Fluid flow in large-capacity horizontal continuous casting tundishes

The configuration of the tundish for a two-strand horizontal continuous caster was designed and optimized through water modeling. Three designs of the tundish were studied： the original tundish without any flow control devices, the tundish with a turbulence inhibitor at the bottom, and the tundish with an inlet launder and an inclined dam. The residence time, the location and size of the dead zone, and the fluid field pattern were investigated. At the same time, the asymmetry flow field and wavy inlet jet in the horizontal tundish were observed and the reasons for them were discussed. The results indicate that the mndish with an inlet launder and an inclined dam is the best of the three designs.

Validation of the numerical simulation of fluid flow in the continuous casting tundish

The 3-dimensional fluid flow in a water model of the continuous casting tundish is simulated with the k-ε two-equation turbulence model. The methods to decide the size of wall-adjacent grids and the effects of residuals and mesh size on the simulation accuracy are discussed. The current investigation concludes that the following condition should be satisfied to get accurate enough simulation results: (1) If the dimension of the domain is in the order of cubic meters, the average size of cells in the mesh system should be at least smaller than 30 mm; (2) The normalized non-scaled residual should be reached at least smaller than 10-4.

INFLUENCE OF SOME FACTORS ON FLUID FLOW IN CONTINUOUS CASTING TUNDISHES

The influence of some factors on velocity field in continuous casting tundishes has been veri- fied by means of computer simulation.These factors are tundish wall inclination;the dimensionless geometric size of tundish,the double inclined wall tundish;the dimension and location of weir and dam.

A Feedforward Controller to Regulate the Chemical Composition of Molten Steel in a Continuous Casting Tundish

A feedforward controller for the automatic regulation of chemical composition of molten steel in the tundish of a continuous casting machine is proposed in this work. The flow of molten steel inside the tundish is modeled as a distributed parameter system, and the resulting partial differential equation is transformed into a set of ordinary differential equations by means of the finite differences technique. From the above set and using a proper boundary condition, a feedforward control law is synthesized. No experimental tests are reported, however, the dynamic performance of the controller is illustrated by means of numerical simulations.

Flow Control in Six-Strand Billet Continuous Casting Tundish With Different Configurations

A 1∶2.5 scale tundish model was set up in laboratory for a six-strand billet continuous casting tundish with different configurations to investigate fluid flow characteristics under different operational conditions by measuring residence time distribution curves.It was found that minimum residence time,maximum concentration time and average residence time of the three strands on the same side of the tundish with the former configuration under normal operation,that is,six strands were open,were small and non-uniform and the tundish had large dead volume fraction.Vortexes easily formed on the liquid surface in the pouring zone of the tundish.The fluid flow characteristics in the tundish with the optimal turbulence inhibitor and baffles were improved and became less non-uniform among the strands.Vortexes were not found on the pouring zone surface in the optimal tundish.For non-normal operation,that is,one strand was close,it was important to choose which strand to be closed for maintaining flow characteristics of the rest two strands.It was found from this investigation that fluid flow characteristics in the optimal configuration tundish with closing strand 2 were better than those with closing strand 3 on the same side.

Optimization of flow control devices in a tenstrand billet caster tundish

The physical model of a ten-strand billet caster tundish was established to study the effects of various flow control devices on the melt flow. Before and after the optimization of the melt flow, the inclusion removal in the tundish was evaluated by plant trials. The physical modeling results show that when combined with a baffle, the turbulence inhibitor, instead of the impact pad, can significantly improve the melt flow. A turbulence inhibitor with a longer length of inner cavity and without an extending lip at the top of the sidewall seems to be efficient in the improvement of the melt flow. Various types and designs of baffles all influence the flow characteristics significantly. The "V" type baffles are better than the straight baffles for flow control. The "V" type baffle with four inclined holes at the sidewall away from the stopper rods is better in melt flow control than the one with one inclined hole at each sidewall. The combination of a well-designed turbulence inhibitor and an appropriate baffle shows high efficiency on improving the melt flow and an optimal proposal was presented. Plant trials indicate that, compared with the original tundish configuration in prototype, the inclusions reduce by 42% and the inclusion distribution of individual strands is more similar with the optimal one. The optimal tundish configuration effectively improves the melt flow in the ten-strand billet caster tundish.

