Compensation Control Model of Superheat and Cooling Water Temperature for Secondary Cooling of Continuous Casting

In this paper, a compensation control model of secondary cooling process of billet continuous casting for quality steel has been presented. The effects on the spray control of the various parameters such as steel superheat, casting speed, cooling water temperature and chemical component of steel were considered. The parameters of control model were determined to associate with the two‐dimensional heat transfer equation and solved by finite‐difference method. Effects of steel superheat and cooling water temperature on surface temperature, solidification structure and solidifying end point were discussed. Results indicate that steel superheat significantly affects solidification structure and solidifying end point but has a little effect on slab surface temperature. Moreover, secondary cooling water temperature affects surface temperature and solidifying end point but has a little effect on solidification structure. The surface temperature and solidifying end point can be maintain stabilized through applying the compensation control model when steel superheat and cooling water temperature vary. The models have been validated by industrial measurements. The results show that the simulations are in very good agreement with the real casting situation.     

厚板坯连铸二次冷却传热数学模拟

在考虑二冷边界换热的条件下,建立了与厚板坯连铸机相适应的传热数学模型。用远红外测温仪测试X65管线钢230 mm×1650 mm铸坯表面温度,实验结果同模拟结果吻合较好。应用数学模型,对不同拉速下管线钢的连铸凝固过程进行了仿真计算,分析了拉速对出结晶器坯壳厚度、铸坯表面温度和液芯长度的影响,得出在给定的二冷条件下,为得到合理的铸坯表面温度,管线钢的拉速应为0.9～1.2m/min。     

Optimal control of secondary cooling for medium thickness slab continuous casting

Abstract

A software to simulate the solidification, heat transfer and water flowrate distribution in slab continuous casting was developed by establishing a mathematical model for the heat transfer and solidification in medium thickness slab casting. This model was validated by pin shooting and surface temperature measurement experiments. A reasonable target surface control temperature was found by testing the high temperature mechanical properties of Nb bearing ship plate steel, and then the water flowrate of each loop of the secondary cooling zone was determined by the software. The influence of uneven secondary cooling in the slab width direction on the quality of the slab was also investigated, which provided data for the optimisation of the secondary cooling of the slab caster. On the basis of the above research, an optimisation scheme for a secondary cooling system was proposed. Experimental results showed that the quality of the slab was significantly improved after optimisation. The centreline macrosegregation was reduced, and the ratio of equiaxed grains was increased by 3·18%. In addition, the transverse cracking of the slab was almost eliminated.     

连铸板坯三维二冷动态配水与精准压下研究与应用

在现有工艺条件下,校验和完善二冷区铸坯凝固传热计算数学模型,开发三维二冷配水模型,解决目前设备状况下冷却水分布不均匀对铸坯温度的影响,从而控制铸坯表面质量,特别是铸坯的角部裂纹,同时对板坯连铸二冷配水制度进行改进和优化,使之满足高效连铸生产条件和改善铸坯质量的需要。提出压下参数计算公式,结合所开发三维二冷配水模型,优化现有压下工艺,提出并应用精准可控单段压下、非稳态压下控制,集中解决连铸板坯中心偏析、中心疏松和缩孔等内部质量问题。同时优化模型数据库,使之数据更加完备,模型计算更加准确,同时模型具备异钢种混浇过程二冷及压下控制功能,能够进行凝固终点W形预测与控制,可进一步提高模型适用性和准确性。模型开发并成功在多家钢厂现场应用,有效改善了铸坯裂纹和偏析等铸坯表面和内部的质量问题。      

Dynamic Water Modeling and Application of Billet Continuous Casting

The continuous casting process is used for solidifying molten steel into semi-finished steel.The technology of secondary cooling is extremely important for output of the casting machine and billet quality.A dynamic water model was introduced,including solidification model in the secondary cooling,feedforward control strategy based on continuous temperature measurement in tundish,and feedback control strategy based on surface temperature measurement.The mathematical model of solidification process was developed according to the principle of solidification,and the solidification model was validated by measuring billet shell thickness through shooting nail and sulfur print.Primary water distribution was calculated by the solidification model according to procedure parameters,and it was adjusted by the other two control strategies online.The model was applied on some caster and billet quality was obviously improved,indicating that the dynamic water model is better than conventional ones.     

