Preparation And Investigation Of Wear Behavior And Anti-wear Mechanism Of Resin-type Pantograph Contact Strip Materials

As the key component, pantograph contact strip helps electric locomotive power supply system to obtain electrical energy from the contact wire, which has become a hot research point in the field of the coupling system of pantograph/catenary. At present, the contact strips, such as dual-lubricating copper matrix powder metallurgy contact strip, Al-coated pure carbon contact strip, Al-coated metal impregnation carbon contact strip, were mainly applied on high-speed electrification railway at home and abroad, which were limited by different shortcomings during the operation. Furthermore, few investigations and reports about the electrical sliding wear behavior of high speed were presented on arc starting and extinguishing mechanism of contact strip against copper. In order to resolve the problems that contact strip is difficult to coordinate the coupling system of pantograph/catenary due to material defect to avoid high abrasion with current and to reduce the wear rate of contact strip. Based on the structure and property of resin-type function composite well controlled and relatively simplicity in manufacture, the preparation process and wear behavior and anti-wear mechanism of the resin-type contact strip materials were investigated in this paper.(1) The batch formula and preparation process of the resin hot-pressing type contact strip were investigated in this paper. With modified resin as bonding agent, three-step pressing and solidification technology was presented to prepare the resin hot-pressing type contact strip. The effects of the kinds and content of bonding and graphite, the moulding process on the structure and performance of the resin hot-pressing type contact strip were studied. The result showed that the resin hot-pressing type contact strip which was prepared with polybismaleimide resin (PBMI)/cashew nut oil phenol formaldehyde resin (YM) as bonding agent and P flake graphite as lubricating phase had perfect wear resistance. The combination property of the resin hot-pressing type contact strip was the best when the content of bonding agent is 10.5 mass% and the content of P flake graphite is 10 mass%.(2) The variable-speed wear behavior at room temperature, thermal wear behavior and electrical sliding wear behavior of the resin hot-pressing type contact strip against copper were studied systematically under laboratory conditions with a wear tester which simulated the train motion. The results showed that current is the most important factor which affects the wear rate of the resin hot-pressing type contact strip and the wear rate increases with the increase of current density. They also showed that variable-speed wear rate at room temperature and thermal wear rate of the resin hot-pressing type contact strip when initial ambient temperature is equal to 200℃are both equal to the Siemens carbon contact strip. And the thermal wear rate when initial ambient temperature is equal to 350℃, electrical sliding wear rate of the resin hot-pressing type contact strip are higher than those of Siemens carbon contact strip.(3) The batch formula and preparation process of the resin-calcination type contact strip were investigated in this paper. With Zn-coated graphite as the arc extinguishing agent and lubricating agent, modified resin as the bonding agent, the resin-calcination type contact strip was prepared by the methods of blending hot-pressing and carbonization technology. The effects of roasting technics, the kinds and content of bonding agents, the amount of Zn-coated graphite on the structure and property of the resin-calcination type contact strip were studied. The results showed that the resin-calcination type contact strip with the best properties of wear behavior and conductivity are those which was produced by using 3⁵ mass% PBMI/YM resin and 28 mass% Zn-coated graphite at the heating rate 20℃per hour at 135⁴25℃, and at the heating rate 15℃per hour at 425⁶30℃and then keeping at 630℃for 4 hour. The results showed that the electroplating Zn on graphite greatly improve the interfacial combination between graphite and copper and remarkably decrease the wear rate of the contact strip. The wear rate of the former was only one-third of the latter with the current density of 285A/cm² and at the sliding velocity of 41.7m/s.(4) The electrical sliding wear behavior of the resin-calcination type contact strip against copper was also studied systematically under laboratory conditions with a wear tester which simulated the train motion. The results showed that the electrical sliding wear rate of the resin-calcination type contact strip increases with the increase of current density and the sliding velocity. It also showed that the wear rate of the new resin-calcination type contact strip is approximately equal to Siemens carbon strip, Toyo metal impregnation carbon contact strip and Zhuzhou Xinfangyuan Electrical Carbon Co., Ltd. carbon strip (a certain type of domestic carbon contact strip) without current. The wear rate of the new resin-calcination type contact strip is 1.51×10^-5mm³/(N·m), which is almost 0.917 times lower than a certain type of domestic carbon contact strip, 1.53 times that of Siemens carbon strip and 1.42 times that of Toyo metal impregnation carbon strip with the current density of 285A/cm² and at the sliding velocity of 41.7m/s.(5) The wear behavior and mechanism of resin-type contact strip were investigated in this paper. The results showed that the main wear mechanism of the resin hot-pressing type contact strip against copper without current is low stress grain abrasive and slightly adhesive wear. At elevated temperature, the wear mechanism evolves from adhesive wear to thermal wear with slight delamination wear. While arc erosion wear and oxidation wear are the dominate mechanisms of the resin hot-pressing type contact strip against copper with current, which is accompanied by adhesive wear during electrical sliding wear process. Moreover, the main wear mechanism of the resin-calcination type contact strip against copper is arc erosion wear and oxidation wear.(6) The arc erosion processes and function mechanism models of the resin-type contact strip with current were investigated in this paper when the contact between the contact strip and the copper disk was broken. The results showed that the arc discharge drive contact regions of the resin hot-pressing type contact strip to sequentially experience four cycle stages: arc generation when the contact was broken; the thermal decomposition of polymer during the stage of arc arising, the oxidation of carbon based materials, the phase transition of hot molten metal; the carbonization of resin at high temperature, the flow of molten metal, the thermal decomposition of metal-oxide; the solidification of molten metal during arc quenching and the shedding of oxide, etc. The resin-calcination type contact strip sequentially experienced the circulation processes such as: the occur of arc when the contact was broken; the soft metal softened; the oxidation of carbon based materials, the phase transition of hot molten metal and vaporization; the solidification of metal and material transfer, etc.(7) Arc erosion resistance mechanism of arc-extinguishing medium was investigated. The effects of impregnating agents with silicon oil on electrical sliding wear behavior and arc erosion wear resistance of the resin hot-pressing type contact strip and the resin-calcination type contact strip against copper were respectively studied in this paper. The effects of arc extinguishing medium with soft metal on electrical sliding wear rate and the dynamic stability with current of the resin-calcination type contact strip against copper were investigated as well. The results showed that silicone oil, as the impregnating agent in the resin hot-pressing type contact strip, could abirritate the fluctuation of contact resistance, lower the instantaneous high temperature of the contact point and the wear rate of contact strip with current. The Zn-coated graphite and the soft metal tin of the resin-calcination type contact strip can promote the forming metallurgical bonding structure of metal phase on the corresponding interface. In the courses of arc erosion, the evaporation related heat absorption of metallic zinc with high ionization energy and can decrease the electron concentration among the arc gap. Meanwhile, the cladding of formation between metal vapor and copper-matrix can reduce contact resistance at the contact zone and the probability of electric arc occurring, and thus reduce electrical sliding wear rate of the contact strip. These studies on arc erosion resistance mechanisms can provide a scientific basis for arc extinguishing researches and their practical applications of resin-type contact strip.