上限原理在重轨万能轧制过程平均温度计算中的应用

Application of the upper-bound principle for calculating the mean temperature in heavy rail rolling by universal mill

在重轨万能轧制过程中,首先建立了简化的三维几何模型,然后分别给出了轨腰、轨头及轨底的运动学许可速度场以及相应的应变速度场和剪应变速度强度。根据上限原理分别求出了轨腰、轨头及轨底在运动学许可速度场下的塑性变形温升和摩擦温升,并且求得了轧件在相邻机架之间的穿梭温降。根据水平辊和立辊的能量平衡条件求出了接触温降,得到了轧件在单个机架上变形前后的温度变化。为了验证理论模型,对轧制过程的温度变化进行了刚塑性有限元仿真,得到了钢轨各部分的平均温度的有限元解。通过比较理论解、有限元解和实测表面温度可知,上限原理求得的平均温度值大于表面温度实测值,而且接近于有限元解,能更准确地表示轧件温度。因此,根据上限原理控制轧制温度从而控制钢轨的微观组织变化以得到高质量钢轨是可行的。

In heavy rail rolling by universal mill,a simplified 3-dimention geometrical model has been built firstly.The kinematically admissible velocity field of the web,head and base of rail have been determined respectively,moreover the corresponding shear strain rate have been also obtained.Then the temperature rise for plastic deformation and friction in corresponding deformation zone have been proposed by the energy principle,and the temperature drop of workpiece for shuttling between two adjacent stands has also been solved.Moreover,according to the equation of heat equilibrium of horizontal roll and vertical roll,the temperature drop for contact can be obtained.So the mean temperature of workpiece can be predicted.For verifying the theoretical model based on the upper-bound principle,the rolling process has been simulated by Rigid-Plastic FEM and a solution of mean temperature from FEM can be obtained.Compared with the result from FEM and experimental data,the mean temperature from upper-bound principle is greater than the surface temperature measured on the rolling field and approaches the solution from FEM.It can represent the true temperature well.So,it is reliable and feasible to predict the temperature and control the evolution of microstructure for obtaining a high-quality rail by the energy-principle.