Effects of Electromagnetic Brake,Mold Curvature and Slide Gate on Fluid Flow of Steel in a Slab Mold

The influence of mold curvature, slide gate and magnetic forces on the steel flow in a slab mold was studied with a 3‐D mathematical model. The slide gate application induces a biased flow toward the mold side where its opening is located in the submerged entry nozzle (SEN). Turbulence and asymmetry of flows are more intense in a curved mold than in a straight mold. The effect of an electromagnetic brake (EMBr), located in the discharging ports to control flow turbulence, is only appreciable when magnetic flux density is higher than 0.1 T. The magnetic flux density does not affect the velocity profile in the discharging ports in the SEN because its construction material is insulated. Increasing the magnetic flux density leads to a decrease of the discharging jets angle and to the elimination of the two upper roll flows. The use of the EMBr in a curved mold equipped with a slide gate eliminates the meniscus velocity spikes observed in the mold corners. These results help to demonstrate that EMBr eliminates the asymmetry in a curved mold even under the excessive turbulent conditions existing in curved continuous casting molds.     

Oscillating Jet Flows in a Thin Slab Mold and their Influence on Meniscus Stability

Sustainability of oscillating liquid steel jets discharging from a submerged, two‐port entry nozzle in thin slab molds has been studied through a water model and mathematically simulated using the Reynolds Stress Model of turbulence combined with the Volume of Fluid model to capture dynamics of the water‐air interface. At casting speeds of 5 and 7 m/min, both jets yield long range time‐dependent Reynolds stresses with high gradients which induce oscillating upper roll flows in the mold providing permanent flow asymmetry. Intermittent vortexes at the water‐air interface are generated by the interaction between the flow arising from the upper roll toward the SEN and a high velocity flow which goes through the gap between the SEN shaft and mold wall oriented toward the narrow wall. These flows gather at expansion of the mold funnel generating intermittent vortexes. Meniscus oscillation decreases in narrower molds even at high casting speeds. At lower casting speed like 5 m/min meniscus oscillation decreases considerably in wide and narrow molds. Turbulence understanding in thin slab molds would help to design submerged entry nozzles for higher steel casting speeds through wide molds with better meniscus stability.     

Cyclic Turbulent Instabilities in a Thin Slab Mold. Part I: Physical Model

A water-physical model of a funnel-type thin slab mold fed by a two-port submerged entry nozzle (SEN) was employed to characterize the flow of liquid steel using dye tracer, particle image velocimetry, and video recording experiments. The overflow fluid flow pattern was the typical double-roll flow. A cyclic, low-frequency (≈0.01 s⁻¹), and energetic flow distortion of a short-lived (8 to 12 seconds) inducing high meniscus oscillation was identified. Its intensity grew with high casting speeds (5 and 7 m/min) and with a shallow SEN immersion position (200 mm from the meniscus level to the SEN tip). This distortion originated from the apparent existence of vortex flows located below the two discharging jets, which are formed by shear stresses in their ends that act on the surrounding fluid. These vortexes exert momentum transfer upward through a cascade mechanism from the lowest part of the discharging jets until reaching the region close to the SEN tip. This cascade momentum transfer widens the separation of both jets, enhancing the fluid velocities of the upper rolls, which promotes a high-amplitude standing wave. It is inferred, based on the experimental results, that this flow distortion originated from an instantaneous unbalance of the turbulent kinetic energy in the discharging jets. The negative production of kinetic energy is ascribed as the source of this unbalance, which is compensated by a higher contribution of the turbulent kinetic energy through mean convection and turbulent transport mechanisms manifested through higher velocities. After the restoration of the energy balance, the system yields a stable meniscus to repeat the low-frequency cycle.     

Dynamics of coupled and uncoupled two-phase flows in a slab mold

Two-phase flows in a mold of a slab caster are studied using water modeling, particle-image velocimetry (PIV), and computational fluid-dynamics techniques. Two-way coupled flows are observed in liquidgas systems, because both phases influence each other’s momentum transfer. In addition to this concept, PIV measurements indicate the existence of structurally coupled flows, where the velocity vectors of both phases observe similar orientations. When the drag forces of the liquid, exerted on the bubbles, exceed a certain value of the inertial forces of the liquid phase, at high mass loads of gas (ratio of mass flow rates of the gas phase and the liquid phase), the flow becomes structurally coupled. These types of flows promote large oscillations of the meniscus level. Two jets, liquid and bubble, were identified; the latter always reported larger angles than the first, independent of the gas load. Thus, a gas-rich jet is located closer to the lower edge of the submerged entry nozzle (SEN) port, and the liquid-rich jet is found above this position. The liquid-jet angle approaches that of the SEN port when the flow becomes structurally coupled. Structurally uncoupled flows report gas jets that follow torrent-type patterns which are well explained using a multiphase fluid-dynamics model. Structurally coupled flows yield gas jets with a continuous pattern.     

