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.     

Simulation on Effect of Divergent Angle of Submerged Entry Nozzle on Flow and Temperature Fields in Round Billet Mold in Electromagnetic Swirling Continuous Casting Process简

A new process for swirling flow generation in the submerged entry nozzle （SEN） in continuous casting process of steel was proposed. A rotating electromagnetic field was set up around the SEN to induce swirling flow by Lorentz force. The flow and temperature fields in the SEN and round billet mold with electromagnetic swirling were numerically simulated and then verified by the electromagnetic swirling model experiment of low melting point alloy. The effects of divergent angle of the SEN on the flow and temperature fields in mold with electromagnetic swirling were investigated. The electromagnetic swirling flow generator （EMSFG） could effectively induce swirling flow of molten steel in the SEN, which consequently improved greatly the flow and temperature fields in the mold. Below the nozzle outlet in mold, with the increase of divergent angle, the stream of bulk flow diverged more widely, the high temperature zone shifted up, and the temperature field became more uniform. Above the nozzle outlet in mold, with 350 A electromagnetic swirling, when the divergent angle of the SEN increased, the upward flow velocity and the meniscus temperature first increased and then decreased. With a divergent angle of 60~, the upward flow velocity and meniscus temperature reaced the largest value.     

Numerical study of an application of a divergent reverse TurboSwirl nozzle in the billet continuous casting process

The swirling flow has widely been investigated for liquid steel flowing in the continuous casting process. In this paper, a new design of the submerged entry nozzle (SEN) is applied by using a reverse TurboSwirl device with a divergent nozzle. This divergent reverse TurboSwirl nozzle (DRTSN) is shown to gain a more beneficial flow pattern compared to the straight nozzle. A stronger swirling flow can be obtained at the SEN outlet, which leads to a calmer flow field and an appropriately active meniscus flow that could improve the heat and mass transfer near the meniscus. The swirl number in the SEN is independent of the casting speed, while a lower casting speed yields a lower maximum wall shear stress. The DRTSN is connected to the tundish by an elbow and a horizontal runner. A longer horizontal runner supplies a more uniform velocity profile and a more symmetrical flow pattern.     

Effect of SEN Parameters on 3D Flow Field in Mould of Beam Blank Continuous Caster

Duringtheprocessofcontinuouscasting ,theflowfieldofmoltensteelinfluencesdirectlyonthetemperaturefield ,heattransfer ,slaginclusionfloatationandcomposi tionuniformityinthemould ,thusrelatesdirectlytothein ternalandsurfacequalityofcastblank .Soitisveryimpor…     

旋流水口对圆管坯连铸结晶器内钢水流场的影响

借助于流体力学分析软件Fluent,在圆管坯连铸浸入式水口上施加电磁力,对结晶器内钢水产生电磁搅拌作用使模型水口出流成螺旋状态的钢水流场进行了数值模拟。结果表明:旋流式水口有利于改善结晶器内的流场,有效降低冲击深度,增大液流向弯月面区域的回流和热流上传,提高了液面的活跃程度,增强钢水表面融渣的效果。     

圆坯结晶器水口优化的模拟研究

以大圆坯结晶器为原型,采用数值模拟与物理模拟相结合的方法,分别研究了使用直通式水口和4孔旋转水口时该圆坯结晶器内钢液流场和温度场的分布情况,对比分析了2种水口的优劣。数值模拟和物理模拟结果表明,使用目前常用的直通型水口时钢水冲击深度大,易在弯月面处形成死区,不利于圆坯内部及表面质量的提高;4孔旋转水口比直通水口的钢液冲击深度浅,回旋区位置明显比直通水口更靠近自由液面,这将有利于夹杂物的上浮去除和热区中心的上移。温度场模拟结果显示,使用旋转水口时自由液面温度比直通型水口高14℃,更有利于结晶器内钢水过热耗散及保护渣的熔化,可防止液面结壳。     

Analysis of Mould,Spray and Radiation Zones of Continuous Billet Caster by Three‐dimensional Mathematical Model based on a Turbulent Fluid Flow

