Flow Control in the Thin Slab Mould at the Corus Direct Sheet Plant

Thin slab casting forms the most important development in continuous casting of the past two decades. Within a short period of time the technology developed into a serious alternative for conventional slab casting, both with respect to productivity and product quality. Corus implemented the technology in its Direct Sheet Plant (DSP) enabling the production of thin‐gauged coils. The development of thin slab casting technology has not come to an end yet. Further increase in productivity can be expected still respecting high quality standards. The control of the mould fluid flow is one of the key technologies for thin slab casting. Here not only the (complex) design of the submerged entry nozzle is important. A strong interaction exists with the shaping of the funnel mould and the layout of the electromagnetic brake (EMBR). Modern physical and numerical modelling techniques enable a detailed design study of all aspects of the process. This resulted in a new design of the EMBR for the DSP thin slab caster, based on a multi‐pole approach. One pole is controlling the symmetry of the flow, where another two poles control the speed of the liquid steel in the meniscus area. By using this technology the operational window can be enlarged significantly without deterioration of the situation in the mould.     

结晶器保护渣试验条件探讨

介绍了影响结晶器保护渣试验效果的主要浇注工艺因素,对结晶器保护渣试验条件进行了探讨。试验时必须考虑钢水质量和温度、浇注液面的稳定性、水口插入深度及对中精度、保护浇注效果、氩气大小以及保护渣操作等各方面因素的影响。通过保护渣反复试验,不断调整保护渣理化指标和连铸机浇注工艺条件,保护渣性能才能不断满足工艺质量的要求。     

Water Modeling of the Fluid Flow Instability in Continuous Thin Slab Casting Mould

Flow instability in continuous thin slab casting moulds has been studied using a full scale water model with particle image visualization. The results show that jet impinging depth, circumfluence centre position and wave height are unsteady and periodical. The probabilities of jet impinging depth and circumfluence centre position seem to be Poisson distributions with the highest frequency near the average position. The flow pattern is asymmetrical for a short time and the phase difference of jet impinging depth, circumfluence centre position and wave height on the two sides of the mould centreline is half a period. The average jet impinging depth, average circumfluence centre position, average meniscus wave profile and the highest and lowest meniscus positions are generally symmetrical to the mould centreline.     

Investigations of Unsteady and Asymmetric Flow Phenomena in Continuous Casting Moulds by Advanced Simulation Techniques

For further improvement of the continuous casting process a more detailed insight into the unsteady flow conditions in the mould is of great importance. Due to the difficulties to obtain this information directly in an operational plant, simulation techniques can be successfully used to extend the relevant knowledge. Therefore, simultaneously measurements of both, unsteady flow velocity using particle‐image‐velocimetry and mould level fluctuations using ultrasonic sensors, were carried out in physical models providing correlation between casting parameters and asymmetric flow behaviour. The numerical simulation of unsteady multiphase flow conditions shows time‐dependent varying local mould level fluctuations indicating an asymmetrical distribution across the mould. Both simulation approaches provide important information for increase in process stability, productivity and product quality.     

Mould Powder Requirements for High‐speed Casting

Mould powders play an important role in the stability of the continuous casting process of steel. The main functions of mould slag (i.e. molten powder) are to provide sufficient lubrication and to control the heat transfer between the developing steel shell and the mould. Sufficient lubrication requires an undisturbed melting of mould powders and uniform infiltration of mould slag. Based on the casting practice in IJmuiden, it is found that these demands become even more important for the applied high casting speeds in thin slab casting at 5 to 6 m/min. At Corus RD&T, mould powders were characterised by X‐ray diffraction and subsequent fully quantitative Rietveld analysis. Additionally, the melting of mould powders has been studied in‐situ using high‐temperature X‐ray diffraction, to gain crucial knowledge about melting relations. Slag rims obtained from the thin slab caster mould were characterised using extended microscopic techniques in order to describe the mechanisms of rim formation and growth. Finally, slag films obtained after casting were characterised. As a result, not only the melting process of mould powder, but also the mechanism of formation and growth of slag rims is much better understood. This knowledge will be applied to define the demands on the composition and properties of mould powder for even higher casting speeds.     