Water Modeling of Swirling Flow Tundish for Steel Continuous Casting

A conventional turbulence inhibitor is compared with a swirling chamber from the points of view of fluid flow and removal rate of inclusion in the tundish. Comparing the RTD curves, inclusion removals, and the streamlines in water model experiments, it can be found that the tundish equipped with a swirling chamber has a great effect on improving the flow field, and the floatation rate of inclusion is higher than the tundish with a turbulence inhibitor. Because of the introduction of the swirling chamber, the flow field and inclusion removal in a two-strand swirling flow tundish are asymmetrical. Rotating the inlet direction of swirling chamber 60 degree is a good strategy to improve the asymmetrical flow field.

Fluid Flow and Interfacial Phenomenon of Slag and Metal in Continuous Casting Tundish With Argon Blowing

The fluid flow and the interfacial phenomenon of slag and metal in tundish with gas blowing were studied with mathematical and physical modeling, and the effects of gas flowrate, the placement of porous beam for the generation of bubbles, and the combination of flow control devices on the flow and slag-metal interface were investigated. The results show that the position of gas bubbling has a significant effect on the flow in tundish, and the placement of porous beam and gas flowrate are the two main factors affecting the entrapment of slag in tundish. The closer the porous beam to the weir, the more reasonable is the flow, which is in favor of the control of slag entrapment in tundish.

Flow Characteristics and Inclusion Removal in a Ten-strand Continuous Casting Tundish:Physical Modelling and Industrial Trials

The flow characteristics and inclusion removal in a ten-strand continuous casting tundish were investigated with physical modelling and industrial trials. The results show that, among the strands, the strand with the mini mum dimensionless time of the first appearance of tracer at the tundish exit appears to be the worst one for inclusion removal, while the strand with the maximum dimensionless mean residence time shows the best inclusion removal efficiency. The inclusion number decreases with increasing inclusion size for all strands. The inclusion number distri bution among strands is the same for all inclusion sizes and the descending order of inclusion number is basically con sistent with the ascending order of dimensionless mean residence time among individual strands. However, when the strand with the minimum dimensionless time of the first appearance of tracer at the tundish exit is not the same one with the minimum dimensionless mean residence time, the former seems to be inferior to the latter for inclusion re moval.

Upward Molten Flow for Optimization of Fluid Flow in Continuous Casting Tundish

Fluid flow pattern and buoyancy force support the motion of nonmetallic inclusions toward thetundish slag. Upward molten flow was investigated. To understand the fundamentals of the process, physical modelling was carried out with the utilization of a 1 ： 4 scale model. Numerical modelling was carried out in line with the physicai modelling to examine details of the flow pattern and rotational effect caused by the upward flow with the Commercial CFD （Computational Fluid Dynamics） package environment, FLUENT. The two-equation κ-ε model was used to simulate the turbulence. Multiphase fluid flow was numerically simulated by using the Volume of Fluid （VoF） method. The simulation can predict free surface waves and other phenomena, which can be used to optimize these important metallurgical operations.

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

Through coupling electromagnetic field equations with turbulent flow equations,the numerical prediction has been conducted on the flow field of molten steel and the trajectory of inclusion particle in the continuous casting mold effected by electromagnetic field.The difference between the maximum and the minimum of the shear stress on mold wall is used to scale the impingement strength of molten steel discharged from immersed nozzle to the solidifying shell on the narrow wall of mold.The flow field of molten steel in the mold is changed greatly and the impingement strength of the jet is reduced while electromagnetic field is applied.It is found that the successful control of flow field depends on the current and location of coil.At the same time,the new floating paths of inclusion particles are formed and the upward particles that are far away from the solidifying zone on the narrow wall of mold change their moving directions with the change of flow field,so that the particles can avoid being entrapped by the solidifying shell.

