优化高拉速板坯连铸中间包控流装置的水模型和数值模拟

通过建立模拟高拉速板坯连铸中间包内钢液流动的水模型和数值模拟,研究了挡渣墙、坝和抑湍器等控流装置对中间包内流体流动特性的影响.结果表明,有无冲击板对中间包流动特性的影响不大,抑湍器与单墙双坝的合理搭配对中间包内夹杂物有效去除的流动特性十分重要,否则会起负面影响.提出了一个控流结构优化设计的方案.     

三流Τ型中间包内控流装置优化的物理模拟

通过三流T型连铸中间包物理模拟实验,研究了直挡墙、V型挡墙及其与抑湍器组合控流装置对中间包流动特性的影响。结果表明,直挡墙控流装置的控流效果优于无控流装置的中间包,但不如设计合理的V型挡墙控流装置;V型挡墙与挡坝组合控流装置（方案Ⅴ）的控流效果较好,在其基础上加入抑湍器后控流效果并不理想。因此,提出了针对三流T型中间包控流装置的优化设计方案。     

通钢FTSC薄板坯连铸中间包控流装置的优化改进

借助水模试验,对通钢FTSC(Flexible Thin Slab Caster)薄板坯连铸中间包控流装置的形式、几何尺寸和位置进行优化改进。中间包的控流装置由原来的抑湍器、墙的单一组合优化为抑湍器、坝、墙的组合,生产实践中钢液流动特性有了明显改观,夹杂物总量减少50%以上,球状和大颗粒夹杂物等级明显降低,充分发挥了中间包冶金的作用。     

宽厚板坯连铸中间包内控流结构优化水模实验研究

通过宽厚板坯连铸中间包水模实验,研究了不同控流装置对中间包内流动特性的影响。结果表明：带顶缘和不带顶缘的抑湍器均能明显提高活塞区的体积分数,且死区体积分数也有不同程度的降低;与带顶缘的抑湍器组合的中间包出口附近的挡坝设计参数对中间包内钢液的流动特性有影响;与带顶缘的抑湍器组合的墙坝间距有一个控制钢液流动特性的最佳值。通过实验研究,提出了优化的设计方案。     

8流一体式方坯中间包控流装置优化研究

针对多流中间包冶金过程存在的问题,通过水模型试验,就影响其流场的因素,采用正交试验的方法对中间包内部控流装置进行优化。综合考虑各种影响因素,钢厂8流一体式T型中间包内合理的控流装置是带导流孔的V型挡渣墙+双坝的组合。     

八流一体式小方坯中间包结构的优化研究

通过数理模拟,对采用正交法设计的某钢厂八流一体式中间包控流装置的实验方案进行钢液流场、温度场及流动特征的研究,并以此设计出新的控流装置.研究结果表明,采用新方案(湍流控制器十带导流孔的“V”型挡渣墙+双坝组合的控流方式),延长了近流水口响应时间及平均停留时间,各水口钢液的流动模式趋于一致,中间包内钢液的流动特征得到明显...     

改善六流中间包内流体流动特性的研究

通过六流方坯连铸中间包水模拟实验,研究了不同控流装置对其流动特性的影响。研究发现:中间包控流装置为原挡渣墙时,其控流效果较差。与原挡墙相比,中间包的控流装置改为新挡渣墙后,表征中间包流动特性的因素有了明显的改善。在新挡墙的基础上,对加稳流器和挡坝控流装置的控流效果进行了研究,发现加稳流器的控流装置极大地改善了中间包流体的流动特性。通过对比和分析几种优化实验方案对改善中间包流动特性的效果后,确定了最优方案。     

板坯连铸异型中间包卷渣水模型实验研究

为改善连铸板坯质量,通过水力学模拟研究了中间包内钢液的流动,并测量了在非稳定浇注条件下避免钢液卷渣的中间包内钢液的临界高度,确定了在中间包内设置抑湍器、坝和堰的混合控流方案。结果表明：中间包设置控流装置后,平均停留时间增加,有利于夹杂物的上浮;同时确定了中间包卷渣的临界高度。     

两流中间包控流装置优化的物理模拟与应用

以太钢两流对称板坯连铸中间包为研究原型,采用物理模拟的方法研究抑湍器以及挡墙、挡坝位置对中间包流场的影响。物理模拟结果表明,中间包未设置任何控流装置时存在短路流,死区比例高达36.47%;中间包使用抑湍器后,响应时间增加了13.5 s,平均停留时间延长了34.8 s,死区体积降低了6.33%;保持挡墙的位置不变,将挡坝距长水口的距离增加100 mm,更利于改善中间包流场。通过现场试验表明,中间包优化后铸坯全氧质量分数由平均2.02×10~(-7)降低至1.55×10~(-7),减少了30.32%。     

