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Registered Member #222
Joined: Mon Feb 20 2006, 05:49PM
Location:
Posts: 96
Please take a look at the attached teaser images.
The third generation railgun was fired on May 16, 2008. The target was a 1/4" thick steel plate, and the projectile was made from GLIDCOP AL-15 and had a mass of 2 grams. It almost went through the steel as there is a large bump on the back of the plate. The projectile was accelerated from rest, and I had to use a hammer to load it in the railgun.
Does anyone know why there is so much material around the impact crater?
Registered Member #1320
Joined: Sat Feb 16 2008, 01:31AM
Location:
Posts: 67
Wow, I would love to know more about this one. Anyways the material around the crater is due to aluminum (your projectile) being the softer metal. Quite common to see the same thing from soft lead shells as well.
Registered Member #222
Joined: Mon Feb 20 2006, 05:49PM
Location:
Posts: 96
The projectile is made of GLIDCOP AL-15, which as a copper alloy, not aluminum. However, the first projectile I used was a 600mg aluminum block, and it broke into 3 pieces before hitting the steel plate.
The capacitor bank stores about 20kJ. The SCR is rated for 1kA continuous and 14kA pulsed. It is used as a sacrificial switch since it would be too expensive otherwise. I will show you a picture of what happened to the stud mount SCR. The stud mount SCR didn't do too well, so I switched to the hockey puck type. I had them donated to me for a separate unrelated project that never went.
The whole project cost probably well under $2000.
I have high speed video running at 25000 fps, but it is 8megs. You can't see much in the video because the muzzle flash was too bright.
Registered Member #1381
Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74
Well you know , some parts of the the projectile/armature also the surface of the rails , melt/evaporates , cause of the joule heating and friction , this metalic vapor is also blown out from the gun (same as gunpowder from a convecional firearm) and it cooled down on contact with the steel plate
Registered Member #222
Joined: Mon Feb 20 2006, 05:49PM
Location:
Posts: 96
Alloy 110 copper and flame retardant electrical grade fiberglass.
When an aluminum projectile is used, aluminum film covers the area around the crater. There might be a spec or two of copper, but it is mostly the material from the projectile.
Registered Member #222
Joined: Mon Feb 20 2006, 05:49PM
Location:
Posts: 96
The capacitor bank is composed of 70 electrolytic capacitors, each rated for 3900uF at 400V. They are in all parallel. The actual capacitance is 0.2585 +/- 0.005 F.
It has only been fired 2 times. It looks like the rails have to be replaced each time as well as the sacrificial SCR. Future work would be to improve the design to allow the rails to last longer. The bending of the naked rails at the breech side don't help.
I have attached a picture of what I meant about the two types of projectiles creating craters covered with material mostly from the projectile.
Also, I have loaded a picture of the capacitor bank. The lightbulbs are used to discharge any residual energy in the caps.
Rails are 0.125" thick, and the enclosure is 3"x2" cross sectional. The gun is 16" long
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Third generation railgun project
