水口结构对板坯连铸结晶器流场的影响

结晶器内钢液流场是研究连铸机内传输行为的基础。利用数值模拟方法分析了水口结构(凹底、平底和尖底)、结晶器宽度和拉坯速度下结晶器内钢液流动规律。数值结果表明,在凹底、平底和尖底三种浸入式水口结构下,结晶器内钢液流场相似,但尖底结构水口下钢液液面速度最大,平底次之,凹底最小。随着结晶器宽底的增加,结晶器上部和下部回流区范围增大;随着拉坯速度的增加,结晶器液面速度增加,但是钢液流股对结晶器窄面的冲击位置保持不变。     

板坯连铸结晶器内钢液流场的数值模拟

以计算流体力学理论为基础,利用Fluent软件建立了连铸结晶器内钢液流动的三维数学模型,运用模型低雷诺数方程对板坯结晶器内钢液的流场进行了模拟研究.通过数值计算研究了水口浸入深度、拉坯速度等上艺参数对结晶器内钢液流动状态的影响,为优化结品器内的钢液流场分布、合理设计连铸结晶器装置和指导实际生产提供了依据.     

水口长度对结晶器流场数值模拟的影响

为了论证通过缩短甚至忽略水口长度来减少网格数量,减少工作量对于结晶器流场模拟的准确性,采用Fluent流体力学软件对方坯连铸结晶器内钢液流动进行了数值模拟。研究结果表明:水口长度的改变对结晶器流场的计算结果有较大影响,水口长度由1 000 mm到0 mm时,水口出口最大流速降低了17.3%;液面最大流速降低了4.27%;冲击深度变深了1.32%;涡心高度变深了3.45%。水口长度1 000 mm时,钢液流股在水口出口处,仍没有充分发展,为保证模拟计算的准确性,推荐使用原型水口长度。     

不同拉速条件下FTSC结晶器内钢液流动行为的物理模拟研究

通过物理模拟研究FTSC结晶器内的钢液流动行为,考察了拉速对结晶器内液面波动、液面裸露、卷渣及夹杂物去除的影响作用。实验结果表明:在本实验条件下,使用4孔水口浇注会在FTSC结晶器内水口一侧形成4个明显的回流区。随着拉速的增加,结晶器内液面波动逐渐加剧,出现液面裸露及卷渣的几率逐渐增大,夹杂物的去除率逐渐减小。     

150 mm×150 mm断面小方坯结晶器电磁搅拌磁场与流场耦合的数值模拟研究

以国内某厂150 mm×150 mm断面小方坯结晶器电磁搅拌器为研究对象,建立了描述小方坯结晶器电磁搅拌过程的电磁场与流场耦合的三维数学模型,并采用有限元软件进行求解。研究了电磁搅拌电流和频率对结晶器内钢液流动的影响规律。研究结果表明:随搅拌电流的增大,钢液的切向流速增加,上部环流区缩短,下部旋转流动区域上移并扩大,搅拌电流和频率对钢液流动的影响相反;在电磁搅拌过程中,电磁搅拌使结晶器内钢液产生旋转流动阻止过热钢液下移,减弱冲击深度,使热区明显的上移。     

板坯连铸结晶器内部流场的数值模拟

连铸结晶器作为控制钢水清洁度的最后环节,结晶器液面波动不仅影响连铸生产的稳定性,还会引起卷渣、拉漏、钢水裸露氧化等。本文采用数值模拟方法,利用Fluent软件的k-ε湍流模型对板坯结晶器内钢水流动状态和液面波动规律现象进行模拟研究,分析了拉速和吹氩量对结晶器内流场的影响。结果表明:随着拉速的不断提升,钢液对铸坯窄面冲击深度不断增大,结晶器内自由液面表面流速增加,液面波动加剧;氩气量增加,钢液对铸坯窄面的冲击位置上移,液面波动剧烈程度增加,容易导致结晶器卷渣和钢水裸露氧化。     

内装式整体浸入水口在方坯连铸机的应用实践

通过对浸入式水口堵塞机理的分析研究,提出改变外装式分段水口为内装式整体浸入水口的方案,同时进行水口几何尺寸及材质的优化选择.改进后的水口在实际生产中.连铸结晶器液面波动次数减少70％,钢中非金属夹杂物缺陷率由2.91％下降为0.5％.     

