Friction And Wear Behavior Of Armature-Rail Sliding Electrical Contact Surface

Transition is an important issue in rail electromagnetic launches which limits the performance of electromagnetic launch systems. In the launch progress, wear on contact surface of armature significantly affects the morphology of contact surface and armature structure. Studying wear, contact resistance and sliding friction coefficient of the contact surface is important to understand principles of transition and suppress transitions in electromagnetic launches.By using electron microscope, morphology characteristics of the surface of armatures post-launch are studied. The wear mechanism on armature surface during launch progress is then analyzed. By cataloging the different morphology characteristics and their related causes, the wear on armature surface is divided into two types, non-melt wear and melt wear.Based on the characteristics of these two kinds of wear, experiments are designed to study the wear rate, contact resistivity, and sliding friction coefficient of armature-rail contact, respectively. The affecting principle of launch parameters like current or pressure on the results is also analyzed.Eletric-tribometer is employed to study non-wear melt. The experiments measured wear of 6063 aluminum alloy and 7075 aluminum alloy pins on copper plate. Result shows that non-melt wear increases with the increase of load and current, the average aluminum debris thickness is within 0.1-0.5μm. Without current, the sliding friction coefficient of the contact pair increases with pressure increasing, until reaches 0.3. Sliding friction coefficient decreases to 0.1-0.15 from 0.3 with current loaded. It is concluded that using electric-tribometer could simulate non-melt wear with current density lower than 4A/mm2,Special designed armature, which makes the wear on armature contact surface all melt wear, is used in rail launch experiments to measure the wear rate of melt wear and the effects of loading on wear.Launch experiment results show that wear is faster if the amplitude of current was bigger. The wear rate is represented by the average thickness of the aluminum debris left on the rail. The average debris thickness is in a range of 3-11μm in the experiments. The average debris thickness has direct ratio about 0.88×10-6μm/(A2·mm-4) to the square of current density amplitude.Based on the idea of melt wear is the main part, the heat transmission of armature contact surface in launch process was analyzed. It is concluded that melt-wear absorbs mounts of heat generated on the surface, and the left heat goes into rails through the contact. The heat transmission based equations was then derived, which established relationship among melt wear, launch parameters and material parameters.According to the heat equations obtained, the data of launch experiments was then calculated. The result shows that the contact resistance of 80mm2 contact area 6061 aluminum alloy armature to brass rail is 2.5564μΩ, t contact resistance of 50mm2 contact area 6061 aluminum alloy armature to brass rail is 4.0924μΩ, and the sliding friction coefficient are both 0.1131.