Water Modelling Experiments of Argon Bubbling Curtain in a Slab Continuous Casting Tundish

Fluid flow characteristics in a two‐strand slab tundish with Ar bubbling curtain were studied in water modelling experiments. It was found that the Ar bubbling curtain can greatly improve the flow characteristics in the tundish with a weir, a dam and a turbulence inhibitor. It dramatically increased the peak concentration time and plug volume and greatly decreased the dead volume, but hardly influenced the minimum residence time. Therefore, the fluid flow characteristics in a tundish with Ar bubbling curtain were favourable to the flotation and separation of inclusions from molten steel. The flow characteristics with low gas flow rate and short distance of the Ar bubbling curtain from the tundish outlet were better than those with high gas flow rate and large distance of the curtain from the outlet.     

Fluid flow behaviour in slab continuous casting tundish with different configurations of gas bubbling curtain

Abstract

Fluid flow characteristics in a two strand slab continuous casting tundish with different configurations of argon gas bubbling curtain (GBC) were investigated in physical modelling experiments. It was found from this research that the GBC with a small flow rate acted as a gas dam and could greatly improve the flow characteristics in the tundish. It increased dramatically the peak concentration time and plug flow volume, decreased greatly the dead volume, created surface directed flow and eliminated short circuiting. Therefore, the fluid flow characteristics in a tundish with GBC were favourable to the floatation and separation of inclusions from molten steel. The flow characteristics with low gas flow rate and short distance of the bubbling curtain from the tundish outlet were better than those with high gas flow rate and large distance of the curtain to the outlet. The optimal configuration for the improvement in fluid flow characteristics was turbulence inhibitor (TI)–weir–dam–GBC (TI–W–D–GBC), followed by TI–channel weir (CW)–GBC, TI–W–GBC and TI–GBC.     

中间包气幕挡墙去除夹杂物的数值模拟

以湍流控制器加单坝结构的FTSC中间包为原型,采用气-液-固三相流数值模拟手段,研究了气幕挡墙对不同粒径夹杂物的去除情况.结果表明,中间包气幕挡墙能够改善钢液的流动特性,提高夹杂物的去除率,尤其对小颗粒夹杂物,去除效果更明显.     

气幕挡墙中间包仿真优化及其冶金效果

根据水钢炼钢厂150 mm×150 mm六流连铸32 t中间包的结构操作工艺参数,采用数模仿真法研究了气幕挡墙技术对中间包内钢液流动特性及夹杂物去除的影响,并对HPB235和65钢进行了工业试验。结果表明,气幕挡墙可以有效改善钢液的流动状态,均衡各出口停留时间,有效延长钢液的平均停留时间,降低死区体积,提高夹杂物去除率。该技术适应多流中间包纯净钢冶炼的需求。     

鞍钢宽厚板坯中间包气幕挡墙研究

以相似原理为基础,通过实验室水模拟实验,对鞍钢单流宽厚板坯连铸中间包应用气幕挡墙进行了优化研究。水模实验主要研究了原型中间包和气幕挡墙、耐火挡墙不同组合方案钢液的流动特征,将实验确定的最佳方案在大生产上进行了工业试验。结果表明,工业试验和水模实验的结果具有一致性。中间包应用气幕挡墙提高了钢的洁净度,显微夹杂物降低了23.73%,大型夹杂物降低了28.15%。     

板坯连铸中间包气幕挡墙夹杂物去除的研究

分析了中间包不加气幕挡墙和加气幕挡墙吹氩时夹杂物上浮速度与气泡直径、夹杂物直径和密度的关系。气泡尺寸对夹杂物的上浮速度影响比较明显,夹杂物的密度对上浮速度的影响不大。进行了中间包气幕挡墙的工业试验,试验表明:中间包底吹气对钢液中小夹杂物的去除作用不明显,而对大型的夹杂物去除效果显著。     

Hydraulics and Mathematics Simulation on the Weir and Gas Curtain in Tundish of Ultrathick Slab Continuous Casting

The molten steel flow pattern in continuous casting tundish could be improved if the flow control devices were properly used. With reasonable application of weir and air curtain, the disturbance at injection zone of the tundish was reduced. The flow path of the molten steel was changed, and the short-circuit flow was eliminated. Therefore, the residence time was lengthened. An air curtain with bubbles floating could promote the surface flow and improve inclusions removal. The application of weir and air curtain in an ultrathick slab continuous casting tundish was investigated with hydraulics and mathematics simulation. The residence time and dead volume fraction were studied through orthogonal experiments with different positions of the flow control devices. The efficiency of three factors was analyzed, and the optimum positions of the weir and air curtain were obtained. Besides, the discrete phase model was suitable for simulation of the interaction between gas bubbles and molten steel, and the mathematics results shown the optimum one got larger inclusion flotation rate.     

