Simulation of the continuous casting process by a mathematical model

A computational three-dimensional (3D) heat transfer model has been developed and applied to calculate the temperature distribution and solid shell thickness profile of a continous cast slab in a steel plant. This developed model includes non-linear material properties of specific heat and thermal conductivity as well as phase changes during solidification. A general thermo-fluidmechanics computer program, PHOENICS, was employed to numerically solve the heat transfer equation with the associated source terms. The thermal profile and solid shell thickness calculated by mathematical model agree with those predicted by an industrial model and experimental measurements. The model could also be used to predict the optimum process parameters on casting speed, heat removal rates and associated water flow rates and roll force. These parameters could be monitored by suitable sensors and controlled through a feed back system that interfaced with the mathematical model and the sensors.     

Design and implementation of an automated secondary cooling system for the continuous casting of billets

This paper describes a heat transfer model based automatic secondary cooling system for a billet caster. The model aims to minimize the variation in surface temperature and excessive reheating of the billet strands. It is also used to avoid the low ductility trough of the solidifying steel, which aggravates the tendency of steel to crack. The system has been designed and implemented in an integrated steel plant. A Programmable Logic Controller (PLC) based automation system has been developed to control the water flow in the secondary cooling zones of the strand. The results obtained through field trials have shown complete elimination of internal and off-corner cracks for the fifty billet samples that were monitored.     

Modelling vertical continuous casting with temperature-dependent material properties

An extension of the analytical model for vertical continuous casting of bars previously developed by the authors (Johnson and Cherukuri. Proc. Roy. Soc. London A 455 (1999) 227) is presented. The new features include temperature dependence of thermal conductivity and the constitutive equations. The model can be used to readily predict the effect of various process parameters such as cooling conditions, liquid pool pressure, casting speed on the solidification process. Consequently, it can be readily implemented in a control system to adjust the process parameters of a typical solidification process. In addition, it can also be used as a guide to gain insight into the nature of the solution prior to conducting more general and expensive finite element simulations.     

塑料薄膜与流延辊换热过程的模拟分析

为实现流延辊辊面温度场的均匀性和稳定性,保证塑料薄膜的高质生产,应用F luent软件对双向回流式螺旋流道的流延辊的换热过程进行了数值模拟;分析了流延膜在流延辊上冷却时的导热、对流、辐射综合的非稳态传热过程,了解了流延膜冷却过程中的传热机理,得出了流延辊内部流道结构、冷却水的流量对流延辊换热强度的影响趋势。研究结果表明,该研究可以为流延辊结构的合理设计、流道参数的优化提供指导。     

基于模糊控制的挤压铸造模温控制系统研究

针对挤压铸造模具温度难于控制的特性,分析了挤压铸造工艺及挤铸模具温度影响因素。根据现有挤铸模具加热及冷却方式,结合分析研究影响挤铸模温的多因素与多变性,建立了新的挤铸模具温度控制模型,并运用模糊控制方法来实现温度控制。在设计好模糊控制器后,利用Matlab软件中的Simulink模块建立了模温控制系统模型并实现了仿真分析。仿真结果表明:与传统的PID控制相比,模糊控制系统具有良好的控制特性。     

Novel technologies for the lost foam casting process

Lost foam casting (LFC) is a green precision casting process categorized as a near net forming technology. Yet, despite its popularity, it still suffers from some technological problems, such as poor filling ability of the castings, coarse and non-dense microstructure, low mechanical properties for the Al and Mg LFC processes, and defective carburization for the low carbon steel LFC process. These drawbacks restrict the development and widespread application of the LFC process. To solve these problems, the present study developed several novel LFC technologies, namely, LFC technologies under vacuum and low pressure, vibration solidification, and pressure solidification conditions; expendable shell casting technology; and preparation technology of bimetallic castings based on the LFC process. The results showed that the LFC under vacuum and low pressure evidently improved the filling ability and solved the oxidization problem of the alloys, which is suitable for producing complex and thinwall castings. The vibration and pressure solidifications increased the compactness of the castings and refined the microstructure, significantly improving the mechanical properties of the castings. The expendable shell casting technology could solve the pore, carburization, and inclusion defects of the traditional LFC method, obtaining castings with acceptable surface quality. Moreover, the Al/Mg and Al/Al bimetallic castings with acceptable metallurgical bonding were successfully fabricated using the LFC process. These proposed novel LFC technologies can solve the current technological issues and promote the technological progress of the LFC process.     

