| With the high development of the electrified railway, the work condition of the pantograph strip becomes worse and worse, which is the most important current-collecting element of the electric locomotive. Based on the existing problems of the pantograph-catenary system of high-speed railways, a series of friction and wear tests were carried out to explore the solution to the problems. The test work and relevant results are presented as follows:1. The contact resistance of the contact strip and the contact wire will change as the train is running. The changing contact resistance will change the Joule heat and will effect the temperature of the contact material. The physical and chemical properties of the material will change because of the local rising temperature, which will lead to serious wear. In the third chapter, the influence of the offline distance, contact force and relative sliding speed on the contact resistance behavior of the pantograph-catenary system of the high-speed railway at the condition of v=50-200 km/h,I=50?250 A, Fn=30-140 N is studied. The influence of the contact resistance on the current-carrying efficiency and the analysis of the strip wear morphology is also performed. Results show that the contact resistance between the contact strip and the contact wire will increase with the increase of the relative sliding speed, and will decrease with increasing contact force in a certain range. There is a small contact resistance at about 0.0224 ? when the contact between the contact strip and the contact wire is good, and the contact resistance will increase with the increasing of the contact distance in a certain range. The reslut also shows that the current-carrying efficiency will decrease with the increasing of contact resistance. The worn surfaces of the strip are analyzed using scanning electron microscopy (SEM) and optical microscope (OM). It is found that the arc ablation will increase with the increasing of the relative sliding speed, and there are lots of ablation points and spalling on the worn surface.2. Since the tmperature of the worn surface has an improtant influence on the wear of the contact materials, it is important to investigate into the variation in temperature during sliding electric contact. Therefore, a series of experimental tests with different electric sliding parameters are carried out to study the influence of different parameters on the temperature rise of a carbon strip in the fourth chapter. The results show that the temperature rise increases with the increase of sliding speed, electric current and arc discharge energy, while it decreases with the increase of contact force. The observation of the worn surfaces of the carbon strip indicates that the temperature rise of the carbon strip has a large influence on the morphology of the carbon strip. It is found that the higher the temperature of the carbon strip, the severer the wear of the carbon strip will become. The wear mechanisms of the carbon strip are different at different temperature rises. At the temperature rise of 50 ?, the wear of the carbon strip was mainly caused by exfoliating mechanical wear. At the temperature rise of 90 ?, the main wear of the contact strip is mechanical wear with slight electric ablation. Arc erosion wear is the main wear mechanism when the temperature rises is in the range of 180??200? with a large arc erosion area. When the temperature rise is larger than 300 ?, fatigue cracks are observed and arc erosion is the main wear mechanism.3. The material transfer is an important physical phenomenon of arc erosion. A series of experimental tests on a block-on-ring tester were carried out to obtain a new understanding of severe material transfer in the process of contact strips rubbing against a contact wire with electric current in the fifth chapter. Three types of contact strip materials including an aluminium-based strip, a copper-based strip and a pure carbon strip are tested in electric sliding against two contact wire materials including a pure copper contact wire and a copper-silver alloy contact wire. Test results show that there are serious material transfers in these three different friction couples in electric sliding. The aluminium-based strip has the severest material transfer, followed by the copper-based strip. The pure carbon strip has the minimum material transfer. It is found that the material transfer increases with the increasing of the sliding speed, the arc discharge intensity and the contact pressure. In the presence of electric current, contact strip materials are always transferred to the contact wire. EDX analysis shows that the material transfer direction is bidirectional. SEM analysis show that in the absence of electric current the main wear mechanisms of aluminium-based strip include adhesice and abrasive wear, and the wear mechanisms of the copper-based strip are dominated by particle wear mechanism, along with adherence wear and oxidation wear mechanisms, and the main wear mechanisms of the carbon strip include abrasive wear and adhesive wear. It is found that in the presence of electric current, there are arc erosion and fusion in addition to exfoliates on the worn surface of the aluminium-based strip, there are a small amount of electric arc ablation, exfoliates and a large number of surface scratches on the worn surface of the copper-based strip and there are several thermal stress cracks and a lot of ablation spots on the worn surface of the pure carbon strip.4. The influece of many parameters (contact force, sliding velocity, time, coefficient of friction and arc energy) on the wear of the contact stip are considerd comprehensively in the sixth chapter, and analysis of the correlation between various parameters and the wear of the pure carbon strips were carried out. Parameters sensitivity test shows that the contact force between the contact strip and the contact wire, relative sliding speed of the contact strip, electric current, running time and the energy of arc discharge have large impacts on the friction and wear behavior of the pantograph-catenary systems. The correlation between various parameters and the wear volume of the contact strip is analyzed. The variable importance in the projection (VIP) is used to assess the impact of different parameter on the wear volume of the contact strip. The prediction formula of wear volume is established by the partial least-square regression (PLS) method to predict the real wear volume of the contact strip under actual running operations, and the relative error between the predicted wear and the measured wear is less than 10%. Analysis results show that there was a linear correlation between the wear volume of the contact strip and respective variable. The wear rate of the contact stip has a high correlation with the current, velocity and arc discharge energy. The arc discharge energy and the relative sliding speed have the most impact on the wear of the contact stip, the current and time have a less impact, and the contact force and the friction coefficient have the least impact. |
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