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PVC layered in kevlar/carbon fiber?

A place to ask general spud cannon related questions.
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Unread postAuthor: K8TOW » Sun Sep 16, 2012 10:31 am

i went to a boat maker who is a frind of mine,and he said the pvc wrapped in carbon fiber wouldnt work,because the pvc expands just slightly with pressure.
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Unread postAuthor: sharpshooter11000 » Sun Sep 16, 2012 2:51 pm

I think this could actually work, some diving tanks and a lot of the air tanks firemen use are made from carbon fibre and hold a lot of pressure. Although they are made comercially...
Edit: Sorry, just noticed how old this topic is :roll:
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Unread postAuthor: Crna Legija » Mon Sep 17, 2012 5:56 am

K8TOW wrote:i went to a boat maker who is a frind of mine,and he said the pvc wrapped in carbon fiber wouldnt work,because the pvc expands just slightly with pressure.

that's why you put the fibre wrapping to hold it all in.
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Unread postAuthor: Marseyus » Tue Nov 06, 2012 11:09 am

I know this is an old post, but i love physics and since i'm new i figured i could try to help out some.

Everyone is right about coating the outside of pvc with fiberglass or carbon fiber. Also the heat that some fiberglass and carbon fiber two parts produce can weaken the pvc shell. As well as the pvc cracking inside the shell, and if carbon fiber of fiberglass let's loose under pressure it shatters, causing pain and hospital visits.

So what's the answer, the same thing firefighters do with carbon fiber tanks. (as stated in an earlier post) The carbon fiber tanks firefighters wear are rated anywhere from 2200psi all the way up to 7500 on some newer models. How does a small carbon fiber tank hold this amount of pressure? well a steel liner of course. On the inside of the carbon fiber tanks is a reinforcing steel liner. The combined strength of the two can hold 7500 psi together while inside a burning building (as we all know heat increases pressure) I've seen the 7500 psi tank hold up to 9800 psi before bursting.

So the next question, how to apply this technology to pvc? You gotta think outside, the box, well actually inside the pipe would be more like it. Coating the inside of the pvc with fiberglass would help a tremendous amount with pressure stability. Or adding a thin, but tight fitting metal sleeve. It wouldn't take much, but depending on what pressures your trying to hold back would designate the material. Metal would work better because of the similarity in expansion rates. Also if your looking for increased stability and safety on the outside, starting thinking screen meshing. The meshing would expand with the pvc, but also if there was a pop, the mesh would relieve some of the pressure to prevent shattering, and would simply allow cracking.

But for tater cannons your best option is simple, coat the inside with several layers of fiberglass, and if you really wanted slide a metal sleeve down inside before the fiberglass hardened. To prevent the heat from dis-tempering the pvc polymers simply use slow hardener and do it outside on a cold day, or in your fridge, or pack ice around it. It will take longer to harden, but the temp will rise less and at a slower rate, but still facilitate proper hardening of the fiberglass epoxy. OH but what about the material fatigue caused by expanding and contracting? Well west system makes an epoxy called g-flex, that by itself can hold 5200 psi, and is flexible.

If you need me to go further just re post or message me i'd be glad to help walk anyone through the process that is interested.
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