上水口环形吹氩对中间包内渣眼形成的影响

 中间包上水口环形吹氩可以在塞棒周围形成清洗钢液的环形气幕,同时部分氩气泡随钢液进入上水口内,可以减少非金属夹杂物在水口内壁的黏附,起到防止水口堵塞的作用。然而,不合理的吹氩量会导致中间包内液面渣层受过强的气液羽流冲击而形成渣眼,使得钢液裸露并发生二次氧化,严重影响铸坯质量。采用标准 k ε 湍流模型研究中间包内流体流动,采用DPM模型和VOF模型耦合方法,研究上水口环形吹氩条件下渣眼的形成及演化规律。结果表明,上水口环形吹氩在塞棒周围形成较强的上升流,塞棒上部邻近区域存在多个涡流区;在钢液涡流的影响下,中间包液渣下层远离塞棒区域,上层向塞棒区域迁移;随着吹氩量的增大,平均湍动能增大,塞棒附近钢液速度逐渐增大,钢渣界面钢液速度先增大后减小,渣眼边缘钢液速度先增大后减小然后再增大,速度与垂直方向夹角逐渐减小;增大吹氩量,中间包熔池液面形成以塞棒为中心的渣眼,渣眼面积逐渐增大。试验条件下不产生渣眼的临界吹氩量为4.2 L/min,对应的钢渣界面最大速度为0.247 m/s,与垂直方向夹角为70°。     

板坯连铸结晶器电磁制动技术及其应用

叙述了板坯连铸结晶器中应用电磁制动技术的发展、研究状况。电磁制动技术可以控制结晶器内钢液的流动，减少结晶器保护渣的卷渣，有利于结晶器内夹杂物的去除，从而提高铸坯质量，并有利于提高铸坯拉速。研究结果表明电磁制动特性取决于板坯宽度、浇铸速度、氩气流速和浸入式水口(SEN)形状等浇铸参数，介绍了各种浇铸参数对电磁制动效果的影响。     

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。     

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。     

Bubble Entrapment on Solidified Shell caused by Unsteady Steel Flow in Mold

The molten steel flow in the continuous casting mold and entrapment of inclusions and bubbles on the inner surface of the solidified shell are examined to clarify the mechanism of internal defects in steel products. Defects on steel sheets are caused by bubbles and inclusions entrapped on the solidified shell during casting. It was found that bubbles penetrate deeply due to an unbalanced time‐dependent flow. This phenomenon can be explained by the Large Eddy Simulation model, which can predict the time‐dependent flow. The number of inclusions increases as the bubble diameter and the distance of the position of entrapment from the top free surface increase. This indicates that bubbles collect inclusions while traveling in the molten steel in the continuous caster. A simple mathematical model is presented to explain the mechanism by which inclusions become attached to bubbles.     

Effect of Slide Gate and EMBr on the Transport of Inclusions and Bubbles in Slab Continuous Casting Strands

This study is to investigate the effect of electromagnetic brake (EMBr) on fluid flow and particle motion in steel slab continuous casting strands. The effect of slide gate moving on fluid flow pattern was discussed. A strong swirl and asymmetrical flow at the outports and, subsequently, inside the slab mold, was induced by slide gate. The application of EMBr would be a remedy to the swirl flow in the casting mold. Flow pattern has great influence on the trajectories of injected bubbles and nonmetallic inclusions. More bubbles tend to release from the top surface near the wide face opposite to the gate opening side without EMBr; while, they escape at the center place of the slab thickness when the EMBr was applied. Local brake type EMBr has a little effect on the overall removal fraction of nonmetallic inclusions, especially for the small ones. However, EMBr affects the distribution of inclusions on the cross section of the slab, and more inclusions were observed in the sub‐surface layer of the slab.     

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...     

