复合磁场作用下板坯结晶器内流场与温度场的数值模拟

提出了一种用于板坯流动控制的复合磁场,在弯月面附近施加电磁搅拌,在浸入式水口附近施加电磁制动,以形成对流场及温度场的复合控制.使用Fluent软件建立了结晶器内复合磁场作用下的钢液流场与温度场三维计算模型.通过与无磁场作用的钢液流动及传热行为进行对比,揭示了复合磁场对结晶器钢液流场和温度场的作用规律.结果表明:复合磁场在一定电磁参数条件下可以减弱水口出流主流股对窄面的冲击,冲击位置处的最大湍动能值降低62％,减少下返流侵入深度;弯月面附近得到了充分的搅拌,结晶器壁面附近的钢液流速增强30％,有利于凝固前沿的冲刷;同时结晶器壁面附近温度提高了1～2 K,均匀了结晶器内温度分布.结晶器电磁搅拌与电磁制动的流场控制优势得以同时发挥.     

全幅一段与全幅二段电磁制动对薄板坯连铸结晶器流场的影响

介绍了连铸结晶器流场电磁制动的有限差分数学模型.通过水力学模拟对计算程序首先进行了验证.随后分别计算了实际水口结构条件下全幅一段电磁制动与全幅二段电磁制动的结晶器流场,初步分析了电磁制动工艺对结晶器流场、液面波动的影响.结果表明,通过施加全幅一段电磁制动,能够有效地使结晶器内钢水流速平均化,减小对结晶器窄面凝固壳的撞击,降低液面波动.而全幅二段电磁制动对液面波动的效果更加明显.     

静磁场控制板坯连铸结晶器液面波动

 用Pb Sn Bi低熔点合金进行了热模拟实验,研究了在静磁场作用下板坯连铸结晶器内的液面波动行为。实验结果表明可应用静磁场控制结晶器内金属液面的波动,且磁场对表面波动的抑制作用有一最佳值,即磁感应强度为05 T时液面平均波动最小。为此,为了减少由于液面波动引起的连铸板坯中的卷渣缺陷,有必要在一定的浇铸条件下优化磁感应强度。吹入氩气加剧了表面波动,且随着氩气流量的增加扰动加大。施加电磁制动能够使吹入氩气引起的液面波动受到显著的抑制。     

方坯连铸结晶器电磁搅拌的数值模拟

根据麦克斯韦电磁理论,利用有限元分析软件ANSYS对240 mm×280 mm方坯结晶器电磁搅拌的磁场进行数值模拟。分析电流强度、电流频率及结晶器铜管等对搅拌器内磁场分布的影响,得到了磁场特性与电磁搅拌参数的关系。研究结果表明:旋转磁场在结晶器搅拌区域内产生旋转电磁力,使钢液在水平方向形成旋转流动;磁感应强度随电流强度的增大呈线性递增;在低频搅拌条件下频率对电磁搅拌强度的影响较小,而铜管厚度对磁场强度影响较大;模拟结果与实测结果基本吻合。     

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。     

旋流水口对圆管坯连铸结晶器内钢水流场的影响

借助于流体力学分析软件Fluent,在圆管坯连铸浸入式水口上施加电磁力,对结晶器内钢水产生电磁搅拌作用使模型水口出流成螺旋状态的钢水流场进行了数值模拟。结果表明:旋流式水口有利于改善结晶器内的流场,有效降低冲击深度,增大液流向弯月面区域的回流和热流上传,提高了液面的活跃程度,增强钢水表面融渣的效果。     

板坯结晶器电磁制动的模拟研究

采用低熔点金属模拟板坯电磁制动条件下结晶器内流场,使用超声多普勒测速仪测量结晶器内金属液流速.实验结果表明:电磁制动不仅能够抑制结晶器内金属液流动,而且能够改变流动方向和调节流速分布;单条型电磁制动能够增强上环流的流动,增大冲刷强度;流动控制结晶器能够改善上环流的流动,降低结晶器上部的冲刷强度.     

电磁场作用下板坯连铸结晶器内的弯月面行为

用Pb-Sn-Bi低熔点合金进行了热模拟实验.从液面波动人手,研究了在单条形电磁场作用下板坯连铸结晶器内的弯月面行为.实验结果表明可应用磁场控制结晶器内金属液面的波动.当水口角度为向下30°时,磁场对表面波动的抑制作用有一最佳值,即磁感应强度为0.5 T时液面平均波动最小,液面较稳定.施加磁场使弯月面处温度明显提高,使水口出流的向下冲击深度受到抑制,这有利于夹杂物的上浮分离,达到提高板坯内部质量的目的.     

