水口吹氩工艺参数对180mm×700mm板坯结晶器宽面含气率分布的影响

通过建立的6:10几何相似比的模拟180mm×700 mm板坯结晶器的水模型（108 mm×420mm）,使用数字图像处理技术,分析了水量2.54~3.16 m³/h,气量0.037~0.110 m³/h,滑板开口度51%~100%,水口浸入深度78~108 mm等参数对水口吹氩板坯结晶器水模型内宽面含气率分布的影响。结果表明,当水量3.16 m³/h（相当于原型1.50m³/h）,气量0.037 m³/h（原型0.120 m³/h）,水口底部形状为凹形,滑板开口度51%,水口浸入深度78 mm（原型130 mm）时,水模型内气泡分布相对均匀,有利于流场的改善和夹杂的上浮去除。180 mm×700mm铸坯的生产性试验表明,采用优化的参数生产的超低碳钢连铸坯中≥30μm的夹杂物量和夹杂物总量均显著降低。     

板坯连铸结晶器内氩气泡行为的模拟研究

针对氩气泡在板坯连铸结晶器中的运动行为,以190 mm×1 900 mm板坯连铸结晶器原型为研究对象,采用水力学模型及数值模拟的方法,重点研究了拉速为1.7 m/min时不同水口吹气量对结晶器内气泡大小、气泡分布、液面波动、渣-金行为等的影响。研究结果表明:随着水口吹气量增加,气泡尺寸逐渐增加,结晶器窄边气泡数量不断减少,气泡大都聚集在水口附近上浮,水口吹气量是引起乳化卷渣、水口附近液面裸露及卷渣等的主要因素。     

静磁场下气泡在板坯连铸结晶器内运动行为的物理模拟

以水银和氩气作为模拟介质,通过物理模拟研究了高拉速板坯连铸结晶器内电磁制动和水口吹氩耦合作用下的气泡运动和分布行为.采用电阻探针测量了结晶器内气泡的运动和分布情况,分析了磁场、吹氩量等不同工艺参数对气泡占空比、气泡数量和气泡脉冲宽度的影响规律.实验结果表明:在一定的拉速条件下,施加磁场改变了气泡在结晶器内的分布规律,有利于气泡的上浮,降低了气泡在结晶器内的冲击深度,减少了到达结晶器窄面的气泡数量;磁场的施加和吹氩量的增加都使得脉冲宽度较大的气泡数量增多,且主要集中在结晶器1/4宽度和水口之间区域.

     

水口吹氩工艺板坯结晶器内气泡运动行为的物理模拟

以1300 mm × 230 mm板坯连铸结晶器的相似比0.4的物理模型,研究了拉速1.1 m/min、水口插入深度160 mm、水口吹气量0～15 L/min时连铸结晶器内气泡的运动行为,及其对钢液流股冲击深度、液面波动和液面裸露的影响。实验结果表明,随水口吹气量增加,结晶器内气泡的数量和尺寸都有所增加,气泡在钢液内水平方向扩散范围增大,且气泡最大穿透深度亦增加;当水口吹气量增大到5 L/min时,气泡逸出后在液面由全部向水口方向运动变为以集中逸出位置为中心的四散运动。     

结晶器内氩气泡分布及钢渣界面波动行为

建立了1∶0.6的结晶器水模型和结晶器原型数学模型,采用高速摄像机及分析软件研究了连铸工艺参数对结晶器水模型内气泡分布行为的影响;采用离散相模型和VOF模型的数学模拟方法,研究了连铸工艺参数对结晶器内气泡分布和钢渣界面波动行为的影响。结果表明,通过数学模拟获得的结晶器内气泡分布和水模型试验结果吻合性较好;增加吹氩量,结晶器内氩气泡尺寸增大,分布更均匀;吹氩可以降低结晶器窄面附近区域钢液的波高,但会导致水口附近波动加剧;增大拉速时,结晶器内氩气泡尺寸减小,分布更均匀,结晶器窄面波高增大,水口附近液面波高显著降低;增大水口倾角和浸入深度,有助于抑制水口附近和窄面附近的波动,气泡在结晶器内的分布相对较为均匀,气泡尺寸变化不显著。拉速为1.2 m/min、水口倾角为15°、水口浸入深度为160 mm,较优的吹氩量为4 L/min。研究结果可以为优化工艺参数、防止钢液卷渣、提高铸坯质量提供理论依据。     

宽板坯连铸结晶器SEN结构和操作参数优化试验研究

以宽板坯连铸结晶器的4种断面宽度为原型,采用1∶1水模型进行试验,得到了在结晶器液面波动较合理时,倾角、底部形状和吐出孔数量等最优的浸入式水口结构参数,以及水口浸入深度、水口吹气量、拉速范围等最优的工艺操作参数.     