水口结瘤对结晶器流场影响的物理模拟

以某厂板坯结晶器为原型建立1：1的物理模型,通过监测液面波动,研究浸入式水口结瘤物对结晶器流场造成的影响。实验结果表明：水口结瘤物的存在会导致结晶器水口两侧流场的明显不对称,水口堵塞侧钢液更多集中于结晶器上部,下回流占据区域较小;未堵塞一侧漩涡卷渣出现的频率较高;较大拉速下,随着水口倾角的增大,液面平均波动逐渐减弱;拉速提高会造成水口两侧平均波高的差距变大,结瘤物脱离水口后液面恢复稳定的时间延长;结瘤物脱离瞬间会导致流场迅速恶化,影响铸坯质量。     

圆坯结晶器内钢液流场的数值模拟

电磁搅拌特性直接影响着结晶器内钢液流动行为。基于包含电磁力的Navier-Stokes方程,采用数值方法研究了电磁搅拌作用下的钢液流场。数值结果表明:电磁搅拌下圆坯结晶器内钢液所受电磁力呈轴对称分布,其值从圆坯边缘到中心逐渐递减,施加电磁搅拌后,钢液的冲击深度减少,结晶器液面流速增加。     

板坯连铸机内钢液流动和夹杂物行为

采用数值模拟方法研究了板坯连铸机内钢液流动和夹杂物传输行为。数值结果表明，由于夹杂物的上浮速度远小于钢液流速，因此钢水的流动直接影响着结晶器内夹杂物分布。夹杂物具有与钢液流场相似的上下两个回流区的结构；在液面处，大粒径夹杂物的浓度较大；在窄面处，小粒径夹杂物的浓度较大。     

电弧炉用氧技术的多相流数值模拟研究

对150 t电弧炉冶炼过程中单支氧枪供氧流量分别为500,1 450,1 800,2 000 m<'3>/h时氧气射流冲击熔池进行了三维三相流数值模拟.模拟研究表明,随着供氧流量的增加,熔池中钢液和渣液的流动速度、裸露钢液面面积及射流的冲击深度均增大.由数值模拟和水模得到的供氧流量与射流冲击深度的规律得到了很好的吻合....     

Transient thermal structure, turbulence, and heat transfer in a reattaching slot jet flow

The role of turbulent fluctuations on mean heat transfer coefficient in a reattaching slot jet flow is studied experimentally. Convective heat transfer rate and near-wall fluid flow are examined in the recirculation, reattachment, and post-reattachment regions for two nozzle-to-surface spacings of 0.25 and 0.75 times the width of the nozzle bottom plate. In the reattachment region, results indicate a strong correspondence between variances of near-wall velocity fluctuation and peak heat transfer rate for both spacings. Thermal structures that vary in the spanwise direction are identified in the recirculation region from low-frequency transient infrared thermographs of the heated surface. While these thermal structures are confined to regions in the vicinity of nozzle bottom plate for the low nozzle spacing, they span the entire recirculation region at larger spacings. Thermal streaks are observed past reattachment for the larger nozzle spacing, suggesting a periodic breakup and re-formation of the jet curtain. The scaling of heat transfer distribution is affected by the flow structure in the geometrically non-similar area of the recirculating flow beneath the nozzle. A correlation for peak Nusselt number is presented.     

近终形异型坯连铸机的设计和生产工艺

总结了近终形异型坯连铸机的设计关键技术,包括钢水浇铸模式及浸入式水口设计、中间罐设计及流场模拟、结晶器设计及流场分析和热力学研究、连铸机辊列设计与计算、结晶器液压振动设计和振动参数确定、异型坯二冷凝固特点研究及二次冷却系统设计、扇形段及拉矫机和引锭杆设备设计等;概述了异型坯连铸机的生产操作要点,如钢水温度控制、钢水成分控制、结晶器保护渣优化、预防漏钢、二冷配水控制、加强设备维护和检查等;分析了异型坯的主要质量缺陷,包括表面缺陷和内部缺陷。     

Developing a new 2D model for heat transfer and foam degradation in EPS lost foam casting (LFC) process

In this study, a 2D model is developed for heat transfer, foam degradation and gas diffusion at the interfaces of the liquid metal, foam pattern and gaseous gap in between, for EPS lost foam casting process. In this model based on mass and energy balance between gas and molten metal, radiation and conduction between foam and molten metal and convection between gas and molten metal are considered, both metal and foam surfaces are tracked and gap volume and pressure are calculated. A combination of energy balance and geometric correlations is used to define receding foam surface during mold filling. Gas flow in the gap is considered as wedge flow and Nusselt number for a laminar incompressible wedge flow is used for it. To apply our model to an example case, SOLA-VOF algorithm was used to simulate the flow of molten metal with free boundaries. Model results are compared with some data reported in the literature which show acceptable agreement. It is found that besides radiation in the gaseous area between foam and molten metal, conduction also plays an important role in foam degradation and control of molten metal velocity. This model can acceptably predict the effect of some parameters like foam density, coating permeability and foam degradation temperature.     