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。     

高速连铸用结晶器保护渣

概述了高速铸的特点及其对结晶器保护渣的要求,给出了高速连铸用结晶器保护渣的理化性能及所应具有原成分;总结顾高拉速结晶器用保护渣的研究现状。     

韶钢板坯连铸结晶器保护渣的选择和应用

连铸结晶器保护渣对铸坯表达质量具有显著影响。通过对保护渣的作用，物理、化学性能及影响因素的分析，提出了适合我厂板坯连铸机的保护渣的各种性能指标。     

厚板坯连铸结晶器流场数值模拟

针对鞍钢新轧钢第一炼钢厂厚板坯连铸结晶器建立了三维湍流数学模型和三维实体模型.应用有限元软件对厚板坯连铸结晶器内的流场进行了模拟,计算了铸机拉速、浸入式水口出口倾角和水口浸入深度等工艺参数对结晶器内钢液流动的影响.对比表明,数值模拟结果与水模实验结果相符.     

Effect of Nozzle Angle on Flow Field and Temperature Distribution in a Billet Mould when using Swirl Flow

Recently, interesting effects have been noted in studies of swirl flow, particularly regarding billet moulds when considering a specific divergent angle of the immersion nozzle. Therefore, in the present work a numerical analysis and water model study of the mould region of a continuous casting apparatus are performed with changing the outlet divergent angles of the immersion nozzle using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mould. To make our studies consistent with the previous research, which was done based on a square billet, this time we investigate round billets. The results show that the distance from the meniscus of the centres of both the lower and upper circulation loops decreases systematically with increasing the divergent angle. This, in turn, leads to: (i) a more active heat and mass transport near the meniscus (particularly over 100°); (ii) a gradual change from a concentric circulation to a more clearly logarithmic spiral from the mould wall to the nozzle on the meniscus, which leads to more active heat and mass transfer; (iii) a decreased penetration depth of nozzle outlet flow (even at a comparatively small divergent angle such as 20°) and a superheat dissipation in the melt.     

薄板坯连铸结晶器铜板温度及热流密度分布

薄板坯连铸结晶器的传热过程直接影响到铜板的寿命,有必要研究薄板坯连铸结晶器的传热特征。为了研究薄板坯结晶器的热流密度,通过开发的结晶器温度监测软件检测了珠钢结晶器铜板的温度。根据在线实测的铜板温度以及薄板坯连铸机冷却参数,建立了薄板坯结晶器铜板传热模型,计算并验证了结晶器热流密度的分布函数,同时通过二次回归得出了结晶器热流密度与结晶器高度的关系式。结果表明,在宽度方向上铜板温度和热流密度的分布具有相似的规律性,距离弯月面越近,热流密度和温度的波动越大。弯月面处热流密度值大于4．2MW／m^2,是造成结晶器铜板被侵蚀的主要原因。     

Crystallization Extent and Phase Constitution of Slag Films Taken from Continuous Casting Moulds for Stainless Steels

Slag film samples were taken from the mould wall after casting of stainless steel slabs of grade 304, 321, 409L and 430, which represent austenitic, ferritic and titanium stabilized stainless steels. The chemical compositions of the samples were analysed and their phases were identified using a combination of scanning electron microscope (SEM), energy dispersive X‐ray analysis (EDX) and X‐ray diffraction (XRD). Finally the crystallization ratio was determined by SEM. The results show that the chemical compositions of the films during casting differ from the original designed flux composition. Concerning the heat transfer in the mould, the film taken during casting of steel grade 304 showed the highest insulation ability whereas the film taken during casting of steel grade 409L had the lowest insulation ability. The films taken during casting of steel grades 321 and 430 showed average heat insulation abilities. The solidification conditions in the mould during casting of steel grades 304, 321, and 409L matched the solidification requirements of the corresponding steel grades. However, the basicity of the powder for steel grade 430 should be decreased a little in order to improve the lubrication function and counteract sticking tendencies. Perovskite crystals, which usually precipitate at relatively high temperature, were found in the film taken during casting of steel grade 321. This is harmful in view of the safety of the casting process and the surface quality of the slab.     

连铸板坯表面纵向裂纹缺陷的检验与分析

凝固组织宏观检验和金相检验证明,连铸板坯表面纵裂起因于结晶器弯月面初生凝壳厚度的不均匀性.这种不均匀性与碳含量、浸入式水口插入深度及其结构方式、保护渣理化性能等诸因素有关.     

