大圆坯连铸凝固传热过程的数值模拟

以Φ600 mm大圆坯连铸为研究对象,建立了描述连铸大圆坯凝固传热的柱坐标一维瞬态传热数学模型,计算了连铸坯的温度场,并分析了拉速、过热度和钢种对铸坯表面温度和凝固进程的影响.分析结果表明拉速对凝固终点位置影响明显,拉速每提高0.05 m/mm,凝固终点后移约3.87m.其计算结果与实际生产的实测数据吻合良好.     

考虑圆坯周向冷却均匀性的传热模型研究及应用

圆坯周向上冷却的均匀性对铸坯的质量有着重要影响,易引发纵裂纹、椭圆度等质量问题。基于此,特建立圆坯的径向和周向二维凝固传热模型,充分考虑其在圆周向上喷淋冷却的均匀性。利用喷嘴与圆坯间的几何映射关系,结合喷嘴冷态性能测试数据,推导并计算出沿圆坯周向上的水流密度分布。相比于板坯等平面喷淋,圆坯曲面喷淋沿周向上水流密度衰减更为急剧,喷淋的均匀性更不易控制。将模型应用于某大圆坯连铸机的凝固传热计算,考察了铸坯各二冷区末端周向上的冷却均匀性,其中一区最大温度偏差19℃,二区12℃,三区7℃,四区5℃。除此之外,计算了铸机保温罩设计对铸坯温度场的影响,相比于无保温罩,铸坯表面温度在保温罩出口区域提升了61℃,凝固终点向后推移了约1 m。     

普通绞线钢的连铸二冷技术研究

通过热模拟试验研究了钢绞线用钢连铸坯的高温塑性曲线,结果表明为保证铸坯质量,须确定连铸拉矫温度在1 020℃,并建立了连铸二冷配水模型,通过PROCAST仿真模拟钢绞线用钢凝固过程的冷却曲线。射钉试验和生产实践证明采用该二冷配水技术可有效改善铸坯质量,降低铸坯低倍检验中的裂纹缺陷级别。     

热送热装工艺中板坯出连铸机温度的分折

用连铸坯凝固过程传热模型模拟了热送热装工艺中不同工况下铸坯凝固壳厚度和铸坯出连铸机的温度变化。模拟结果与实测值吻合很好。影响铸坯出连铸机温度的主要因素是铸坯尺寸、连铸机拉迪和冷却制度。适当提高拉速及改善连铸机二冷区冷却制度有利于高温铸坯的生产。     

热送热装工艺中板坯出连铸机温度的分析

用连铸坯凝固过程传热模型模拟了热送热装工艺中不同工况下铸坯凝固壳厚度和铸坏出连铸机的温度变化。模拟结果与实测值吻合很好。影响铸坯出连铸机温度的主要因素是铸坯尺寸、连铸机拉速和冷却制度。     

超宽板坯热装直送工艺实践研究

中厚板坯热装直送工艺可大幅度降低加热炉能耗，降低钢材生产成本。南钢超宽板坯因宽厚比大，极易产生纵向裂纹，南钢板材铸机表面纵向裂纹发生率高，且超宽板坯因铸坯平整度差去毛刺困难，且在热装直送过程中因两相区温度区间入炉，导致钢板表面产生了热装裂纹，因此宽板坯纵向裂纹、去毛刺和热装裂纹问题成为南钢板材铸机实现流程优化、铸坯热装直送和节能降耗的关键问题。详细描述了南钢超宽板坯铸机热装直送工艺实践过程，优化铸机去毛刺工艺，并对产生的板坯纵向裂纹和钢板表面热装裂纹产生原因进行分析，优化影响板坯表面纵向裂纹连铸生产工艺制度，同时根据钢种成分特点，调整优化不同钢种成分钢种坯料堆冷时间和控制入炉温度，避开热装裂纹敏感温度区，避免了热装裂纹，实现了超宽板坯热装直送工艺，降低了轧钢加热炉生产能耗。     

