热轧带钢层流冷却过程温度场研究

 建立了热轧带钢层流冷却过程中温度场的三维有限元模型,对3 mm厚带钢轧后冷却过程带钢温度场进行模拟计算,得出卷取温度比现场测量值低9.5 ℃,相对误差为1.42%,验证了模型和假设的合理性。研究了上喷嘴直径对带钢温度的影响,带钢上表面宽度方向上存在2种不同的冷却区域：位于喷嘴正下方层流冷却过程中交替经过冲击区和平流区的区域和位于两喷嘴之间层流冷却过程中只经过平流区的区域,这造成带钢宽度方向上温度分布不均匀。计算结果表明,喷水量保持不变的情况下,存在一个最佳喷嘴直径,使带钢宽度方向上温度分布更均匀。喷水速度保持不变,增加喷嘴的直径有利于带钢宽度上方温度均匀,但增加了喷水量,降低了带钢的卷取温度。     

横向温度分布对无取向电工钢热轧板形的影响

摘要： 电工钢热轧凸度和楔形难以满足日益增高的板形质量要求。为了揭示横向温度分布对无取向电工钢热轧板形的影响规律,建立了三维弹塑性有限元模型,有限元模型中的带钢材料模型以其热塑性本构模型为依据进行设定。通过有限元仿真计算分别研究了电工钢热轧过程两相区和单相区轧制温度条件下带钢横向温度抛物线分布、边部温度下降和横向温度倾斜分布3种典型温度分布特征对板形的影响规律。研究发现,两相区轧制时,横向温差易引发凸度增大、边降增高等板形问题;单相区轧制时,横向温差则会导致凸度减小甚至下凹、边部翘起等问题;较小的横向温度倾斜分布即会引发巨大的楔形缺陷。电工钢热轧过程应严格控制横向温差,以降低其对板形的不良影响。     

机架间冷却数学模型计算带钢温度分布

为提高带钢终轧温度的控制精度 ,对精轧过程中导致带钢温度变化的热交换过程进行了分析 ,以此作为机架间冷却控制的传热模型和自学习模型的理论依据 ,给出了带钢厂热轧机组机架间冷却在线控制的传热和自学习模型的算法 ,通过程序开发对精轧机组内带钢的温度分布进行了离线模拟 ,终轧温度计算值与实际生产数据符合较好 ,并对所用数学模型的实际计算结果进行了分析     

热轧带钢轧后冷却过程卷取温度的设定策略

为了提高热轧带钢卷取温度控制精度,针对热轧带钢轧后冷却过程非线性、强耦合性等特性,建立了具有非线性结构特征的热轧带钢轧后冷却过程控制的温度数学模型,并对热轧带钢轧后冷却过程卷取温度的设定策略进行了研究,同时在该模型基础上开发了系统软件,通过现场实际应用对模型功能进行了验证.结果表明,该冷却数学模型的卷取温度设定计算结果与实测结果吻合较好,卷取温度控制精度可达到±10℃,表明该模型取得了较好的应用效果,能够达到较高的控制精度.     

带钢层流冷却过程中冲击穿透深度的数值模拟

带钢在层流冷却过程中距表面较近的区域温度存在反复升降的现象,造成厚度方向上组织和性能的差异。结合酒钢CSP热轧带钢生产数据,建立一维热轧带钢有限元模型,计算层流冷却过程中带钢的温度场。提出了冷却过程中带钢冲击穿透深度的概念,并初步探究其影响因素。厚度为3和4mm的带钢计算得出的卷取温度比实测温度分别高3和8℃,相对误差分别为0.44%和1.16%,验证了模型和假设的合理性。结果表明,冷却过程中冲击穿透深度受带钢的导热系数、平流区的对流换热系数、带钢表面温度和喷嘴分布的影响;带钢上表面喷嘴分布较少,冲击穿透深度随对流换热系数的增大而增加,下表面喷嘴分布密集起主导作用,增加对流换热系数,冲击穿透深度几乎不受影响。     

基于有限元和试验的热轧带钢残余应力减量化

 研究残余应力减量化技术可提高热轧带钢板形质量。有限元技术及相应的试验验证已广泛应用于工业生产,采用该方法对带钢层流冷却过程中的温度、相变及应力耦合进行求解,对于分析带钢轧后冷却不均、应力应变不均及翘曲具有重要意义。基于ABAQUS建立热轧带钢在密集冷却工艺条件下的有限元模型,实现温度、相变和应力三者的耦合计算,并进行温度测试、材料微观组织测试及应力测试等多个试验验证。计算结果表明,减小带钢进入层流冷却前的初始温差、采用边部遮挡技术对减少带钢残余应力均具有积极的意义。通过一个改善初始温差分布进而改善带钢残余应力的实例,验证了提出的方法和结论的正确性。     

