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圓坯凝固末端電磁攪拌作用下的流動與傳熱行為

Melt flow and heat transfer at the crater end of round billet continuous casting using final electromagnetic stirring

  • 摘要: 以特殊鋼圓坯連鑄為研究對象, 建立了研究凝固末端電磁攪拌作用效果的三維耦合數值模型.利用分段計算模型獲得末端電磁攪拌區域鋼液流動與凝固的實際狀態, 并采用達西源項法處理凝固末端鋼液在糊狀區的流動, 研究了不同電磁攪拌工藝參數下的電磁場分布及鋼液的流動與傳熱特征.通過測量攪拌器中心線磁感應強度和鑄坯表面溫度驗證了模型的準確性.研究結果表明: 電流強度每增加100 A, 攪拌器中心磁感應強度增加19.05 mT, 電磁力隨著電流強度的增加顯著增大.在20~40 Hz范圍, 隨著電流頻率的提高, 中心磁感應強度略微下降, 但電磁力仍有所增加.在攪拌器區域, 液相穴內的鋼液在切向電磁力的作用下旋轉流動, 其切向速度隨著電流強度和頻率的增加而變大.末端電磁攪拌可促進鋼液在圓坯徑向的換熱, 隨著電流強度和頻率的提高, 鑄坯中心軸線上的鋼液溫度降低, 同時末端攪拌位置處的中心固相分率增加.

     

    Abstract: Final electromagnetic stirring (F-EMS) is widely used in the billet and bloom continuous casting process because it effectively improves the as-cast quality. Numerous industrial trials on F-EMS have been conducted; however, the real melt flow and heat transfer characteristics at the crater end remain unclear. In this study, based on a round billet special steel continuous casting process, a coupled three-dimensional numerical model was developed to describe the F-EMS phenomenon. The flow and solidification behavior of the melt in the F-EMS region were obtained by a segmentation calculation model, and the Darcy source term method was employed to suppress the velocity within the mushy region. The effect of stirring current intensity and frequency on the electromagnetic field, melt flow, and heat transfer was investigated numerically. The model was validated using the measured data of magnetic flux density in the stirrer center and the strand surface temperature. According to the simulation results, with every 100 A increase in the current intensity, the maximal magnetic flux density increases by 19.05 mT. The electromagnetic force significantly increases with the increase in current intensity. With the increase in current frequency within 20-40 Hz, the magnetic flux density decreases slightly, whereas the electromagnetic force increases. Moreover, a swirling flow field in the stirrer region is observed under the rotary electromagnetic force, and the tangential velocity of melt increases with the increase in current intensity and frequency. Additionally, the swirling flow enhances the local melt heat transfer at the radial direction of the round strand. As the current intensity and frequency increase, the temperature of the melt in the liquid core decreases, and the center solid fraction at the F-EMS-implemented position increases accordingly.

     

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