Experimental Investigation of Fluid Flow in CC Mold With Electromagnetic Filed

Fluid flow in continuous casting mold is one of the key factors to influence the process, because the operation of the casting process and most of the defects in steel quality are closely associated with fluid flow in the mold. Electromagnetic field(EMF) has been applied to control the fluid flow as an efficient technology, and a lot of research works on the effect of the EMF has been done by numerical simulation. Aware of the limitation of the numerical simulation of the flow under a static EMF, low melting metals have been adapted to the investigation of flow in EMF. In the report, some of works on electromagnetic brake ruler (EMBR) and Flow Control Mold (FC-Mold) in slab casting with mercury as an analogue of liquid steel are presented. In the experiment, the flow in the mold and fluctuation of meniscus were measured by the ultrasonic DOP2000 velocimeter. The effects of the magnetic flux density and location of the magnets on the flow in the mold have been studied. The results showed that the flow discharged from the SEN was suppressed, both of the distribution of the kinetic energy and the turbulence intensity were changed, and the flow stability of liquid metal in the mold was enhanced. In electromagnetic brake ruler when Bmax was more than 0.29T, the surface level fluctuations were suppressed,the flow at the meniscus became stable and the flow pattern at the meniscus were improved, and the impact strength of liquid metal was weakened simultaneously, and the penetration depth was reduced. It was beneficial to improve the flow in the upper eddy, fluctuation of meniscus and stability of the flow when the magnet was located near the SEN. However, it was good to reduce the impact action and penetration depth when the magnet was away from the SEN. Compared with EMBR, it was more effective to use FC-Mold for improving the flow in the upper eddy, fluctuation of meniscus and stability of the flow. Nevertheless, it was more effective for lower flow to reducing the impact action and penetration depth using EMBR. The     

立式组合电磁制动对CSP结晶器内钢液流动及偏流控制

紧凑型带钢(CSP)薄板坯连铸结晶器在浸入式水口下方设置水平式的全幅一段电磁制动器(Ruler-EMBr),在进一步提高薄板坯连铸拉坯速度的情况下,不能有效控制CSP结晶器自由表面的钢液流速和液面的稳定性.为此提出一种新型的立式组合电磁制动(VC-EMBr)技术,并利用商业软件ANSYS FLUENT数值模拟研究了全幅...     

Simulation of meniscus fluctuations in the feeding system used in strip casting

The feeding system used in the strip casting process delivers molten metal from the tundish to the pool that is bordered by side dams and rolls and is one of the key units in the production of high quality strip metal.The traditional method for studying this key unit is to use a combination of a water model and a mathematical model.However,the relations in the model with and without roll rotation have not been clearly revealed in previous studies.A 2D transient model based on a continuity equation,momentum equation,turbulent equations,and a VOF equation was established in this study and used to simulate the meniscus fluctuation.A half model with a structured grid was used for the reported simulation.The simulation showed that significant differences existed in the fluctuation in the flow fields and wave length with or without the roll rotation.The wave fluctuation exhibited uncertainty and an unstable character in the roll rotation condition.The level fluctuation employing different process parameters such as rotating speed and immersion depth of tip angle was simulated and compared with and without roll rotation.The study results showed that the meniscus fluctuation of twin-roll strip casting was primarily affected by the roll rotation,and the level fluctuation increased with the increase in rotation velocity and decreased with immersion depth.     

Effect of EMBr on Flow in Slab Continuous Casting Mold and Evaluation Using Nail Dipping Measurement

The nail dipping method was developed to investigate the effect of electromagnetic brake on the mold top surface flow in a certain slab caster with different casting speed and submerged entry nozzle (SEN) depth. The shape of the meniscus profile and direction of flow were quantified by analyzing the angular profile of the lump for each solidified nail, and the error evaluation for the nail dipping measurement was also determined. The results show that the meniscus level fluctuates with time variation; the electromagnetic force suppresses the high‐speed flow and decreases the meniscus flow velocity, which makes the meniscus level flatter and slower. A stronger meniscus velocity and fluctuation were created by increasing casting speed and decreasing the SEN depth. Furthermore, the effect of magnetic field on the fluid flow in the mold has been investigated.     