电弧炉流程20CrMnTi齿轮钢洁净度研究

采用气体分析法、化学分析法、扫描电镜、大样电解等方法,对20CrMnTi生产过程的中非金属夹杂物进行了研究.结果表明：LF炉渣黏度高时使得炉渣结壳,钢水易造成氧化,同时VD到中间包的过程钢液的二次氧化严重;精炼过程显微夹杂物主要为钙铝酸盐、硅铝酸盐复合夹杂及氧化产物,硫化物较少;大样电解结果显示连铸坯中大型夹杂物含有较多的TiO2和K2O,是钢液的二次氧化和卷入的结晶器保护渣所致;连铸坯中心弧线大型夹杂总量高,大型夹杂物平均总量为1.592mg/10kg.     

A THERMOMECHANICAL MODEL OF SOLIDIFICATION ON A MOLD MOVING WITH CONSTANT VELOCITY

A thermomechanical model of pure metal solidification on a moving mold plate is considered. The goal of the model is to obtain a formula for the contact pressure at the shell/mold interface as the mold moves into the molten liquid. From the contact pressure it is possible to infer the effects of the mold velocity and the mold microgeometry on the time and location of gap nucleation which results from irregular distortion of the shell as it grows from the melt. The mold, which moves at a constant velocity into the molten liquid, has a sinusoidal surface with a low aspect ratio: this means that its wavelength greatly exceeds its amplitude. The mold is of infinite area and is assumed to be perfectly conducting and thermomechanically rigid. We therefore neglect the complexities associated with the physics of edge constraints and/or free boundaries of the solidifying shell and the interacting distortions between deformable mold and shell materials along their interface. The ratio of the velocity of the solid/liquid interface to the mold velocity is identified as another dimensionless parameter in the analysis. In order to arrive at an analytical solution for the contact pressure along the shell/mold interface, we assume that this parameter is small. This makes the velocity ratio a convenient perturbation parameter for the analysis of thermomechanical distortion of the thin shell material as it grows from the melt. This necessarily limits the analysis to situations where the mold moves at faster rather than slower speeds. It is assumed that there is zero tangential shear stress between the fluid and the solidifying shell. As the molten liquid flows over the mold, it perfectly wets the surface. This precludes wetting effects due to surface tension. A hypoelastic constitutive law, which is a rate formulation of thermoelasticity, is assumed to govern deformation of the shell as it grows from the molten liquid. Latent heat liberated at the freezing front is extracted across a constant contact resistance at the shell/mold interface. Peculiar fluid motion at the tip is neglected. A solution for the contact pressure that is valid near the liquid surface (i.e., the meniscus) is derived from the main theoretical developments. Beyond the time of gap nucleation at the shell/mold interface, the model is no longer valid since it cannot account for gross distortion of the shell (i.e., distortions that greatly exceed the spatial perturbations considered in the model).     

Annular Impinging Jet Controlled by Radial Synthetic Jets

This experimental study focuses on generation and control of annular impinging jets. The annular nozzle used in the investigations was designed with an active flow control system using 12 synthetic jets issuing radially from the central nozzle body. Measurements of the control effects were made on the impingement wall. The data acquisition involved wall pressure and wall mass transfer (by the naphthalene sublimation technique) using air as the working fluid. Also measured was time-mean flow velocity (by a Pitot probe) in the jet flow field. Moreover, flow visualization was carried out. Two main flow-field patterns (A and B) were identified. The patterns differ in the size of the separated-flow recirculation regions that develop attached to the nozzle central body: While pattern A is characterized by a quite small recirculation region (bubble) extending not far from the nozzle exit, pattern B exhibits a large recirculation region, reaching up to the impingement wall, on which it forms a stagnation circle. The control action modifies the flow field, resulting in changes of the corresponding heat/mass transfer distributions. The convective transfer rate on the stagnation circle can be demonstrably enhanced by 20% at a moderate nozzle-to-wall distance, equal to 0.6 of the nozzle outer diameter.