摘要
大电流高速滑动电接触环境下,多次发射后轨道表面出现铝沉积现象.电枢与铝沉积层在界面热源作用下发生熔化磨损会改变接触状态,严重影响滑动电接触性能.界面热源在电枢和沉积层轨道间的热分配特性是研究界面材料熔化磨损的基础,因此有必要对滑动电接触界面热量分配过程进行研究.该文首先建立了电枢和沉积层轨道热传递模型,获得了电枢和沉积层轨道温度分布方程.根据界面温度连续性,推导热分配控制方程,应用最小二乘估计法优化误差函数,提出了基于最小二乘估计法的界面热分配数值计算模型.基于热分配数值计算模型,研究分析了材料热参数、速度对热分配特性的影响规律,结果表明:材料热参数影响热分配曲线的初始值,速度影响热分配曲线的衰减速率,速度越大热分配随时间衰减越快.最后,通过理论分析探讨了枢轨界面热分配过程的物理机制,理论分析结果与数值计算结果一致.研究成果可以为界面热过程提供更加深入的理解,为界面材料熔化磨损特性的研究提供技术支持.
Abstract
Aluminum deposition phenomenon occurs on rail's surface after a multishot at high-speed sliding electrical contact with a large current. The melt-wear of armature and deposited aluminum at the interface due to huge heat source's thermal effect can change contact condition,significantly affecting sliding electrical contact performance. The heat partition characteristics at interface between armature and deposited rail are crucial for investigating melting and wear of interface materials. Therefore,it is necessary to study the heat partition process at sliding electrical contact interface. Initially,this study established a thermal transfer model to derive the temperature distribution equations for armature and deposited rail. Control equation for heat partition is obtained by utilizing the principle of interface temperature continuity. Applying the least squares estimation method to optimize error function,a numerical calculation model for interface heat partition is proposed.Heat partition curves are calculated for varying material parameters based on numerical model for heat partition. Numerical results for heat partition's initial value are consistent with analytical solution. The results show that:the larger the heat absorption coefficient,the smaller the heat partition's initial value. As time progresses,the heat partition value is gradually decaying. While maintaining constant velocity,the heat partition decaying curves closely coincide across different material parameters. In order to study the effect of velocity on heat partition value,the actual launching velocity is compared with uniform velocity and uniform acceleration,assuming that three forms of motion reach 300 m/s at 0.5 ms. It can be found that heat partition is maximum for actual variable acceleration motion and is minimum for uniform velocity. At started-up stage for armature,velocity is maximum under uniform velocity and the heat partition curve decays faster,but as the velocity increases,the heat partition curve decays fastest in the actual variable acceleration case. It shows that the velocity curve determines the change trend for heat partition curve,the larger the velocity the smaller the heat partition,and the larger the acceleration the faster the heat partition decays. However,the heat partition values are also approximately equal when armature velocity are equal at the same moment. For example,if uniform velocity,uniform acceleration,and actual variable acceleration all reach 300 m/s at 0.5 ms,the heat partition values in the three forms of motions at the moment of 0.5 ms are all around 0.25.In the end,physical mechanism of the heat partition process at the interface between the armature and rail is discussed theoretically. It is found that the theoretical analysis results are consistent with the numerical calculation results. The following conclusions can be drawn from above analysis:(1) Heat partition value is related to launching velocity,material thermal parameters,contact length,and launching time. Material thermal parameters affect initial value of the heat partition curve and does not change its decaying rate. (2) Launching velocity affects the heat partition's decay rate,the larger the velocity the faster the heat partition decays with time. Under the same moment and velocity conditions,the heat partition value is equal. (3) During the entire launching process,the heat partition decreases with increasing velocity,and when the velocity reaches a very high level,the heat partition tends to a stable value,and most of the heat at the interface is finally transferred into the rail.
维普
万方数据