An analysis of mould, spray and radiation zones of a continuous billet caster has been done by a three‐dimensional turbulent fluid flow and heat transfer mathematical model. The aim was to reduce crack susceptibility of the billets and enhance productivity of the billet caster. Enthalpy‐porosity technique is used for the solidification. Turbulence is modelled by a realizable k‐ε model. The three‐dimensional mesh of the billet is generated by Gambit software, and Fluent software is used for the solution of equations. In various zones, different standard boundary conditions are applied. Enhanced wall treatment is used for the turbulence near the wall. In the mould region, Savage and Prichard expression for heat flux is applied. In the spray cooling zone, the heat transfer coefficient for surface cooling of the billet is calculated by knowing the water flow rate and the nozzle configuration of the plant. The model predicts the velocities in the molten pool of a billet, the temperature in the entire volume of billet, the heat transfer coefficient in the mould region, the heat flux in the cooling zone and radiation cooling zone, and the shell thickness at various zones. The model forecasts that the billet surface temperature up to the cutting region is above the austenite‐ferrite transformation temperature (which is accompanied by large volume change). The model predicts a temperature difference of maximum 700 K between the centre and surface of the billet. The entire solidification takes place at 11.0 m length at 3.0 m/min. For the same casting arrangement, increasing the casting speed up to 4.0 m/min has been explored. Based on the simulation results, recommendations to alter the spray water flow rate and spray nozzle diameter are presented to avoid a sudden change of temperature.     

板坯连铸结晶器钢液流场的数值模拟

 运用Fluent软件,对断面150 mm×460 mm的板坯结晶器钢液流场进行了数值模拟,研究了不同水口侧孔面积和长宽比条件下流场的变化情况,并对倾角和插入深度等参数进行了优化。结果表明,长宽比一定时,面积比越大则液面最大速度越小,冲击深度和冲击压力也越小。面积比一定时,大的长宽比有利于减小液面最大速度、冲击压力以及流股对窄面的冲刷。确定了在不改变水口内径、底面形状和出口形状的前提下,适合该结晶器水口的侧孔断面为25 mm×40 mm,倾角为15°,插入深度为200 mm。     

Flow of Steel in Mold Region During Continuous Casting

 The particle image velocimetry (PIV) technique was used to study the fluid flow phenomena that occurred during continuous casting, using a water model with dimensions of 1 840 mm×280 mm. Two types of solidified shells, ie, the smooth type and the coarse type, were used to characterize the dendrite in order to simulate different liquid solid interfacial conditions. The influence of the nozzle angle and the immersion depth of nozzle, as well as the casting speed on the flow behavior was investigated quantitatively. The results were as follows: (1) There are two large recirculations above and below the fluid jet in the mold, respectively, under the smooth interface condition. However, in the case of the dendrite solidified shell, it was found that the flow velocity of the fluid decreased and more smaller vortices appeared in the upper region of the mold. (2) The angle and the immersion depth of nozzle are two important factors affecting the flow pattern, and they are also capable of bringing about the change in the flow direction. (3) The higher the casting speed, the higher are the jet stream and the impacting point on the narrow face. However, the high casting speed causes serious fluctuation of the meniscus, and correspondingly leads to various defects.     

Three-dimensional FEM study of fluid flow in mould for beam blank continuous casting: influence of nozzle structure and parameters on fluid flow

Abstract

The aim of this work was to analyse the influence of the nozzle structure and parameters on the molten steel flow in beam blank continuous casting. A three-dimensional steady state finite element model was developed to compute the flow field and the meniscus fluctuation in the mould. The volume of fluid model was used to track the free surface evolution at the meniscus. It can be concluded that compared with a through conduit submerged entry nozzle (SEN), a three lateral hole SEN will reduce the impact depth, change greatly the velocity at the free surface and intensify the fluctuation of the free surface. As a whole, the fluid flow in the mould will be improved, which will help to melt the mould powder and improve the absorption of non-metallic inclusions, thus improving steel cleanness. The most rational rake angle for the three lateral hole SEN is 9°. Meanwhile, the SEN immersion depth should be in the range 200–250 mm if the casting speed is about 0·9–1·1 m min^?1.     

