宽度对CSP漏斗形结晶器电磁制动效果影响的数值模拟

 铸坯尺寸是影响电磁制动效果的重要因素。以某钢厂薄板坯CSP漏斗形结晶器为研究对象,建立了描述CSP漏斗形结晶器电磁制动的三维数学模型,研究宽度对电磁制动效果的影响。研究表明：3种铸坯宽度下,电磁制动均可使涡心位置上移并降低下部漩涡范围;电磁制动可降低自由液面水平方向流速,抑制弯月面波动,提高弯月面温度;在结晶器出口处,使用电磁制动可使铸坯宽面坯壳厚度更均匀并提高窄边凝固坯壳厚度;随铸坯宽度增加,电磁制动效果变得不明显。     

电磁制动对CSP结晶器内夹杂物行为的影响

利用数值模拟方法研究了电磁制动对涟钢CSP结晶器内钢水夹杂物行为的影响,并进行了现场验证.数值模拟表明,无电磁制动时,粒径在50 μm以下的夹杂物颗粒其上浮概率几乎为零,200μm夹杂物颗粒上浮概率为6%;有电磁制动时,粒径在50μm以下的夹杂物颗粒的上浮概率为25%,200 μm夹杂物颗粒上浮概率为38%,现场试验表明,采用电磁制动与没有电磁制动相比,铸坯中200～300 μm的大型夹杂物降低了15.9%,300～400μm的大型夹杂物降低了30.2%,大于400μm的夹杂物降低了39.1%.电磁制动数值模拟的结果与现场试验结果有一定的吻合性.     

CSP结晶器EMBr的冶金效果和流场理论分析

对邯郸钢铁股份有限公司CSP结晶器EMBr冶金效果分析表明,在其它工艺条件相近的条件下,使用EMBr后,薄板坯w(T[O])比未使用EMBr的薄板坯w(T[O])降低了40%,薄板坯中大型夹杂物降低了61%;无电磁制动时,结晶器液面波动为±7 mm,使用电磁制动时,结晶器液面波动为±4 mm,薄板坯内部质量明显改善.应用CFX软件数学模拟了电磁制动及无电磁制动情况下的CSP结晶器流场,模拟结果表明结晶器弯月面钢水中心线速率降低了4倍,湍动能降低了3倍左右.电磁制动可明显提高薄板坯洁净度水平.     

电磁制动对CSP漏斗形结晶器开浇过程影响的数值模拟

 建立了描述电磁制动(EMBr)下CSP漏斗形结晶器开浇过程暂态流动现象的三维数学模型,研究不同磁场强度对开浇过程中结晶器内流场影响。利用流体体积方法(VOF)捕捉钢液-空气界面。采用动网格模型实现引锭杆的移动。研究结果表明：电磁场可显著抑制钢液湍流流动,降低引锭杆启动瞬间的弯月面波动;开浇过程电磁制动的使用可改善拉坯过程中结晶器内钢液流态;电磁制动的使用可将自由稳定时间提前约10s;使用电磁制动可明显减轻漏斗形结晶器内钢液偏流现象。     

Numerical Investigation of Shell Formation in Thin Slab Casting of Funnel-Type Mold

The key issue for modeling thin slab casting (TSC) process is to consider the evolution of the solid shell including fully solidified strand and partially solidified dendritic mushy zone, which strongly interacts with the turbulent flow and in the meantime is subject to continuous deformation due to the funnel-type mold. Here an enthalpy-based mixture solidification model that considers turbulent flow [Prescott and Incropera, ASME HTD, 1994, vol. 280, pp. 59–69] is employed and further enhanced by including the motion of the solidifying and deforming solid shell. The motion of the solid phase is calculated with an incompressible rigid viscoplastic model on the basis of an assumed moving boundary velocity condition. In the first part, a 2D benchmark is simulated to mimic the solidification and motion of the solid shell. The importance of numerical treatment of the advection of latent heat in the deforming solid shell (mushy zone) is specially addressed, and some interesting phenomena of interaction between the turbulent flow and the growing mushy zone are presented. In the second part, an example of 3D TSC is presented to demonstrate the model suitability. Finally, techniques for the improvement of calculation accuracy and computation efficiency as well as experimental evaluations are also discussed.     

电磁制动对CSP漏斗型结晶器流场和液面波动的影响

针对铸坯断面为1 500 mm×90 mm的漏斗型结晶器,在拉速为5 m/min的条件下,通过耦合湍流模型、多相流模型以及电磁制动模型,计算了电磁场作用下结晶器内流体流动与液面波动特征.数值模拟结果表明,应用电磁制动能显著改变结晶器内钢液流动行为,使结晶器内流场分布更加均匀.此外,当施加的磁场强度为0.2和0.3T时,结晶器最大液面波动高度从未施加电磁制动时的15mm减小至9.2mm和2.33 mm.综合考虑到电磁制动效果与生产成本,合理的磁场强度应控制在0.2～0.3 T.     

