板带轧机工作辊温度场和热变形研究及其在热带钢连轧中的应用

【作者】 李兴东；

【导师】 刘宏民；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2005， 博士

【摘要】 工作辊热变形是影响带材板形和断面质量的一个重要因素。随着轧制节奏的提高、轧制规格的拓展和市场需求的提高,轧辊热变形在生产实践中对带材板形和断面质量的影响已开始日益凸现出来。在热轧轧制过程中,由于轧辊热变形的影响因素多、边界条件复杂和许多物理常数很难精确测定,准确预报轧辊热变形已成为热轧板形和断面质量控制技术中的难点。本文以热轧板带轧机工作辊温度场、热变形及其复杂边界换热条件为研究对象,进行了深入的理论和工业实验研究。首先,采用控制容积平衡法建立圆柱体三维温度场内部和边界节点差分方程,使得边界节点的差分方程更加准确和符合物理实际。分析热轧工作辊温度场的复杂边界条件,考虑到温度场仿真模型求解的复杂性,建立板带轧机轧辊二维温度场有限差分模型。首次结合带钢跑偏建立轧辊热凸度修正模型,为提高板带轧机在线热凸度计算精度提供了一个新的方法。详细分析了轧辊热流输入输出关系及特征并进行合理的工程简化,采用改进的遗传算法——实数编码、新的适应度值标定和最优个体保存策略设计了遗传操作,建立适用不同轧机工作辊关键边界换热系数的遗传算法优化模型。应用上述两个模型,考虑压下规程、轧件规格、温度、轧制节奏、冷却水流量和分布等因素的影响,对宝钢1580热带钢连轧机工作辊的温度场和热凸度进行仿真计算和工业实验,得到了工作辊下机温度场、热凸度以及工作辊下机后空冷时的温度场和热变形变化曲线。计算值和实测值吻合良好,为生产实践中实现合理的辊型磨削提供了依据。在此基础上,定量地研究了各种轧制条件对工作辊热凸度的影响。其次,全面系统地分析了宝钢1580热连轧精轧机组工作辊下机辊型从中凸形状到中凹形状波动的形成机理,首次提出了可变宽度冷却思想。以工作辊温度场和热凸度计算模型为工具,对宝钢1580热连轧机组各种典型轧制规格的工作辊冷却水轴向分布进行优化。优化结果表明:根据产品规格采用不同的冷却制度,对轧辊热辊型波动有很大的改善作用。设计制造了可变宽度工作辊水幕冷却模拟试验系统,并在实验室进行原理性和可行性试验研究。试验结果表明:所设计的装置可以实现连续的层流水幕,沿辊身轴向能够进行宽度调整;在流量无干扰区域,可实现中部水流量大于边部水流量的预期效果。为进一步研究应用于生产实际的装置提供了重要的依据。最后,将辊系弹性变形模型、磨损模型、热凸度模型和金属变形模型相耦合,建立了热连轧机带钢横断面形状模拟系统。其仿真结果与实测结果吻合良好。分析了工作辊热变形对带钢横断面形状的影响,首次提出了轧制节奏过快会导致带钢边部反翘的结论。冷轧带钢钢卷边包严重影响带钢的板形和表面质量。在1220冷轧带钢厂对钢卷边包进行大量的工业调查并首次提出探索边包根源的实验方案。通过对实验结果进行系统分析可知:冷轧钢卷边包不是由冷轧带钢的板形不良引起的,而是由冷轧带钢存在边部局部高点,且边部局部高点厚度明显大于带钢中间厚度引起的,而带钢的楔形加剧了边包。根据工作辊热变形对带钢横断面的影响规律,在1450热轧生产线进行了降低轧制节奏的工业实验。实验结果证明上述推断的正确性,从而为冷轧钢卷边包缺陷的治理提供了重要依据。更多还原