Numerical investigation of the effect of transitory strand opening on mixing in a multistrand tundish

In a multistrand,the outlet near the inlet produces short circuiting flow.This leads to the formation of dead zones inside the tundish,and consequently,the mean residence time decreases.In the present study,numerical investigation of mixing inside a delta shaped tundish with sloping boundaries was carried out by solving the Navier-Stokes equation and employing the standard turbulence model.To decrease the dead zone volume inside the tundish,the effect of closing the outlet near the inlet for a small amount of time and further opening it on the mixing behavior of the tundish was studied.The outlets near the inlet were closed for varying amount of time,and the transient analysis of fluid flow and the tracer dispersion study were carried out to find the mixing parameters of the tundish,namely,mean residence time and the ratio of mixed to dead volume of the tundish.An optimum closure time of the near outlet has been found,which yields best mixing inside the tundish.The numerical code was validated against the experimental observation by performing the tracer dispersion study inside a multistrand tundish and the reasonably good match between the experimental and numerical results in terms of residence time distribution （RTD） curves.The results obtained from the present study confirm the strong role of choosing the right time for opening and closing the outlets to get improved characteristics for the fluid flow and mixing behavior of the tundish.The educational version of computational fluid dynamics （CFD） software PHOENICS was used to solve the governing equations and interpret the results in different forms.

Molten Steel Flow in a Slab Continuous-casting Tundish

Fields of fluid flow and temperature, and residence time distribution(RTD) curves were investigated by mathematical simulation in a one-strand tundish for continuous casting. It was known from the investigation that a big "spring uprush" formed on surface around the long shroud when molten steel flowed into a turbulence inhibitor(TI) with extending lips and rushed up reversely out of the TI, while four small "spring uprushes" existed on surface when a TI without extending lips because the liquid steel flowed mainly out of the 4 corners of the TI. The flow of liquid steel in the former tundish configuration was not reasonable and the height of an area where temperature was less than 1819 K was about half of liquid surface height on the right side of the stopper, which meant that big dead zone existed in the former tundish configuration. In the optimal one, the height of such area was only seventh of the liquid surface height. The RTD curves obtained from the mathematical simulation basically agreed with those from the physical modeling and the flow characteristics obtained from these two methods agreed with each other.

Extensive Analysis of Multi Strand Billet Caster Tundish Using Numerical Technique

Continuous casting of steel involving different grades in the same casting sequence remains a challenge to billet caster operators. The intermixed composition obtained during the grade change does not meet the specification of either grade and must be downgraded. Incorrect identification of this intermixed region may result in non-conforming products reaching the customer. In this study, a numerical model based on CFD (computational fluid dynamics approach) has been developed which predicts the start and end of the intermixed composition and the tonnage to be downgraded under different casting conditions. This model was validated and the results were in good agreement with the actual plant data for a 6-strand billet caster at LD-1 of TATA Steel, India. This model is used to calculate transition tonnage for different scenarios, e.g. when one of the outermost strands is not functional or some combinations are not functional and varying casting speed during operation. Furthermore, impact of different design of baffles on performance of Tundish has been evaluated to find a way to reduce transition or intermixed composition.

Effect of flow control mold on flow field during high-speed continuous casting

An experimental mold was built to study the flow in a flow control mold under high speed continuous casting. The effect of the magnetic field on the flow was investigated using mercury. The results show that the magnetic field can not only dampen the flow of liquid metal but also change its direction, and then redistribute the flow in the mold. When maintaining a constant distance between magnets, the fluctuation of the free surface is dampened because of the increasing magnetic flux density. The flow at the free surface is improved, and the penetration depth of the downward stream is reduced. The decrease in the dis- tance between magnets promotes the brake effect and the flow is dampened in the upper eddy.

DISTRIBUTION OF THE MAGNETIC FIELD AND ITS CONTROLEFFECT ON THE MOLTEN METAL FLOW IN FLOW CONTROLMOLD

A thermo-simulation experimental continuous caster was established to study the effect of two static magnetic fields imposed the whole width of the mold on the molten metal flow. Low melting point Bi-Pb-Sn alloy and silicon oil were adopted to simulate the molten metal and mold powder respectively. The results show that the control effect of electromagnetic fields on the molten metal flow in the different zones of mold is different. Therefore it is important to study and design new types of magnetic fields to satisfy the request of controlling the molten metal flow in the mold.

