Research On The Current-melt Erosion Effect Of Small Caliber Armature Electromagnetic Launch

Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current.In the armature contact zone,the nonuniform electric contact and motion of armatures cause current concentration which results in localized overheating and material melting.The effect is known as current-melt erosion(CME)which is the main mechanism for armature deterioration at the low speed stage of launches.The CME effect is a major contributor of armature-rail contact interface condition and a main source of the deposition layer on multi-launched rail.The deposition layer in turn has an impact on CME process.The present related researches have some problems which include the incompleteness of CME mechanism study and the lack of study on the deposition layer impact on launch process and CME effect.In our study,electromagnetic launch experiment on clean rail was conducted.The experiment adopted the separated load method for the first time,obtaining good measurement results of erosion patterns from recycled armatures.Based on the morphology on erosion patterns under different launch current measurement results,we put forward three patterns of CME and discussed their lubrication effect with kinematics calculation.It is found that the different output of liquid aluminum results in the different patterns of CME and changes the interface contact condition.The cohesive erosion pattern corresponds to the solid-solid contact of the pivot,and the expansive mode is in the form of solid-solid contact and solid-liquid-solid contact.The through-type erosion mode corresponds to a wide range of solid-solid contact,different contact state of the lubrication characteristics are also quite different.The influences of the current linear density and the emission velocity on the current erosion were also studied by designing the narrow armature and changing the weight of the load.Finally,the development process of current erosion is discussed based on the simulation results of the shape and current distribution.The results show that the initial interference pressure distribution and the liquid layer flow in the interface are the two main factors that affect the current erosion.Under the condition of 20kA/mm linear current density launch,eight repetitive launch experiments were carried out to study the deposition regularity of the rail surface and the effect of deposition layer on the current erosion effect.The results show that the thickness of deposition layer increases rapidly with the number of launch times,and increases rapidly in the first 2-3 times.With the increase of the thickness of the deposition layer,the maximum erosion depth of the armature surface decreases after each launch,and the expansion distance of the melting hole along the side to the leading edge will gradually increase,which may lead to the change of the erosion pattern.Based on the theory of magnetic diffusion and the theory of heat conduction,an electrical contact analysis model of the geomagnetic thermal coupling of the initial contact pressure distribution and the orbital deposition layer is established.The current distribution and the electrical distribution of the interface under the condition of the deposition layer are analyzed.It is found that the higher the thickness of the sedimentary layer,the lower the conductivity,the stronger the uniform distribution of the armature surface current,and the tendency of the current to be transferred to the trailing edge of the armature.The simulation results are larger than the experimental measurements.With the thickness of the deposition layer increases,the gap between the simulation results and experimental results is increasing.This is due to the fact that the liquid aluminum produced at the interface of the pivot changes the current distribution.