板坯连铸新型浸入式水口研究

采用1∶1水力学模拟方法研究了板坯连铸结晶器内流场,探讨了双侧4孔水口出口方向对结晶器内液面波动、表面流速和注流冲击深度的影响趋势,得到了双侧4孔水口出口方向对板坯连铸结晶器内流场的影响规律。研究结果表明:4个孔都向下(α<β,α与β都向下)的双侧4孔水口的方案较优,此水口的冲击深度低,液面波动小,表面流速适中,比普通双侧孔水口效果好。     

板坯连铸结晶器内液面波动的水模型研究

以某厂板坯连铸结晶器为原型,采用1:1的水模型进行试验,以瞬时波高为判断依据,研究了拉速、浸入式水口出口角度、水口浸入深度、水口底面结构等工艺参数对板坯结晶器内流场和液面波动行为的影响.提出了优化结晶器流场的工艺参数,为在实际生产中减少结晶器内卷渣提供了依据.结果表明:拉速对板坯连铸结晶器内液面波动的影响最大,水口倾角...     

板坯连铸浸入式水口控流的物理和数值模拟

浸入式水口结构从根本上决定了结晶器内的钢液流动形式，采用物理模拟和数值模拟方法研究了水口结构及铸坯断面尺寸对板坯结晶器流动行为的影响。通过解析速度云图、表面流速、液面波动、冲击深度及保护渣覆盖情况等特征参数，对结晶器内钢液流动行为进行多角度定量表征。结果表明，水口侧孔倾角向上对1 600 mm×220 mm断面结晶器流场液面扰动较大，其倾角向下15°时射流冲击深度较大，倾角向下8°时最为适宜。水口底部形状会影响钢液的湍动能耗散及流场对称性，对比后得出凹底水口为最佳水口形状。侧孔形状对表面流速影响较小，但对自由液面波动有显著影响，可能导致钢液裸露；当水口侧孔面积一致时，矩形侧孔水口条件下的结晶器液面裸露面积小于跑道形侧孔和方形侧孔情况。而在浇注不同断面尺寸时，仅通过改变水口结构和使用工艺难以获得合理的结晶器流场，还需要借助其他控制流动的手段来推动未来板坯多元化生产的发展。本研究可为改善板坯质量提供理论与工艺指导。     

立式板坯连铸机结晶器液面控流的物理模拟

为研究低拉速下结晶器流动控制装置对流场的影响,以宝钢立式板坯连铸机结晶器为研究对象,采用1:1的物理模型进行了水模试验,研究了两种浸入式水口条件下液面加控流装置与否、控流装置位置及其插入深度对液面波动及流场分布的影响.研究表明:水口侧孔倾角向下时,MFCD对流动模式的改变不大,但使得液面波动量有所减小;而水口侧孔倾角向...     

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。     

静磁场控制板坯连铸结晶器液面波动

 用Pb Sn Bi低熔点合金进行了热模拟实验,研究了在静磁场作用下板坯连铸结晶器内的液面波动行为。实验结果表明可应用静磁场控制结晶器内金属液面的波动,且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。为此,为了减少由于液面波动引起的连铸板坯中的卷渣缺陷,有必要在一定的浇铸条件下优化磁感应强度。吹入氩气加剧了表面波动,且随着氩气流量的增加扰动加大。施加电磁制动能够使吹入氩气引起的液面波动受到显著的抑制。     

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.     

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.     

宽板坯连铸结晶器内液面波动的数值模拟

以150 mm×(1 600～3 250) mm宽板坯连铸结晶器为研究对象,利用大型商业软件ANSYS CFX10.0建立了一个三维有限体积模型,采用多相流的VOF模型对结晶器内保护渣-钢液界面波动进行数值模拟,重点研究了拉速、水口倾角、铸坯断面宽度等工艺参数对结晶器内液面波动的影响.结果表明:随着结晶器宽度、拉速的增加,液面波动明显增大;采用较大的水口倾角,可以抑制液面波动,减少卷渣.     

浸入式水口结构对板坯结晶器液面波动的影响

以1∶2. 3的几何相似比,建立了断面230 mm×1 930 mm板坯结晶器的钢液流动物理模型,研究不同的浸入式水口对结晶器流体流动和液面波动的影响,并进行了工业试验,测定了实际结晶器钢液面的波动。结果表明,凸底特别是较高凸底的浸入式水口容易在板坯结晶器两侧产生明显的不对称流动,结晶器两侧交替出现明显的液面凹陷,使得液面各点的波动差别大,且随浸入式水口浸入深度的增加液面波动不降低,在结晶器宽面1/4附近区域的液面波动比其它区域大。凹底的浸入式水口能够减轻结晶器两侧的不对称流动,从而避免液面凹陷的发生,液面各点的波动差别减小,液面波动随浸入式水口的浸入深度增加而下降。工业试验中优化的浸入式水口的结晶器液面波动的平均波高、最大波峰和最大波谷比原浸入式水口分别降低21. 70%,30. 70%和29. 18%。     

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     

连铸结晶器内钢液弯月面行为的研究

在自行设计的可以实现振动、水冷及拉坯的连铸模拟装置上,用低熔点的Pb-Sn-Bi合金模拟钢液,用硅油模拟保护法对弯月面行为进行了研究.结果表明：增加过热度使得弯月面与结晶器壁的接触角变小,弯月面的高度降低;在弯月面区域加上电磁场时,弯月面向结晶器中心拱起,其拱起程度随着电磁强度和磁场频率的增加相应增大,但液态金属高的过热度会削弱电磁场的作用效果;结晶器振幅增大及拉速提高均会使弯月面处液态金属的波动程度增大.通过测定正、负滑脱期弯月面处液态金属的速度场,验证了前人提出的振痕形成的机理.     

