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Air tank alternative: fiberglass-reinforced soda bottles

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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Unread postAuthor: saefroch » Fri Jul 29, 2011 10:02 am

In my experience, epoxy will ignore grease. It sort of pushes it out of the way. The only things I've found that it won't adhere to are polyolefins, commonly used to make heat-shrink tubing.
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Unread postAuthor: aEx155 » Fri Jul 29, 2011 11:47 am

saefroch wrote:In my experience, epoxy will ignore grease. It sort of pushes it out of the way. The only things I've found that it won't adhere to are polyolefins, commonly used to make heat-shrink tubing.


If that's the case, how do people cast epoxy pistons if grease doesn't work?

I know that epoxy has a hard time adhering to PET (the plastic that soda bottles are made from), so I'm not sure if I want to glue a PVC fitting onto the bottle or cast threads with it.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 29, 2011 11:53 am

aEx155 wrote:The greased bottle would be inside the fitting, and I would pour epoxy between the bottle and the fitting. That way I would have a bottle-PVC adapter instantly.


Just make sure the bottle doesn't have an interrupted thread, otherwise you're not going to be able to get it out.

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Unread postAuthor: Gun Freak » Fri Jul 29, 2011 11:54 am

I know that epoxy has a hard time adhering to PET (the plastic that soda bottles are made from)

Really? I was gonna cast some epoxy around a bottle for part of my stirling engine... :?
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 29, 2011 11:59 am

PET is flexible and can't really be abraded, not a good candidate for epoxy adhesion.

About threads though, I've cast them in epoxy before to fit a suppressor I made on my Yunker:

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For my ghetto BBMG, I had epoxied a bottle cap in a larger plastic cap as the female thread:

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Unread postAuthor: Gun Freak » Fri Jul 29, 2011 12:03 pm

Thanks for the info on PET, I'll have to find a different cylinder material. Suggestions for ~3" diameter clear pipe?
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 29, 2011 12:45 pm

Gun Freak wrote:Suggestions for ~3" diameter clear pipe?


the dessicant cartridge on our FT-IR spectrophotometer at work?
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Unread postAuthor: Gun Freak » Fri Jul 29, 2011 1:56 pm

Yeah I'll go dig one out of my closet :lol:
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Unread postAuthor: aEx155 » Fri Jul 29, 2011 7:15 pm

Gun Freak wrote:Yeah I'll go dig one out of my closet :lol:


If you don't use epoxy you can still use a plastic bottle. Polyurethane-based adhesives do a better job of adhering to the plastic, and one of the most commonly used ones (in water rocketry, for gluing bottles together for longer pressure vessels) is PL Premium Construction adhesive. It does foam a bit, but if that isn't a problem, it's something you can use. Another, slightly weaker (but non-foaming) alternative is Sikaflex 11FC.
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Unread postAuthor: Gun Freak » Fri Jul 29, 2011 11:33 pm

I'm gonna put a bit on a bottle and see how well it adheres. It might be good enough for my purposes.
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Unread postAuthor: dart guy » Tue Jun 25, 2013 10:36 pm

i have an idea
do you think that if you fiberglass a thin pvc pipe it would make it hold more psi ? if so i think i would try that for my l96 plans under "want to build but plans suck" in the pematics fourum
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