Behaviour of Argon Gas Bubbles in an Electromagnetic Driven Swirling Flow

An innovative steelmaking process is suggested using an electromagnetic driven swirling flow in the up‐leg of an RH vacuum degassing vessel. The effectiveness of this new process depends on the two‐phase flow behaviour of molten steel and argon gas. A physical and a mathematical model are developed to understand the effect of electromagnetic driven swirling flows on the behaviour of gas bubbles in the up‐leg of an RH vessel. Both water model experiments and numerical simulation show the distribution and trajectories of the gas bubbles. The gas bubbles’ trajectories are spiral and move towards the centre of the up‐leg in the swirling flow field. The accumulation of gas bubbles depends on the swirling number. At the same time, the swirling flow can prolong the residence time and trajectories of non‐metal inclusions in the vessel. The viscous drag force becomes important for small bubbles in the RH degassing vessel, and small bubbles have the trend to rotate with the swirling flow.     

底吹气中间包内钢液流动及夹杂物去除模拟研究

通过40 t中间包的1:3水模型实验,对小方坯连铸6流中间包内钢液的流场进行了测定,研究了5种不同底吹气方案对中间包内钢液流动特性和夹杂物去除的影响。结果表明,在注流区吹气能延长钢水在中间包内的停留时间,减弱湍流强度,同时注流区内吹气可将气泡击碎成弥散小气泡促进了夹杂物上浮,夹杂物去除效果最佳。在近流与中流水口之间吹气,可改善各流的流动特性,中间包内的流动状况最佳,但近流处夹杂物去除效果略差。在中流和远流水口之间吹气,流场改善效果不理想。     

长水口吹氩生成微小气泡工业实验研究

在连铸生产中采用大流量长水口吹氩,并采用“冷钢片沾钢法”沾取中间包钢液试样,成功沾取了中间包钢液中微小氩气泡。冷钢片沾样表面气泡为中间包上部钢/渣界面和炉渣中氩气泡,尺寸主要位于1.0~3.0 mm,但该尺寸不能反映中间包钢液内部长水口吹氩生成气泡,冷钢片沾样内部气泡为钢液内部长水口吹氩生成的气泡。结合扫描电镜和共聚焦显微镜对沾取试样内部气泡形貌、尺寸和数量进行了分析,结果表明大部分气泡为独立圆形气泡,偶见少量粘连和聚合气泡;钢液内部氩气泡尺寸主要位于100~1000 μm,平均尺寸为500 μm左右;气泡在长水口出口及其下方较为弥散,气泡数量可达15.2 cm?2。采用扫描电镜结合能谱分析,发现部分气泡内粘附有夹杂物,有些气泡粘附多个夹杂物;气泡粘附Al₂O₃夹杂物的几率高于粘附CaO(?MgO)?Al₂O₃?SiO₂复合夹杂物的几率。      

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 Analysis of the Influences of Operational Parameters on the Braking Effect of EMBr in a CSP Funnel-Type Mold

A three-dimensional mathematical model of the magnetic field, flow field, and temperature field in a 1500 mm × 90 mm CSP funnel-type mold is used to numerically study the effect of an electromagnetic brake (EMBr) on flow and heat transfer behavior of molten steel. A number of effects of EMBr on the flow pattern and temperature distribution of molten steel are simulated. The jet flow discharge from the submerged entry nozzle (SEN) is significantly suppressed. In addition, heat transfer in the upper part of the mold increases under the influence of EMBr, which can improve the mobility of liquid steel at the meniscus and achieve low superheat casting. The relations between casting speed and magnetic flux density, and between SEN submergence depth and the installation position of the EMBr device, are taken into account to study the effects of braking on molten steel. The results show that the braking effect is weakened with an increase in either the casting speed or the SEN submergence depth. In order to insure the efficient and stable operation of a continuous casting production, the magnetic flux density should be increased by approximately 0.1 T when the casting speed increases by 1 m/min. In addition, an optimal braking effect for molten steel can be obtained when the distance between the bottom of the nozzle and the upper surface of the EMBr device is 100 mm.     