Effect of Fluid Transport Characteristics on the Level Fluctuation in the Pool of Twin‐Roll Strip Casting

The fluid transport characteristics and level fluctuations in the pool of twin‐roll strip casting are studied using a water model and mathematical simulations. The level profile depends on the transport characteristics of the flow in the pool. A full scale water modeling experiment has been conducted to address the relationship between the fluid flow and level fluctuation in the narrow strip pool. The residence time of fluid at the ports of nozzle and nip points of caster are measured to evaluate the fluid flow uniformity in the caster. The level fluctuations are measured with wave gauge and sensors. Mathematical modeling is also established to help anticipate flow patterns in the pool and residence time at the exits of nozzle and caster. The results show that a strong jet flow impinging on the both sides of delivery system is generated and free surface oscillations increase at the most lateral ports of delivery system. The fluids are uniformly distributed along the direction of roll width at the narrow pool zone. The flow patterns are complex near side dams' zone. Calculated results are in good agreement with residence time and average wave height measurements.     

结晶器电磁制动技术的应用研究

论述了板坯连铸结晶器中应用电磁制动技术的发展、研究和应用状况。电磁制动技术可以控制结晶器内钢液面的波动,减少结晶器保护渣的卷渣,有利于结晶器内夹杂物的去除。鞍钢电磁制动的研究结果表明,电磁制动可降低液面波动50%以上,可提高目标拉速0.5m/m in。     

Coupled Simulation of Flow and Thermal Field of Twin-Roll Strip Casting Process

The steel industry is moving ahead along the di-rection of low cost,short process,good quality andlow capital investment. Strip continuous castingwhich can directly cast a thin strip with thicknessless than 10 mm from molten metal and can elimi-nate the expansive and complex hot rolling,is ex-pected to reduce both the capital investment and thecost of production as compared with the convention-al continuous casting process. Among various pro-cesses under development,the twin- roll strip cast-i…     

电磁制动下结晶器内流体流动行为的数值研究

 数值模拟了在电磁制动作用下结晶器内金属液的流动行为,并研究了诸如磁感应强度,水口出口角度和磁场位置等各种操作条件对电磁制动效果的影响。数值模拟结果表明：应用电磁制动使结晶器内的流场有很大的改变。施加0.5 T的磁场使结晶器内金属液的表面流速最小,这一计算结果与实验结果十分吻合。为此,应用磁场对结晶器内的流场进行控制,有必要在一定的浇注条件下优化磁感应强度的大小。当磁感应强度、拉坯速度和水口出口角度一定时,磁场位置与水口浸入深度之比有一最佳值,可达到理想的电磁制动效果。     

双辊铸轧过程轧制力计算的研究

 在对熔池内金属凝固和变形的机理分析的基础上,将铸轧区域分为2个求解区域。采用流体力学中Navier Stokes方程并引入流函数,对液相区、糊状区的流变特性进行分析并建立相应的速度场,同时引入固相百分率计算模型和粘度计算模型,根据速度边界条件推导出该区域单位压力分布解析式。对于凝固区的铸轧力建模仍沿用传统热轧模型。利用上述模型进行铸轧力计算,计算结果与实测结果吻合较好,为建立双辊铸轧过程铸轧力控制策略的提供了有力的支撑。     

Physical and Numerical Simulation of Fluid Flow and Solidification at the Twin‐Roll Strip Casting Process

The fluid flow in a twin‐roll strip caster is investigated by physical and numerical simulation on a 1:1‐scale water model. A laser‐optical measurement technique (Laser Doppler Anemometry ‐ LDA) is used to validate the numerical results for the water flow. The numerical simulations are then transferred to the melt flow in the strip caster. The investigations are focused on different SEN concepts (submerged entry nozzle), a single‐nozzle system with two outlet ports and a double‐nozzle system with one outlet port each. The Influence of these concepts on the velocity, turbulence, and temperature distribution inside the liquid pool between the casting rolls and on the solidification and growth of the strip shells are investigated by numerical simulations (Computational Fluid Dynamics ‐ CFD). The non‐isothermal melt flow is calculated considering the solidification enthalpy as well as the behaviour of the solidifying melt. In addition to the numerical simulations of the melt flow inside the pool the temperature distribution in the cast strip is simulated. The SEN concept directly correlates with the temperature distribution Inside the strip. Furthermore, the surface temperature of the strip below the outlet of the roll gap is measured using a line‐scanner and is compared with the CFD simulation. In order to simulate the shape of the free surface in the liquid pool, CFD simulations of the water flow in the physical model are carried out using a Volume of Fluid model (VoF). This two‐phase model is able to reproduce free surface waves.     