Real-Time,Model-Based Spray-Cooling Control System for Steel Continuous Casting

This article presents a new system to control secondary cooling water sprays in continuous casting of thin steel slabs (CONONLINE). It uses real-time numerical simulation of heat transfer and solidification within the strand as a software sensor in place of unreliable temperature measurements. The one-dimensional finite-difference model, CON1D, is adapted to create the real-time predictor of the slab temperature and solidification state. During operation, the model is updated with data collected by the caster automation systems. A decentralized controller configuration based on a bank of proportional-integral controllers with antiwindup is developed to maintain the shell surface-temperature profile at a desired set point. A new method of set-point generation is proposed to account for measured mold heat flux variations. A user-friendly monitor visualizes the results and accepts set-point changes from the caster operator. Example simulations demonstrate how a significantly better shell surface-temperature control is achieved.     

基于瞬态传热数学模型的板坯连铸二冷设计

以超高强度钢(UHSS)为对象,研究板坯连铸二冷设计。首先,基于凝固传热学基本理论,建立了二维板坯瞬态传热数学模型;其次,根据高温塑性实验曲线,结合二冷区冶金原则,确定二冷区各段终点的表面目标温度;最后,根据制定的铸坯表面目标温度,采用增量型PID算法调整二冷区各回路的水量。     

Analysis of thin-slab casting by the compact-strip process: Part I. Heat extraction and solidification

This article reports on an extensive experimental and modeling study undertaken to elucidate the thermal evolution of thin slabs during their passage through the mold and secondary cooling system of a compact-strip process (CSP) caster. In industrial trials covering a wide range of casting conditions, temperature measurements were carried out at (1) the copper plates of an operating mold and (2) the stainless steel frame of an operating grid. Separately, water-flux and heat-flux distributions generated by the several water and air-mist sprays produced by the different nozzles used in the process were determined in the laboratory. The analysis of these pieces of information, together with a detailed consideration of the geometry of the mold and the arrangement of the rolls and spray nozzles, were used to establish appropriate boundary conditions for a two-dimensional, curvilinear-coordinate, unsteady-state heat-conduction model for predicting the solidification rate of thin slabs. The predicted slab surface temperatures show very good agreement with corresponding measured values taken in plant tests at several locations along and across the secondary cooling system. The validation trials involved a wide range of low- and medium-carbon steel grades, casting speeds, slab widths, and secondary cooling strategies. The second part of this article combines the solidification model with a creep model of the shell to yield useful information about design parameters and casting conditions associated with undesirable bulging behavior of the slab after the last support roll, which causes stoppage of the process by slab clogging at the pinch rolls.     

板坯连铸机二次冷却均匀性的分析与优化

针对某厂连铸板坯裂纹频繁出现的问题,结合连铸机的喷嘴布置特点,在测试分析铸机喷嘴的喷淋冷却特性的基础上,以Q235G钢为对象,考虑板坯宽度方向二冷水流密度分布状态,采用数值仿真方法模拟计算了200 mm×1350 mm连铸坯的凝固壳生长形貌及铸坯表面内弧温度分布.研究表明:板坯铸机二冷前期足辊段与零段原喷嘴布置及水流密...     

攀钢板坯连铸机的铸坯温度测量与分析

在工业生产条件下测量了攀钢板坯连铸机的铸坯表面温度分布，建立了连铸板凝冷却过程的二维传热数学模型，全面探讨了连铸工艺参数对铸坯热状态的影响，深入分析，讨论了凝固终点的控制及铸坯保温输送的模拟计算效果。     

宝钢在线二冷控制模型的研发与应用

针对连铸生产过程中的二冷配水问题,建立了铸坯的凝固传热数学模型。通过实时模拟计算铸坯的温度场,并与PID控制技术相结合,开发了在线二冷控制模型。模型能自动根据钢种、铸坯规格及工艺参数的变化动态调整二冷控制水量,将铸坯的表面温度控制在工艺目标值附近。通过设计合理的控制系统架构,确保了二冷控制系统的稳定性及可靠性。在线测温结果表明,模型具有很高的计算精度。当拉速、浇注钢水过热度变化时,模型能快速将水量调整到目标值,速度快且超调小,从而确保铸坯的表面温度跟踪误差始终限制在较小范围内;当浇注过程处于相对稳态时,铸坯的表面温度保持在目标值。目前,模型已经应用于宝钢内外的多台连铸机,应用效果良好。     

板坯连铸过程数值模拟分析

基于传热学基本原理、凝固理论和有限单元法,建立了凝固传热有限差分数学模型,对连铸凝固全过程进行模拟分析,结果表明,拉速越大,铸坯中心及表面温度越高,出结晶器坯壳厚度越薄;过热度增大,铸坯中心及表面温度均上升,出结晶器坯壳厚度减薄;冷却水量相对增大时,铸坯出结晶器坯壳厚度增大,二冷区温度下降较快。连铸坯凝固模型可用来确定常规拉速范围及不同拉速下的凝固壳厚度、凝固末端位置以及铸坯表面温度分布。     