宽板坯连铸结晶器内氩气分布的水模型

 针对塞棒、上水口吹氩时,吹入的氩气有多少进入到结晶器钢水内和氩气在结晶器断面上如何分布的问题,采用1：1水模型,重点研究了吹气量、吹气方式、拉速、浸入式水口倾角等工艺参数对不同宽度结晶器内气体分布状况的影响。结果表明,吹气量和吹气方式对结晶器内气体分布几乎没有影响,而拉速和水口倾角基本上就决定了宽度方向上的气体分布状况。小的结晶器断面宽度、小的水口倾角、高拉速时窄面附近含气比例更高,氩气泡更易被凝固坯壳所捕捉而使铸坯产生气泡缺陷。     

板坯结晶器水模型内气泡运动行为的数学模拟

建立了吹氩板坯结晶器水模型内气泡运动行为的数学模型.以水模型实验获得的整个结晶器内各气泡尺寸和数量浓度为气泡的初始条件,对不同尺寸气泡的运动行为进行数值模拟.结果表明:当水流量为2.54 m3/h,气流量为0.037m3/h,水口浸入深度为78 mm时,气泡都分布在上回流区,没有卷入下回流区.较大的气泡在水口附近上浮,较小的气泡在距离水口较远的区域上浮.这和实验结果相吻合.     

宽板坯连铸结晶器内卷渣现象试验研究

结合宽板坯连铸结晶器的4种断面尺寸,采用1:1水模型进行试验,研究了浸入式水口吹气量、水口浸入深度、水口吐出孔数、水口底部形状、拉速和结晶器断面宽度等工艺参数对结晶器内流体流动行为的影响情况,观察到结晶器内水口周围有旋涡卷渣和液面扰动卷渣,断面1/4区域是液面扰动卷渣,窄面区域有"类旋涡"卷渣和剪切卷渣.结果表明,结晶器内的卷渣与各种工艺参数是相关的,对工艺参数进行优化,就可减少卷渣的发生.     

浸入式水口堵塞过程板坯结晶器内流动与液面波动的模拟

用水模型研究拉速为1.4 ~2.4 m/min的220 mm x 1 300 mm板坯连铸结晶器浸入式水口发生 堵塞和吹氧时,结晶器内的液面与流动行为。结果表明,水口发生堵塞时,水口两侧的流股不对称,气泡的平 均直径减小,气泡进入结晶器的深度增加,引发卷渣和气泡缺陷的机率将明显增加。     

Transient Asymmetric Flow and Bubble Transport Inside a Slab Continuous-Casting Mold

A one third scale water model experiment was conducted to observe the asymmetric flow and vortexing flow inside a slab continuous-casting mold. Dye-injection experiment was used to show the evolution of the transient flow pattern in the liquid pool without and with gas injection. The spread of the dye was not symmetric about the central plane. The flow pattern inside the mold was not stationary. The black sesames were injected into water to visualize the vortexing flow pattern on the top surface. The changes of shape and location of single vortex and two vortices with time had been observed during experiments. Plant ultrasonic testing (UT) of slabs was used to analyze the slab defects distribution, which indicated that the defects are intermittent and asymmetric. A mathematical model has been developed to analyze the time-dependent flow using the realistic geometries, which includes the submerged entry nozzle (SEN), actual mold, and part of the secondary cooling zone. The transient turbulent flow of molten steel inside the mold has been simulated using the large eddy simulation computational approach. Simulation results agree acceptably well with the water model experimentally observed and plant UT results. The oscillating motions of jet and the turbulence naturally promote the asymmetric flow even without the effects of slide gate nozzle or the existence of clogs inside the SEN. The periodic behavior of transient fluid flow in the mold is identified and characterized. The vortexing flow is resulted from asymmetric flow in the liquid pool. The vortices are located at the low-velocity side adjacent to the SEN, and the positions and sizes are different. Finally, the model is applied to investigate the influence of bubble size and casting speed on the time-dependent bubble distribution and removal fraction from the top surface inside the mold.     

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.     

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。     

连铸浸入式水口水模型研究

为控制结晶器内流场，对浸入式水口的底部和侧孔形状进行了研究，确定了合适的底部及侧孔形状。     

Large Eddy Simulations of the Effects of EMBr and SEN Submergence Depth on Turbulent Flow in the Mold Region of a Steel Caster

Transient turbulent flow in the mold region during continuous casting of steel is related to many quality problems, such as surface defects and slag entrainment. This work applies an efficient multi-GPU based code, CUFlow, to perform large eddy simulations (LES) of the turbulent flow in a domain that includes the slide gate, SEN, and mold region. The computations were first validated by comparing the predicted surface velocity with plant measurements. Then, seven LES simulations were conducted to study the effects of casting speed, electromagnetic braking (EMBr) field strength, and submerged entry nozzle (SEN) depth on the transient flow. The results show that EMBr has an important influence on flow inside the SEN, in addition to flow in the mold. With EMBr, an “M-shaped” flow profile is seen inside the SEN. The swirling flow behavior in the SEN and ports is more symmetrical at high casting speed and with higher EMBr strength. The position of the SEN ports relative to the peak magnetic field affects the EMBr performance. The results confirm and quantify how applying EMBr greatly lowers both the magnitude and turbulent variations of the surface velocity and level profile.     