中间包底吹氩行为的数值模拟

 根据某钢厂连铸中间包的实际操作参数,采用欧拉两相流模型,气体入口边界条件按照多孔介质进行处理,利用CFX软件模拟计算了底吹氩中间包内钢液的流场。结果表明:底吹氩气技术代替上挡墙或下挡墙2种情况下,注入区钢液混合加剧,有利于夹杂物碰撞长大。浇注区靠近液面处速度提高易引起卷渣。当采用湍流控制器、上挡墙、下挡墙、底吹氩技术时,吹氩位置对钢液流动的影响较大,当在湍流控制器和上挡墙之间吹入气体时,钢液的流动特性有利于夹杂物的上浮去除。     

板坯连铸中间包内夹杂物去除的数值模拟

以某厂50tT型2流中间包为研究对象,利用大型商业软件ANSYS CFX10.0建立了三维有限体积模型,采用多相流模型对中间包内钢液的流动特性、温度分布与夹杂物去除规律进行了数值模拟,重点研究了不同堰-坝组合方式、湍流抑制器形状、拉速、夹杂物粒径等工艺参数对中间包内钢水平均停留时间、夹杂物上浮率的影响。结果表明:湍流抑制器对夹杂物的上浮去除影响不大;随着夹杂物粒径的增大,夹杂物的上浮率迅速增大;20μm以下的夹杂物则很难在中间包内上浮去除;随着拉速的增大,夹杂物的上浮率是不断减小的;采用堰A=300cm、坝B=400cm、方形瓦楞湍流抑制器、过滤器组合式控流装置时夹杂物的上浮去除效果最好。     

中间包内流体流动及夹杂物去除的研究

采用湍流流动的数学模型方法,对板坯中间包内的钢液流动及夹杂物去除率进行了模拟研究。系统分析了在中间包内设置控流设备对钢液流动状态、平均停留时间以及夹杂物颗粒排除率的影响。结果表明,设置挡墙和坝后,中间包内有效防止了短路流,延长了平均停留时间,夹杂物整体排除率明显提高,大大改善了中间包的冶金效果。     

Numerical Investigation of the Fluid Flow in Continuous Casting Tundish Using Analysis of RTD Curves

 A detailed mathematical procedure of the optimization of the fluid flow in a tundish water model with and without flow control devices (weir and dam) was carried out using the commercial CFD code FLUENT 60. The (k ε) two equation model was used to model turbulence. The residence time distribution (RTD) curves were used to analyze the behavior of the flow in tundish. The location of flow control devices in the tundish was studied. The results show that the flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel. Comparing the three geometric configurations that are considered (bare tundish, weir, weir+dam), the tundish equipped with the arrangement (weir+dam) is a best and optimal geometric configuration of tundish.     

吹氩技术及其对中间包流场影响的研究

研究了基于有限元分析软件对吹氩技术、中间包流场的影响,结果表明在中间包注入流与堰之间安装多孔透气砖可促进夹杂物的去除。确定透气砖在距水口中心700 mm、气量在7 L/min时,中间包内流体的流动特性最佳,可有效提高了钢水质量。     

三流中间包流场的物理模拟试验

以莱钢特殊钢厂三流中间包为研究对象做水模拟试验,通过RTD曲线分析和流场观察,结合生产实际及应用的方便、可行性等因素,通过设置、改进挡渣墙、湍流抑制器以及各种挡渣墙与湍流抑制器的组合,试验设计了29组方案。结果表明,原型中间包的内部结构不合理,中间包流场存在严重的短路流、死区比例过大、各流滞止时间差大及夹杂物上浮困难等问题;1型挡渣墙+10°+垫底+4号湍流抑制器方案的中间包内流场结构比较合理。     

薄板坯连铸中间包吹氩行为的物理模拟

中间包吹氩是适应洁净钢冶炼的新技术、新方法。依据相似原理,在实验室建立了一定相似比的薄板坯连铸中间包物理模型。比较了传统堰坝组合,吹氩气幕挡墙分别代替堰、坝对中间包流体流动特征的影响,并尝试在中间包内采用双气幕挡墙的控流方式。结果表明,气幕挡墙分别代替堰、坝,中间包停留时间和死区体积与堰 坝组合十分相近;双气幕挡墙代替堰 坝组合,除死区体积较大外,停留时间接近堰 坝组合。上述结论为气幕挡墙技术的进一步应用提供了参考依据。     

