I finally got around to disassembling the gun and examining/photographing its internals. A lot can be learned from how this design worked, and how it failed, and this knowledge will be applied on a new, superior design, which is being designed and built at the moment.
The original Rail Gun was designed in two sections: a polycarbonate injector with Teflon Rails, and a Rail Gun section with copper rails and a Garolite G-9 fiberglass composite. The injector was made from polycarbonate due to its very high tensile strength (10000PSI) and resistance to shock loads. With the 1/2" thick polycarbonate sheets holding the Teflon rails under a maximum of 500PSI injection pressure, it was not believed that this design could fail, thus using polycarbonate represented a cost saving over the stronger, but much more expensive G-9, which was used for the rail enclosure where higher forces would be encountered. In fact, this design was strong enough that it could never have failed under the calculated load produced by even the highest possible energies available at the capacitor bank. Failure occurred not due to Lorenz forces, but rather due to the intense pressure produced when plasma armatures were repeatedly fired at high energy levels; this higher pressure was expected, and incorporated into the over design of the gun, but what was not expected was that the plasma shock actually traveled back into the injector, and produced enough pressure there to shatter the material in 5 different places. The breakage of the gun occurred at the mating point between the polycarbonate and the G-9 materials, indicating that this connection was clearly the weakest point of the gun. The use of a weaker material, a two-stage design, and countersunk holes in the injector bolt holes proved insufficiently strong to withstand repeated shots at over 10 000Joules. The force of the discharges was enough that, aside from shattering the Polycarbonate, it bent the steel bolts that held the injector together, de-laminated the G-9 side supports for the rails, and deformed the Teflon rail insulators. There is also ample evidence of plasma blow by past the insulators. This is clearly a source of inefficiency as the blow by bleeds pressure which would otherwise go towards accelerating the projectile.
Rail and injector enclosure opened up. Notice buckling of rail insulators.All of these design weaknesses have been resolved for the Rail Gun 2.0, which will be a vastly stronger accelerator, capable of firing reliably and repeatedly at energy levels of at least twice those seen in this first design. The rail enclosure will now be a single piece made of Garolite G-11 (a stronger material than G-9) with no counter sunk holes or mating points. The rail connector exit points in the gun will also be optimized to minimize stress concentrations. Another advantage of this re-design is that rail/injector alignment and rail positioning accuracy will be much greater. It will also be gas tight, which will provide greater efficiencies when firing plasma armatures.
The Rails:
The rails held up surprisingly well; after 12 shots without any kind of servicing they were completely covered in black carbon soot. This carbon came from the adhesive in the aluminum tape used in the plasma armatures burning up. It was useful in evidencing the plasma blow by in the region of initial rail/armature contact.
After cleaning the rails show evidence of cratering and pitting; classic effects of electrical arc erosion. Significant amounts of copper have been removed, and a copper/aluminum alloy formed in the bottom of the craters. The amount of erosion was lower than expected given the number of shots fired and their energy level (over 150 000Joules were run through these rails). The insulators were also virtually undamaged by all the discharge, evidencing that Teflon is a very suitable insulator for this particular application.
Interestingly, a second arc crater formed 5.6 inches from the breech. I believe this was due to the armature not making contact with the rails until that point during a lower voltage shot. That, together with the extensive arc damage, evidence to the need for closer machining tolerances and a tighter rail/armature fit, both planned for the next Rail Gun.
LordBoomstick Community Member 
|
|