Mould heat transfer and continuously cast billet quality with mould flux lubrication Part 2 Quality issues

Abstract

With many billet producers adopting mould powder lubrication, there is a need to clarify the gains in quality that can be achieved with this practice. Over the past three decades considerable research has been conducted to establish the relationship between mould behaviour and defect formation for billets continuously cast with oil lubrication, but little has been done to compare oil cast billets with powder cast billets. In this study, conducted at a Canadian minimill, four faces of a copper mould were instrumented with thermocouples and mould temperatures and billet quality were monitored with mould powder lubrication during casting of 208 × 208 mm billets. In the first part of this two part series (in Ironmaking & Steelmaking No. 1 2000), the results of the mould heat transfer analysis and the influence of variables were presented, together with a comparison between oil and powder lubrication. In the present paper, Part 2, billet quality is examined in detail. The difference in turbulence at the meniscus between oil and powder lubrication is established, and the need to tune mould level sensors when switching to mould powders is demonstrated. Previous work has shown that mould level fluctuations have a strong influence on defects such as offsquareness and transverse depressions, both of which are markedly reduced when casting with mould powders. The inherent stability of the meniscus is improved when employing mould powder lubrication and a submerged entry nozzle. Furthermore, the significant reduction in mould heat transfer at the meniscus, when mould powders are employed, particularly for medium carbon steels has been shown to correlate well with the observed reduction in offsquareness. The paper also elucidates the reasons for the reduction, and in most cases, elimination of transverse depressions in B–Ti grades when casting with mould powders. The mechanism of longitudinal depression formation and subsurface cracking observed in many of the powder cast, medium carbon billets has also been established.     

大方坯径向水口旋流效应及其对凝固的影响

通过改变水口侧孔钢水流动方向可以控制结晶器内钢水流动与换热。采用流体动力学与凝固模拟方法对比研究了浸入式四分径向水口不同出流方向对大方坯连铸结晶器内流动、传热和凝固行为的影响。结果表明,侧孔方向对浇注过程结晶器内钢水的流动与凝固行为有显著影响。当水口侧孔水平旋转角度为30°时,结晶器内形成较好的水平旋流,可以有效降低侧孔出流钢水对坯壳的冲刷作用,并有利于结晶器内自由液面过热度的提高。比较不同侧孔出流角度发现,利用普通径向四分水口在一定安装角度下的旋流效应不仅对于初生坯壳的均匀生长以及自由液面的冶金效果产生有利影响,还可能在不改变水口结构条件下获得类似结晶器电磁搅拌的旋流效应。     

Analysis of variability and non-uniformity of mould heat extraction for round billet continuous casting in plant trials

Abstract

Maintaining a stable and uniform heat transfer from steel shell to mould is important to produce high quality casting billet. In the present paper, a large amount of measured data of heat flux and temperature for round billet continuous casting mould from a plant trial has been analysed to shed light on the variability and non-uniformity of mould heat transfer around the perimeter. The results show that the variability and non-uniformity of heat extraction from the steel through the mould is affected slightly by operational parameters, such as pouring temperature, casting speed, meniscus, electromagnetic stirring current, but strongly by the steel carbon content and mould powder type. The installation of the mould in caster machine determines the magnitude of non-uniformity of heat transfer to a great extent. The relative root mean square (rRMS) of mould heat flux, presenting the variability and non-uniformity of mould heat transfer around the perimeter in transverse section, has wider range of variation and higher mean value compared with that of temperature. When the abnormality of heat transfer happens, such as deposit, the non-uniformity of mould heat transfer is also studied.     

Effects of several casting parameters on slag entrapment in mould (part B:numerical modeling)

Based on the effects of several casting parameters on slag entrapment in the mould (water modeling),the numerical modeling was researched. The results show that the flow field with a submerged nozzle section dimension of 65 mm×80 mm is better than that with a submerged nozzle section dimension of 40 mm×40 mm and is favorable for avoiding slag entrapment. In this paper,low surface velocity,small level fluctuation and proper impact depth can be achieved with a nozzle of an outlet angle of 25° and an immersion depth of 150 mm,or with a prototype nozzle of an outlet angle of 15° angle and an immersion depth of 150 mm.     

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.     

