【作者】 陈伟；

【导师】 厉英；

【作者基本信息】 东北大学 ， 冶金工程， 2014， 硕士

【摘要】 现代连铸工艺虽然采用了浸入式水口、保护渣、气体保护等措施,使得铸坯质量得到很大改善,但是,直到采用了电磁搅拌技术,才可能对铸坯组织结构进行控制。扩大铸坯的等轴晶区,减轻铸坯的中心疏松、中心偏析和中心缩孔,是连铸电磁搅拌技术在连铸生产中得到广泛应用的重要原因。本文以国内某大型钢企电炉圆坯连铸机的旋转型结晶器和凝固末端组合电磁搅拌器为研究对象,在ANSYS Workbench平台下,采用ANSYS Maxwell和ANSYS Fluent对结晶器电磁搅拌和凝固末端电磁搅拌分别建立了数学模型并进行研究计算,揭示了结晶器内钢液和凝固末端液芯的磁场、流场分布规律。在结晶器电磁搅拌(M-EMS)条件下,磁场以与励磁电流相同的频率绕轴线旋转,钢液所受电磁力以2倍于励磁频率的变化率旋转。在铸坯轴向方向上,从钢液面处向搅拌器中心铸坯内的磁感应强度和电磁力逐渐增大,从搅拌器中心向结晶器出口方向磁感应强度和电磁力逐渐减小。随着电流强度的增大铸坯内的磁感应强度和切向电磁力都增大；随着励磁频率的增加铸坯内的磁感应强度降低；在2-8Hz的励磁频率时钢液所受切向电磁力随励磁频率的增加而加大,在励磁频率超过9Hz后,随着励磁频率的增加切向电磁力减小；励磁频率在2-8Hz范围内时,随着励磁频率的升高,钢液的周向流速越大,在电流强度在200～400A范围内,随着电流强度的提高,钢液的搅拌强度也越大。在搅拌器横截面内,从铸坯中心向边缘方向磁感应强度和电磁力都逐渐增大,电磁力呈周向分布,与磁场旋转方向一致,铸坯中心处切向电磁力几乎为0；钢液的周向流速从铸坯中心向铸坯边缘不断增大,在铸坯边缘处附近达到最大值,在励磁频率为8Hz,电流程度为400A时最大为0.25m/s,在结晶器壁面附近切向流速趋于O。由于切向电磁力导致钢水的流动方向由向下改变为倾斜向铸坯边缘,使从水口流出的高温钢水的冲击深度变浅,从而提高温区,同时使径向温度提高,减小凝固前沿的温度梯度,有利于传热。在凝固末端电磁搅拌(F-EMS)条件下,钢液凝固前沿处磁场强度随励磁频率的升高而小幅度降低,随电流强度的增大近似线性增加,在励磁频率为12Hz,电流强度为600A时搅拌器中心铸坯凝固前沿处磁感应强度为900Gs；钢液凝固前沿处电磁力在频率为9-12Hz范围内随励磁频率升高而增大,在12-20Hz范围内随励磁频率升高而减小,在励磁频率为12Hz,电流强度为600A时达到最大值630N/m3；钢液凝固前沿最大周向速度在频率为9-12Hz范围内切向流速随励磁频率升高而增大,在12-20Hz范围内切向流速随励磁频率升高而减小,在励磁频率为12Hz,电流强度为600时达到最大值0.19m/s。更多还原

【Abstract】 Modern continuous casting process have using the protection measures of submerged nozzle, protecting slag and inert gas, which made the slab quality being greatly improved. But, until the electromagnetic stirring technique has being used, it is possible to control the slab structure of the organization. Expanding isometric zone of slab, reducing the osteoporosis of slab center, center segregation and shrinkage cavity at center, these were why continuous casting technology electromagnetic stirring widely used in continuous casting production.In this paper, we take the rotary type mold electromagnetic stirrer and solidification ending electromagnetic stirrer in a large steel mills in China as the research object. In platform using ANSYS Workbench and ANSYS Fluent we have established mathematical the model of mold electromagnetic stirring and final electromagnetic stirring. Also, the model has been studied and calculated, revealing the distribution of electromagnetic fields and flow field of steel in the mold and solidification.Under the conditions of Mould Electro Magnetic Stirring (M-EMS), electromagnetic fields rotate about the axis in the same frequency with excitation current and electromagnetic force rotate about the axis in the frequency of twice over excitation current. In the axial direction of the slab, from the steel surface to blender center, magnetic induction and electromagnetic force are increasing. From the center of stirrer to the crystallizer, magnetic induction and electromagnetic force are reduced. With the increase of the intensity of current, the magnetic induction and tangential electromagnetic force are also increased. With the increase of the excitation frequency increases the magnetic flux density is reduced. Tangential electromagnetic force increases with increasing frequency when excitation frequency is in the range of 2Hz to 8Hz. The electromagnetic shear force decreases with the increase of the excitation frequency when the excitation frequency more than 9Hz. As the excitation frequency increases the greater of the flow rate of molten steel when excitation frequency is in the range of 2Hz to 8Hz. With the increasing of current intensity the stirring intensity is greater when current intensity in the range of 200A to 400A. In the cross-section of the agitator, from the center of the slab to slab edges, magnetic induction and electromagnetic force are increase. Electromagnetic force is circumferential distribution. The electromagnetic force and the direction of the magnetic field direction of rotation is the same. The tangential electromagnetic force of slab center is almost zero. From slab center to the slab edge molten steel flow rate is increasing. It achieved the maximum value in the slab edge. When excitation frequency is 8Hz and the intensity of electric current is 400A. Molten steel flow velocity is 0.25m/s. The liquid steel near mold wall flow velocity is almost zero. Because of the tangential electromagnetic force, the direction of the flow of the molten steel is from down turn to tilt to the slab edge. Make the high temperature molten steel from the submerged nozzle impact depth becomes shallow to improve the temperature range. It increasing the radial temperature, meanwhile, reducing the temperature gradient on the front edge of solidified shell, which is good for heat transfer.On the condition of Final Electro Magnetic Stirring (F-EMS), with the increases of excitation frequency the Magnetic induction is small amplitude decrease. With the increase of current intensity the magnetic induction is near linear increase. Magnetic induction intensity in slab solidification front is 900Gs when the intensity of electric current is 600A and excitation frequency is 12Hz. The electromagnetic force in slab solidification front is increasing with excitation frequency increasing when excitation frequency in the range of 9Hz to 12Hz. The electromagnetic force in slab solidification front is decreases with excitation frequency increasing when excitation frequency in the range of 12Hz to 20Hz. When excitation frequency is 12Hz and the intensity of electric current is 600A tangential electromagnetic force achieve the maximum value 630N/m3. The liquid steel in slab solidification front flow velocity increasing with increased excitation frequency when excitation frequency in the range of 9Hz to 12Hz. The liquid steel in slab solidification front flow velocity decreases with increased excitation frequency when excitation frequency in the range of 9Hz to 12Hz. Molten steel tangential velocity achieve the maximum value 0.19m/s when excitation frequency is 12Hz and The intensity of electric current is 600A.更多还原