RH精炼真空度对超低碳钢夹杂物去除的影响

 大尺寸非金属夹杂物是引起超低碳钢冷轧钢板表面线状缺陷的重要原因。以IF钢为例,铸坯中大尺寸夹杂物主要有3类,即结晶器保护渣卷入后被凝固坯壳捕获;连铸过程中钢水二次氧化产生且未上浮去除的;钢液中未充分去除的夹杂物在浸入式水口处粘连、堵塞,后续堵塞物脱落被凝固坯壳捕获。钢液一次脱氧生成的夹杂物中,不低于100 μm的夹杂物在RH处理过程中较容易去除,100 μm以下的夹杂物受钢液的流动影响较大,特别是不超过20 μm的夹杂物由于其上浮时间长、钢液流动的跟随性好,去除难度较大。RH是超低碳钢最重要的精炼设备,也是夹杂物去除的关键环节,研究RH去除20 μm夹杂物的新技术具有重要的意义。研究了RH脱碳结束加铝后真空度对夹杂物去除的影响,创新性提出了低真空度去除不超过20 μm夹杂物的新技术。研究结果表明,与高真空度处理工艺(常规工艺)相比,低真空度(压力5 kPa)处理的钢液中夹杂物数量降低更显著,中间包钢液总氧质量分数平均降低0.000 2%,钢液增氮水平相当。冷轧钢板因炼钢原因导致的线状缺陷降级率比常规工艺降低了29%。夹杂物在钢液中的跟随性理论分析表明,低真空度处理工艺下RH内钢液循环流量和钢液流速减小,降低了RH处理过程中夹杂物随钢液的跟随性,提高了不超过20 μm夹杂物的去除效率,有效改善了水口堵塞程度、提高了轧板表面质量。     

Fluid Flow-Related Transport Phenomena in Steel Slab Continuous Casting Strands under Electromagnetic Brake

In the current study, a three-dimensinal (3D) numerical model is built to investigate the effect of a local-type electromagnetic brake (EMBr) on the fluid flow, heat transfer, and inclusion motion in slab continuous casting strands. The results indicate that the magnetic force affects the jet characteristics, including jet angle, turbulent kinetic energy, and its dissipation rate. To reduce the top surface velocity and stabilize the top surface, the magnetic flux intensity should be larger than a critical value. With a 0.39 T magnetic flux intensity, the top surface velocity and its fluctuation can be well controlled, and less slag is entrained. The motion of argon bubbles is also studied. More bubbles, especially >2.0-mm bubbles, escape from the top surface between the mold submerged entry nozzle (SEN) and \frac14 \frac{1}{4} width for the case with a 0.39 T EMBr. This may push the top slag away and create an open “eye” on the top slag. Small bubbles (≤1 mm) tend to escape from one side of wide face no matter with or without EMBr, which is induced by the swirl flow from the SEN outport. EMBr has a little effect on the overall removal fraction of inclusions; however, it affects the local distribution of inclusion in the slab. With EMBr, more inclusions accumulate the region just below the surface, thus a worse subsurface quality, whereas the inner quality of the slab is better than that without EMBr. For heat transfer in the mold, the heat flux on the narrow face and the area of possible break-out zones can be reduced by using EMBr. Prevention of bias flow and/or asymmetrical flow in mold by EMBr is also concluded.     

Three-dimensional analysis of molten steel flow in slab continuous casting mould with rotated ports in submerged entry nozzle

Abstract

The purpose of this study is to develop a three-dimensional (3D) analysis system capable of analysing the flow field of molten steel in the slab continuous casting mould with rotated ports in the submerged entry nozzle. The ultimate goal is to obtain the optimal design for the entry ports of the submerged nozzle, which can introduce favourable flow patterns to remove non-metallic inclusions and avoid entrapment of molten slag and casting powder to produce steel slab of high cleanliness. In this study, a computational fluid dynamics technique, Sola-Surf, is employed to conduct the 3D fluid flow analysis. The technique has the capability of treating fluid flow problems with a free surface that slightly vibrates. The slightly vibrating free surface presents fairly accurately the behaviour of the molten slag–casting powder layer in the continuous casting mould. The developed simulation system is then tested on a slab continuous casting mould to analyse the fluid flow behaviour of molten steel under various nozzle designs. The design conditions include submerged depth of the nozzle, tilted angle of the nozzle port, and rotated angle of the nozzle port. The results of the simulations show that of the various design factors rotation of the nozzle entry ports has the greatest effect on the flow pattern. It can prolong the residence time of the molten steel and stabilise the molten slag–casting powder layer, which is very favourable for obtaining continuous casting slag of high cleanliness.     