高碳耐磨球钢大方坯连铸过程凝固性能的仿真分析

应用有限元分析软件建立290 mm×380 mm大方坯连铸过程凝固传热模型,模拟不同碳质量分数高碳耐磨球钢大方坯宽面和窄面凝固坯壳的生长规律。研究结果表明:该模型通过计算得到铸坯宽面的外壳温度还有铸坯宽面、窄面中心的凝固坯壳厚度进行对比分析,验证了该数学模型可以表达凝固坯壳厚度的分布情况,最终达到准确推测凝固终点位置的目的。在弯月面到二冷出口这一阶段,凝固时间和凝固坯壳厚度d显示出线性关系。在距弯月面10 m到凝固终点这一阶段,凝固时间t1/2和坯壳厚度d并不是线性关系,且铸坯中心等轴晶区域出现。     

薄板坯连铸传热过程与应力状态仿真软件的开发

基于准稳态二冷凝固传热数学模型和高温弹塑性应力应变数学模型,开发了薄板坯连铸传热过程与应力状态仿真软件CISDI_HPSS FOR THIN SLAB R2009,其中详细考虑了二冷区存在的多种传热方式和铸坯宽度方向上喷淋冷却的非均匀性以及夹辊支承、钢水静压力、拉坯、矫直等因素对铸坯高温力学变形的影响,软件对凝固传热和应力应变的耦合计算功能强大,具有良好的通用性和适用性,其仿真结果可用于优化薄板坯连铸机的工艺和设备参数,为相关工艺技术的开发和铸机工程设计提供重要的理论支撑。     

小方坯帘线钢末搅参数的优化研究

以小方坯帘线钢的连铸生产为研究对象,采用ProCast商业软件根据实际生产的工艺参数建立铸坯的凝固传热模型,并利用射钉试验对模型进行校正以提高模型的准确性。结果表明,该凝固传热模型可以模拟帘线钢的连铸生产过程。根据射钉试验和数值模拟结果,对末搅位置进行改进,可发现铸坯中心缩孔等级下降,等轴晶率增大。     

利用旋转坐椅施行经皮肺穿术

连铸坯的热送热装是目前国内外正在研究的重要课题之一，减少连铸坯在辊道输送过程中的温降是提高热装温度的重要途径。本文根据板坯在输送过程中的散热二维数学模型，分别研究了辊道上部加保温罩和不加保温罩两种情况下对板坯温降的影响，经现场测试验证，所建模型可用，计算结果可供现场生产参考。     

热处理钢板气雾冷却数学模型的开发与应用

针对某钢厂新建的热处理钢板气雾冷却装置,基于有限差分传热仿真计算,开发了相应的热处理钢板气雾冷却数学模型,其中详细考虑了钢板在冷却区内所经历的多种传热边界条件,包括水冲击传热、辊子接触传热、辐射传热和自然对流传热。通过现场的钢板表面温度测试工作表明,模型预测值与实际测试值之间的吻合情况良好,模型具有较高的仿真精度。应用该模型,按照一定的热处理工艺要求(主要指对出口温度和钢板表面/中心温降速率的控制),对气雾冷却区进行了冷却水表的理论设计(即各种厚度规格钢板所对应的冷却水流量),其设计结果已成功地应用于生产现场。     

板坯连铸异常事件在质量诊断模型中的冶金考虑

在板坯质量在线诊断分析预测模型CISDI_SQDS ONLINE R2011中详细考虑了浇铸过程中可能发生的各类异常事件,并按事件发生的等级程度引入其对相应裂纹生成指数的影响大小,同时针对事件状态的读取采用人工设定和自动判定两种方式,且分别讨论了各类事件在当前铸流中的影响范围.模型已成功投入现场工业应用,运行结果表明:模型对异常事件状态的读取准确可靠,事件的影响因子取值合理,能正常反映出事件对相关质量缺陷的影响程度.     

A multi-zonal integral method for problems involving unsteady one-dimensional heat conduction with change of phase

A method is presented for calculating the temperature in a solidifying slab of molten material with greatly differing cooling rates on the inner and outer surfaces. For the purposes of analysis the slab is divided into a number of zones having time-varying boundaries, e.g. solidification or conduction fronts. Appropriate approximations are made for the temperature profile and the heat-balance integral equation applied separately in each zone. This leads to systems of first-order ordinary differential equations which can be integrated numerically by using simple standard methods. Results are presented which correspond to the industrial casting of polypropylene film.     

