| Electric locomotive is a kind of modern railway transport, and pantograph contact strip is the most important unit of electric locomotive to import electricity. At present, widely used pantograph contact strip mainly includes steeped metal contact strip and carbon contact strip. But as the operation speed of the electric locomotive unceasingly increased, all traditional contact strips show different degrees of defects, therefore it is very significant to develop a type of contact strip with high conductivity, high strength, good wear resistance and suitable for contact line. This paper used the carbon fiber as reinforced phase, copper as conductive phase, modified phenolic resin as binder, and graphite as lubrication phase prepare carbon fiber reinforced hot-pressed/calculated contact strip, and also studied the formulation, technology, performance, arc erosion characteristics and wear mechanism.The formulation and preparation technology of contact strip samples were studied. Contact strip sample was prepared by compression molding, and the influence of mould temperature, mould pressure and mould time to the slide’s performance was researched. Finally, the reasonable mould conditions were determined:preheat temperature100℃, preheating time6min, hot pressing temperature170℃, mould pressure60MPa and mould time60min. Using Minitab software simulated and analyzed the performance of contact strip with different formula, to determine the formula content’s influence on the slide’s performance. It was found that carbon fiber content is the key factor to affect the impact strength of slide sample, that copper content of conductive phase plays an important role in determining the slide’s resistivity, and that fiber content, graphite content and phenolic resin content had a great deal of influence on the wear-resisting performance of the sample. The best formula of the slide sample was as follows:copper mesh15wt.%, carbon fiber cloth17wt.%, short carbon fiber5wt.%. phenolic resin33wt.%, graphite22wt.%, copper powder5wt.%and acrylonitrile butadiene rubber3wt.%. The performance of the sample was as follows:resistivity8.63uΩ·m, impact strength78kJ·m-2, volume wear rate0.558×10-5mm3·N-1·m-1, friction coefficient0.200, compressive strength>200MPa and bending strength140-200MPa.In order to improve the invasion of enhance phase carbon fiber and matrix phenolic of carbon fiber reinforced pantograph contact strip, and improve the strength of the composite material, liquid phase oxidation/coupling agent coating method is adopted to modify carbon fiber’s surface. The structure and morphology of carbon fiber before and after modification were observed by the Raman spectrum (Raman), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrum (FTIR) and Scanning electron microscopy (SEM), and mechanics properties of carbon fiber and its composite materials were tested by the fiber fineness tester and universal testing machine. The results showed that:the mechanical properties of carbon fiber gradually declined with the time of liquid phase oxidation increase, surface was gradually etching, disorder parameter of carbon fiber’s surface structure improved, and fiber surface oxygenic functional groups content gradually raised. After treatment of APS coupling agent, silanol group reacted with the carbon fiber surface active functional groups, formed a layer of film in the surface of the carbon fiber, and was beneficial to improving the carbon fiber tensile strength and elongation at break. O-C=O group on the carbon fiber surface would react with silanol group, so O-C=O functional group content on the carbon fiber surface would decrease. After modification treatment on carbon fiber, composite materials’impact strength and interlaminar shear strength were increased. Along with the liquid phase oxidation treatment and coupling agent treatment proceeding, carbon fiber’s volume and resistivity increased slightly. The impact of liquid phase oxidation modification treatment on the resistivity of the prepared composite material was not big, and resistance rate of coupling agent modified contact strip declined slightly. Surface treatment could improve the slide wear-resisting performance significantly, after silane coupling treatment, the slide wear was lowest, and it was down about35%than that of untreated.In order to improve the thermal stability of contact strip, the experiment used IC method to prepare roasting type pantograph contact strip, and the impregnation process and effect were studied. The800℃carbonization could improve the slide’s thermal stable performance in an instant high temperature. The experimental dipping conditions were as below:phenolic resin impregnation liquid ethanol concentration60%, dipping temperature60℃, dipping time1.5h. After heat treatment, resistance rate reduced about26%. the impact strength reduced, volume wear increased and the porosity was higher. It was better to dip samples for4times. After densification, resistivity, porosity and volume wear of the contact strip gradually decreased along with the increase of the time of carbonization-dipping treatment. Compressive strength, bending strength and hardness gradually improved along with the increase of the time of carbonization-dipping treatment.With the carrier density of resin hot pressing contact strip rising, its wear rate gradually increased, but the friction coefficient gradually reduced. With the increase of the friction velocity, wear rate increased, basically growing linearly. At the same velocity, the slide’s wear under load flow was significantly greater than that under no load flow. In no load flow conditions, the wear rate of sample generally growed linearly with the increase of the contact pressure and friction coefficient increased and ultimately tended to be stable. In load flow conditions, sample’s volume wear and voltage was U change. Under no load flow, the wear rate gap of resin roasting slide and pure carbon slide was small, and their values were0.85×10-5mm3·N-1·-m-1and0.91×10-5mm3·N-1·m-1respectively. The wear rate of both slides increased along with the increase of current density. With the increase of friction velocity, friction coefficient trended to decrease. Wear rate of these two types’contact strip was also in U change with load changes. Load flow efficiency of three kinds of slide above referred decreased with the increase of current density, increases with the increase of the load, and increased after first decrease with the change of planing speed.The abrasion of the resin roasting contact strip prepared to copper wheel and copper plate was less than resin hot pressing contact strip, and in the current conditions, the abrasion of the contact strip to copper plate is similar with that of pure carbon slide. Resin hot pressing slide and resin roasting contact strip had superior mechanical properties than imported pure carbon contact strip and a certain domestic chopped fiber reinforced slide. In the same conditions, the wear rate of the resin hot pressing contact strip was close with that of pure carbon slide, but friction coefficient of resin hot pressing slide was a bit higher. Wear resistance of resin roasting slide was a bit poorer than that of imported carbon contact strip, and in the same conditions, the abrasion of a certain domestic slide to copper plate was the biggest, and that of imported pure carbon contact strip to copper plate was minimum. The performance of both two kinds of carbon fibre reinforced contact strip prepared was superior to the performance of a certain domestic contact strip.In the same conditions, the arc discharge degree from low to high was:import pure carbon contact strip, resin roasting contact strip, resin hot pressing contact strip and a certain domestic contact strip. The arc erosion of contact strip in the process of friction wear with the load flow mainly included material transfer, melt splashing and evaporation erosion. Contact strip’s friction and wear mechanism was as follows: under flow friction with no load and wear conditions, the main mechanical friction and wear form of resin hot pressing contact strip and resin roasting contact strip was abrasive wear and adhesive wear, and in the load flow conditions, the mechanical friction and wear form was mainly arc erosion wear and oxidation wear, accompanied with the abrasive wear, adhesive wear and mechanical wear. |
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