电磁场作用下板坯连铸结晶器内的弯月面行为

用Pb-Sn-Bi低熔点合金进行了热模拟实验.从液面波动人手,研究了在单条形电磁场作用下板坯连铸结晶器内的弯月面行为.实验结果表明可应用磁场控制结晶器内金属液面的波动.当水口角度为向下30°时,磁场对表面波动的抑制作用有一最佳值,即磁感应强度为0.5 T时液面平均波动最小,液面较稳定.施加磁场使弯月面处温度明显提高,使水口出流的向下冲击深度受到抑制,这有利于夹杂物的上浮分离,达到提高板坯内部质量的目的.     

板坯连铸结晶器保护渣卷渣及其影响因素的研究

对板坯连铸结晶器保护渣卷渣进行的水力学模拟研究结果表明,主要有三种类型的卷渣,即窄边附近的剪切卷渣、浸入式水口附近的旋涡卷渣和水口吹入的氩气泡上浮冲击钢渣界面引起的卷渣.拉速增加、减少浸入式水口浸入深度、减小水口出口倾角和增加吹入的Ar流量均会加大表面流速和液面波动,增大结晶器内卷渣的倾向,而其中拉速增加对卷渣的影响最大.当结晶器宽度为1 900 mm、采用1.4 m/min的拉速时,选择向下25°的水口出口角度、250 mm的水口浸入深度和10 L/min的Ar流量可将板坯结晶器内流场的表面流速和液面波动控制在合理的范围内,从而减小和避免结晶器内卷渣.     

电磁搅拌作用下板坯连铸结晶器熔池液面稳定性研究

液面波动是连铸过程的重要问题。推导了电磁搅拌作用下板坯连铸结晶器熔池液面稳定性指数(F)的函数表达式,分析了电磁场、结晶器、水口、浇铸速度等对F数的影响,评估了实际连铸系统工艺参数的稳定性。主要结果:(1)基于自由射流理论,建立了电磁搅拌下板坯连铸结晶器液面稳定性指数的理论公式;(2)各连铸参数按照影响液面稳定性由大到小排序依次是:磁感应强度、水口浸入深度、拉坯速度、板坯宽度、搅拌频率、水口倾角等;(3)对于厚度为230 mm的板坯连铸,现有各种板宽—拉速匹配下的F数均处于3~5之间,但在宽板宽—低拉速时参数优化的稳定性空间更大。     

插钉法研究板坯连铸结晶器液面特征

 采用可以同时获取板坯连铸结晶器内弧侧、厚度方向中心面和外弧侧液面信息的插钉板,通过在结晶器内连续插取,研究了板坯连铸结晶器液面特征。得到了结晶器内不同时刻、不同位置处液面高度;发现了连铸生产过程中内、外弧侧液位有差异,提出了对称流不仅只是以水口为中心结晶器左右两侧流场的对称,还应包括以结晶器厚度方向中心面为中心,内弧侧与外弧侧流场的对称;预测了该工况下结晶器内液面波动较大以及卷渣发生频率较高的位置为水口附近和窄面与宽度方向1/4之间液面流速较大的部位;验证了插钉试验不仅可以获得连铸结晶器内的液面流速,还可通过多次插钉试验研究液面波动特征,在传统的物理模拟和数值模拟方法之外提出了一种直接、接触式测量连铸结晶器液面轮廓进而研究液面波动的方法。     

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。     

基于紊流射流理论的连铸结晶器液面波动

 为研究结晶器内液面波动特性的规律,防止连铸坯卷渣,提高铸坯质量,利用紊流淹没射流理论建立了浇注过程中钢液流股撞击结晶器窄边速度和撞击点位置理论模型,推导出液面波动指数的解析公式;通过与试验结果对比,验证了该理论模型的预测结果;利用数值仿真模拟1 000 mm×130 mm板坯连铸结晶器在不同液面波动指数下的液面波动情况。计算结果表明,该理论模型结论与试验结论偏差为－4%～2.5%,可较好地评价结晶器内液面波动的剧烈程度,该型号板坯连铸结晶器最佳拉速为1.4 m/min。     