Flow Oscillations and Meniscus Fluctuations in a Funnel-Type Water Mold Model

Transient flows in a funnel-type continuous casting process model were studied experimentally to investigate the flow oscillations inside the mold and the meniscus fluctuations. A full-scale water model was used with dimensions of 2000 mm (length) × 1350 mm (width) × 100 mm (thickness). Particle image velocimetry (PIV) was employed to measure the flow oscillations. To minimize high shear flow errors near the submerged entry nozzle (SEN) exit, the window deformation technique was adopted. The meniscus levels were extracted by edge-detection image processing. Three types of SEN and two funnel thicknesses (180 mm and 220 mm) were tested to examine the flow characteristics under five flow rates (10, 20, 30, 40, and 50 m³/h). The vortex generation mechanism inside the mold was analyzed across the various mold conditions studied.     

Numerical Analysis of Coupled Fluid Flow,Heat Transfer and Macroscopic Solidification in the Thin Slab Funnel Shape Mold with a New Type EMBr

As an expansion of our former work, a series of numerical simulations of fluid flow, heat transfer, and macrosolidification under the control of both the conventional and the new type electromagnetic brake (EMBr) were carried out. In the present work, the physical models and parameters remain the same as those measures in our former research, and the solution processes of the flow field and electromagnetic field are similar. The specific heat method is used to treat the latent heat of solidification, and the Darcy’s Law-type porous media treatment is used to account for the effect of phase change on convection. User-defined functions (UDFs) are compiled for the following two aspects: One is the Darcy source term, and the other is the thermal conductivity, which varies in mushy zones. From the comparisons of two kinds of EMBr produced by two type magnets separately, the new type EMBr gives its superiorities of the effects on the flow field, heat transfer, and solidification with lower cost of electrical energy.     

Study on Flow in Mold With EMBr in Slab Continuous Casting

A mercury model has been developed to investigate the influences of Electromagnetic Mold Brake Ruler(EMBr-Ruler)and Flow Control Mold(FC Mold)on metal flow in slab continuous casting mold with the practical casting speed 1.0,1.3 and 2.0 m/min respectively.FC-Mold can efficiently repress the surface flow and its fluctuation.The expanding space of the jets is compressed by EMBr-Ruler and FC-Mold respectively,then theflow passagewhere the vertical velocity of flow increases sharply is developed near the narrow wall with EMBr-Ruler and FC-Mold.It is bad for the development of the plug like flow.Only the nozzle ports are placed in the braking magnetic field region and the casting speed is suitable,EMBr can be beneficial to the formation of the plug like flow.The flow regime is improved with FC Mold when the casting speed is high(2.0 m/min),but EMBr can improve the flow field with medium casting speed(1.3m/min),but when the casting speed is low(1.0 m/min),the effects of two types of EMBr are both unsatisfactory.     

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.     

Effect of Electromagnetic Ruler Braking (EMBr) on Transient Turbulent Flow in Continuous Slab Casting using Large Eddy Simulations

Static electromagnetic braking (EMBr) fields affect greatly the turbulent flow pattern in steel continuous casting, which leads to potential benefits such as decreasing flow instability, surface defects, and inclusion entrapment if applied correctly. To gain a fundamental understanding of how EMBr affects transient turbulent flow, the current work applies large eddy simulations (LES) to investigate the effect of three EMBr ruler brake configurations on transient turbulent flow through the bifurcated nozzle and mold of a liquid-metal GaInSn model of a typical steel slab-casting process, but with deep nozzle submergence and insulated walls with no solidifying shell. The LES calculations are performed using an in-house graphic-processing-unit-based computational-fluid-dynamics code (LES-CU-FLOW) on a mesh of ~7?million brick cells. The LES model is validated first via ultrasonic velocimetry measurements in this system. It is then applied to quantify the mean and instantaneous flow structures, Reynolds stresses, turbulent kinetic energy and its budgets, and proper orthogonal modes of four cases. Positioning the strongest part of the ruler magnetic field over the nozzle bottom suppresses turbulence in this region, thus reducing nozzle well swirl and its alternation. This process leads to strong and focused jets entering the mold cavity making large-scale and low-frequency (<0.02?Hz) flow variations in the mold with detrimental surface velocity variations. Lowering the ruler below nozzle deflects the jets upward, leading to faster surface velocities than the other cases. The double-ruler and no-EMBr cases have the most stable flow. The magnetic field generates large-scale vortical structures tending toward two-dimensional (2-D) turbulence. To avoid detrimental large-scale, low-frequency flow variations, it is recommended to avoid strong magnetic fields across the nozzle well and port regions.     

