| After the railroad has been running for a period of time,there are various kinds of damages on the rail surface,such as rail corrugation,surface spalling,fatigue crack and so on.If these surface damages are not removed in time,the operation safety of railway will be seriously affected.Rail grinding as an effective and economical way to alleviate surface damage is widely used in the maintenance of railway track.The grinding effect of the rail-grindstone interface in grinding process makes most of the energy enter the rail surface.Unreasonable parameters will make the rail material micro-structure change even there are "rail grinding blue" phenomenon.Therefore,it is important to study the influence of different grinding parameters on the temperature rise of rail grinding interface and t he grinding burn behavior of rail,which has important guiding for improving rail grinding quality.In this study,a real-time temperature measurement system was designed for measuring the temperature of the interface of rain and grinding stone.A n inserted semi-artificial thermocouple method(ISTM)is used to evaluate the effects of grinding pressure,rotational speed and grinding stone size on grinding rail temperature.In particular,the mechanism of rail grinding burn and the relationship between grinding temperature and rail burn are clarified using various micro-examinations.And a thermo-mechanical simulation model is used to research the influence of different test parameters on the surface residual stress after grinding.The main conclusions are as follows:(1)An inserted semi-artificial thermocouple method was used to accurately evaluate the evolution of rail grinding temperature.The grinding temperature of every grinding cycle can be divided into three stages including rapid rising stage,index falling stage and slow cooling stage.The maximum surface temperature of grinding rail increases with an increase in rotational speed and the decrease of grain size of grinding stone.The temperature increases with the increase of the grinding pressure.Whe n the grinding pressure is 1000-1500 N,the increasing trend of the grinding temperature is more obvious.But the grinding pressure is 1500-2000 N,it becomes slow down.(2)The essence of rail grinding burn is that the grinding temperature rise causes the aggravation of rail surface oxidation and the accumulation of nonferrous oxides.When the grinding temperature is above 600 °C,the grinding burn occurs on the rail grinding surface and accompanies by the formation of WEL.The thickness of WEL immediately increases when the grinding temperature exceeds complete austenitizing temperature of rail material.(3)The grinding temperature has a significant impact on the status of grinding rail surface.The relationship of surface state,grinding burn and grinding temperature of rail specimen is established.As the grinding surface temperature increases,the color of burn surface turns from normal color and yellow to blue and purple.The surface roughness first increases and then decreases.However,the surface hardness first increases and then decreases,eventually it increases again.When the grinding temperature ascends to 802 °C,visible grinding cracks and quenching cracks are observed on the rail surface.The tensile stress resulting from mechanical and therma l effects may cause the initiation of grinding rail surface cracks.(4)The thermal stress plays a leading role in the grinding process.With the increase of grinding pressure and rotational speed,the surface residual stress increases.With the increase of grinding train speed,the surface residual stress decreases. |
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