Insulator Tests in A High Performance, Square-Bore Railgun

The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has developed a 1 m long, 1.27 cm square-bore railgun for testing different rail, insulator, and projectile materials. This railgun incorporates a unique frame assembly which allows the gun to be assembled and then pressed into the containment vessel with little pressure. After it is pressed together, an external clamp is assembled around it in order to provide the necessary preload to activate the bore seals. The unique feature of the gun assembly allows stock geometry, 2.54 cm x 0.635 cm (1 in. x % in.) cross section, insulating materials to be installed and tested with minimal down time between shots. To date the 1-m long, 1.27 cm square-bore railgun has been used to test the following insulator materials: float glass, polycarbonate, 40% glass filled polycarbonate, G-7 laminate, and quartz glass. The best results have been obtained with quartz glass and glass-filled polycarbonate. Copper and molybdenum flame-sprayed copper have been tried as rail materials with the latter showing greatest success. Currently molybdenum flame sprayed copper rails and glass filled polycarbonate insulators have been repetitively fired at 350 kA levels while maintaining a rail-to-rail resistance of greater than a megohm. During the experiments performed at CEM-UT, much effort was invested in producing a consistent, high-quality bore finish. The indication is that candidate materials to be tested cannot be accurately evaluated if the bore finish is not accurate and smooth.