板坯质量在线诊断分析系统的研究与开发

针对板坯表面裂纹和内部裂纹两大类质量缺陷,基于凝固传热仿真、应力应变计算及连铸相关冶金工艺理论分析,并结合浇铸异常事件专家知识库方法,开发了CISDI板坯质量在线诊断分析数学模型及其应用软件CISDI_SQDS ONLINE R2011,其中引入裂纹生成指数来作为质量评级的参考理论指标,并在其计算过程中耦合考虑了与浇铸冶金准则密切相关的质量损失因子和异常事件对应的调节因子,实现了理论解析与专家系统的有机结合,为板坯质量的预测和控制提供了重要的理论工具,以期在板坯连铸生产中得以有效的推广应用。     

Estimation of the transient surface temperature and heat flux of a steel slab using an inverse method

In the steel industry it is of great importance to be able to control the surface temperature and heating- or cooling rates during heat treatment processes. An experiment was performed in which a steel slab was heated up to 1250 °C in a fuel fired test furnace. The transient surface temperature and heat flux of a steel slab is calculated using a model for inverse heat conduction. That is, the time dependent local surface temperature and heat flux of a slab is calculated on the basis of temperature measurements in selected points of its interior by using a model of inverse heat conduction. Time- and temperature histories were measured at three points inside a steel slab. Measured temperature histories at the two lower locations of the slab were used as input to calculate the temperature at the position of the third location. A comparison of the experimentally measured and the calculated temperature histories was made to verify the model. The results showed very good agreement and suggest that this model can be applied to similar applications in the Steel industry or in other areas where the target of investigation for some reason is inaccessible to direct measurements.     

板坯内部裂纹质量损失因子的理论研究

针对板坯内部裂纹质量缺陷的在线理论诊断分析,基于板坯连铸冶金限制准则的全面考虑,从传热状态、力学行为和钢种特性等多方面着眼,在数学模型中引入了多个重要的质量损失因子用以计算相应的裂纹生成指数,并结合板坯连铸生产的冶金特点、通过深入的理论研究获得了相关损失因子的数值计算方法及其对质量缺陷的影响效果,为板坯质量诊断模型的开发提供了必要的理论支持,具有良好的理论意义和应用价值.     

Evaporative cooling of water in a mechanical draft cooling tower

A new mathematical model of a mechanical draft cooling tower performance has been developed. The model represents a boundary-value problem for a system of ordinary differential equations, describing a change in the droplets velocity, its radii and temperature, and also a change in the temperature and density of the water vapor in a mist air in a cooling tower. The model describes available experimental data with an accuracy of about 3%. For the first time, our mathematical model takes into account the radii distribution function of water droplets.Simulation based on our model allows one to calculate contributions of various physical parameters on the processes of heat and mass transfer between water droplets and damp air, to take into account the cooling tower design parameters and the influence of atmospheric conditions on the thermal efficiency of the tower. The explanation of the influence of atmospheric pressure on the cooling tower performance has been obtained for the first time.It was shown that the average cube of the droplet radius practically determines thermal efficiency. The relative accuracy of well-defined monodisperse approximation is about several percent of heat efficiency of the cooling tower. A mathematical model of a control system of the mechanical draft cooling tower is suggested and numerically investigated. This control system permits one to optimize the performance of the mechanical draft cooling tower under changing atmospheric conditions.     

Dynamic model for ladle preheater performance evaluation

Molten steel produced in an electric arc furnace is poured into a ladle and transported to a continuous casting machine. In order to minimize the heat losses during transportation, the inner surface of the ladle is lined with refractory material. Also, this inner surface needs to be preheated to prevent the cooling of the molten steel below the casting temperature. The paper describes a dynamic model for a ladle preheater with the objective of predicting the heat-up time. It has been validated by experiments performed on an existing ladle in an iron and steel mill. The results predicted by the model are sufficiently accurate for practical use. The model is further used to investigate several important operating parameters that are expected to shorten the heating time, conserve energy and increase the productivity.