四流方坯连铸中间包结构优化

在实验室建立了4流中间包流体流动的物理模型,通过测定停留时间分布(RTD)曲线,研究不同的控流装置组成的中间包结构对流体流动特性的影响。研究结果表明:沟槽或者圆孔槽均能明显改善各流流动特性的一致性,与带"V"型挡墙组合的挡坝高度对中间包内钢液的流动特性有影响;适当高度的坝与湍流控制器、沟槽、"V"型挡墙组合的控流装置在控制流体流动方面效果较好,在其基础上将沟槽改成圆孔槽控流效果更佳。根据实验研究提出最佳方案,即带湍流控制器、孔径φ150mm的"V"型挡墙、高300mm的坝和圆孔槽的中间包组合。     

Three-dimensional mathematical modeling of fluid flow in slab tundishes and its verification with water model experiments

A three-dimensional mathematical model has been developed based on the incorporation of a computational fluid dynamics technique, called SOLA-SURF, and theK-ε turbulence model. Numerical solutions of the three-dimensional turbulent Navier-Stokes equations and theK and ε equations together with the free surface treatment are presented to study the turbulent flow behavior of molten steel in tundishes. Computed results describing the three-dimensional flow field, particle path lines, residence time distribution curve during steady-state operation are presented. The values oft _min,t _peak, andt _mean derived from the residence time distribution curve are used to evaluate the effects of using various combinations of flow control devices such as dams, weirs, and dams with a hole in the flow field. The computed results were compared with the experimental data obtained from a full-scale plexiglas/water model of tundish. The comparisons exhibited good consistency.     

Physical and mathematical modeling of metal flow in the continuous casting of Steel and Aluminum

For a long time it has been recognized that flow of metal in the liquid pool at the head of a continuous caster can have a significant effect on the operability of the caster and the quality of the steel produced. Poorly engineered flows can result in thinning of the shell produced in the mold, with consequent danger of breakouts, entrapment of inclusions or gas bubbles, as well as macrosegregation. There can be similar impacts of the flow in the DC casting of aluminum, Flows are controlled, in the case of steel casting, by the design of the submerged entry nozzle (SEN) and by auxiliary devices sych as electromagnetic brakes and stirrers. In the case of aluminum casting, it is common practice to place a ceramic “bag” around the SEM to control the flow. Usually the design of these devices involves much empiricism; the metal pools arc hot and difficult to access, and flow measurements are therefore difficult. Some use has been made of mathematical and physical models in developing flow control devices. The difficulty with the former is that the flows are turbulent and in a volume with an irregular geometry; consequently, model predictions are questionable unless tested in some way. Such testing can be done using physical models which can also provide their own insights into the nature of the flow. Unfortunately, most physical modeling of casters in the past has been qualitative, or semi-quantitative. The paper describes a project at Berkeley where quantitative results are being obtained from a physical model of a caster with the help of particle image velocimctry (PIV), In this technique (cross correlation PIV), a digital camera records an image of tracer particles scattered throughout the flow. A second image is recorded 33milliseconds later and the two digital images are interrogated by commercial software (Optical Flow Systems. Edinburgh. Scotland) to determine the motion of the particles from one image to the next and yield a vector map of the flow. The technique has been extended to yield time averaged velocity vectors for turbulent flows (the case in the casters and models) by ensemble averaging the vectors from many pairs of images. Water models, including full sized ones, have been constructed for steel and aluminum casters. Various SENs and bags can be used in the model and their effects measured by PIV. Results show that the orientation of the two ports at the bottom of the SEN has a strong effect on the flow in steel casting. The water model of the aluminum caster has shown the strong effect of the bag geometry, and of bag misalignment, on flow in the liquid pool. The commercial software FIDAP has been used to compute time averaged velocities in the physical models. Agreement between measurements and predictions varies from good to fair, depending on conditions.     

涟钢二流板坯连铸中间包水模型研究

以相似原理为基础,建立1∶3的水模型,对涟钢二流板坯连铸中间包进行研究.结果表明,单纯的湍流控制器+挡坝,中间包活塞区体积偏小,死区体积偏大;挡坝开孔能使中间包死区减小,而不会产生明显的短路流;有利于改善中间包钢液流动的控流装置组合为挡堰+开孔挡坝+湍流控制器,得出了其具体位置;优化后的中间包平均停留时间由343 s延长至387 s,死区体积由20.0％下降至9.8％,滞止时间由61s延长至99 s.     