套类铸钢件凝固特性的数值模拟

用数值模拟法研究了不同壁厚、不同内径的套类铸钢件在普通砂型铸造条件下的凝固时间分布规律和凝固系数的变化,有助于认识此类铸件凝固特性和热节位置,对防止成形过程中产生收缩缺陷十分必要。     

智能控制在模具温控成形中的应用

模具的温度控制和调节是高效而经济地生产高质量成形零件的必不可少的条件.介绍了智能控制在模具温控成形过程中的应用现状,指出数值模拟对温控成形过程温度场的研究有助于控制成形过程,实现对模具温度的智能控制,使零件的质量得到充分保证.     

发动机冷却系统中流动与传热问题数值模拟进展

着重论述利用数值模拟技术研究发动机冷却系统中流动与传热问题的发展现状,包括水套单相流及气液两相流流动、流－固耦合传热、一维与三维联合模拟等该研究领域的热点内容。耦合系统之间联合分析的方法准确反映了发动机各部件之间的影响关系,这种分析方法是目前研究的重点,但其中仍存在一些问题。基于此状况提出改进办法：针对不同工况选用循环平均参数作为燃气侧传热边界条件;水套进出口的流动边界条件,在稳态工况下设为定值,在过渡工况下通过循环一维仿真计算确定;应采用整体耦合方法进行计算,计算模型应尽量完整,但可以进行适当的简化,并总结出模型简化的原则。     

折流板换热器壳程流体流动与传热特性数值模拟

根据流体动力学和计算传热学理论,建立了折流板管壳式换热器计算模型,运用CFD技术对换热器壳程流体的流动与传热问题进行了三维数值模拟,得到了不同壳程进口雷诺数Re条件下换热器壳程流体的流场和温度场。对数值模拟结果进行分析,以总传热系数h．壳程总压降△p以及单位压力损失下的传热系数h／Ap作为换热器性能的衡量标准,分析了不同折流板间距和不同折流板圆缺高度时管壳式换热器壳程总传热系数h、总压降△p以及h／Ap随壳程进口雷诺数的变化规律。结果表明：随着壳程进口流速的增大,换热器壳程总传热系数和总压降增大、h／Ap减小：在壳程流体流量不变的情况下,结合单位压力损失下的传热系数h／Ap,适当减小折流板间距或减小折流板圆缺高度。可提高换热器的换热性能。     

草甘膦合成过程建模与控制策略研究

针对草甘膦生产过程中的大时滞、非线性对象,把Sm ith预估控制原理和模糊控制器参数的自适应调整方法结合起来,提出带积分的自适应模糊-Sm ith控制策略,基本控制级采用模糊控制,协调级采用自适应机制实时调整控制器的量化和比例因子,积分器实时进行积分。MATLAB仿真结果表明,该控制策略具有良好的动静态特性及更强的鲁棒性,是解决草甘膦合成过程温度控制问题的一种有效策略。     

连续 ECAP 大应变的数值模拟研究

基于刚塑性有限元理论,采用有限元软件DEFORM-3D对5052铝合金连续ECAP(Equal Channel Angular Pressing)大应变成形过程进行了三维数值模拟研究,研究了工件的变形过程以及应变均匀性,温度的分布规律。模拟结果表明,金属变形剧烈部位主要集中模具的拐角区域,该区域的等效应变呈层状分布,而且变化梯度较大并且温度最高。模拟结果对实际生产具有很好的指导作用。     

FE numerical simulation of mould temperature field during the continuous casting of steel

In this paper, the three-dimensional transient model of the mould temperature is established and the temperature variation is analyzed when the thickness of the mould wall and the cooling rates are different. For the numerical computation, a corresponding finite element method (FEM) program is developed with FORTRAN language, and six-face and eight-node isoparameter elements are applied; the Newton method is used to solve the heat equations. The experimental data have been used to validate the model. It is shown that the appropriate mould wall thickness is 10 mm and the different parts of the mould should correspond with cooling water of different rates.     

