mm 水口双侧孔尺寸/mm 水口浸入深度/mm 水口内径/mm 拉坯速度/(m∙min−1) 1450 ×230800 4000 65×80 170 80 1.8 钢液密度/(kg∙m−3) 钢液黏度/(Pa∙s) 钢液电导率/(S∙m−1) 钢液磁导率/(H∙m−1) 液渣密度/(kg∙m−3) 表面张力/(N∙m−1) 磁场强度/T 7020 0.0062 7.14×105 1.26×106 3500 1.2 0.1 0.2 0.3 
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表 2 计算域内不同网格节点数的误差统计结果
Table 2. Statistic results of error with different grid node numbers in the computational domain
网格 M1 M2 M3 网格节点数 490,000 735,000 1,102,500 $ {h_{{{\text{M}}_i}}} $ 25.8 25.2 24.9 $ {\delta _h} = {{\left| {{h_{{{\text{M}}_i}}} - {h_{{{\text{M}}_1}}}} \right|} \mathord{\left/ {\vphantom {{\left| {{h_{{{\text{M}}_i}}} - {h_{{{\text{M}}_1}}}} \right|} {{h_{{{\text{M}}_1}}}}}} \right. } {{h_{{{\text{M}}_1}}}}} $ 0 2.3% 3.5% 注：表中h为渣金界面波动高度最大值，即波峰与波谷间的垂直距离，mm；δh为渣金界面波动高度的相对误差，%。
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