板坯连铸二冷动态配水的研究与应用

以津西钢铁集团股份有限公司2~#板坯连铸机为研究对象,建立凝固传热数学模型,分析了连铸坯的温度场及其坯壳厚度以及二冷各段的回温,同时通过凝固坯壳射钉测厚对模型进行校正。采用离线计算在线控制的二冷动态配水模式,在传热模型的基础上通过优化建立拉速、过热度和冷却水量的关系。经过实际应用验证了配水方案的有效性。     

基于目标温度的方坯连铸二冷配水方案优化

通过建立铸坯传热数学模型,对连铸凝固过程进行了解析。制定了二冷配水制度优化原则,基于目标温度控制原则开发出二冷配水控制模型。对不同钢种、拉速等工艺条件下的连铸工艺设计出二冷总水量、水量分配和水量与拉速的关系式,并对配水方案进行了凝固与传热的预测和验证。     

济钢参数控制法二冷自动配水模型的设计

介绍了济钢第一炼钢厂5#超低头板坯铸机参数控制法二冷自动配水模型的设计方法。生产实践表明,该配水模型在铸机投产和正常生产过程中,经不断优化,达到了改善铸坯表面及内部质量、提高铸机拉坯速度和稳定铸机生产的目的。     

大圆坯连铸机二冷段改造实践

针对马鞍山钢铁股份公司大圆坯连铸机全水冷却的二冷段在开发高质量车轮钢时,存在着等轴晶率低,碳偏析大等不足,对连铸机的二冷段实施以气雾冷却为主要内容的改造,改造后的铸坯表面温度更加均匀,铸态组织更加的致密,等轴晶率提高了约8%,碳元素偏析指数降低了0.03。     

Q235B钢板坯连铸凝固传热行为的数值模拟计算

基于涟钢板坯连铸机结构参数和冷却条件,建立了Q235B 230 mm×1 280 mm板坯连铸过程凝固传热的数值模型,研究了铸坯温度分布和坯壳厚度变化规律以及过热度和拉速对铸坯温度和凝固末端位置的影响规律。得出:随过热度和拉速的增加,铸坯中心和角部温度整体呈升高趋势,在其它参数不变的条件下,过热度每升高10℃,铸坯凝固末端和液相消失位置分别后移约0.38 m和0.31 m;拉速每升高0.1 m/min,凝固末端和液相消失位置分别后移2.06 m和1.4 m。通过数值模拟研究,掌握了铸坯温度和凝固末端位置的变化规律。     

板坯动态二冷增量型PID控制研究

为解决连铸拉速工况变化时因使用一级水表配水控制所引起的铸坯表面温度波动的问题,建立了考虑铸坯纵向导热的板坯传热瞬态模型.通过Gleeble试验获得钢的热塑性,制定了铸坯的目标温度.采用增量型PID控制方法开发了动态二冷控制软件Visual Cast.结果表明:与传统的一级水表相比,当拉速发生变化时VisualCast能...     

On the Formation of Interdendritic Internal Cracks During Dendritic Solidification of Continuously Cast Steel Slabs

In this study of solidification during the continuous casting of steel slabs, the effect of the different spray cooling conditions on the interdendritic internal cracks formed between the columnar dendrites has been examined by a metallographic study of the slab samples and by performing a set of mathematical analyses. The metallographic study involved plant trials to measure the slab surface temperature within different secondary spray cooling conditions. Also, macro/microexaminations of the collected samples from plant trials, measurements of dendrite arm spacing, and interdendritic distance between the columnar dendrites, as well as a segment length of interdendritic crack, have been performed. The experimental results show that the morphology of the interdendritic cracks described by the segment width and length fluctuate with the distance from the slab surface based on the secondary spray cooling conditions. A one-dimensional mathematical model of the heat transfer, solidification, structure evolution, interdendritic strain, and elementary interdendritic area (EIA) has been developed. This model takes into account also calculating the width of interdendritic crack. The model predictions are in a good agreement with the measurements. The results pointed out also that this criterion can be considered as the most important tool to measure the inner quality of the continuously cast steel slabs. Therefore, it helps also to define the required mechanism and reduction level of hot working deformation to close these interdendritic internal cracks. The formation mechanism of these cracks during the dendritic solidification of continuously cast steel slabs has been discussed and the available solutions have been proposed.     

宽厚板坯连铸二冷工艺开发与应用

利用GLEEBLE 3500测定了船板钢A36-1B的高温塑性,并基于天钢4号板坯连铸机设备参数,设计开发了板坯连铸凝固传热数学模型,分析了不同冷却工艺和浇铸条件下连铸坯的温度分布,并对二冷工艺进行了优化。工艺投用结果表明,连铸坯裂纹缺陷得到了有效改善。