板坯结晶器内电磁制动过程流场的数值模拟

应用描述结晶器电磁制动过程的三维流动数学模型,并利用所开发的计算程序ＭＯＬＤ－ＥＭＢＲ３Ｄ１．０进行了数值模拟,结果表明：电磁制动能明显减缓钢水主流股的流速,缓解对铸坯窄面的冲击,有效地抑制表面波动,减小钢水的冲击深度;磁场和流场的相互作用程序直接影响电磁制动效果,磁场位置的升高或降低会出现双涡现象。     

高拉速厚板坯连铸结晶器流场影响因素的模拟研究

运用数值模拟研究方法,研究高拉速厚板坯连铸结晶器流场的影响因素;研究浸入式水口结构、水口控流方式、水口出口角度、水口浸入深度、结晶器宽度、结晶器厚度、吹氩等因素对结晶器流场、液面流速以及初生坯壳的影响.结果表明在高拉速下,结晶器的流场不稳定因素增多,工艺参数对结晶器流场的影响因数增加.在高拉速下结晶器流场流速高,液面波动大,液钢流束冲击深度大,势必造成产品质量的下降趋势,因此高拉速厚板坯连铸过程必须采用电磁制动或流场控制技术,降低高流速带来的不利影响;水口结构与结晶器规格最优化与匹配能得到适宜的结晶器流场;同时发现高拉速钢液流束对结晶器初生坯壳的影响严重,是高拉速漏钢率高的直接原因之一.     

Experimental Investigation of Fluid Flow in CC Mold With Electromagnetic Filed

Fluid flow in continuous casting mold is one of the key factors to influence the process, because the operation of the casting process and most of the defects in steel quality are closely associated with fluid flow in the mold. Electromagnetic field(EMF) has been applied to control the fluid flow as an efficient technology, and a lot of research works on the effect of the EMF has been done by numerical simulation. Aware of the limitation of the numerical simulation of the flow under a static EMF, low melting metals have been adapted to the investigation of flow in EMF. In the report, some of works on electromagnetic brake ruler (EMBR) and Flow Control Mold (FC-Mold) in slab casting with mercury as an analogue of liquid steel are presented. In the experiment, the flow in the mold and fluctuation of meniscus were measured by the ultrasonic DOP2000 velocimeter. The effects of the magnetic flux density and location of the magnets on the flow in the mold have been studied. The results showed that the flow discharged from the SEN was suppressed, both of the distribution of the kinetic energy and the turbulence intensity were changed, and the flow stability of liquid metal in the mold was enhanced. In electromagnetic brake ruler when Bmax was more than 0.29T, the surface level fluctuations were suppressed,the flow at the meniscus became stable and the flow pattern at the meniscus were improved, and the impact strength of liquid metal was weakened simultaneously, and the penetration depth was reduced. It was beneficial to improve the flow in the upper eddy, fluctuation of meniscus and stability of the flow when the magnet was located near the SEN. However, it was good to reduce the impact action and penetration depth when the magnet was away from the SEN. Compared with EMBR, it was more effective to use FC-Mold for improving the flow in the upper eddy, fluctuation of meniscus and stability of the flow. Nevertheless, it was more effective for lower flow to reducing the impact action and penetration depth using EMBR. The     

Optimum Position of Electromagnetic Brake on Slab Caster

SymbolList　　B———Magneticfluxdensity ,T ;　　CD———Dragcoefficient;　　d———Diameter ,m ;　　g———Gravitationalacceleration ,m·s-2 ;　　h———Timestep ,s ;　　J———Currentdensity ,A·m-2 ;　　la,lb———Sizeofslabcross section ,m ;　　ln———Immersiondepthofnozzle ,m ;　　p———Pressure ,Pa ;　　t———Time ,s ;　　u→ ———Velocity ,m·s-1;　　vc———Castingspeed ,m·min-1;　　X→ ———Displacement ,m ;　　———Electricpotential,V ;　　ρ———Density ,kg·m-3;…     

Numerical Analysis of the Influences of Operational Parameters on the Braking Effect of EMBr in a CSP Funnel-Type Mold

A three-dimensional mathematical model of the magnetic field, flow field, and temperature field in a 1500 mm × 90 mm CSP funnel-type mold is used to numerically study the effect of an electromagnetic brake (EMBr) on flow and heat transfer behavior of molten steel. A number of effects of EMBr on the flow pattern and temperature distribution of molten steel are simulated. The jet flow discharge from the submerged entry nozzle (SEN) is significantly suppressed. In addition, heat transfer in the upper part of the mold increases under the influence of EMBr, which can improve the mobility of liquid steel at the meniscus and achieve low superheat casting. The relations between casting speed and magnetic flux density, and between SEN submergence depth and the installation position of the EMBr device, are taken into account to study the effects of braking on molten steel. The results show that the braking effect is weakened with an increase in either the casting speed or the SEN submergence depth. In order to insure the efficient and stable operation of a continuous casting production, the magnetic flux density should be increased by approximately 0.1 T when the casting speed increases by 1 m/min. In addition, an optimal braking effect for molten steel can be obtained when the distance between the bottom of the nozzle and the upper surface of the EMBr device is 100 mm.     