热轧带钢层流冷却过程的温度预测模型

 通过分析热轧带钢在层流冷却过程中的能量变化,利用焓法模型建立了热轧带钢通过层流冷却段的能量平衡方程。然后利用相变热力学和相变动力学模型得到热焓,最后采用有限差分求解能量平衡方程,得到层流冷却过程中带钢的温度场和热焓场,该模型的计算结果与实测值符合良好,能够准确地预测带钢冷却后的温度分布,同时明确了冷却过程实际上是带钢能量传递给周围环境的过程,并非温度不断下降的过程。     

PC轧机轧制宽带钢过程轧制力与轴向力分布规律研究

针对PC轧机带钢热轧过程的工艺特点和存在问题,利用ANSYS/LS-DYNA建立轧辊和带钢耦合的三维轧制过程的有限元模型,模拟计算不同工艺条件下的带钢变形。重点分析了PC轧机轧制过程中的轧制力和轴向力变化规律。     

基于温度观测器的层流冷却路径控制

热轧带钢需要更加灵活的冷却控制策略,保证带钢能够按照设定的冷却路径冷却,以充分发挥冷却过程的相变、析出等强化功能。为此,提出了基于温度观测器的带钢温度控制方法,通过物理模型构造温度观测器在线观测带钢温度并根据测量温度在线修正观测器模型参数。在此基础上应用最优控制方法,实时优化各个冷却单元阀门设定,保证温度观测器估计值与目标温度分布曲线设定值偏差最小。实际应用结果表明,该方法能够较好的控制带钢温度,同时能够克服固定冷却制度的限制,实现冷却路径控制。     

热轧带钢在冷却过程中的内应力解析

针对热轧带钢的冷却过程,开发了温度、相变的内应力的耦合解析模型,该模型采用有限元法,同时考虑了相变的温度依存性、相变潜热、相变膨胀。通过该数值解析模型,能够模拟热轧带钢在冷却过程中温度一组织内应力的演变过程,计算结果与实测值符合良好。     

热轧带钢温度场数值模拟研究现状

综述了热轧带钢温度场数值模拟的研究现状，包括加热炉内钢坯加热、轧制过程轧制件传热，层流冷却过程带钢数值模拟等研究。利用有限差分法分法或有限元法模拟扎件的温度变化，能有效优化轧制工艺，提高产品质量，对生产有重要指导意义。     

热连轧轧辊瞬态温度场研究

考虑水冷、空冷、轧辊与轧件接触热传导等动边界条件，采用有限差分法，建立了热连轧轧辊瞬态温度场变步长分析计算模型。该模型能实现轧辊温度场的动态分析和精确计算，预测轧制时以及终轧后空冷的轧辊瞬态温度场。试验和仿真结果表明，所建立的分析计算模型考虑因素全面、合理，计算精度较高，计算值与实测值吻合良好，真实地反映了轧辊的温度变化情况。     

Full-length model with multi-point settings for finishing rolling

Thickness,width,temperature,and profile are considered as control targets in process control of hot strip finishing rolling. The pre-calculated settings of the model information include rolling force,cooling water flow between stands,bending force,and roll shifting position. Without changing the load distribution,the interaction among thread speed,rolling force,rolling power,and cooling water flow between stands is comprehensively considered based on the quantifiable relationship among speed,force,and temperature. This paper proposes a full-length multi-point-setting model that uses the settings of strip head to combine the rolling speed diagram with the target finishing mill delivery temperature( FDT) to achieve the calculation of the control parameters along full length of strip. Traditional models cannot effectively predict rolling force of strip body or the maximum and minimum temperatures of FDT. It is also difficult for traditional models to suppress fluctuations in shape accuracy of full-length strip or improve the shape accuracy of the product. Calculation results show that the proposed full-length multi-point-setting model can provide the control parameters for temperature and rolling-force over full length of strip,predict the risk of rolling exceeding the equipment capability,and improve the shape accuracy and rolling stability of hot-rolled products.     

Modelling the Temperature Distribution along the Length of Strip during Hot Rolling Process

Hot strip rolling process includes four main stages, which are reheating process, roughing and finishing process, laminar‐cooling process, and coiling process respectively. Temperature is the most sensitive parameter and has direct effect on the microstructural evolution and further the mechanical properties, and the accurate control of temperature guarantees the quality of products and homogeneity of properties along the strip length. However, for the conventional hot strip rolling process, thermal history along the strip length is very complex, the related temperature variation concerns air cooling, water cooling, heat transmission by roll contact, heat generation by deformation and friction. Based on the actual hot strip mill, the thermal models are established in this paper to simulate the temperature distribution along the whole strip length from the reheating furnace exit to the down coiler. Different interface heat transmission coefficients are selected for the scale breaking and spray water‐cooling process, and a self‐learning algorithm is thus employed to improve the calculation accuracy. This model is characterized as simple and fast, and convenient for on‐line/off‐line prediction of temperature. Finally the simulated results are verified by the on‐line temperature detection at typical points such as roughing exit (RT2), finishing exit (FT7) and coiling position (CT).     