浇铸参数对结晶器液面波动影响及其工业应用

 板坯连铸结晶器液面的波动行为是结晶器内钢液流动、结晶器自身振动以及辊子挤压铸坯内部未凝固的钢液造成液面波动综合作用的结果。结晶器液位波动的稳定性对板坯连铸过程的卷渣行为有直接影响。在工业板坯连铸生产实践中,一般在结晶器某一区域(比如结晶器中部)利用放射源或涡流传感器检测液位波动来代表该工况下的整体波动水平。利用三维气液两相流动的数学模型研究了浇铸参数对结晶器液位轮廓的影响,浇铸参数包括拉速、吹氩流量、浸入式水口出口角度和浇铸断面。研究结果表明,结晶器不同宽度位置的波动幅值差异较大,且与工艺参数密切相关。液面的波峰与波谷之差随着拉速的增加在窄面附近逐渐增大,随着吹氩流量的增加在水口附近逐渐增大。在水口出口角度15°条件下,水口和窄面附近的液位波动均较大,而在水口出口角度45°条件下,仅在水口附近存在较大的液位波动。研究结果表明,使用板坯连铸常规的15°浸入式水口,当铸坯宽度大于800 mm时,结晶器液面检测需要在水口和窄面附近同时布置液位检测设备,以便更全面反应结晶器的真实液面行为,使液面波动对轧板表面质量指导性增强,有效提高连铸工艺的控制水平。如使用45°浸入式水口可以继续沿用原有的液位检测布置。     

高拉速时连铸结晶器内钢液湍流场及其电磁控制研究

利用数学模型结合低熔点金属合金模型试验研究全幅二段恒稳磁场控制结晶器内气液两相流场和夹杂物粒子的运动轨迹。结果表明,水口喷吹氩气结合施加恒稳磁场的作用,同时达到控制结晶器内弯月面波动、获得活塞流和抑制后凝固区偏析的目的。氩气喷吹和磁场共同作用既能保持液面稳定又能避免凝结发生。吹入氩气能增加夹杂物的去除率。施加磁场时,夹杂物运动速度明显降低．夹杂物的富集率降低。     

本钢板坯连铸结晶器液面波动原因分析及防止措施

通过对本钢230mm×1600mm板坯连铸结晶器液面波动的成因分析,提出了采用合适的包晶钢结晶器保护渣、降低结晶器冷却强度、增大二冷区上部冷却强度等解决板坯连铸结晶器液面波动的措施。     

包晶钢板坯连铸机结晶器液面波动的原因

在板坯连铸机实际生产操作中发现,生产包晶钢的时候明显存在结晶器液面波动的问题。结晶器液面波动的问题致使生产出来的成品表面有裂纹缺陷,直接造成铸坯的不合格率上升。介绍了连铸机的分类、包晶钢连铸工艺以及结晶器液面波动表现形式。分析了连铸机液面波动产生的原因,并提出了优化措施。认为连铸机坯壳厚度不均匀、板坯拉出结晶器阶段产生"鼓肚"、设备精度不够、钢种特性、保护渣的状态以及冷却温度的设定均有可能导致结晶器液面波动。通过对保护渣性能、冷却制度、液面控制系统等方面优化调整,板坯连铸机包晶钢结晶器液面波动情况明显改善,产品质量的稳定性得到大幅提高。     

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.     

Interracial Fluctuation Behavior of Steel/Slag in Medium-Thin Slab Continuous Casting Mold With Argon Gas Injection

The flow field of molten steel and the interfacial behaviour between molten steel and liquid slag layer in medium-thin slab continuous casting mold with argon gas injection were studied by numerical simulation, in which the effects of nozzle submergence depth and port angle, casting speed, and argon gas flow rate on the flow and the level fluctuation of molten steel were considered. The results show that the molten steel is jetted from the submerged entry nozzle (SEN) with three ports into the mold and forms three recirculation zones including one upper recirculation zone and two lower recirculation zones. Argon gas injection results in a secondary vortex flow in the upper zone near the nozzle. For a given casting speed and argon gas flow rate, increasing the side port angle and submergence depth of nozzle can effectively restrain the steel/slag interfacial fluctuation. Increasing the casting speed would prick up the level fluctuation. For a fixed casting speed, argon gas flow rate has a critical value, the interfacial fluctuation with argon gas injection are stronger than the case without argon gas injection when the argon gas flow rate is less than the critical value, but when the argon gas flow rate exceeds the critical value, the level fluctuation is calmer than that without argon gas injection.     

