Numerical Accuracy Test on Heat Transfer in a Single‐belt Strip Casting Simulator

The heat removal rate from the solidifying molten metal is one of the most important issues in casting processes. The analysis of the inverse heat conduction problem (IHCP) with an assumption of one‐dimensional heat flow is a typical approach to clarify the heat transfer characteristics between the solidifying metal and the mould, and the authors have also developed a single‐belt strip casting simulator applying this technique. In this study the effects of the mould geometry and the temperature measurement on the estimation accuracy of surface temperature and interfacial heat flux in this method were examined through numerical experiments. The mould profile of the simulator where a side dam is integrated generates a multi‐dimensional heat flow and causes a non‐uniform heat flux along the metal‐mould interface. The heat flow in the central part, however, is unidirectional in the initial period and the thermal status at the interface can well be reproduced by the IHCP analysis. Furthermore, the disturbances in the temperature measurement, for example the interfacial thermal resistance between the inserted thermocouples and the casting mould, directly cause estimation errors and should be removed. These results indicate that the single‐belt strip casting simulator developed by the authors is capable to measure the interfacial heat flux and the surface temperature in the casting process although the measuring period and the location are limited. They also suggest the methods how to imporve the measurement accuracy for the various casting simulation techniques.     

一种薄带连铸工艺中瞬态界面传热模拟测量方法

研究和开发了一种可以测量钢水在铜辊表面凝固过程中瞬态界面传热的模拟装置及相应的界面热流计算方法.结果显示,钢水和铜基体接触的瞬间,热流达到最大值9 MW/m2左右,随后很快降低至4 MW/m2,然后维持在2～5 MW/m2之间.对比前人的研究结果,该模拟装置可以有效地用于研究薄带连铸中的界面传热现象.     

韩国浦项公司薄带铸轧工艺的最新进展

介绍了韩国浦项公司开发出的创新型PoStrip薄带铸轧工艺的发展历程、基本原理、流程的布置和最新进展,根据其热试结果分析了PoStrip工业化生产的优势和需要解决的问题,指出PoStrip生产线具有环境友好的特点,能够将铜水直接浇铸成厚度为2～4 mm的薄钢带,如果PoStrip生产线能够稳定地工业化生产,可大幅度地降低设备投资、能源消耗和生产成本。     

Research methods and influencing factors of interfacial heat transfer during sub-rapid solidification process of strip casting

Interfacial heat transfer behavior between the molten steel and twin-rolls is a key issue in the strip casting process,and it has already attracted wide attenti...     

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     

待定系数法确定双辊薄带铸轧中的边界热流

熔池与铸轧辊接触的边界热流是进行双辊薄带铸轧数值模拟研究的重点,通过铸轧过程中金属凝固机制和传热过程的研究,提出结晶辊和熔池接触的边界热流分布函数形式,利用凝固初始位置、薄带坯出坯厚度,再结合能量守恒原理进行求解,确定函数中的待定参数,避开传统方法需要求解坯壳和铸轧辊间气隙热阻的难题;通过施加所提出的边界热流函数对某试验铸轧辊温度场进行求解,结果与实测结果相吻合,这表明文中提出的边界热流分布函数形式与实际相符合。     

Numerical Simulation of Filling Process During Twin-Roll Strip Casting

The modeling and controlling of flow and solidification of melt metal in the filling process is important for obtaining the optimal pool level and the formation of the solidified metal layer on the surface of twin-rolls during the twin-roll strip casting. The proper delivery system and processing parameters plays a key role to control flow characteristics in the initial filling stage of the twin-roll strip casting process. In this paper, a commercial CFD software was employed to simulate the transient fluid flow, heat transfer, and solidifications behaviors during the pouring stage of twin-roll strip casting process using different delivery systems. A 3D model was set up to solve the coupled set of governing differential equations for mass, momentum, and energy balance. The transient free-surface problem was treated with the volume of fluid approach, a k–? turbulence model was employed to handle the turbulence effect and an enthalpy method was used to predict phase change during solidification. The predicted results showed that a wedge-shaped delivery system might have a beneficial impact on the distribution of molten steel and solidification. The predicted surface profile agreed well with the measured values in water model.     