两流非对称中间包结构优化与应用研究

采用水模型实验、数值模拟相结合的方法分析了原型中间包和优化中间包在钢流流场、中间包流动特性方面的差异.结果表明:优化中间包2#水口平均停留时间延长了8.0%,两水口流体平均停留时间之差下降了36.3%.流体在优化中间包内流动轨迹更加复杂,延长了流体在中间包内停留时间.通过工业实验证实了优化方案的可行性.工业试验表明:采用圆形湍流控制器加单挡墙组成控流装置的原型中间包,两水口钢液平均温差为5℃,浇注得到的钢坯试样中,140~300μm夹杂物数量为0.7 mg;而采用非对称长方形湍流控制器加多孔挡墙组成控流装置的中间包,两水口钢液平均温差为3℃或2℃,约为原型中间包两水口钢液平均温差的1/2;浇注得到的钢坯试样中,140~300μm夹杂物数量为0.2 mg,约为原型中间包的1/3.说明采用非对称长方形湍流控制器加多孔挡墙组成控流装置的中间包对两水口温度的均一性起到了显著作用,且更能有效地去除钢液中的夹杂物.     

带过滤器63t中间包钢液流场的物理和数学模拟

通过采用几何相似比0.29:1的水模型和数学模型分别对(a)湍流抑制器和挡墙+坝(原结构),(b)湍流抑制器,挡墙+坝和过滤器,以及(c)湍流抑制器,挡墙和过滤器3种结构两流板坯连铸中间包钢液流场、温度场和夹杂物运动轨迹进行模拟研究。结果表明,原中间包结构(a)活塞区体积偏小,死区体积偏大;加入通道式钢液过滤器(b)后短路流基本消失,中间包死区减小6.83%,钢液的平均停留时间由287.04 s延长至373.76 s,有利于夹杂物的上浮去除,且过滤器的加入对钢液的温降影响不大;用钢液过滤器代替挡坝(c)后优化效果最为明显,中间包钢液平均停留时间由287.04 s延长至404.26 s,峰值时间由原来的95,4 s延长至190.8 s,死区体积由36.10%减小至8.76%。     

中间包夹杂物的去除与控制新技术

通过对中间包中不同去除夹杂物的手段进行综合分析,得到各环节中间包均应保护浇注和防止卷渣卷气,中间包应具有合理的控流装置（上下挡墙、湍流抑制器、旋涡抑制器）以得到理想的流场;利用钢包注流生成的小气泡、中间包气幕挡墙和电磁搅拌离心流动可以有效去除中间包内钢水中夹杂物;连续真空处理对脱气和去除夹杂物有良好效果但其可调性差,电磁过滤可作为辅助方法去除夹杂物。     

气幕挡墙中间包钢水流动的数值模拟

根据二流连铸1500mm×250mm板坯时中间包的操作工艺参数,采用欧拉两流体模型,多孔介 质模型和拉格朗日随机轨道模型,模拟计算了采用湍流控制器和气幕挡墙技术的中间包内钢液流动特性和 夹杂物的运动轨迹,并用Monte-Carlo法统计了夹杂物的总去除率。模拟结果表明,采用中间包气幕挡墙技术 可以有效改善钢液的流动特性,延长钢液停留时间,减小死区体积;当吹气量为0.90m³/h时,夹杂物去除率比 不吹气工艺增加15.6%     

二流T型23 t中间包控流装置的数值模拟和结构优化

通过计算流体力学软件FLUENT建立的数学模型对钢厂200 mm×1 600 mm铸坯二流T型23 t中间包现挡墙和坝、湍流控制器和坝、湍流控制器和现挡墙以及新挡墙4种结构方案进行三维数值模拟,研究原中间包及安装不同控流装置后的钢水流动特性。结果表明,在所有的设计方案中安装有湍流控制器和坝的中间包能够达到最佳优化效果;中间包的死区体积分率由30.18%降到16.51%,活塞流区与死区的体积分率比R_Vp/Vd由55.80%增大到129.44%;中间包内流动稳定,有利于夹杂物的上浮。     

薄板坯连铸中间包内抑湍器的模拟研究

控制中间包内钢液的合理流动对夹杂物的排除有重要影响,为此建立了模拟薄板坯连铸中间包流动情况的水模型。通过测定停留时间分布(RTD)曲线,研究了不同组合控流装置对中间包流体流动特性的影响。结果表明,结构及尺寸合理的抑湍器能延长水口响应时间及平均停留时间、提高活塞流区体积分数及降低死区体积分数;抑湍器与单坝组合的控流装置在控制流体流动方面效果极佳,而抑湍器与单墙单坝、单墙双坝组合的控流装置的控流效果不太理想。