板坯连铸结晶器电磁制动技术及其应用

叙述了板坯连铸结晶器中应用电磁制动技术的发展、研究状况。电磁制动技术可以控制结晶器内钢液的流动，减少结晶器保护渣的卷渣，有利于结晶器内夹杂物的去除，从而提高铸坯质量，并有利于提高铸坯拉速。研究结果表明电磁制动特性取决于板坯宽度、浇铸速度、氩气流速和浸入式水口(SEN)形状等浇铸参数，介绍了各种浇铸参数对电磁制动效果的影响。     

Effects of Electromagnetic Brake,Mold Curvature and Slide Gate on Fluid Flow of Steel in a Slab Mold

The influence of mold curvature, slide gate and magnetic forces on the steel flow in a slab mold was studied with a 3‐D mathematical model. The slide gate application induces a biased flow toward the mold side where its opening is located in the submerged entry nozzle (SEN). Turbulence and asymmetry of flows are more intense in a curved mold than in a straight mold. The effect of an electromagnetic brake (EMBr), located in the discharging ports to control flow turbulence, is only appreciable when magnetic flux density is higher than 0.1 T. The magnetic flux density does not affect the velocity profile in the discharging ports in the SEN because its construction material is insulated. Increasing the magnetic flux density leads to a decrease of the discharging jets angle and to the elimination of the two upper roll flows. The use of the EMBr in a curved mold equipped with a slide gate eliminates the meniscus velocity spikes observed in the mold corners. These results help to demonstrate that EMBr eliminates the asymmetry in a curved mold even under the excessive turbulent conditions existing in curved continuous casting molds.     

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

 The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product. The multiphase flow phenomena of molten steel, steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation, and the effect of electromagnetic brake (EMBR) and argon gas blowing on the process were investigated. The relationship between wavy fluctuation height near meniscus and the level fluctuation index F, which reflects the situation of mold flux entrapment, was clarified. Moreover, based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification, the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux, temperature and stress of shell in slab continuous casting mold were described.     

Numerical Simulation of Level Magnetic Field

TheLMF (LevelMagneticField)technologybasedonstaticmagneticfieldcanbeusedtoimprovecontinuouscasting ,suchasforreducingimpactonnarrowsidesofshell ,eliminatinglargenonmetallicinclusions ,preventingmoldfluxentrappingandim provingslabcleanliness ,etc[1,2 ] .Theeffectofstaticmagneticfieldonsolutebehaviorandcrystallizationduringsolidificationwasinvestigated[3 ] .Theknowl edgeanddesignofmagneticfieldisveryimportantbaseofLMFtechnology .However ,themagneticfieldwasgenerallytakenasaone dimensionalfie…     

The Effects of Electromagnetic Brake on Liquid Steel Flow in Thin Slab Caster

Computational fluid dynamics (CFD) model with magneto hydro dynamics (MHD) is developed for a thin slab caster to investigate the effects of electromagnetic brake (EMBr) on liquid steel flow in continuous casting mold and to determine the EMBr practices which lead to optimal flow structure. Particle Image Velocimetry (PIV) tests in water model and meniscus flow measurements in real caster are performed to validate the predictions obtained with CFD models. The performance of different submerged entry nozzle designs, SEN 1 and SEN 2, are evaluated. The effects of nozzle submergence in relation to the applied magnetic field on mold flow structure are quantified. There are significant differences between flow structures obtained with SEN 1 and SEN 2, even though both designs have fundamental similarities and contain four ports. EMBr mainly reduces the meniscus velocities for SEN 2 as opposed to the foremost influence of EMBr for SEN 1 that is to significantly slow down the downward jet coming from the bottom ports. In addition, reducing the EMBr strength for shallow nozzle submergence and increasing the EMBr strength for deep nozzle submergence help to maintain similar meniscus activity for all conditions.     

Effect of EMBr on Flow in Slab Continuous Casting Mold and Evaluation Using Nail Dipping Measurement

The nail dipping method was developed to investigate the effect of electromagnetic brake on the mold top surface flow in a certain slab caster with different casting speed and submerged entry nozzle (SEN) depth. The shape of the meniscus profile and direction of flow were quantified by analyzing the angular profile of the lump for each solidified nail, and the error evaluation for the nail dipping measurement was also determined. The results show that the meniscus level fluctuates with time variation; the electromagnetic force suppresses the high‐speed flow and decreases the meniscus flow velocity, which makes the meniscus level flatter and slower. A stronger meniscus velocity and fluctuation were created by increasing casting speed and decreasing the SEN depth. Furthermore, the effect of magnetic field on the fluid flow in the mold has been investigated.