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.

Online forecasting model of tundish nozzle clogging

A nozzle clogging online forecasting model based on hydrodynamics engineering was developed, in which the actual flow rate was calculated from the mold width, thickness, and casting speed. There is a linear relationship between the theoretical flow rate and the slide gate opening ratio as the molten steel level, argon flow rate, and the top slag weight are kept constant, and the relationship can be obtained by regression of the data collected at the beginning of the first heat in each casting sequence when the nozzle clogging does not occur. Then, during the casting, the theoretical flow rate can be calculated at intervals of one second. Comparing the theoretical flow rate with the actual flow rate, the online nozzle clogging ratio can be obtained at intervals of one second. The computer model based on the conception of the nozzle clogging ratio can display the degree of the nozzle clogging intuitively.

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.

Research Development on Refractory Lining for Continuous Casting Tundish

The research development on new dry vibrating refractories, magnesia based slag dam and bubble curtain barricade for contimwus casting tundish was introduced.

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.

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.

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.

Development of Refractories for Continuous Casting

The paper introduces refractories for continuous casting, especially, refractories for continuous casting for clean steel in baosteel. Developing direction of refractories for continuous casting has been pointed out to satisfy the new metallurgical operating practice.

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。

ER70S-6焊丝钢连铸全保护浇注工艺优化实践

唐钢公司长材事业部在拉拔生产ER70S-6焊丝钢时因氮质量分数高出现脆断情况,对此从焊丝钢连铸全过程保护浇注工艺改进以及连铸长水口、中间包密封、覆盖剂、浸入式水口和保护渣设计优化等方面采取措施,提高焊丝钢连铸保护浇注效果,降低焊丝钢氮质量分数(氮质量分数整体下降0.0012%),增强塑性和变形能力,避免焊丝钢因氮质量分数高导致其在拉拔和加工过程中金属流动性差造成的脆断现象。

提高中间包连浇炉数的生产实践

通过对影响中间包连浇炉数的因素进行深入分析,结合湛江钢铁的合同结构、装备情况、生产物流特点,针对性地提出提升湛江钢铁连浇炉数的举措并进行落地。实践证明,通过采取提高耐材寿命、优化连铸机分工、提高钢种连浇炉数上限、优化合同结构和生产组织及强化现场操作管理等措施,钢种中间包连浇炉数上限最多提高60%,炼钢内部对中间包连浇炉数影响下降61.29%,2023年湛江钢铁中间包连浇炉数较2021年提升1.9炉/中间包,效果显著。

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。

管坯用圆钢12Cr1MoVG表面长裂纹原因分析及改进措施

按照GB/T 31212—2014标准对12Cr1MoVG管坯用圆钢进行了表面漏磁探伤,结果表明,深度>0.30 mm的长裂纹比例占15%左右,分析发现造成管坯用圆钢表面长裂纹的主要原因是铸坯角部裂纹。通过采取将中包钢水过热度由15~30℃提高到35~45℃,铸坯拉速由0.85 m/min提高到0.95 m/min,铸坯采取弱冷和均匀冷却等措施来解决了该问题。12Cr1MoVG管坯用圆钢长裂纹比例降到了3%以下。

Influence of non-iso-velocity casting on flow-field index of a 41-ton six-strand Tundish by physical and numerical modeling

The flow-field index in a 41-ton six-strand tundish is considered through adjusting the ratio of the casting velocity between the strands to eliminate the negative impact of iso-velocity casting in multi-strand tundish on the consistency of each strand due to the large ratio of length to width with narrow shape structure,resulting in poor consistency of each strand.In particular,the response time of strand-1 and strand-6 is relatively long,which affects the uniformity of the temperature field and flow field of the entire tundish.On the basis of verifying that the error between the numerical simulations and hydraulic experiments is less than 6%,six cases with the casting velocity ratio changing from 0.8 to 1.3(with an interval of 0.1)are considered by calculation of numerical models.It is concluded that the consistency of each flow can be obviously improved by increasing the casting velocity ratio between side-strand and middle-strand.With increasing the casting velocity ratio,the flow field in the tundish became much active,the temperature field presented well uniformity,and the tracer concentration distribution in local dead zones was improved.

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。

Water modeling of molten steel flow in a multi-strand tundish with gas blowing

Fluid flow characteristics in a four-strand tundish with gas blowing were studied by water modeling experiments.It is found that gas blowing can greatly improve the flow characteristics in the tundish with a turbulence inhibitor.It dramatically increases the peak concentration time,and greatly decreases the dead volume,and reduces the minimum residence time.The gas blowing location,gas flow rate,and porous plug area greatly influence the flow characteristics in the tundish; the gas blowing location near the baffle,smaller gas flow rate,and smaller porous plug area are better for improving the fluid flow characteristics.Using gas blowing can reduce the difference of flows at the middle outlets and side outlets for the multi-strand tundish.Bubbles produced by gas blowing can absorb small inclusions and provide the condition for inclusion collision and aggregation.Therefore,introducing gas blowing into a tundish and combining the turbulence inhibitor can improve inclusion floating and removal,and the cleanness of molten steel can be advanced.

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.

Process optimization of billet continuous caster and practice verification

This study analyzes the factors of influence on 0~# continuous caster in No.1 Steelmaking Plant of Xinjiang Bayi Iron & Steel Corporation(hereinafter referred to as Basteel).Diameter of tundish upper nozzle is small,and the molten steel leakage accidents have been greatly manifolded in the high casting speed.In order to increase yield of 0~# continuouse caster in No.1 Steelmaking Plant of Xinjiang Bayi Iron & Steel Corporation,and a series of amelioration measure was put forward.Through enlarging diameter of tundish upper nozzle(fromφ21 mm toφ21.5 mm ),after the water distribution of the secondary cooling was optimized.Based on stabilizing the quality,improving the average casting speed and work rate of the caster,the capacity of the billet continuous caster was improved.A better results was gained;the average casting speed had been increased from 3.04 m/min to 3.21 m/min.Production of the caster had been improved from 1 005 179.926 t in 2008 to 1 040 853.075 t in 2009.Quality of the concasting billets and production had also been stabilized.

Technology of nitrogen-argon mixed gas blowing on the tundish stopper

Bubble defect is one of the main defects of an automobile sheet.To solve this defect,the technology for nitrogen-argon mixed gas blowing on the tundish stopper is developed,the theoretical research on nitrogen absorption in the molten steel is performed,the nitrogen-argon mixed gas blowing equipment is developed and experimented in the plant.The expected effect is achieved in the industrial test,and the slab inclusion density and quality degradation ratio of the automobile sheet are significantly reduced.