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what pressures will glass withstand

A place to ask general spud cannon related questions.
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Unread postAuthor: rna_duelers » Fri Jul 07, 2006 6:10 pm

Why not make it,i would like to see a glass cannon i have never seen one befor do you think you could post a pic with your glass hybrid Rambo?or a link if its already posted here.
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Unread postAuthor: carlbelcher » Fri Jul 07, 2006 6:18 pm

I too would like to see the glass hybrid not that I don't believe you I just want to see how thick the glass is, and how you connected the bottle to the cannon.
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Unread postAuthor: boilingleadbath » Fri Jul 07, 2006 6:26 pm

Our cannons can't produce supersonic velocities with a barrel attatched, and wan't deliver much velocity at all to the fragments. Enough velocity to do harm, sure, but certainly not much velocity by our typical standards.

Furthermore, there is a big difference between a beaker and a beer bottle; a ratio of 1.5 or so in diameter, maybe 2-3 in wall thickness, and a shape acctualy ment to contain pressure. This gives <b>at least</b> a 3-5 times higher pressure resistance in a bottle than a beaker, probably close to 5-10.

Glass is stronger than you guys give it credit for. It's picky, addmittedly, as it has a high coeficient of expansion, low elasticity, and cracks spread easily... but those don't matter that much for the pressure-holding charistics of a container.

Of course, summing it all up, one still comes to the conclusion that even in the unlikely case of a rupture, it could do some unhappy damage.
And for what? A soda bottle would work nearly as well and without the fragmentation risk.
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Unread postAuthor: carlbelcher » Fri Jul 07, 2006 6:35 pm

Our cannons can't produce supersonic velocities.


I said "near supersonic"

I would like to add that I'm not against trying new ideas/materials I just don't want to see anyone get hurt and/or maimed in the process. I don't mess with glass but that doesn't mean you can't.
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Unread postAuthor: Rambo » Sat Jul 08, 2006 12:46 am

I was talking about auto combustion wich uses two times more O2 in the mix.
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Unread postAuthor: boilingleadbath » Sun Jul 09, 2006 2:37 pm

Carblecher, you are missing the point:

A 60" barrel shooting tight-fitting projectiles with a SD of 30g/in^2 will yeild velocities of approx. 400 fps. (with a 1:1 CB ratio)
Meanwhile, the glass on the bottles we are talking about is aprox. .1" thick, for a SD of ~5g/in^2.

To reach the same velocity, the glass would have to be launched from a 10" barrel.

And that's not even <i>near</i> supersonic... you would need a 50" barrel to get the glass up to that speed.

Looking at it a different way, even assuming energy was transfered from the chamber into the fragments with the same effectivness it is with a well-fitting projectile, a beer bottle (120g, 28 cubic inches) only contains enough energy to get it's fragments up to 140 fps.
It would take roughly 60 times more energy to get the fragments to the speed of sound.

...and I'll leave you to geuss how the efficiency of a barrel compares to that of an explosion.
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Unread postAuthor: trae08 » Sun Jul 09, 2006 2:51 pm

ok well if i were u i would set it up where i dont have to b n e where near it when i fire it an if it works asome then u put it in ur room some where and never use it again tell ur friends u do and it looks like its been used from the first shot so its all kool but a glass gun would look wickidly sweet
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Unread postAuthor: carlbelcher » Sun Jul 09, 2006 4:43 pm

boilingleadbath it was an exaggeration used to refer to the although not "near supersonic" but never the less flying shards of glass that would result from a glass chamber explosion. I really don't care if the pieces are flying at only 25 mph the point is that it's probably not going to feel very good to get hit by one. I'm not trying to start a physics argument with you, nor do I care exactly how fast the pieces would be flying!

Thank you for enlighting me, and let this be an end to it. Your right, I'm wrong, the shards would not be even near supersonic! :D
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Unread postAuthor: Atlantis » Sun Jul 09, 2006 9:32 pm

Not only would the glass shatter, it will shatter into very small pieces, unlike PVC, which means the doctor will probably miss a few pieces which could tear up your organs over time. Sorry for being blunt, I'm just telling you what might happen.
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