【Abstract】 The roll’s thermal deformation is an important factor for the strip shape and section quality. With the increase of rolling rhythm, the development of rolling specification and the increase of market demand, the influence of roll’s thermal deformation on the strip shape and section quality is becoming a problem in the productive practice. In the hot rolling process, it is an difficulty for strip shape and section quality control technology to accurately predict roll’s thermal deformation because the influence factors of roll’s thermal deformation are complicated, the boundary condition is intricate and many physical constants are hard to accurately measure. The roll’s temperature field, thermal deformation and complicated boundary heat exchange of hot strip rolling mill are selected as researching subject, closely theoretical study and industrial experiments are carried out.First, internal and boundary node difference equations of the cylinder’s three-dimensional temperature field are established by control volume balanced method, so that the boundary node difference equations are more accurate and according with the physical practice. The complicated boundary condition of hot rolling work roll’s temperature field is analyzed. With a view of the complexity to solve simulation model of temperature field, roll’s two-dimensional temperature field finite difference model of plate and strip mill is established. For the first time, combined with off tracking of the strip, modified thermal crown model of the roll is established, and it provides a new way for improving the computing accuracy of in-line thermal crown of plate and strip mills. The heat flow input and output of the roll are analyzed in detail and reasonably simplified. Genetic operation are designed by the improved genetic algorithm——real code, new calibration of sufficiency value and conservation of the best individual, and the optimization model of genetic algorithm about key boundary heat exchange parameters suitable for the roll of different mills is established. Considering the influence of screwdown regulations, rolled piece specification, temperature, rolling rhythm, flux and distribution of cooling water, the simulation and industrial experiments of temperature field and thermal crown of work roll are made in Baogang 1580 hot rolling mill by the above two models. The temperature field and thermal deformation curves of work roll after rolling and cooled in the air are attained and the computation values coincide better with the measured values. It provides a basis for the realization of appropriate roll shape grinding in the productive practice. Then, influence of rolling conditions on thermal crown of work roll was researched quantificationally.Second, the formation mechanics is systematically analyzed that thermal shape of work roll after rolling changes from the convexity to the concave in Baogang1580 hot rolling mill. The variable-width cooling idea is first put forward. The optimization is made for the axial distribution of cooling water of work roll corresponding to each typical rolling specifications in Baogang 1580 hot mill by the temperature field and thermal crown model. The optimization results indicate that the fluctuation of thermal roll shape is greatly improved by the cooling system determined by the product specification. The variable-width work roll’s curtain wall cooling analog experiment system is designed and manufactured, and the principle and feasibility experimental researches are made in the laboratory. Experimental results indicate that the designed devices can realize continuous laminar curtain wall, the adjustment in the roll axial direction, and the anticipated effect that middle flux is greater than the marginal flux in the no flux-disturbed area. It provides the important basis for further research on the device for the productive practice.At last, coupled the rolls deformation model, wear, thermal crown and the metal flow models, the strip cross section simulation system of hot tandem mill is established. The simulation and measured values coincide better. The influence of work roll thermal deformation on strip cross section is analyzed, and that faster rolling rhythm can cause marginal spring of strip is first brought forward. The side convex defect of strip coil of cold rolling seriously influences the shape and surface quality of the strip. On the basis of large quantity of field researches in 1220 cold rolling strip factory, experiment scheme is first brought forward for exploring the root of side convex of strip coil of cold rolling. The experiment results are systemically analyzed and can be known that the side convex of strip coil is not the result of the bad strip shape of strip coil of cold rolling, but the side local high spot of the strip, and that the thickness of side local high spot of the cold rolling strip is larger than the middle thickness, and that the wedge shape aggravates the side convex of cold rolling coil. Based on the influence of work roll thermal deformation on strip section, the industrial experiment of reducing the rolling rhythm is made in 1450 hot rolling production line. Experimental results indicate that the above deductions are correct. Then, it brings forward the important basis for the cure of the side convex defect of cold rolling coil.更多还原