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Acrylic and Polycarbonate Chambers

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Acrylic and Polycarbonate Chambers

Unread postAuthor: noname » Tue Jul 03, 2007 10:31 am

At the plastics store where I get all my cool stuff (including vortex block material), I've noticed some large acrylic and polycarbonate tubes. The largest diameter is 6" polycarbonate, but the walls are only 1/8."
I also found a 1 foot long piece of 4" acrylic with 1/4" walls for $15, think that's safe enough to use as a chamber?
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Unread postAuthor: singularity » Tue Jul 03, 2007 12:28 pm

isn't pressure rated but combustions don't generate too much pressure. also i remember reading that acrylic doesn't shatter like glass, it breaks into large dull pieces. so i say where a thick sweatshirt when testing and a face mask or some kind.... or just test using a remote ignition system. and isn't polycarbonate the stuff they use in safety glasses, that would probably be the better choice.
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Unread postAuthor: Gepard » Tue Jul 03, 2007 12:38 pm

That's 'cos it's impact resistant.....

Use the burst pipe formula and sub in the Young's Modulus for Acrylic and it'll tell you whether you can use it.

Personally I wouldn't use it.....

Michael
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Unread postAuthor: Fnord » Tue Jul 03, 2007 12:46 pm

By polycarbonate, do you mean lexan polycarbonate?
Lexan is ideal for clear chambers as it is extremely durable and doesn't fragment(to my knowledge). I would use 3/16 or 1/4 lexan rather than 1/8, just because 1/8 seems kinda flimsy to make a sturdy chamber from.

I've heard mixed things about acrylic. I believe someone used it for a chamber before though. Just remote fire it a bunch first. If you can get a small piece and smash it to tests its failure characteristics.
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Unread postAuthor: Gepard » Tue Jul 03, 2007 12:49 pm

Lexan is the registered trademark of Polycarbonate....

It's like saying "By car, do you mean Ford car?"

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Unread postAuthor: Fnord » Tue Jul 03, 2007 1:27 pm

wikipedia wrote:LEXAN is a registered trademark for General Electric's brand of highly durable polycarbonate resin thermoplastic intended to replace glass where the need blah blah blah...


There is more than one type of polycarbonate, and polycarbonate is not a company. I'm not sure how many share the same properties of impact resistance, so I asked to verify what he found. Lexan is the most common around here.
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Unread postAuthor: Gepard » Tue Jul 03, 2007 2:08 pm

Oops....that's why I dropped Business. I meant Lexan is a brand name of Polycarbonate (i know it's now a company).

That's why I used the car example - 'cos it makes it clearer.....

I know what I mean :D

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Unread postAuthor: joannaardway » Tue Jul 03, 2007 2:25 pm

Polycarbonate is polycarbonate is polycarbonate - the brand means bugger all as to whether it's polycarbonate or not.

Any type of polycarbonate is exceptionally strong. 6mm mild steel is considered enough to stop most bullets (obvious exceptions are stuff like SPAS tungsten slugs, and anti-materiel rifles). 12mm polycarbonate sheet (properly coated) is almost as tough.

It's not quite the same stuff, but lookhere for a rough idea of toughness.

The problem you'll have is gluing it together - it needs special adhesives.
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Unread postAuthor: Gepard » Tue Jul 03, 2007 2:34 pm

I've never understood why bullet proof glass is made from high impact resistant acrylic (got some downstairs.....hmmmm...anyone got a gun I could test it with :D) when Polycarbonate is naturally impact resistant.....

Anyone know what property acrylic has over Polycarbonate that means acrylic is the preferred material?


The problem isn't gluing it - it's buying the stuff over here. Costs a fortune compared to the states....

Michael
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Unread postAuthor: paaiyan » Tue Jul 03, 2007 2:58 pm

Well just think of it this way, the stuff may not be pressure rated, but it can apparently stop a .45 bullet. Imagine how many PSI that stuff is taking when that bullet hits. I would think it could take the trivial 85 PSI of a standard combustion.

EDIT: As for a pneumatic, if you've got the money, buy it and pressure test it. We're all interested in the results.
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Unread postAuthor: noname » Tue Jul 03, 2007 7:37 pm

The 4" acrylic is about 5/16" thick, I'll try that first. The only polycarbonate they have in stock currently is 6" diameter and 1/8" thick.

I'll test the acrylic first, because I don't know if you guys work with it much, but it's my main vortex block material. When it cracks, it shatters into very sharp pieces, almost like glass.

As for securing it, I'll do what I do with any weird kind of pipe I'm not sure about. I cement it to a PVC joint with a bunch of silicone sealant, then put usually around 20-25 machine screws in to prevent them from blowing apart. You may doubt this method, but I've done it with normal PVC joints too and they hold as much (if not more) pressure as regular solvent welded joints do.
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Unread postAuthor: Scotty » Wed Jul 04, 2007 10:20 pm

It would be much safer to use Polycarb, however i have made a whole gun with Acrylic (barrel and all -except for the chamber plugs) It is only a mini 22cc.

I have made another but i used a 4.5 mm thick sleeve that goes inside the chamber (it's transparent Polyurethane) so you can still see everything that's going on inside (Looks cool at nightime, you can see the flame in all it's glory!)

I didn't use glue, i drilled and used M4 bolts to hold it together.
It's capacity is around 260ml and with a 17mm barrel (1.2 Metres long) you can put Nylon slugs through a metal fuel drum (both sides).

I work with these materials everyday so i have a bit of an advantage there.
Acrylic WILL shatter but into fairly large sized pieces (they will still be razor sharp however) thats why i would recommend the Polycarb. It will NEVER shatter like Acrylic (it may crack if it is exposed to U.V. for long enough- like years).

The only other difference is that Polycarb is Hydroscopic and Acrylic is not.

I encourage you to make your chamber clear, it's soooo much better when you can see you gun "work" and people seem to much more impressed and in awe (NOOBIES are like woah man thats STUPENDOUS!)

If you do go with the Acrylic use a blunt drill bit when making holes, a sharp one will crack the Acrylic in no time- First hole probly.

If anyone has any questions about Plastics or fabricating processes with Plastics P.M. me and i will endeavour to answer.

Peace
Scotty
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Unread postAuthor: noname » Thu Jul 05, 2007 10:23 am

I know how to drill acrylic; or I would be losing quite a bit more cash than I make on vortex blocks. :wink:
I'll try to find some smaller diameter polcarbonate, but I'll get the 6" if I have to.
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Unread postAuthor: WOW!! » Thu Jul 05, 2007 11:58 am

What is the name of the store you get your stuff at?
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Unread postAuthor: noname » Thu Jul 05, 2007 1:01 pm

<a href="www.tapplastics.com">Tap Plastics</a>
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