Ab‐initio Predictions of Interfacial Heat Flows during the High Speed Casting of Liquid Metals in Near Net Shape Casting Operations

When metals are cast into solid shapes, the quality of the solid casting depends on many things, but heat flow management is a critical factor. It is relatively easy to predict heat flows through the liquid metal, and the solid mould, but heat flows through the interconnecting interface have been much more difficult to quantify. In the present work, following a review of our progress up to date on near net shape casting, the approach is to model this interfacial resistance from first principles. By conducting experiments in which liquid aluminum is cast at high speed (～0.5 m/s), onto a copper substrate, fitted with extremely sensitive embedded thermocouples, heat fluxes from the first moments of metal contact, to final freezing of the strip, have been measured. Similarly, by using a 3D profilometer that is able to rapidly characterize and quantify the surface topography of a substrate, to ±1 µm, one can have the necessary data to mathematically model the transfer of heat from the overlaying metal, through the interfacial layer, into the copper substrate. The thermal model briefly described, makes the assumption of point contact between pyramidal peaks of the metal substrate and molten metal, with gas pockets trapped in the “valleys” of the substrate, through which heat must be transferred by conduction. Ab‐initio instantaneous heat fluxes predicted in this way proved to be in good agreement with those measured, provided adjustments were made for expansion of the “air gap”.     

304不锈钢2mm连铸薄带中的裂纹分布和形成分析

用扫描电镜(SEM)观察和分析了双辊连铸法生产的304不锈钢1 200 mm×2 mm铸带表面和内部裂纹的形貌和形成。由于采用导热性好的铜制结晶辊,薄带表面和内部产生了长140 mm、深0.33 mm的裂纹,薄带断面有分层现象。试验结果表明,铜制结晶辊使钢液的冷却速度达到(1~4)×10³K/s,薄带接触辊面温度低,凝固区的温度梯度高达10⁵K/m,温差产生的内应力和应力集中导致裂纹产生;MnS、MnO、Cr₂O₃等夹杂物是裂纹源。     

Development of laboratory scale thin strip caster and investigation of direct casting of AISI 304 stainless steel

Abstract

An unequal diameter (1 : 3), two roll thin strip casting machine has been designed and fabricated for investigation of the direct casting of thin strip on a laboratory scale. The system consists of a preheatable shallow tundish with online heating facility, water cooled rotating rolls (chill and auxiliary) for solidification of the liquid metal, and a stripper assembly. The machine has a variable speed. Roll gap setting and roll pressure adjustment are two important features of the machine. It is also possible to vary the placement angle of the auxiliary roll with respect to the chill roll. A heat transfer model was developed, based on experimental casting results. Experiments were conducted using AISI 304 grade stainless steel. Up to 100 kg of steel was cast without interruption into strips of widths 100 and 200 mm and thickness varying between 1 and 2 mm. Some of the process parameters affecting the quality of the strip were identified.     

Simple model for thermal calculation in twin-roll strip casting process

The numerical model for the solidification process of metal in the twin-roll type strip caster is presented in this paper. In the model the temperature change as well as the eliminating process of latent heat is calculated along the stream lines obtained by a comparatively simple velocity field. The calculations are carried out on the strip casting of type 304 stainless steel under various casting parameters. The results so obtained show a good fit to the experimental ones, and suggest that the control of the height of molten pool is of importance to the establishment of the optimal operation.     

薄带连铸生产低碳钢的专利技术分析

介绍了国外几家公司接近产业化的薄带连铸技术的发展概况.根据国内外薄带连铸和薄板坯连铸的专利和生产实践,认为目前适合应用薄带连铸技术生产的碳钢为低碳硅锰镇静钢.也介绍了国外公司生产硅锰镇静钢的成分和性能.通过控制钢中的总氧含量,钢中可形成低熔点的夹杂物,并均匀地分布在铸带的厚度方向,从而有利于快速凝固过程中的高速传热.同时,还应该控制好钢中的碳、氮、氢含量,以获得表面质量良好的产品.     