Study on fluid flow in the mold with electromagnetic braking

Multiphase flow control w ith electromagnetic braking( EMBr) is w idely used in the continuous casting of steel slabs. The basic aim of the flow control system of the process is to deliver molten steel from the ladle through the tundish,upper tundish nozzle,slide gate,and submerged entry nozzle into the mold region w ith minimal defects. This requires the optimization of turbulence levels at a meniscus to avoid both an excessively fast flow( which creates high fluctuations of the meniscus level in addition to slag entrapment,surface nonuniformities,and surface defects) and insufficient slow flow( w hich leads to meniscus solidification,inadequate flux infiltration,and surface defects). In this study,a Eulerian-Lagrangian approach is used to investigate the effects of EM Br and Ar bubble injection on the surface flow velocity. The results show that high Ar injection rates can lead to an increase in surface velocity.     

日本高磁感取向硅钢连铸坯生产技术

为了生产高磁感取向硅钢板用板坯,钢中添加Bi：0．0005％～0．05％,加入时,在中间包的外侧的钢水池中形成上围堰,并且用被覆了铁的圆桶,桶内装入Bi或Bi的合金加入到钢水中,钢水流量除以喷嘴内面积求出浸渍喷嘴内的钢水流量密度Q（≥0．9t／（m^2·s^-1））,为了使结晶内液面形成旋流,采用电磁搅拌,其推力F要满足关系式（3．000≤F≤10．000Pa·m^-1）。     

电磁搅拌对特大方坯结晶器内流场及温度场影响

以某厂断面为410 mm × 530 mm的特大方坯结晶器为原型,利用ANSYS有限元软件建立三维数值模型,研究电磁搅拌对结晶器流场及温度场的影响。施加电磁搅拌后,钢液受到径向电磁力,液面呈现旋转流动趋势。结晶器内钢液最大切向速度随着电流的增加而增大,随着频率的增加而减小。电磁搅拌的电流大小由0 增加到500 A时,液面波动由1.21 mm增加到4.35 mm。电磁搅拌能够使钢水的高温区局限于连铸结晶器上部,钢水温度更加均匀。同时钢液的水平旋流能够抑制初生坯壳的生长,降低坯壳的生长速度,使结晶器出口处坯壳厚度变薄。综合分析,该厂在实际生产时合理的电磁搅拌的电流大小应为400 A,频率为1.5 Hz,此时钢渣液面波动约为2.73 mm,温度场较为均匀。      

汽车钢板表面线状缺陷控制技术

针对线状缺陷是制约汽车钢板表面品质的关键问题,对汽车钢种热轧板和冷轧板的表面缺陷进行SEMEDS分析。研究发现保护渣是引起汽车板线状缺陷的主要原因。提高钢液洁净度可以缓解水口堵塞,进而减少保护渣卷入与内壁大尺寸夹杂物脱落,此外优化结晶器流场也可以防止卷渣的发生。某钢厂通过工艺优化,使加铝前钢液溶解氧降低明显,并有效减少连铸过程钢液的二次氧化,提高了钢液洁净度。此外还通过对浸入式水口结构进行优化,降低了结晶器上回流强度,使液面波动明显减小。采取上述工艺优化,轧板表面线状缺陷的发生率显著降低。     

铝镇静冷镦钢CaS结瘤机理及改进

 对铝镇静冷镦钢在浇铸过程中出现的浸入式水口结瘤问题进行了系统研究,结瘤物中主要为C12A7(12CaO·7Al₂O₃)、CaS以及少量的MgO、TFe等,CaS所占比例达到36.91%,CaS含量过高,是造成水口结瘤的主要原因。结合生产过程分析发现,当钙处理时钢水中硫含量偏高,或喂入钙含量过多时,则生成大量的CaS夹杂,促使水口结瘤。通过改进脱氧造渣工艺、优化钙处理工艺等一系列措施,将钙处理前钢水中硫质量分数控制在0.005 0%以下,钙处理后钢水中钙质量分数控制在0.001 4%～0.002 6%,使钢水中Al₂O₃夹杂改性充分,同时避免生成CaS夹杂造成水口结瘤,有效解决了CaS夹杂引起的水口结瘤问题,提高了铝镇静冷镦钢钢水浇注性能,使连浇炉数由最低的10炉/中间包提高至16炉/中间包以上。