Experimental Study On Low Adhesion And Improving Adhesion Measures

With the rapid development of railway transportation, especially the implementation of high-speed and heavy-haul strategies, the power locomotive produces and the force transmitted between wheels and rails increase gradually. The acceleration and deceleration capabilities of rolling stock are limited by wheel-rail adhesion which is influenced by many factors. Thus, study on wheel-rail adhesion is an important and basic subject which railway departments pay more attention on. Research on how to improve the wheel-rail adhesion has an important guiding significance for the safe operation of trains.According to Hertz simulation rule, the common external factors of causing low wheel-rail adhesion, such as water, oil, leaves, etc, was investigated using the MMS-2A wheel-rail tribological simulation facility. The creep ratio and water temperature were changed to observe the adhesion coefficient change. The effect of alumina particles, sand and abrasive agent on improving adhesion under water condition, namely low adhesion condition, was analyzed. Wear properties and surface damage behaviors of wheel/rail with three different third media were investigated in detail using various examinations such as electronic balance (TG328A), hardness tester (MVK-H21), optical microscope (OLYMPUS BX60M) and scanning electron microscope (FEI Quanta200). According to the experiment, this paper arrived at conclusions as follows:(1) With the increase of creep ratio, the adhesion coefficient increases firstly and then gradually drops to a stable value under different conditions under dry, water and oil conditions. Under water and oil conditions, the adhesion coefficient decreases significantly and low adhesion more likely to occur. It decreases the most under oil condition. The adhesion coefficient becomes lower under the water condition by reducing water temperature. Saline water decreases adhesion coefficient more compared with water.(2) Under water and oil conditions, the effect of improving adhesion by spraying alumina is the best, sand the second, abrasive agent the worst. With sand or alumina in the contact the adhesion coefficient fluctuates quite a bit. However, a smoother curve is acquired under abrasive agent condition.(3) Under water condition, the effect of alumina particles, sand and abrasive agent on increasing adhesion coefficient is obvious. With sanding, the roughness of wheel/rail surfaces increases the most and the wear loss is the biggest. Meanwhile, the hardness increases significantly, the spalling of surfaces becomes more serious, and the plastic deformation layer is the thickest. Compared with sanding, with alumina particles, the wear volume is smaller and the plastic deformation layer is thinner. With abrasive agent, the wear volume is the smallest and no obvious plastic deformation layer can be observed. The wear mode is predominated by abrasion and adhesive wear under sands or alumina particles conditions, but only abrasion wear under abrasive agent condition.(4) The adhesion coefficient decreases more under fallen leaves condition than oil. And it decreases further when the fallen leaves are mixed up with water. The adhesion coefficient is the smallest with fresh leaves. Some scratches and deep indents could be seen under fresh leaves and the increases the surface roughness. Under fallen leaves condition, alumina particles, sand and abrasive agent could increase adhesion coefficient. The sand increases the adhesion coefficient the most while aggravates the disc surfaces.