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Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current. Melt erosion is caused by the current concentration on the contact surface of armature. Because the current melt erosion (CME) was considered to be a main mechanism of armature-rail contact failure, it was experimentally and theoretically studied in the early years using current density of 30–40 kA/mm, which is the exact driving current of rail launches. However, the critical behavior at the onset of CME cannot be observed due to the serious melt erosion at such high current densities. In this paper, the CME of armatures has been experimentally studied in the current range of 10–20 kA/mm with a lab-scale rail launcher. A payload separated method was used to keep the recovered armatures intact. The critical process for the onset of melting was observed and the erosion spreading patterns on the contact surface was analyzed. It is found that the current melt-wave model postulated in early years cannot describe the development of CME in our experiments. The result shows that current erosion mostly occurs at the static and the low-velocity stage of armature. The CME begins at the point of maximum contact pressure provided by armature-rail interference fit, and then, the melt erosion spreads longitudinally and transversely. The current erosion is affected by both current distribution and the movement of liquid aluminum. In longitudinal direction, the flow of liquid aluminum results in erosion propagation to leading edges. The transverse width of erosion zone expands with increasing current magnitude along the edge of interference fit. [ABSTRACT FROM PUBLISHER]

Monolithic C-type armature is one of the most important armatures in electromagnetic railgun. Some key parameters of monolithic C-type armature in rectangular caliber railgun system—width of armature X, height of armature Y, thickness of armature’s throat d0 , length of armature’s tail d1 , thickness of trailing edge of armature’s tail d2 , and angle of armature’s tail $\theta $ —are studied in this paper. By introducing current carrier margin coefficient named $\alpha $ , ratio of armature thickness to armature width named $\beta $ , ratio of armature height to armature width named $\gamma $ , and ratio of length of armature’s tail to armature height named $\kappa $ , equations of some key parameters of monolithic C-type armature in rectangular caliber railgun system are proposed. Based on analysis of mass of armature, electromagnetic contact force between armature and rail, mechanical strength of armature’s tail, and inductance gradient, relationship of some key parameters of monolithic C-type armature in rectangular caliber railgun system are proposed. Conclusion can be drawn that increase of $\theta $ can reduce mass of armature and improve mechanical strength of armature’s tail, but electromagnetic contact pressure between armature and rail will be decreased. Decrease of $\gamma $ could be a considerable way to remarkably increase inductance gradient, and then increase launch system efficiency. [ABSTRACT FROM PUBLISHER]

By introducing current carrier margin coefficient named $\alpha $ , ratio of armature thickness to armature width named $\beta $ , and ratio of armature height to armature width named $\gamma $ , equations of some key parameters of rectangular caliber railgun system, which is related to linear current density, are proposed. Then, some key parameters for different caliber railgun system are studied. Based on the analysis of electromagnetic contact pressure between armature and rail, $+ di/dt$ skin effect, velocity skin effect, and melt wear of armature, it can be obtained that current density of rail/armature interface is directly proportional to the linear current density. Thus, in order to decrease rail/armature interface current density, it is necessary to reduce linear current density. It can also be obtained that current density of rail/armature interface in current ramp-up is inversely proportional to the root of current rise time. Thus, it is necessary to increase current rise time to decrease rail/armature interface current density. Average melt wear rate of armature is directly proportional to the square of linear current density. [ABSTRACT FROM PUBLISHER]