中间包等离子体加热技术研究进展及应用

在钢铁行业面临转型升级的新常态形势下,借助智能装备驱动钢铁产业向绿色高端化发展,有望实现钢铁生产组织的最优化。连铸中间包实现恒温、低过热度浇铸可有效改善钢材质量,为此发展中间包加热技术十分必要。针对近年来日益受到重视的中间包等离子体加热技术的相关热点问题,系统阐述了其加热原理和设备特点,介绍了等离子体加热技术国内外设备、冶金功能研发以及应用进展状况,重点分析了等离子体加热技术对中间包内钢液流场、温度场、夹杂物去除、钢液化学成分的影响,以及实际应用冶金效果。基于对等离子体加热技术研究和应用的深入认知,探讨了国内自主研发新型中空石墨电极加热过程发现的新问题,以及进一步提高其冶金效果的途径。分析表明,国内自主研发的中空石墨电极等离子体加热装置,更好的适配了国内钢铁行业变革需求,是解决浇铸钢水过热度不稳定、钢水洁净度水平低和钢水组织成分不均匀问题的有效途径,补齐精准定位“一键加热”中间包的智能化短板。

大方坯中间包控流装置及冶金效果的研究

以某炼钢厂五流大方坯连铸中间包为研究对象,采用数值模拟方法,研究不同控流装置及操作参数下的中间包内钢液流动特性。研究结果表明,设计结构合理的湍流器、挡墙和挡坝组合的中间包结构,对钢液流动状态具有重要影响,可延长中间包内钢液停留时间,达到去除夹杂物和均匀各流钢水温度的冶金效果。优化后的中间包结构能够更好地满足高品质特钢质量的要求。

粒子群PID在感应式连铸中间包温度控制中的应用

中间包是连铸工序中钢坯结晶前的最后一环,由于中间包热辐射及对流传热、耐火材料吸热等原因,中间包的钢液温度难以稳定。利用电磁感应原理制成的感应式中间包能够完成中间包钢液温度的补偿。由于中间包温度控制具有非线性和大滞后性的特点,常规PID无法精确地控制其温度,故将粒子群算法(PSO)用于优化常规PID,实现系统的PID参数自整定,克服常规PID调参工作量大和控制精度低的缺陷。在实际生产中,由于换包过程、浇铸初期和末期会出现较大的温度波动,故在仿真某一时刻给模型加入了一个较大的降温干扰。在Matlab/Simulink中编写PSO算法并建立仿真模型。仿真结果显示,经PSO优化后的PID算法超调量减小74.28%,达稳态所需时间缩短27.2 s,在面对较大的温降干扰时,比常规PID响应速度更快且恢复稳态时间更短。

连铸中间包内流体运动形态模型分析研究

针对通过RTD曲线结合水模型流场可视化分析中间包内流体运动形态的方法较为复杂,且无法精确地给出死区区域分布的问题,提出了连铸中间包内流体运动形态模型分析方法。基于物理模拟所得RTD曲线分析结果,通过数值模拟判定死区,并确定了死区临界速度值与入口速度值的关系。以死区临界速度为基础,通过数值模拟可实时在线确定死区的占比和区域分布结果,进而评估单流和多流中间包内流体运动形态,并探究了连铸拉速及中间包构造对中间包内死区的占比和区域分布的影响。结果表明,采用流体运动形态模型能快速判定中间包死区,实现了死区的定量化和可视化。同时对比同一构造单流中间包时,死区临界速度随连铸拉速的提高而增大,死区体积分数则相反,而死区分布模式不发生改变。此外,可直观对比多流中间包内不同挡墙导流孔孔径和仰角下死区的大小和区域分布。当多流中间包内挡墙导流孔的孔径为70 mm,开孔仰角为19°时,多流中间包内死区体积分数仅为7.64%,且死区集中在中部水口和侧壁附近。