薄板坯连铸结晶器内涡流及卷渣行为的研究

利用1／4水模型对薄板坯连铸结晶器内的涡流及卷渣行为进行观察研究。在实验中考察了水口形状、水口浸入深度和浇铸速度等对漩涡及卷渣行为的影响,并考察了偏流以及在水口与结晶器宽面之问加翼片,阻止结晶器表面流股相互流动的漩涡（卷渣）现象。     

Investigation of Fluid Flow and Steel Cleanliness in the Continuous Casting Strand

Fluid flow in the mold region of the continuous slab caster at Panzhihua Steel is investigated with 0.6-scale water model experiments, industrial measurements, and numerical simulations. In the water model, multiphase fluid flow in the submerged entry nozzle (SEN) and the mold with gas injection is investigated. Top surface level fluctuations, pressure at the jet impingement point, and the flow pattern in the mold are measured with changing submergence depth, SEN geometry, mold width, water flow rate, and argon gas flow rate. In the industrial investigation, the top surface shape and slag thickness are measured, and steel cleanliness including inclusions and the total oxygen (TO) content are quantified and analyzed, comparing the old and new nozzle designs. Three kinds of fluid flow pattern are observed in the SEN: “bubbly flow,” “annular flow,” and an intermediate critical flow structure. The annular flow structure induces detrimental asymmetrical flow and worse level fluctuations in the mold. The SEN flow structure depends on the liquid flow rate, the gas flow rate, and the liquid height in the tundish. The gas flow rate should be decreased at low casting speed in order to maintain stable bubbly flow, which produces desirable symmetrical flow. Two main flow patterns are observed in the mold: single roll and double roll. The single-roll flow pattern is generated by large gas injection, small SEN submergence depth, and low casting speed. To maintain a stable double-roll flow pattern, which is often optimal, the argon should be kept safely below a critical level. The chosen optimal nozzle had 45-mm inner bore diameter, downward 15 deg port angle, 2.27 port-to-bore area ratio, and a recessed bottom. The pointed-bottom SEN generates smaller level fluctuations at the meniscus, larger impingement pressure, deeper impingement, and more inclusion entrapment in the strand than the recess-bottom SEN. Mass balances of inclusions in the steel slag from slag and slab measurements show that around 20 pct of the alumina inclusions are removed from the steel into the mold slag. However, entrainment of the mold slag itself is a critical problem. Inclusions in the steel slabs increase twofold during ladle changes and tenfold during the start and end of a sequence. All of the findings in the current study are important for controlling slag entrainment.     

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.     

Combined Electromagnetic Tomography for Determining Two-phase Flow Characteristics in the Submerged Entry Nozzle and in the Mold of a Continuous Casting Model

This article describes experiments on the combined determination of the distribution of liquid metal and argon in the submerged entry nozzle (SEN) and of the flow in the mold of a small-scale physical model of a continuous slab caster. For visualizing the metal distribution in the SEN, mutual inductance tomography (MIT) is applied, while the flow in the mold is determined by contactless inductive flow tomography (CIFT). The results of the latter are validated in part by ultrasonic Doppler velocimetry (UDV). Accompanying measurements provide information about the levels in the tundish and in the mold, as well as on the pressure in the SEN. Depending on the gas flow rate, various flow regimes are identified, among them pressure and mold level oscillations, transitions between double and single vortex flows, and transient single port ejections.     

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.     

板坯连铸结晶器液面的周期性瞬态特征

 采用1[∶]1水模型和工业试验研究了常规板坯连铸结晶器液面的瞬态特征。研究发现,常规板坯结晶器液面存在“周期性畸变”。该现象表现在液面每隔20～30 s出现约5 s的畸变。畸变期间窄面处液面凸起,宽度1/4处液面凹陷且表面流速达到极大值,易导致卷渣。定义上次液面畸变结束到本次畸变结束时间为畸变周期。水模型结果显示,提高拉速畸变周期减小,而提高水口浸入深度与倾角液面畸变周期增大,但改变这些参数不能消除周期性畸变。对液面畸变周期的影响程度为：水口倾角>拉速>水口浸入深度。工业试验也证实液面周期性畸变的确存在。适当增大水口倾角有利于减少液面周期性畸变导致的卷渣。     

连铸机结晶器流场与温度场和夹杂物排除数理模拟

以板坯连铸机结晶器为研究对象,采用数值模拟和水模试验相结合的研究方法,模拟了两种水口浇注条件下结晶器内温度、速度场分布以及钢中夹杂物上浮排除状况.试验发现,原有水口存在上循环弱、热交换慢、保护渣融化不均匀等缺点是铸坯出现表面纵裂纹和夹杂物上浮排除困难的主要原因;而新水口增强了结晶器内上循环速度,促进了钢中夹杂物的上浮.工业大生产应用结果表明,新水口能明显地降低板坯表面纵裂纹和改善铸坯洁净度.     