Interfacial Fluctuation Behavior of Steel/Slag in Medium-Thin Slab Continuous Casting Mold With Argon Gas Injection

 The flow field of molten steel and the interfacial behaviour between molten steel and liquid slag layer in medium-thin slab continuous casting mold with argon gas injection was studied by numerical simulation, in which the effects of nozzle submergence depth and port angle, casting speed, and argon gas flow rate on the flow and the level fluctuation of molten steel were considered. The results show that the molten steel jet from the submerged entry nozzle (SEN) with three ports into the mold and form three re-circulation zones including one upper re-circulation zone and two lower re-circulation zones. Argon gas injection results in a secondary vortex flow in the upper zone near the nozzle. For a given casting speed and argon gas flow rate, increasing the side port angle and submergence depth of nozzle can effectively restrain the steel/slag interfacial fluctuation. Increasing the casting speed would prick up the level fluctuation. For a fixed casting speed, argon gas flow rate has a critical value, the interfacial fluctuation with argon gas injection are stronger than the case without argon gas injection when the argon gas flow rate is less than the critical value, but when the argon gas flow rate exceeds the critical value, the level fluctuation is calmer than that without argon gas injection.     

Numerical Analysis of Fluctuation Behavior of Steel/Slag Interface in Continuous Casting Mold with Static Magnetic Field

Utilizing ANSYS CFX commercial software and volume fraction of fluid （VOF） model, fluctuation behav- ior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided in- to three zones： frontal valley zone, back valley zone and horizontal zone~ as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/ slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0.5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag inter- face fluctuation can be properly controlled and slag entrapment can be prevented.     

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

 The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product. The multiphase flow phenomena of molten steel, steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation, and the effect of electromagnetic brake (EMBR) and argon gas blowing on the process were investigated. The relationship between wavy fluctuation height near meniscus and the level fluctuation index F, which reflects the situation of mold flux entrapment, was clarified. Moreover, based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification, the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux, temperature and stress of shell in slab continuous casting mold were described.     

Modeling of biased flow phenomena associated with the effects of static magnetic-field application and argon gas injection in slab continuous casting of steel

Biased flow occurs frequently in the slab continuous casting process and leads to downgraded steel quality. A mathematical model has been developed to analyze the three-dimensional biased flow phenomena associated with the effects of static magnetic-field application and argon gas injection in the slab continuous casting process. By moving the submerged entry nozzle (SEN) from center to off-center, the biased flow and vortexing flow in the mold can be reproduced in the numerical simulation. The existence of a vortexing flow is shown to result from three-dimensional biased flow in the mold. A vortex is located at the low-velocity side adjacent to the SEN. The vortex strength depends on the local horizontal velocity of molten steel and decreases gradually with distance from the free surface. The vortexing-zone size depends on the biased distance of the SEN, and the intensity of the vortexing flow depends on the casting speed of the continuous caster. Only when the location and strength of the magnetic field are properly chosen, can the vortexing flow be suppressed by a static magnetic-field application. The effect of argon gas injection on the vortexing flow is not remarkable. The combination of magnetic-field application and argon gas injection can correct the biased flow and suppress the vortexing flow by suppressing the surface velocity and removing the downward velocity near the SEN in the mold.     

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。     

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.     

复合电磁场对连铸结晶器弯月面金属液运动 行为及铸坯质量的影响

为了获得高质量的连铸坯 ,提出了在连铸结晶器外施加复合电磁场的电磁铸造方法。规范和测定了冷坩埚式铜铸型内复合电磁场的分布 ;采用低熔点金属镓和 Sn- 4.5 % Pb合金模拟高熔点钢 ,研究了在水冷铜铸型外施加复合电磁场对结晶器弯月面处金属液运动行为及铸坯质量的影响。实验结果表明 :复合电磁场能够有效地抑制结晶器弯月面处金属液波动变形 ,并改善铸坯的表面质量。随着搅拌线圈磁通密度的增加 ,铸坯的凝固组织由柱状晶转变为等轴晶 ,使晶粒得到细化