负荷分配对精轧带钢温度的影响

用带钢热连轧精轧温度控制模拟软件,系统地研究了负荷分配对带钢精轧轧制过程中变形温升、水冷温降以及精轧出口温度的影响,并总结出了相应的规律,为建立高精度热连轧带钢温度控制模型提供了理论依据.     

方坯直轧工艺中头尾温差消除过程数值模拟

方坯直轧工艺有一个难以避免的问题，即钢坯头尾温差问题，当头尾温差过大时，会对产品长度方向上组织性能均匀性产生不利影响。针对方坯直轧工艺下钢坯“头低尾高”的温度特点，提出采用在精轧前进行“头弱尾强”的变水量冷却策略，或在粗轧前进行“头强尾弱”的变功率感应补热策略，并利用有限元法分别对上述两种过程进行数值模拟，根据计算结果对关键工艺参数进行优化设计，为实际应用提供参考。模拟计算结果表明，对于变水量冷却方式，为消除纵向上线性分布的头尾温差，所需水流密度与轧件长度基本呈抛物线关系；对于变功率感应补热方式，所需补热功率与钢坯长度基本呈线性关系。     

Stress–Strain State of Coiled Steel

In a new mathematical model of the stress–strain state of steel strip in the course of cooling, the nonplanarity, surface roughness, and transverse thickness variation (convexity of the cross section) are taken into account. The stress–strain state of a coil of thin steel sheet has a significant influence on factors such as the temperature distribution in the coil; the scale formation on cooling in the course of hot rolling; the adhesion of adjacent turns in the annealing of cold-rolled strip; and the shape of the coil itself. The mathematical model is based on representation of the coil as individual nested hollow cylinders of finite length. The cylinders are divided into sections over the width. The sum of solutions of the Lame equation for individual sections is shown to converge to the solution for the cylinder as a whole. The model permits calculation of the coil’s stress–strain state, taking account of gap formation between adjacent turns as a result of the transverse variation in strip thickness. The modeling results show how the radial and tangential stress formed in strip winding is distributed within the coil. The model permits calculation of the stress–strain state of the coil in the winding of even strip; in the winding of convex even strip with no tension; in the loose winding of convex even strip with tension less than that in tight winding; in tight winding of even convex strip with the correct tension; and in the winding of convex uneven strip without tension. The decrease in distance between contacting rough surfaces is calculated on the basis of a probabilistic approach. An algorithm is presented for calculation of the coil’s stress–strain state. The result obtained for the stress distribution in the coil is typical for the winding of steel strip. The model is verified for the winding of hot-rolled strip, in terms of the size of the region with tight contact of adjacent turns. The tightness of contact is assessed on the basis of the temper color on the edges of the hot-rolled strip. The discrepancy between the calculated and measured size of the region with tight contact is 3%.     

Analysis of Strip Temperature in Hot Rolling Process by Finite Element Method

 The program was developed by finite element method to calculate the temperature distribution in hot strip rolling. The heat transfer coefficient of air cooling, water cooling and thermal resistance between work roll and strip were analyzed. A new heat generate rate model was proposed according to the influence of source current density, work frequency, air gap and distance to edge on induction heating by finite element method (FEM). The heat generate rate was considered into the thermal analysis to predict the temperature distribution in the induction heating. The influence of induction heating on the strip temperature was investigated with different strip thicknesses. The temperature difference became more and more obvious with the increase of thickness. The strip could be heated quickly by the induction heating both in surface and center because of the thermal conductivity and skin effect. The heat loss of radiation has important influence on the surface temperature. The surface temperature could be heated quickly with high frequency when the strip is thicker.     

数据驱动的卷取温度模型参数即时自适应设定算法

为提高热轧换规格首块钢头部卷取温度命中率,采用数据挖掘技术,从历史带钢冷却数据中推断出与实际带钢相匹配的卷取温度模型水冷换热学习系数,并将其应用于模型预设定计算。首先,对冷却特征参数进行识别,按照相对型、绝对型、相等型和策略型四种方式进行定义,并对实际带钢与历史带钢的各项冷却特征参数进行相似距离计算。当历史带钢的总相似距离满足要求时,将其聚类为实际带钢的相似卷,并考虑各相似卷的时间影响,计算相似权重值;随后,基于相似带钢的头部和尾部信息,建立由卷取温度预报误差、偏离学习系数回归值惩罚项和偏离默认值惩罚项等构成的目标函数以及相应的约束条件,采用梯度下降法求解该二次规划问题,通过三次优化逐步计算出学习系数参考值和表征学习系数与带钢速度及目标卷取温度呈双线性关系的两个参数;最后,根据实际带钢的穿带速度、目标卷取温度等冷却条件计算冷却设定所需的学习系数。现场应用表明:基于十万块历史带钢冷却数据驱动的模型参数即时自适应设定算法可增强卷取温度模型对带钢头部冷却的预设定能力,学习系数即时自适应设定能力随着内存中保存的历史带钢冷却数据的多样性和检索出的相似卷数量的增加而提升。