Effect of electromagnetic stirring in extra-large billet on the flow field and temperature field
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摘要: 以某廠斷面為410 mm × 530 mm的特大方坯結晶器為原型，利用ANSYS有限元軟件建立三維數值模型，研究電磁攪拌對結晶器流場及溫度場的影響。施加電磁攪拌后，鋼液受到徑向電磁力，液面呈現旋轉流動趨勢。結晶器內鋼液最大切向速度隨著電流的增加而增大，隨著頻率的增加而減小。電磁攪拌的電流大小由0 增加到500 A時，液面波動由1.21 mm增加到4.35 mm。電磁攪拌能夠使鋼水的高溫區局限于連鑄結晶器上部，鋼水溫度更加均勻。同時鋼液的水平旋流能夠抑制初生坯殼的生長，降低坯殼的生長速度，使結晶器出口處坯殼厚度變薄。綜合分析，該廠在實際生產時合理的電磁攪拌的電流大小應為400 A，頻率為1.5 Hz，此時鋼渣液面波動約為2.73 mm，溫度場較為均勻。Abstract: As the “heart” of continuous caster, the flow field of mold directly affects the quality of the slab. For a billet caster, in-mold electromagnetic stirring (M-EMS), as its necessary configuration, can improve the flow field in the mold, homogenize the liquid steel temperature, improve segregation, and improve the slab quality. This paper utilized a 410 mm × 530 mm large billet caster in a factory, which is one of the largest section casters in China. Based on it, a three-dimensional numerical model was established using the ANSYS finite element software to study the influence of electromagnetic stirring on the flow field, liquid level fluctuation, and temperature field of the mold. After electromagnetic stirring was applied, the liquid steel was subjected to a radial electromagnetic force, and the liquid surface shows a rotating flow trend. The maximum tangential velocity of molten steel increases with the increase of current and decreases with the increase of frequency. When the current of electromagnetic stirring increases from 0 A to 500 A, the fluctuation of the liquid level increases from 1.21 mm to 4.35 mm. The maximum tangential velocity of the electromagnetic stirring center increases from 0.02 m?s?1 to 0.21 m?s?1. Electromagnetic stirring can restrain the impact of the high-temperature jet from the nozzle, move the high-temperature zone of molten steel upward, and make the temperature of molten steel more uniform. Under the action of a radial electromagnetic force, the horizontal swirl of liquid steel can inhibit the growth of the primary shell, reduce the growth rate of the shell, and reduce the thickness of the shell out of the mold by about 2.3 mm. The comprehensive analysis shows that the reasonable current of electromagnetic stirring is 400 A and the frequency is 1.5 Hz. At this time, the fluctuation of the slag level is about 2.73 mm, and the temperature field is relatively uniform.
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Key words:
- extra-large boom /
- electromagnetic stirring /
- flow field /
- temperature field /
- numerical simulation
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圖 1 結晶器（a）和水口（b）的網格劃分示意圖
Figure 1. Meshed computational model equipped with (a) a mold chamfer and (b) a four-port submerged entry nozzle (SEN)
圖 2 電磁攪拌裝置圖（a）和安裝示意圖（b）
Figure 2. (a) Schematic illustration of the mold electromagnetic stirring(M-EMS) and (b) its install location
圖 3 結晶器中心軸向線電磁攪拌強度測量值和計算值對比
Figure 3. Comparison of the calculated and measured magnetic flux density in M-EMS
圖 4 無電磁攪拌（a）和施加電磁攪拌（b）情況下結晶器流場速度分布圖和流線圖
Figure 4. Velocity contour in the upper part of the mold (a) without EMS and (b) with EMS
圖 5 電流強度對電磁攪拌中心速度的影響.（a）0 A；（b）300 A；（c）400 A；（d）500 A
Figure 5. Effect of the current intensity on the velocity distribution of the stirring center: (a) 0 A; (b) 300 A; (c) 400 A; (d) 500 A
圖 6 不同電流強度下電磁攪拌中心切向速度大小
Figure 6. Tangential velocity of the electromagnetic stirring center under different current intensities
圖 7 鋼渣界面速度大小分布云圖.（a）無電磁攪拌；（b）施加電磁攪拌
Figure 7. Velocity distribution of the steel-slag interface (a) without EMS and (b) with EMS
圖 8 不同電流強度下鋼渣液面高度的分布.（a）0 A；（b）300 A；（c）400 A；（d）500 A
Figure 8. Distribution of the liquid level of the steel-slag surface at different current intensities:（a）0 A;（b）300 A;（c）400 A;（d）500 A
圖 9 電磁攪拌中軸線最大磁感應強度測量值
Figure 9. Actual measurement of the magnetic induction at the axis of electromagnetic stirring
圖 10 頻率對電磁攪拌中心切向速度的影響
Figure 10. Effect of the current frequency on the tangential velocity of the stirring center
圖 11 水口沖擊方向截面的溫度分布和結晶器出口截面的液相分數分布.（a）0 A；（b）300 A；（c）400 A；（d）500 A）
Figure 11. Distribution of temperature in the impinging direction of the nozzle and the liquid fraction at the outlet of the mold: (a) 0 A ; (b) 300 A; (c) 400 A; (d) 500 A
圖 12 坯殼厚度沿鑄造方向的增長情況
Figure 12. Growth of the solidified shell thickness along the casting direction
表 1 模擬計算條件
Table 1. Simulation conditions
Parameters Value Cross section of bloom/(mm×mm) 410×530 Submerged entry nozzle Four-port Casting speed/（m·min?1） 0.43 Casting temperature /K 1790 Density of steel /（kg·m?3） 6970 Density of slag /（kg·m?3） 2500 Viscosity of steel /（kg·m?1·s?1） 0.00623 Liquidus temperature /K 1765 Solidus temperature /K 1698 Steel resistivity /（Ω·m） 1.4×10?6 Copper plate resistivity /（Ω·m） 1.7×10?8 Running current of M-EMS /A 200–600 Running frequency of M-EMS /Hz 1.5–3.5 Permeability of iron core 1000 Permeability of steel 1 
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