Experimental determination of the contact friction for an electromagnetically accelerated armature

Abstract

The friction forces on the contacts of the sliding armature in an electromagnetic launcher represent significant energy losses affecting the overall performance of these systems. Friction produces unwanted heating at the contact-rail interface which leads to accelerated wear and chemical erosion of the contacts. Eventually, the armature material at the interface will soften and melt followed by rapid evaporation due to arcing. To prevent this mode of failure, the contact force must be gauged accordingly; the compliance must account for not only changes in barrel width due to rail unevenness but changes in contact length due to wear. Usually for successful operation at high current densities (greater than 1 GA m −2) armatures with multiple contacts are employed to circumvent this dilemma. An extensive experimental program at Westinghouse Research and Development Center supported by the Defense Advanced Research Projects Agency was instituted to define the limitations of high speed high current contacts for electromagnetically accelerated armatures. One facet of this work, the determination of friction and contact forces for a simple platetype rmature, is presented in this paper.