铜闪速吹炼炉操作参数优化的数值模拟研究

金冠铜业闪速吹炼炉自2013年投产以来,操作参数的持续优化对炉况运行稳定性的大幅提升起到了至关重要的作用。公司前期主要依托生产实践经验对参数进行优化,调控幅度和影响程度缺乏理论数据支持。为此,本文开展了闪速吹炼炉的数值仿真计算,同时,利用正交试验,研究操作参数的影响并寻找闪速吹炼炉最优操作参数。研究表明,工艺风速度越小、工艺风富氧浓度越高以及分散风流量越大,则上升烟道出口烟气中的氧气质量分数越低,反应越充分;与基准工况相比,正交试验得到的最优工况下,上升烟道出口烟气中氧气的质量分数从8.32%减少至6.37%,氧气利用率从88.96%提高至92.67%。     

板坯连铸机械驱动结晶器非正弦振动的探讨

采用运动的叠加原理,改造机械驱动的正弦振动装置为非正弦振动装置.实践证明,它同液压伺服系统驱动的非正弦振动系统相比具有投资省、操作维护方便、可靠性高等优点.应用于板坯连铸机可取得显著的效果.     

CSP结晶器内钢液流动的水模型研究

采用1:1水力学模型对厚度60 mm薄板坯连铸水口浸入深度220～310 mm、出口角度-30°～-60°、拉速4.2～6.0 m/min条件下CSP结晶器内钢液流动行为进行模拟研究。在拉速4.2～5.0 m/min时双侧孔水口下CSP结晶器流场股流冲击深度达850～1010 mm;流场内存在三个滞区,液面波动不稳定;水口角度对结晶器窄面和水口附近波动影响很显著,拉速对结晶器和窄面中心处波动影响较大,浸入深度对水口附近波动影响较大。     

CSP结晶器内初生坯壳的应力计算模型

 为研究结晶器振动对初生坯壳应力状态的影响,利用Marc软件建立了结晶器内初生凝壳的应力计算模型,分析了振动过程中凝壳上应力和应变的分布规律。模拟结果表明横向上最大应力和应变出现在振动的波峰时刻,宽面中部比边部的应力略高;而纵向最大拉应力和应变出现在振动的波谷时刻,纵向拉应力在凸弧位置出现拉压应力的交变边界,在振动波谷和振动的半周期时,边界内铸坯受压应力,边界外铸坯受拉应力作用。     

Large Eddy Simulations of the Effects of EMBr and SEN Submergence Depth on Turbulent Flow in the Mold Region of a Steel Caster

Transient turbulent flow in the mold region during continuous casting of steel is related to many quality problems, such as surface defects and slag entrainment. This work applies an efficient multi-GPU based code, CUFlow, to perform large eddy simulations (LES) of the turbulent flow in a domain that includes the slide gate, SEN, and mold region. The computations were first validated by comparing the predicted surface velocity with plant measurements. Then, seven LES simulations were conducted to study the effects of casting speed, electromagnetic braking (EMBr) field strength, and submerged entry nozzle (SEN) depth on the transient flow. The results show that EMBr has an important influence on flow inside the SEN, in addition to flow in the mold. With EMBr, an “M-shaped” flow profile is seen inside the SEN. The swirling flow behavior in the SEN and ports is more symmetrical at high casting speed and with higher EMBr strength. The position of the SEN ports relative to the peak magnetic field affects the EMBr performance. The results confirm and quantify how applying EMBr greatly lowers both the magnitude and turbulent variations of the surface velocity and level profile.     

Numerical Simulation on Optimization of CSP Tundish Flow Field

Original scheme and optimizing scheme of WISCO CSP tundish have been simulated by software FLUENT. Flow field and temperature field of different schemes have been analyzed. The results which have been proved by hydraulic model experiments are the same with that of numerical simulation. It shows that the dead volume Vd of optimizing scheme decreases to 11.37%, reduced by 67.8% compared with the original scheme. The average residence time Ta of optimizing scheme increases to 639.2s, increased by 172.5s compared with the original scheme. The optimized scheme favors homogenous temperature distribution, more reasonable flow field and inclusions removing in the tundish. It is more adaptive to CSP plant of WISCO compared with the original scheme.     

Analysis of Operational Parameters Affecting the Sulfur Content in Hot Metal of the COREX Process

Metallurgical and Materials Transactions B - The COREX process, which has obvious advantages in environment protection, still has some disadvantages. It has a higher sulfur content in hot metal...     

拉速对小方坯结晶器液面波动影响的数值模拟

利用流体力学软件Fluent建立180 mm×180 mm铸坯结晶器内"钢-渣"两相流模型,对结晶器液面波动行为进行数值模拟,研究浸入式水口自结晶器中心位置偏离量(0~30 mm)和拉速(2.0~3.0 m/min)对结晶器液面波动行为的影响。发现在相同浸入式水口偏离量下增加拉速,钢液面波动的整体趋势增加,且偏移量与拉速越大,液面波动增幅越大;低拉速时,波谷出现在水口边缘,水口周围剧烈波动;高拉速时,波谷出现在结晶器右壁面,使得钢液液面波动加剧,容易产生卷渣。