Study on Suppressing Effect of Deposited Layer on Armature Melting at Sliding Electrical Contact Interfaces

Maintaining good sliding electrical contact performance is crucial for achieving high-frequency and high-efficiency operation in electromagnetic rail launch systems. In the environment of high current and high-speed sliding electrical contacts, an aluminum deposited layer appears on the rail surface during the first launch after rail surface cleaning. During repetitive launches, the armature slides on the deposited rail, causing the deposited layer to melt due to heating. Melting state of the deposited layer affects the melting wear process on the armature’s surface, thereby altering the contact state and influencing the sliding electrical contact performance. Therefore, studying armature’s melting characteristics influenced by deposited layer is of great significance for a deeper understanding of interface melting wear mechanisms and for improving sliding electrical contact performance. Firstly, by analyzing the heating process of the deposited layer, equations for calculating its melting moment and melting thickness were established. Within contact time (tc) between armature and deposited layer, the deposited layer is heated by the interface heat source and undergoes melting. A criterion for determining the melting of the deposited layer was proposed by comparing the contact time with the melting moment. If the heating time (tc) of the deposited layer is greater than melting moment (tm), then melting occurs within the contact time. Analysis of the melting characteristics of the deposited layer under different current conditions reveals that the larger the current load, the larger the melting range of the deposited layer. In addition, the deposited layer is more likely to melt during the low-speed stage and less likely to melt during the high-speed stage. Assuming that the deposited layer completely melts at time tr after the start of contact, the armature and the rail directly engage in heat transfer from time tr onwards. Based on the analysis of the heat balance equation under the condition of complete melting of the deposited layer, a calculation model for the melting wear of the armature under the influence of the deposited layer was established, yielding the melting wear rate of the armature. Finally, repetitive launch experiments were conducted with a 20 mm square caliber inner bore. Keeping current waveform and launch mass unchanged, each launch had a velocity of approximately 140 m/s, with a total of 7 launches conducted in the experiments. After each experiment, the armature and rail samples were recovered, and a profile gauge was used to measure the maximum melting depth on the armature's surface and the thickness of the deposited layer on the rail's surface. The experimental results show that the thickness of the deposited layer gradually increases with the number of launches, while the maximum melting depth on the armature's surface decreases with the increasing number of launches. By analyzing the thickness distribution curve of the deposited layer in conjunction with the criterion for deposited layer melting, it was found that the deposited layer was in a state of complete remelting under the current launch conditions. Using the armature melting calculation model under the condition of complete deposited layer remelting, the average maximum melting depth was further calculated. The calculated results from the model show the same trend as the experimental measurements, indicating that deposited layer melting has an inhibitory effect on armature melting. © 2024 China Machine Press. All rights reserved.