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Piston materials question

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Piston materials question

Unread postAuthor: randompkguy » Mon May 04, 2009 6:32 pm

I'm building a steel cannon out of an old oxygen welding tank (I already cut it, and am still alive) and had some engineering questions for the piston. I plan to take the cannon up to about 200 psi, and with a barrel inner diameter of 3 inches, that means about 1400 pounds of force on the sealing face. I was considering using some 1/4" thick fiberglass for the sealing face, and then 1/2" polycarbonate for the parts that hit the back of the pilot chamber upon firing. Do you guys think these materials are appropriate?
(the piston diameter is 4 inches)
I was thinking fiberglass because it has good tensile and compressive strength, and polycarbonate because it has great impact resistance)

I plan to post up a complete worklog when I get the time, but here is a render of the piston, and a teaser pic:

Image

Image

Thanks for your help :D
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Unread postAuthor: grock » Mon May 04, 2009 6:47 pm

fiberglass wont work to well for the sealing face becasuse its too hard. try using rubber/neoprene
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Unread postAuthor: Carlman » Mon May 04, 2009 7:16 pm

use neoprene and have a washer of some kind (cut one out of 2mm steel) that holds the neo on and is only mm smaller than the inside of your barrel.
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Unread postAuthor: randompkguy » Mon May 04, 2009 7:59 pm

oh, sorry about that, I forgot to mention that will be using 1/8" thick neoprene on the fiberglass for the seal, I just wanted to know if 1/4" fiberglass could take the stress
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Unread postAuthor: Technician1002 » Mon May 04, 2009 9:28 pm

randompkguy wrote:oh, sorry about that, I forgot to mention that will be using 1/8" thick neoprene on the fiberglass for the seal, I just wanted to know if 1/4" fiberglass could take the stress


Make sure your seat is wide enough. You wouldn't want to die cut the neoprene seal to fit inside the barrel. :D
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