Effect of electromagnetic stirring on flow field in mold under submerged entry nozzle clogging

A physical model with mercury as analog was developed to investigate the influences of electromagnetic stirring( EMS) on flow field in slab continuous casting when the submerged entry nozzle( SEN) was clogged with different clogging rates( 0,10%,25%,and 50%). The flow field in mold under different EMS currents( 0,40 A,and 60 A) was measured by an ultrasonic Doppler velocimeter. The results proved that the flow field in the mold was a typical double roll structure under non-clogging SEN. As the SEN clogging rate increased,the flow field structure was transformed from a double roll to asymmetry flow. When the clogging rate reached 50%,the up circulation disappeared on the clogged side. The zone under the meniscus near the narrow face was a non-flowing area. EMS could correct bias flowcaused by SEN clogging and improve the symmetry of the flow field during SEN clogging.     

Flow Oscillations and Meniscus Fluctuations in a Funnel-Type Water Mold Model

Transient flows in a funnel-type continuous casting process model were studied experimentally to investigate the flow oscillations inside the mold and the meniscus fluctuations. A full-scale water model was used with dimensions of 2000 mm (length) × 1350 mm (width) × 100 mm (thickness). Particle image velocimetry (PIV) was employed to measure the flow oscillations. To minimize high shear flow errors near the submerged entry nozzle (SEN) exit, the window deformation technique was adopted. The meniscus levels were extracted by edge-detection image processing. Three types of SEN and two funnel thicknesses (180 mm and 220 mm) were tested to examine the flow characteristics under five flow rates (10, 20, 30, 40, and 50 m³/h). The vortex generation mechanism inside the mold was analyzed across the various mold conditions studied.     

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。     

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.     

Three-Dimensional Flow Behavior Inside the Submerged Entry Nozzle

According to various authors, the surface quality of steel depends on the dynamic conditions that occur within the continuous casting mold’s upper region. The meniscus, found in that upper region, is where the solidification process begins. The liquid steel is distributed into the mold through a submerged entry nozzle (SEN). In this paper, the dynamic behavior inside the SEN is analyzed by means of physical experiments and numerical simulations. The particle imaging velocimetry technique was used to obtain the vector field in different planes and three-dimensional flow patterns inside the SEN volume. Moreover, large eddy simulation was performed, and the turbulence model results were used to understand the nonlinear flow pattern inside the SEN. Using scaled physical and numerical models, quasi-periodic behavior was observed due to the interaction of two three-dimensional vortices that move inside the SEN lower region located between the exit ports of the nozzle.     

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     

宽板坯结晶器浸入式水口结构优化的数值模拟

以某钢厂宽板坯连铸结晶器为研究对象,利用商业软件PHOENICS建立一个三维有限差分模型,模拟宽板坯连铸结晶器内钢液的流动分布.通过分析水口底型、倾角、插入深度等工艺参数对钢液面波动、流股对结晶器窄面的冲击力及涡心高度的影响,得出适用于宽规格结晶器的合理的浸入式水口.通过研究,为优化宽板坯结晶器内钢液的流场及浸入式水口的设计提供了科学依据.     

吹氩板坯连铸结晶器内钢水流态

 采用1[∶]1水模型和工业插钉法研究了吹氩板坯连铸结晶器内钢水流态,并讨论了通钢量、吹氩量、水口浸入深度与水口结构对结晶器流态的影响。水模型结果发现,结晶器内宏观流态主要包括双股流和单股流,钢水通量和吹氩量是影响结晶器内钢水流态的决定性因素。为得到双股流,应采用高通钢量和低吹氩量,缩小断面、增大浸入深度和使用凸底水口有利于双股流形成。基于水模型结果,为维持结晶器内双股流态,在实际浇铸中提出减少连铸过程吹氩量低于临界吹氩量,在宽断面和低拉速下使用凸底水口等措施。工业插钉试验结果与水模型吻合较好,这表明水模型结果可指导现场浇铸实践。     

The Effects of Electromagnetic Brake on Liquid Steel Flow in Thin Slab Caster

Computational fluid dynamics (CFD) model with magneto hydro dynamics (MHD) is developed for a thin slab caster to investigate the effects of electromagnetic brake (EMBr) on liquid steel flow in continuous casting mold and to determine the EMBr practices which lead to optimal flow structure. Particle Image Velocimetry (PIV) tests in water model and meniscus flow measurements in real caster are performed to validate the predictions obtained with CFD models. The performance of different submerged entry nozzle designs, SEN 1 and SEN 2, are evaluated. The effects of nozzle submergence in relation to the applied magnetic field on mold flow structure are quantified. There are significant differences between flow structures obtained with SEN 1 and SEN 2, even though both designs have fundamental similarities and contain four ports. EMBr mainly reduces the meniscus velocities for SEN 2 as opposed to the foremost influence of EMBr for SEN 1 that is to significantly slow down the downward jet coming from the bottom ports. In addition, reducing the EMBr strength for shallow nozzle submergence and increasing the EMBr strength for deep nozzle submergence help to maintain similar meniscus activity for all conditions.