中间包流场控制技术的进展

合理控制中间包的流场有利于促进钢液中夹杂物上浮、均匀钢液成分和温度。水模型试验和数值模拟是两种主要的中间包流场研究方法,各有优缺点应相互补充。数值模拟成本低廉速度快,但受限于边界条件的不确定性和湍流模型的局限性难以完全真实反映中间包内的流场。水模型试验能够较为准确地模拟中间包内流场,但无法准确模拟温度场、水口结瘤、覆盖剂和吹气等对中间包流场的影响。研究表明,湍流控制器对降低长水口钢液射流的湍动能、均匀钢液温度和成分、聚拢射流让其转向向上流动降低死区体积分数、延长平均停留时间和优化流场结构具有很好的作用。湍流控制器、堰、坝和导流挡墙合理组合,协同发挥的控流效果,优于单一控流装置的效果。合理调节堰与包底距离、挡坝高度、堰与挡坝距离、堰与出流口距离、挡坝开孔的个数、尺寸和角度,可以优化中间包流场,促进夹杂物去除。气幕挡墙对钢液进行气洗可以提高钢液洁净度。环形气幕挡墙解决了条形气幕挡墙夹杂物去除率低、且不稳定的问题,提高了夹杂物去除率。最后,中间包流场数学模型精细化,并考虑连铸过程中更多工艺与边界条件的影响是未来发展的趋势。对于中间包流场研究的特定问题,针对性设定优化指标,会使得优化研究工作事半功倍。水模型试验作为中间包控流技术的另一种重要研究手段,同样越趋精确化,不断有研究者以提高试验精度为目的在试验方法和测量原理上进行探索和创新。     

提高奥氏体不锈钢板坯质量连铸工艺实践

通过优化连铸过程中的结晶器铜板使用方法,实现完全消除由于结晶器铜板引起板坯表面裂纹,同时结晶器铜板镀层的过钢量从2万t提高到6万t;为有效去除板坯中大颗粒夹杂物,改进中间包流场设计,保留稳流器,取消挡墙和挡坝,使得钢水的运动轨迹和停留时间发生变化,从而显著降低板坯中10 μm以上大颗粒夹杂物的数量、并能将夹杂物的最大尺寸控制在20 μm以内;通过上述工艺实践,实现大幅提高奥氏体不锈钢板坯质量。     

Optimization of flow control devices for a T-type five-strand billet caster tundish: water modeling and numerical simulation

The optimization of flow control devices(FCDs) for a T-type five-strand billet caster tundish was carried out by water modeling and numerical simulation. In water modeling experiments, flow characteristics of the bare tundish and tundish conf igurations with designed U-type baff les and a round turbulence inhibitor were analyzed using residence time distribution(RTD) curves. Mathematical models for liquid steel in the real plant tundish were established using the fluid dynamics software package Fluent. The flow field, the temperature field, and the RTD curves of liquid steel in the proposed tundish conf igurations were obtained. The results of numerical simulation and water modeling were validated with each other by the predicted and experimental RTD curves. The results of flow field and temperature field were used to ref lect the actual state of a real plant tundish and to choose the optimal FCD. Finaly, from the whole performance of the multi-strand tundish, the optimal scheme was determined by combining the results of water modeling and numerical simulation. With the optimal tundish equipped with U-type baffle with def lector holes and round turbulence inhibitor, not only was the flow characteristic of each strand improved, but also the difference of flow characteristics between multiple strands was smaller.     

FLUID DYNAMICS IN A GAS-STIRRED LADLE——A Separated Flow Model with Stochastical Trajectories

A separated flow model with stochastical trajectories has been developed to describe the fluidflow in a bubble stirred ladle.The bubble dispersion,turbulent characteristics and gas-liquidinteractions can be predicted by this mathematical model.The bubble flow as a dispersedphase is treated in a Lagrangian frame of reference and the analysis of the turbulent flow forliquid phase is conducted in a Eulerian field.The interactions between bubbles and liquidphases are considered as a bubble source term in the control equation for a continuous phase.The Monte Carlo sampling method is used to determine the bubble trajectories.The homoge-neous flow model is also taken into consideration so that it can be compared with the sepa-rated flow model.Numerical predictions using a water model of a ladle show that the pre-dicted results of the separated flow model agree satisfactorily with the experimental results,but the prediction of the homogeneous flow model are not in good agreement with the experi-mental results.     

Optimization of lfow control devices in a ten-strand billet caster tundish

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