基于CASTSoft_CAE软件的铸件缺陷预测

以金属凝固理论为基础,I-DEAS和CASTSoft_CAE软件为平台,建立法兰盘凝固过程的三维模型。对法兰盘凝固过程的温度场和凝固过程进行数值模拟,温度最大值出现在法兰盘中心部位,最小值出现在法兰盘边缘。应用新山判据预测铸件可能出现缩孔、缩松等铸造缺陷的位置,发现在法兰盘中心处出现缺陷。     

基于混合教与学优化算法的炼钢连铸调度

根据炼钢厂的实际生产环境,建立了无等待多工艺路线的炼钢连铸模型,提出一种混合教与学优化算法求解该模型。在混合算法中,引入转换规则的教与学优化算法求解离散问题;采用变邻域搜索调整机器选择,教与学优化算法调整调度顺序的方式,将并行问题串行化。对具体实例进行测试,将人工调度方法、遗传算法、教与学优化和混合教与学优化算法的结果进行比较,验证了所提算法的可行性和有效性。     

Thermal analysis of casting dies with local temperature controller

In high pressure die casting processes, a die plays a critical role in removing heat from the molten metal during the cavity filling and solidification stages. Proper control of die temperature is essential for producing superior quality components and yielding high production rates. In this paper, a computerized intelligent real-time monitoring and control system (IRMCS) is developed for die casting processes involving cooling of a die with multiple channels. A local temperature controller is designed to monitor temperature signals from the die insert and flow rate signals from the cooling lines. The performance of the controller is evaluated, and the effect of the controller on local temperature and heat transfer of casting dies is analyzed. The experimental results obtained from a laboratory die casting process simulator indicate that the developed control system is capable of adjusting the desired supply of cooling water into multiple cooling lines, which effectively controls the local temperature of the die insert within a given range. Hence, the desired thermal pattern of the die becomes achievable.     

高压涡轮动叶气膜冷却的数值模拟

为研究旋转造成的非稳定性对高压涡轮动叶气膜冷却的影响,建立了3维涡轮叶栅通道模型,应用周期性边界条件数值模拟了不同转速下涡轮动叶表面气膜冷却效率和换热系数的分布,冷气进口与涡轮前总压比为1.07,温度比为0.5。转速增加,叶片前缘滞止线从压力面移向吸力面,气膜出流从吸力面移向压力面;压力面气膜冷却效率上升,换热系数下降;吸力面冷却效率先上升后降低;换热系数下降。与静止相比,旋转不稳定性增大了叶片表面气膜覆盖面积。     

连铸辊道冷却系统密封旋转接头泄漏分析

阐述密封旋转接头的工作原理及其失效对系统产生的影响,对密封旋转接头的密封缝隙热变形和机械变形进行分析,也分析了密封旋转接头设计中的重要参数端面比压;同时结合密封旋转接头的结构和现场工况,探讨了泄漏的主要原因,提出解决旋转接头泄漏问题的方法,为提高密封旋转接头的性能提供依据.     

板坯连铸机结晶振动研究

薄板坯连铸实现液压振动是连铸生产线上的最新技术,它对提高铸坯质量起着非常重要的作用,控制结晶器按给定的振动方式运动是连铸生产过程的关键技术.传统的结晶器的正弦振动无法满足需要.传统的机械结构无法实现这一运动规律.因此提出了基于电液伺服系统的液压传动的振动方式.     

铜扁线连续挤压生产控制系统数学模型的实验测定法

挤压腔体温度的控制作为铜扁线连续挤压生产中的主要控制过程,其受到较多因素的影响,通过解析法建立挤压腔体温度变化的数学模型十分困难,因此本文提出一种通过实验测定的方法建立被控对象数学模型的简易方法,并以此应用于系统控制方面的研究参考。