双辊薄带连铸电磁侧封磁场的计算与分析

电磁侧封是双辊薄带连铸工艺中新兴的侧封技术其关键是电磁装置的设计,以在适熔池侧部获得足够大而且分布合理的电磁场.本文利用2D模型计算了电磁侧封装置产生的磁场,分析了电流、线圈、铁芯、辊环、气隙对磁场的影响规律.结果表明:影响磁场的因素按影响程度从大到小排列依次为:辊环磁导率、线圈匝数、磁头间距(气隙宽度)、电流密度、磁头宽度.除磁头间距外,各因素对磁场的影响基本呈线性.因此辊环的设计、线圈匝数与电流是增大侧封磁场的主要途径.     

Strip properties and processing in twin roll casting of stainless and low carbon steels

Metallurgical features of the twin‐roll strip casting process are discussed. The as‐cast structure of two austenitic stainless steels is evaluated using EPMA and metallography. Cleanness levels as reached in twin‐roll strip casting are compared with conventional and thin slab casting. In‐line annealing is described as a method for grain refinement. The scale layer on twin‐roll cast strip is characterised for low carbon and stainless steels.     

Study on Level Fluctuation of Twin Roll Strip Caster by Water Modeling

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浸入式水口对结晶器钢水流动与液面波动的影响

以国内某钢厂220 mm×1800 mm板坯连铸结晶器为原型,根据相似性原理建立相似比为0.6的水模型,利用粒子图像测速技术(PIV)对比不同浸入式水口(SEN)的出口角度、浸入深度及水口底部结构条件下的结晶器内流场流速特征,同时使用波高仪对液面波动振幅进行实时监测,并结合F数分析各SEN条件对结晶器内钢液流动特征.研究发现,在各浸入式水口条件下,位于结晶器液面1/4宽面处附近出现矢量流速向下的剪切流,同时在水口附近发现不规则漩涡.试验结果表明:浸入式水口的出口角度、浸入深度的增加能够强化上回旋区缓冲作用,降低结晶器液面表面流速;尽管凹底结构SEN能减弱钢液湍动能,但其对1/4宽面处剪切流速度的影响不大.另外,液面波动幅度和F数变化规律一致,且当浸入式水口出口角度15°、20°,浸入深度135 mm、145 mm条件下波幅与F数最为合理,从而减小或避免液面卷渣,提高连铸坯质量.      

Modeling of molten metal flow in a continuous casting process considering the effects of argon gas injection and static magnetic-field application

A mathematical model has been developed to analyze molten metal flow, considering the effects of argon gas injection and static magnetic-field application in the continuous casting process. The k-ɛ turbulence model is used to calculate the turbulent variables. A homogeneous fluid model with variable density is employed to tackle the molten metal-argon gas flow. The electromagnetic force is incorporated into the Navier-Stokes equation, and the effects of boundary conditions of the magnetic field on the velocity distribution near the mold wall are included. A good agreement between the numerically obtained flow-field results and measurements is obtained. The argon gas injection changes the molten metal flow pattern, mainly in the upper portion of the mold. By applying the magnetic field, values of the averaged velocity field in the bulk decrease significantly, and, especially at the top free surface, they become very small, which can cause meniscus freezing. When magnetic-field application and argon gas injection are used together, the external flow field out of the gas plume is significantly suppressed; nevertheless, flotation of gas bubbles is still active and is not affected directly by the magnetic field. Although the penetrating length of the gas plume is shortened, the argon gas bubbles in molten steel still cause fluctuation at the top free surface, which prevents the occurrence of freezing.     