Mathematical simulation and physical modeling of unsteady fluid flows in a water model of a slab mold

Fluid flow of water in a model of a slab caster has been simulated using the large eddy simulation (LES) computational approach, and the simulated results are compared with experimental measurements performed using digital particle image velocimetry (DPIV) techniques. Simulation results agree acceptably well with the experimental measurements of instantaneous velocity fields. Flow patterns change with time as a consequence of the vertical oscillation of the jet core. These oscillations are originated by the residual Reynolds stresses that characterize turbulent flows. The asymmetry of fluid flows caused by these stresses provides biased flows. Thus, turbulence originates natural biasing effects without the influence of other operating factors such as the slide gate opening, gas bubbling, or inclusions clogging of the submerged entry nozzle (SEN). Instantaneous velocities follow periodical behaviors with time whose frequencies increase with increases of flow rate of liquid. Periodical flow changes originate velocity spikes, at some given casting speed, which are physically and mathematically identified. These sudden changes of fluid velocities are responsible of unsteady phenomena associated with fluid dynamics during steady operations of the mold.     

Computational and experimental study of turbulent flow in a 0.4-scale water model of a continuous steel caster

Single-phase turbulent flow in a 0.4-scale water model of a continuous steel caster is investigated using large eddy simulations (LES) and particle image velocimetry (PIV). The computational domain includes the entire submerged entry nozzle (SEN) starting from the tundish exit and the complete mold region. The results show a large, elongated recirculation zone in the SEN below the slide gate. The simulation also shows that the flow exiting the nozzle ports has a complex time-evolving pattern with strong cross-stream velocities, which is also seen in the experiments. With a few exceptions, which are probably due to uncertainties in the measurements, the computed flow field agrees with the measurements. The instantaneous jet is seen to have two typical patterns: a wobbling “stair-step” downward jet and a jet that bends upward midway between the SEN and the narrow face. A 51-second time average suppressed the asymmetries between the two halves of the upper mold region. However, the instantaneous velocity fields can be very different in the two halves. Long-term flow asymmetry is observed in the lower region. Interactions between the two halves cause large velocity fluctuations near the top surface. The effects of simplifying the computational domain and approximating the inlet conditions are presented.     

Turbulent flow of liquid steel and argon bubbles in slide-gate tundish nozzles: Part II. Effect of operation conditions and nozzle design

A three-dimensional (3-D) finite-volume model, developed and validated in Part I of this two-part article, is employed to study steady-state two-phase turbulent flow of liquid steel and argon bubbles through slide-gate tundish nozzles. Parametric studies are performed to investigate the effects of gas injection, slide-gate orientation, casting speed, gate opening, bubble size, port angle, and port shape on the flow pattern and characteristics of the jet exiting the nozzle port. Argon gas injection bends the jet angle upward, enhances the turbulence level, and reduces the size of the backflow zone. Gas injection becomes less influential with increasing casting speed. The off-center blocking effect of the slide gate generates an asymmetric flow that changes with the gate orientation. The 0-deg gate orientation creates the worst biased flow between the two ports. The 90-deg orientation generates significant swirl and directs the jet slightly toward one of the wide faces. The 45-deg orientation generates both types of asymmetry and, thus, appears undesirable. The horizontal jet angle indicates asymmetric flow in the horizontal plane. It increases with decreasing gate opening and decreasing gas injection rate and ranges from 3 to 5 deg. Most jet characteristics reach their maximum or minimum values near the critical opening of 60 pct (linear).Larger bubbles exert a greater influence on the flow pattern. The vertical jet angle becomes steeper with a steeper port angle and more slender port shape. These results will be useful for nozzle design and for future modeling of flow in the mold.     

Vortex characteristics due to nozzle clogging in water caster mould: modelling and validation

In continuous slab casting, clogging in the submerged entry nozzle (SEN) ports leads to flow asymmetry and vortex formation in the mould. Knowledge of vortexing and its influence on product quality is fundamental for defect-free production. In this study, the interconnected effects of nozzle clogging and SEN submergence depth, variation on flow asymmetry and vortex characteristics in a 0.4 scale water caster have been characterised by CFD investigation and validated with experimental results from the authors’ previous work. Mean flow velocities at the sub-meniscus and near the port exit predicted by the computational model are compared with the time-averaged values of the impeller probe velocity measurements and found to be in reasonable agreement. Three different clogging conditions (0, 33 and 66% in the left port of the SEN) for SEN submergence depth of 60?mm are studied and the 66% clogging produced vortices having largest diameter, which is consistent with the experimental observations. The effects of SEN submergence depth on flow asymmetry and vortexing are investigated with three different conditions – 40, 60 and 80?mm. It is found that the shallow SEN submergence depth (40?mm) produces vortices of largest diameter and the flow is most stable for a SEN submergence depth of 60?mm among the three cases. Vortex bending towards the SEN as noticed in the experimental observations is also observed in the computational study. This work illustrates the possibility of capturing features of vortexing using validated CFD model.