软接触结晶器电磁连铸技术的发展

介绍了软接触结晶器电磁连铸技术的基本原理，评述了该技术的发展过程，分析了在该技术研究中尚需解决的问题。作者认为，对于该技术的基本原理和规律的研究已较充分，但仍存在某些关键技术问题有待解决，为使该技术实用化，应加强此方面的研究。     

软接触结晶器电磁连铸技术研究现状

 从磁场分布和结晶器设计、磁场对铸坯表面质量改善的机理、电磁场作用下结晶器内弯月面的行为、磁场施加方式的演变等几个方面,综合论述了软接触结晶器电磁连铸技术的发展现状,并指出了该技术未来发展过程中值得注意的几个方面。     

圆坯中频电磁软接触连铸结晶器内磁场分布数值模拟

 用数值模拟方法研究了圆坯中频电磁软接触连铸结晶器内磁场分布,讨论改变结晶器结构参数、工艺参数和电参数等因素对结晶器内磁场的影响。结果表明,结晶器内磁场强度在结晶器高度方向上先增大再减小,在感应线圈中心偏下处,磁感应强度达最大;综合考虑结晶器结构和透磁性,切缝宽度选为05 mm,切缝数为8;当自由液面位于感应线圈的中心位置时能获得最大的磁感应强度;随着电流和频率的增加,结晶器内磁感应强度也随着增加。     

Meniscus Behavior in Electromagnetic Soft-Contact Continuous Casting Round Billet Mold

Using molten Pb-Sn-Bi alloy, the meniscus shape under high frequency magnetic field of φ100 mm round billet caster was investigated. The effect of some parameters on meniscus shape was studied. The results show that for a mold with 12 segments, the meniscus shape is relatively stable. With increasing power input, the menis- cus height increases with intensification of fluctuation. For the given caster, the reasonable power input is about 70 kW. The coil should be near to the top of mold and/or the initial meniscus should be near to the center of the coil. The lower the frequency, the higher is the meniscus height. With increasing frequency, the free surface is more flattened and meniscus becomes more stable. In practice, the power input should be increased simultaneously with frequency. The optimal frequency is about 20 kHz.     

Effect of Structure Parameters on Power and Magnetic Field in Electromagnetic Soft-Contact Continuous Casting System

To design a power source system and mold for electromagnetic soft-contact continuous casting process and to theoretically estimate the heat losses from the charges and the system power, the effect of structure parameters on system power and magnetic flux density distribution was calculated using finite element method. The results show that as for electromagnetic soft-contact continuous casting system with partial-segment type mold, the power consumption is much more than that with a full-segment type mold; about 62% of electric power is dissipated in the mold, and the effective acting range of magnetic field is relatively narrow. Optimizing mold structure is a crucial measure of remarkably reducing mold power consumption and saving electric energy. Increasing slit number, width, and length can remarkably increase the magnetic flux density in the mold and can reduce the electric energy consumption. Among structure parameters, slit number and slit width are relatively more effective to reduce energy consumption. For a round billet electromagnetic continuous casting system with diameter of 178 ram, the reasonable slit number, width, and length are about 24--32, 0. 5--1.0 mm, and 160 mm, respectively.     

连铸结晶器电磁搅拌磁场及钢液流场模拟

 建立了大方坯连铸结晶器电磁搅拌条件下电磁场及钢液流场数学模型,开发了相应的Visual Cast仿真软件,并应用软件模拟分析了大方坯连铸结晶器内磁场、电磁力分布及双侧孔浸入式水口条件下结晶器内钢液流场的分布特征。结果表明,结晶器内磁场分布均匀,并沿横断面水平旋转,电磁力的旋转周期为磁场旋转周期的一半。电磁搅拌改变了结晶器内流场形态,减小回流区和冲击深度,有利于促进钢液中非金属夹杂物上浮排除,提高大方坯洁净度。     

圆坯钢电磁软接触连铸的实验研究

为确定工业实验基本参数,对电磁软接触连铸结晶器进行了优化设计计算,设计制作了φ100 mm圆坯电磁软接触连铸结晶器,利用Sn-Pb-Bi合金实验研究了结晶器内的弯月面行为,并进行了w(C)为0.22%钢坯的电磁软接触连铸实验。结果表明,电磁软接触连铸结晶器内磁场和弯月面变形具有不均匀性,切缝数为12时,磁场周向分布和弯月面变形较均匀。输入功率增加,弯月面高度增高,液面波动加剧。对于100 mm圆坯电磁软接触连铸系统,功率可控制在50~60 kW左右。实际应用中,浇注液面应控制在线圈中心偏上位置。较低的电源频率可获得较高的弯月面,频率应控制在20 kHz左右,可获得较高的周向均匀的磁场。获得了表面质量改善的电磁软接触连铸钢坯。随功率增加,铸坯表面依次会出现环状振痕、无振痕和波纹状振痕等3种振痕形态。     

电磁场对软接触结晶器内钢液流动的影响

采用非交错网格和适体坐标方法数值模拟了电磁场对软接触结晶器内钢液流动的影响规律。讨论了感应线圈电流强度和电源频率等因素的影响。结果表明：电磁力能加强地晶器上部熔池的搅拌强度，并在上部区域形成一明显的回流区，同时还能减小射流的渗入深度;加大电流强度，能加强钢液的回流和对钢液的搅拌，减小射流深入深度。但电流强度有一个最佳控制范围；增加电源频率，射流渗入深度增大，弯月面附近的紊动能和钢液速度提高。电源频率应控制在20kHz左右。     

Solidification Structure of Continuous Casting Large Round Billets under Mold Electromagnetic Stirring

The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software.The actual and simulated solidification structures were compared under mold electromagnetic stirring (MEMS)conditions (current of 300 A and frequency of 3 Hz).There-after,the solidification structures of the large round billet were investigated under different superheats,casting speeds,and secondary cooling intensities.Finally,the effect of the MEMS current on the solidification structures was obtained under fixed superheat,casting speed,secondary cooling intensity,and MEMS frequency.The model accurately simulated the actual solidification structures of any steel,regardless of its size and the parameters used in the continuous casting process.The ratio of the central equiaxed grain zone was found to increase with decreasing su-perheat,increasing casting speed,decreasing secondary cooling intensity,and increasing MEMS current.The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.     