特大圆坯连铸用新型浸入式水口的设计与研究

 针对特大截面圆坯连续浇铸的特点,基于依靠浸入式水口自身结构减小钢流冲击深度,同时保证流动与传热沿周向分布均匀的思想,首次提出了新型浸入式伞形水口设计方案,并建立了结晶器内钢水的流-热-固耦合模型,对钢水的流动、传热和凝固行为进行了数值耦合模拟分析,验证了此水口的优越性与合理性：伞形水口的射流在结晶器内形成上下两个回流区,不仅有利于夹杂物、气体等的上浮分离,还能有效降低钢流冲击深度,使过热钢液均匀分布在结晶器上部,可提高弯月面温度和化渣效果;沿周向凝壳生长均匀,减轻了纵裂纹的萌生概率;在0.35m/min拉速下,出结晶器凝壳厚度达到31.2mm,满足安全生产要求。     

水口结构对连铸中低碳钢流场和温度场的影响

 为研究水口结构形状对连铸中低碳钢结晶器内流场和温度场分布的影响,采用有限容积法建立连铸圆坯三维数学模型,模拟了不同水口形状下圆铸坯的流场和温度场。结果表明,在水口浸入深度为80 mm、其他参数不变时,与直水口相比,旋流水口使钢水冲击深度降低,结晶器内涡流增强,弯月面温度和二冷区凝固率提高,且随着水口数量的增加,弯月面波高和结晶器出口温度降低;采用旋流水口并施加结晶器电磁搅拌(M EMS)时,结晶器中钢液温度升高,弯月面有卷渣行为,结晶器出口未形成凝固坯壳。在实际应用中,应避免同时使用M EMS和旋流水口,或使用旋流水口时采用低强度的M EMS。     

Flow pattern control in continuous slab casting moulds: physical modelling and plant trials

Full-scale water modelling studies combined with nail-dipping industrial trials at Shougang Jingtang (SGJT) Works were carried out in order to investigate the parameters that influence flow patterns in the continuous slab casting mould. The effects of casting speed/mould width combinations, argon bubbling flow rates, submerged entry nozzle (SEN) immersion depths and SEN geometries (port angle and bottom shape) on the flow patterns were examined. A CMI factor defined as casting speed/mould width ratio index is put forward to describe the combined effect of these parameters on the fluid flow patterns in the mould. The results show that the CMI and argon injection rates are the dominant factors that determine the flow pattern. On the basis of the results from this study, critical argon flow rates for different casting combinations have been evaluated. These findings provide operating guidelines for generating optimal flow patterns based on double roll flow with appropriate surface velocities in continuous slab casting moulds. On the basis of these considerations, slab quality at SGJT Works was substantially improved and the percentage of flow pattern-related sliver defects in cold rolled products was decreased from 4.5 to 2.3%.     

方坯高效连铸新型结晶器传热分析与应用

提出了方坯高效连铸结晶器有效结构形式,并通过ansys有限元软件,建立高效连铸结晶器与传统结晶器铜管的传热模型,并对其凝固传热以及温度场进行计算对比,重点讨论不同结构形式的结晶器在传热效率及传热均匀性方面的差异,并讨论其对高拉速下坯壳凝固的影响。结果表明,高效结晶器可以使得结晶器的传热效率提高7.8%,并且使得结晶器铜管热面最高温度降低100℃,热面温差降低到5℃以下。作者根据该理论,通过有限元优化设计,设计制造出方坯高效连铸结晶器,并应用于某钢厂155mm方断面的铸机上,稳定生产拉速达到4m/min,最大拉速达到4.46m/min。     

Water modelling of level fluctuation in thin slab continuous casting mould

Abstract

A water modelling experiment was conducted to study the meniscus instability in a continuous thin slab casting mould using particle image visualisation. The results show that the level fluctuation, circulation centre position and jet impinging depth are unsteady and periodic with a similar period. The probability distributions of the fluctuating meniscus and wave height have been obtained with the highest frequency near the average position. The flow pattern and meniscus profile may be momentarily asymmetrical, and the phase difference of level fluctuation in the two sides of mould centreline is a half period. The average meniscus profile, the highest and lowest meniscus positions are generally symmetrical about the mould centreline. The wave height mainly depends on the jet impinging depth and circulation centre position. The wave height increases as the jet impinging position rises and the circulation centre approaches to the submerged entry nozzle.