Study of meniscus behavior and surface properties during casting in a high-frequency magnetic field

Surface quality of continuously cast metals can be improved by imposing a continuous high-frequency magnetic field from the outside of a mold. Newly proposed concepts of “soft contacting solidification” and “slow cooling solidification,” which is tightly related to the mechanism of improving surface quality, were confirmed in model experiments by using molten gallium and tin. The meniscus motion of the molten gallium accompanied by a mold oscillation and magnetic pressure was measured by a laser level sensor. The shape variation of a meniscus and the process of ripple formation in an oscillation cycle were directly visualized by an optical fiberscope camera. Moreover, molten tin was continuously cast and the relationship between the surface quality and the meniscus motion was studied. A mechanical model for predicting the space between the oscillation marks is proposed. The casting process using intermittent highfrequency magnetic field was developed. New functions of this field were investigated regarding the control of initial solidification. It was found that the surface quality of the continuously cast metal can be improved by the intermittent high-frequency magnetic field as well as the continuous high-frequency magnetic field. Formerly Undergraduate Student, Department of Materials Processing Engineering, Nagoya University,     

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.     

圆坯钢电磁软接触连铸的实验研究

为确定工业实验基本参数,对电磁软接触连铸结晶器进行了优化设计计算,设计制作了φ100 mm圆坯电磁软接触连铸结晶器,利用Sn-Pb-Bi合金实验研究了结晶器内的弯月面行为,并进行了w(C)为0.22%钢坯的电磁软接触连铸实验。结果表明,电磁软接触连铸结晶器内磁场和弯月面变形具有不均匀性,切缝数为12时,磁场周向分布和弯月面变形较均匀。输入功率增加,弯月面高度增高,液面波动加剧。对于100 mm圆坯电磁软接触连铸系统,功率可控制在50~60 kW左右。实际应用中,浇注液面应控制在线圈中心偏上位置。较低的电源频率可获得较高的弯月面,频率应控制在20 kHz左右,可获得较高的周向均匀的磁场。获得了表面质量改善的电磁软接触连铸钢坯。随功率增加,铸坯表面依次会出现环状振痕、无振痕和波纹状振痕等3种振痕形态。     

An improved mathematical model for electromagnetic casters and testing by a physical model

The paper describes a physical model aimed at studying two important phenomena in electromagnetic (EM) casting of aluminum: the support of the molten metal pool and stirring caused by EM forces. The physical model is used both to test an improved mathematical model for EM casting and to provide insight into the effect of design changes on the two EM phenomena. Examples of design changes are changes in inductor current and position and screen position. The improved mathematical model, a two-dimensional (2-D) (axisymmetric) one, constrains the melt surface at the solidification line and neglects (with justification) buoyancy, surface tension, and the impact of flow on meniscus shape. The physical model was a cylindrical one where the solidified metal was simulated by a 248-mm-diameter aluminum bronze cylinder and the molten metal by Wood’s alloy. Measurements were made of electric field, magnetic field, meniscus deformation, and velocities for the two types of caster in commercial use. Generally, good agreement was obtained between the mathematical model and the experimental measurements.     

Physical Simulation of Nozzle Electromagnetic Brake in Twin‐Roll Strip Casting

This paper presents the Nozzle Electromagnetic Brake (N‐EMBR) technology for twin‐roll strip continuous casting. N‐EMBR consists of imposing a stationary magnetic field coupled with direct current inside the nozzle to control the flow and suppress the free surface fluctuation. A low melting point metal model was set up to examine the magnetic field and additional current effect on the velocity near the meniscus and free surface fluctuation. The experimental results showed that the velocity near the meniscus, the amplitude and main frequency of the free surface fluctuation were all decreased with the N‐EMBR technology. It was found that the N‐EMBR technique can be applied successfully in twin‐roll strip casting to suppress the flow near the meniscus and free fluctuation.     

The effect of a uniform direct current magnetic field on the stability of a stratified liquid flux/molten steel system

In continuous slab casting, the instability of the interface between the liquid flux and molten steel is very important, as it is related to the entrapment of liquid flux into molten steel. The entrapment of liquid flux springs up when the velocity under the meniscus exceeds the critical velocity.^[1] This situation is the same as the Kelvin-Helmholtz instability, which is the instability of the interface between two fluids with relative motion. However, few studies of the continuous casting process have related the Kelvin-Helmholtz instability to the entrapment of the liquid flux, and there has been little focus on this instability in metallurgical processes. In addition, the effect of direct current (DC) magnetic field on the Kelvin-Helmholtz instability has not been reported in metallurgical processes. Many researches in other parts for the effect of the DC magnetic field have assumed that the conductivity of fluid is infinite. However, real conducting fluids in metallurgical processes such as molten steel have finite conductivity, and especially, the liquid flux has a very small conductivity compared with molten steel. In this study, the Kelvin-Helmholtz instability of a stratified liquid flux-molten steel system and the effect of DC magnetic field on the instability of the interface between liquid flux and molten steel are studied assuming the conductivity of liquid flux is zero. The results show that when the instability does not occur, the DC magnetic field dampens the fluctuation of the interface between flux and molten steel more than the case with no magnetic field. However, when the instability occurs, the DC magnetic field could not dampen the fluctuation. In addition, the DC magnetic field expands the range of wave numbers of the instability.     

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。