连铸结晶器电磁搅拌对夹杂物的影响

在连铸过程中 ,夹杂物对钢的质量有着重要影响。本文分析了结晶器电磁搅拌对夹杂物的作用机理 ,简要叙述了结晶器电磁搅拌对铸坯内夹杂物含量、大小、分布及其形态的影响     

大方坯连铸结晶器电磁搅拌的数值模拟

对大方坯连铸结晶器电磁搅拌过程的流场和温度场进行了数值模拟,并讨论了搅拌强度对流场和温度场的影响。结果表明：在结晶器电磁搅拌下,搅拌器区域的钢液变为水平旋转,使从水口向下吐出的钢水与向上回流的钢水流股相冲突,流股侵入深度变浅,从而使轴向温度迅速降低,径向温度升高,提高了热区位置,有利于传热;搅拌强度越大,钢水的二次流现象越明显,热区位置越高。     

圆坯中频电磁软接触连铸结晶器内钢液流动的数值模拟

采用有限元方法模拟了中频电磁场对软接触结晶器内钢液流动的影响规律,讨论感应线圈电流强度和电源频率等因素对结晶器内钢液流动的影响。结果表明：电磁力能加强结晶器内上半部熔池的搅拌强度,并在弯月面区域形成一明显的回流区,同时还能减小钢液射流的渗入深度;增大电流强度,能加强钢液的回流和对钢液的搅拌,减小射流渗入深度,同时也加剧了钢液自由表面的波动,因而电流强度有一个最佳的控制范围;增加电源频率时,射流的渗入深度变化不大,但弯月面附近钢液的紊动能和速度都有所提高,综合考量,本研究中将频率控制在2500 Hz左右。     

高频磁场作用下软接触电磁连铸初生坯壳的变形行为

结晶器内初生坯壳的变形行为直接决定着连铸坯的表面质量。笔者运用Reynold润滑方程推导出渣膜内的动压力分布,建立了初生坯壳的二维弹塑性变形有限元模型,研究了施加电磁场前、后坯壳的变形行为。研究结果表明：高频磁场(20kHz)下的感应加热作用会降低保护渣的粘度;电磁压力将增加渣缝的宽度,使施加电磁场后连铸坯初生坯壳的变形行为受到影响,进一步解释了软接触电磁连铸技术改善坯壳表面振痕的机理。     

圆坯中频电磁软接触结晶器内磁场分布实验研究

为了研究中频电磁软接触连铸结晶器内磁场分布,通过实验的方法测量出不同电参数和工艺参数下圆坯中频电磁软接触连铸结晶器内磁感应强度的分布情况。实验结果表明:结晶器内磁感应强度随着功率和感应线圈电流的增加而增加;相同功率时随着电源频率的增加先增大后减小,相同电流时随着频率的增加而增加,但是增幅却在减小;在本实验中,相同功率下频率为2500 Hz时产生的磁感应强度最大;随着自由液面的下降,结晶器内磁感应强度先增大后减小,并且当自由液面位于感应线圈的中心高度时磁感应强度达到最大。     

连续铸钢过程中结晶器的传热研究

 为了研究结晶器内壁温度的分布,设计了模拟结晶器工作过程的实验装置,并进行了实验。实验结果表明,结晶器内壁温度趋近于冷却水温度。基于实验,推导了结晶器边界等效导热系数。该系数用于解决金属和冷却水之间的传热,即反映结晶器的传热能力。用等效导热系数处理结晶器的边界传热,对包括结晶器在内的连铸凝固进程温度场进行数值模拟既简单又方便,并且计算结果与实验结果符合。还讨论了拉坯速度和冷却水流量对结晶器温度场的影响。     

Numerical Prediction on the Flow Field of Molten Steel and the Trajectory of Inclusion in Continuous Casting Mold Effected by Electromagnetic Field

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Effect of Induction Heat on Initial Solidification During Electromagnetic Continuous Casting of Steel

 Aiming at the process of electromagnetic continuous casting (EMCC), a three dimensional finite element model on electromagnetic field and temperature field was developed through the commercial software ANSYS to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in soft contact mold under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases of exciting current frequency and density make the effects of induction heat on solidification process increased remarkably. Especially, with the increase of exciting current frequency, the early solidification process and shell growth become non-uniform in billet circumferential direction. Morever, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is decreased greatly.     

连铸结晶器内钢液流动、凝固和夹杂物的分布

 建立并求解动量、热量和质量传输耦合模型,研究了连铸结晶器内钢液流动、传热、凝固、溶质输送和夹杂碰撞长大行为。数值结果表明,受钢液流动的影响,在连铸机内钢液温度、碳浓度和夹杂物的空间分布与钢水流动特征相似,也可分为上下两个循环区。但是其分布具有各自的特点。在涡心处,钢液温度较低,碳浓度较高,夹杂物体积浓度和数量密度较低。在弯月面处,钢液温度较低,碳浓度较高,夹杂物的体积浓度和数量密度较低。在结晶器出口处的凝固坯壳内,夹杂物的浓度和数量密度分布极不均匀,存在阶跃现象,这与冲击点处凝固坯壳的重熔有关。