水口结构对连铸结晶器内钢水流动的影响

采用雷诺平均（RANS）数学模拟方法,研究波浪形和山形水口底部结构对结晶器内钢水湍流现象及表面流速的影响。通过1∶1结晶器模型水模拟进行了验证,表明采用OA光纤测速仪对结晶器表面流速测量的结果和数值模拟结果吻合较好。研究表明波浪形水口可以抑制水口流出钢水的射流,改善结晶器内钢水流场,降低表面流速稳定液面,进而改善铸坯表面质量。     

Numerical Analysis of Electromagnetic Field and Flow Field in High Casting Speed Slab Continuous Casting Mold With Traveling Magnetic Field

 A three-dimensional mathematical model for describing the electromagnetic field and flow field of molten steel in high casting speed slab continuous casting mold with electromagnetic level stabilizer (EMLS) system was developed, in which the effects of current intensity and frequency on the electromagnetic field and flow field were considered. Simulation results indicate that the electromagnetic force (EMF) along the mold width direction presents the centre-symmetric double-peak parabola distribution. The EMLS system leads to the flow velocity of molten steel decreases, especially near the free surface. Both the EMF increases with the current intensity and frequency (in the range of optimum frequency value), so the flow velocity of molten steel in the mold decreases obviously. As the current intensity increases from 800 A to 1000 A, the maximum free surface velocity decreases from 0.515 m/s without magnetic field to 0.155 m/s and 0.12 m/s, respectively. While the current frequency increases from 2 Hz to 6 Hz, the maximum surface velocity decreases from 0.177 m/s to 0.101m/s. The molten steel flow in mold is influenced obviously by the current intensity and frequency.     

Modelling of Melt Flow and Solidification in the Twin‐Roll Strip Casting Process

A three‐dimensional mathematical model has been developed to simulate turbulent fluid flow, heat transfer and solidification in the pool of a twin‐roll strip caster. A Darcy‐porosity approach was used to study the fluid flow within the mushy solidification zone in the pool. The effect of the heat transfer coefficient and permeability constant on the flow and solidification was also predicted. It was shown that an even flow and temperature distribution of the pool can be obtained by using a suitable feeding system. The heat transfer between the rolls and the solidifying metal has a big influence on the location of the solidification end point. The permeability of the mushy zone is a key factor which affects the flow and solidification in the twin‐roll strip casting process.     

Structure of turbulent flow in a slab mold

The structure of the turbulent flow in a slab mold is studied using a water model, various experimental techniques, and mathematical simulations. The meniscus stability depends on the turbulence structure of the flow in the mold; mathematical simulations using the k-ε model and the Reynolds-stress model (RSM) indicate that the latter is better at predicting the meniscus profile for a given casting speed. Reynolds stresses and flow vorticity measured through the particle-image velocimetry (PIV) technique are very close to those predicted by the RSM model, and maximum and minimum values across the jet diameter are reported. The backflow in the upper side of the submerged entry nozzle (SEN) port (for a fixed SEN design) depends on the casting speed and disappears, increasing this process parameter. At low casting speeds, the jet does not report enough dissipation of energy, so the upper flow roll is able to reach the SEN port. At high casting speeds, the jet energy is strongly dissipated inside the SEN port, the narrow wall, and in the mold corner, weakening the momentum transfer of the upper flow roll, which is unable to reach the SEN port. At low casting speeds, meniscus instability is observed very close to the SEN, while at high casting speeds, this instability is observed in the mold corner. An optimum casting speed is reported where complete meniscus stability was observed. The flow structure at the free surface indicates a composite structure of islands with large gradients of velocity at high casting speeds. These velocity gradients are responsible for the meniscus instability.     

适合漏斗型薄板坯连铸结晶器三孔水口的水模型优化

 采用1∶1的水模型研究了5种不同底孔直径(16～28mm)的三孔水口下漏斗型薄板坯结晶器内的流场、液面特征和卷渣行为。结果表明：在常规工艺参数下,5种三孔水口下结晶器内钢液的流场都是典型的“双辊流”,且流场稳定;在5种三孔水口下结晶器液面波动都较平稳,且波动范围都在±(3～5)mm之间。5种不同水口下结晶器液面主要发生剪切卷渣,漩涡卷渣很少发生。试验得知：在水口浸入深度280mm,拉速为5m/min时,剪切卷渣发生的钢液临界表面速度是0.32m/s,与文献报道的模型计算值较吻合。在水口浸入深度280mm、拉速为5m/min的条件下,适合薄板坯连铸的最佳的三孔水口的底孔直径为22mm。