薄板坯连铸结晶器热流分布研究

通过结晶器温度检测软件在线采集了武汉钢铁(集团)公司CSP结晶器铜板的温度,根据热电偶实测温度及连铸机冷却参数,计算了浇铸不同断面SPHC钢时不同拉速的热流值,并建立了结晶器热流的二维分布模型。结果表明,结晶器受水口射流影响,热流与温度在宽面横向分布很不均匀,表现出明显的双峰结构。相同工况条件下在铜板宽度方向上温度和热流密度分布具有相似性,距离弯月面越近,热流密度和温度的波动越大,弯月面处热流密度最大值达到4.6 MW/m2。     

Influence of Aspect Ratio on Fluid Flow and Heat Transfer in Mould when Using Swirl Flow during Casting

Mathematical modelling was used to study the effect of a changed aspect ratio of a continuous casting mould on the resulting flow field in the upper part of the mould when using a swirl flow in the nozzle. Model predictions were initially compared to physical modelling data. More specifically, the predicted axial velocities were found to differ only at the most ~3 mm/s from the measured data. Thus, the model was concluded to be sound. By changing the aspect ratio of a billet mould from 1 to 3 systematically, a numerical analysis of the mould region of a billet continuous caster was performed with a novel injection concept using swirling flow in the immersion nozzle in order to control the heat and mass transfer in the continuous casting mould. The predictions showed that the aspect ratio of the mould has a large influence on the flow field in the upper part of the mould. The meniscus temperature was found to increase with an increasing aspect ratio from 1 to 2, but the maximum temperature was found to decrease when the aspect ratio was increased above 2.     

MCCR产线110mm薄板坯结晶器流场的数值模拟

摘要：首钢京唐MCCR产线是国内第一条多模式连铸连轧产线,薄板坯高拉速连铸是实现无头轧制模式的基础,结晶器内流场控制是决定薄板坯高拉速连铸的关键。采用VOF两相流模型研究薄板坯连铸结晶器内流场特点,采用插钉法测量实际生产过程结晶器弯月面流速,并与对应工况条件下模拟结果进行对比校验了模型准确性。通过薄板坯连铸结晶器内流场的数值模拟仿真,获得了薄板坯高拉速条件下结晶器内钢液的流动特征。研究了连铸拉速、2.种浸入式水口结构等因素对弯月面流速以及波高差的影响。结果表明：随着通钢量由3.4t/min增加至8.2t/min,采用四孔水口时,结晶器弯月面钢液流速由0.02m/s增加至0.30m/s,结晶器钢液面波高差由2.0mm增加至7.2mm;采用五孔水口时,结晶器钢液面波高差由0.25m/s增加至0.5m/s,结晶器钢液面波高差由2.6mm增加至17.0mm。高通钢量条件下（5.5~8.2t/min）,采用四孔水口更加有利于控制液面波动稳定性。     

板坯结晶器钢液流动传热和摩擦行为的数值模拟

结晶器摩擦力对连铸顺行非常重要,而钢液流动行为会影响铸坯温度场和保护渣分布,可能对铸坯摩擦力产生一定的影响.利用Fluent软件建立结晶器内钢液流动、传热三维数学模型,并将温度场数据导入Ansys计算铸坯应变,然后根据铸坯-保护渣-结晶器摩擦行为数学模型讨论了渣膜润滑情况,对比了不同水口底部形状下结晶器内液态、固态和总摩擦力.结果表明:不考虑水口射流时结晶器总摩擦力比考虑水口时增大约29.4％;浸入式水口底部形状分别为凸底、平底和凹底3种情况下铸坯窄面中心温度依次降低,凝固壳厚度依次增大,固态摩擦力依次增大,总摩擦力依次增大,液态摩擦力相差较小.     

高速连铸结晶器内卷渣机理及其控制研究

利用物理模型研究了高拉速条件下结晶器内的卷渣机理,考察了保护渣粘度、操作参数对结晶器内弯月面波动和卷渣行为的影响。研究结果表明：在高拉速条件下,表面回流卷混是引起卷渣的主要方式,表面速度可以作为判断卷渣发生的特征参数。此外,本研究还给出卷渣发生时的临界表面速度,提出了避免卷渣的改进措施     

薄板坯连铸结晶器技术的最新发展

介绍了近年来国内外薄板坯连铸结晶器热流技术的研究与应用、结晶器长寿技术的开发及CSP新型结晶器的研制情况。     

天钢4~#板坯连铸机结晶器保护渣的优化选择

天钢4#板坯连铸机生产的板坯,存在贯穿表面中心部位裂纹等缺陷。针对此问题,对天钢4#板坯连铸机所使用的A、B型保护渣的物理、化学性能及相关数据进行了采集和分析,确定了A型、B型保护渣所匹配的钢种;通过裂纹缺陷的统计分析,确定了所使用的A型、B型保护渣不是造成铸坯壳中心裂纹缺陷的主要原因;还指出A型、B型保护渣与目前各连铸工艺相匹配,基本能够满足生产要求。