Numerical Simulation Of Coupled Electromagnetic Field, Flow And Heat Transfer In Bloom Continuous Casting With Electromagnetic Stirring

Continuous casting mold with electromagnetic stirring (M-EMS) is becoming an effective method to control the process of solidification, improve the solidification structure and increase the quality of products. So, it is of great significance to understand the process in mold with EMS, for specific continuous casting conditions.This paper regarded a factory bloom continuous casting mold with electromagnetic stirring as the research object, using numerical simulation methods, and a description of electromagnetic field, flow and temperature distribution mathmatical model was established, and the finite element, finite volume method was used to solve those problems respectively. With mold electromagnetic stirring, the distribution laws of magnetic field, flow and temperature were obtained, at the same time, the impacts of exciting current intensity, frequency and casting speed were analyzed. The research shows that:(1) The values of magnetic induction reach its maxium at the middle plane of the stirrer and become smaller towards the two ends of the bloom gradually, and magnetic field distribution is more uniform in horizital plane. Electromagnetic force distributes circumferentially at horizontal plane, and tangential electromagnetic force is proportional to the distance to the bloom centre. The values of tangential electromagnetic force reach its maxium at the centre of the stirrer along drawing direction, in addition, there is another peak value at the exit of mold. Both magnetic induction and electromagnetic force increase with the exciting current intensity. At the frequency of 4.0 Hz, as the exciting current for each additional 100 A, the magnetic induction of stirrer centre increases by about 7.5 mT, and the largest tangential electromagnetic force increases from 325N/m3 at 200A to 2890N/m3 at 600A. With the increase in frequency, magnetic induction in the mold decreases, and electromagnetic force increases first and then decreasees,8.0 Hz at a maximum.(2) Without electromagnetic stirring, molten steel spits out from submerged entry nozzle (SEN), and penetrates deep down the liquid point, and then returns upward along the side of solidification to form a single loop. And electromagnetic stirring, the molten steel out from SEN shifts from vertical downward to horizontal rotary in an effective zone of electromagnetic stirring, forming a rotary movement of the mainstream district; and steel at the top of the mainstream area forms a circulation that is down by the centre and upward by the side of solidification; on the contrary, steel at the bottom of the mainstream zone forms another circulation which is down by the side of solidification and upward by the centre. As the stirring parameters are 400A and 4.0 Hz, the maximum of the tangential velocity is 0.28m/s, and the tangential velocity increases by about 0.073m/s with each additional 100A. The greater the electromagnetic force, the stronger the stirring intensity, the shallower the intrusion of the steel flow shares, the more prominent the secondary flow phenomena.(3) Without electromagnetic stirring, overheated steel spits out from SEN and flows downward. Superheat disappears slowly. In the bloom section, temperature is high in the core and declines sharply toward the side of solidification, and the temperature distribution is like a hump. In the M-EMS conditions, rotating stirring leads to that the flow direction of the molten steel changes from vertical downward to horizontal rotary, blocking the overheated steel out from SEN, which makes its depth of immersion shallower, so that the axial temperature rapidly reduces, and the radial temperature rises, resulting in the temperature gradient of the forefront of solidification increases to heat. The greater the stirring intensity, the higher the location of hot area.(4) The parameters of the electromagnetic stirring range from 400A to 700A and 4.0Hz to 8.0Hz, which are obtained by numerical simulation, and field experiments show that the optimal parameters are 600A and 4.0 Hz. Under that condition, the tangential electromagnetic force is 2890N/m3, the tangential velocity is 0.45m/s, and the top surface speed is 0.051m/s, and the secondary flow phenomena is abvious, the location of hot area is improved.