The key technologies of controlling low carbon steel as-cast strip surface quality

This article is try to explain or analyze the key technologies of controlling the surface quality of low carbon steel as cast strip through investigation of interface heat transfer between solidified shell and liquid steel.The one of the key technologies of controlling surface quality of low carbon steel as cast strip is through the casting roll surface texture in order to achieve the homogeneous solidification on the casting roll.Another is through forming a thin film on the casting roll surface in order to achieve a balance between rapid solidification and homogeneous solidification.This film formed between the twin roll and the molten steel can be controlled by adjusting the chemical composition and inclusion in liquid steel through controlling the amount of all[O]and free[O].     

特大圆坯连铸用新型浸入式水口的设计与研究

 针对特大截面圆坯连续浇铸的特点,基于依靠浸入式水口自身结构减小钢流冲击深度,同时保证流动与传热沿周向分布均匀的思想,首次提出了新型浸入式伞形水口设计方案,并建立了结晶器内钢水的流-热-固耦合模型,对钢水的流动、传热和凝固行为进行了数值耦合模拟分析,验证了此水口的优越性与合理性：伞形水口的射流在结晶器内形成上下两个回流区,不仅有利于夹杂物、气体等的上浮分离,还能有效降低钢流冲击深度,使过热钢液均匀分布在结晶器上部,可提高弯月面温度和化渣效果;沿周向凝壳生长均匀,减轻了纵裂纹的萌生概率;在0.35m/min拉速下,出结晶器凝壳厚度达到31.2mm,满足安全生产要求。     

EAF-CSP流程生产集装箱板连铸工艺优化研究

连铸工序曾是珠钢CSP薄板坯连铸连轧生产集装箱板的薄弱环节。通过对连铸保护渣、二冷水、钢水纯净度、拉速匹配等的优化 ,降低了漏钢率 ,改善了铸坯质量 ,从而保证了板卷性能 ,实现了集装箱板的规模化生产。     

430不锈钢板坯横裂成因分析及控制措施

通过对430不锈钢连铸板坯存在横裂缺陷的试样进行低倍检验、金相检验及韧脆转变温度测定,确定铁素体晶界上大量的碳化物析出相加速裂纹的扩展,致使铸坯更容易发生脆性断裂。提出相应的工艺控制措施：提高铸机的对弧精度,足辊出口对弧精度为0.5mm,零段出口对弧精度为0.33 mm,一段出口对弧精度为0.27mm;板坯在500℃附近快速冷却,避免脆性相的产生;要求wC+wN小于0.03%;铸坯采用带温修磨,修磨温度控制到120℃以上,1周内完成铸坯的转序、轧制。对优化工艺进行工业试验得出,430板坯横裂缺陷得到了有效控制,杜绝了因板坯横裂引起的热轧断带事故及钢带孔洞缺陷,工艺措施效果显著。     

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.     

Control of the Molten Steel Level in the Top Side-Pouring Twin-Roll Casting Process Based on Fuzzy Rules Optimized by Particle Swarm Optimization Algorithm

Twin-roll strip casting is a near-net-shape casting technology that can produce thin steel strips directly from molten steel. Stably controlling the molten steel level is regarded as an important issue to ensure strip quality and casting process stability. As the control of the molten steel level is a time-varying, nonlinear, and multidisturbance complex system, it is difficult to establish an accurate process model for designing a model-based controller. Top side-pouring twin-roll casting is a new kind of twin-roll strip casting technology. This study introduces the control system of the top side-pouring twin-roll casting process. A fuzzy logic controller (FLC) with its fuzzy rules optimized by particle swarm optimization (PSO) is developed to regulate the molten steel level. Simulation results show that the performance of the FLC can be improved while its fuzzy rules are optimized by PSO. The objective function of PSO has a great influence on the optimization of the fuzzy rules. The top side-pouring twin-roll casting experiments are carried out using the FLC with its fuzzy rules optimized by PSO; the results show that strip quality and casting process stability are guaranteed.     

双辊铸轧工艺温度场和流场耦合的数值模拟

 双辊铸轧过程中熔池内金属的流动状态及温度分布直接影响着铸轧过程的稳定性与铸带产品的质量。针对实验室双辊铸轧试验的特点,采用三维有限元法模拟了双辊铸轧过程的热流耦合问题,利用热平衡计算、铸轧实验和模拟相结合的反向方法分段建立了凝固过程中凝壳与铸辊之间热传导系数与铸轧速度、熔池位置之间的关系模型,并分析不同工艺条件下熔池内凝固变化的情况。