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Dry Ice

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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Dry Ice

Unread postAuthor: dgr-c » Thu Jan 04, 2007 4:47 pm

I came across some mention of dry ice as a propellant. Looks like it could be fun but kind of tricky to work with -- pressure builds as the CO2 sublimates but how far and how fast? You have to mount gauge and watch it to make sure you don't over pressure the chamber.

I have a pneumatic with a gauge mounted and could mod it to accept a dry ice load.

Anybody have any dry ice experience? What about pressure gauges that trip a solenoid at a specified pressure?

Enquiring minds want to know!
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Unread postAuthor: medievalman » Thu Jan 04, 2007 5:02 pm

just put dry ice in the chamber, and use a burst disk for a valve.
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Unread postAuthor: dgr-c » Thu Jan 04, 2007 5:14 pm

medievalman wrote:...use a burst disk for a valve.


I thought of that. Any recommendations for disk material that would burst around 100psi? I searched the forum and the Wiki. Nothing in the Wiki, too much in the forum. is there a FAQ I'm missing.
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Unread postAuthor: Pete Zaria » Thu Jan 04, 2007 5:15 pm

PVC does not handle the cold temperatures of dry ice very well whatsoever. It gets very brittle when it gets cold, and pressurizing it in that state is a bad idea.

ABS handles extreme temperatures much better (though I don't know about the -300 temperatures of dry ice), but doesn't handle pressure as well.

Metal is the only good option.

You could, however, make a metal tank (with some warm water in it, to help the dry ice sublimate better) with a pressure gauge and/or regulator and/or meter system to pressurize your PVC cannon with. Once the CO2 has expanded, I think it should be warm enough to put into PVC without problems.

I've considered doing this. Let me know if you decide to try it.

Edit: for burst disks, use circles cut out of a milk jug or pop bottle. Depending on the brand and what part of the container you cut the disk from, they go at between 80-120 psi. You could use an "actuated" burst disk setup if needed. Or simply a pressure-triggered valve. You could also use an electric sprinkler valve to vent a piston automatically at 100 psi using a pressure switch.

Peace,
Pete Zaria.
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Unread postAuthor: singularity » Thu Jan 04, 2007 7:37 pm

well i have made a few dry ice bombs, those water bottles seem to burst around 150psi if i remember correctly, but anyway it takes a while for a dry ice bomb to go off (mine took like 15 min) i would assume you already know that dry ice can give you a burn if you handle it with your bare hands but i thought i should mention it anyway.
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Unread postAuthor: pyromanic13 » Thu Jan 04, 2007 8:11 pm

I used threaded steel pipe when I made mine....
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Unread postAuthor: Deko » Thu Jan 04, 2007 9:07 pm

ive made a dry ice gun using metal pipe and it worked really well but i cant get dry ice very easily so i dont use it much but i will sometimes, i use it in a basic pneumatic with pressure gauge

i have one question thats sorta off topic: my friend let his little sister put salt on his arm and then put a piece of ice on top of that and it litterally ate a hold into his skin, did salt and ice make dry ice or was it some other kind of reaction?
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Unread postAuthor: benstern » Thu Jan 04, 2007 9:21 pm

If you use a burst disk it will mess with your brain.
"OMG ! I've been waiting a few minutes. When is it gonna blow!"

Salt allows water to become colder. Salt water can go below freezing point without becoming ice.
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Unread postAuthor: singularity » Thu Jan 04, 2007 9:52 pm

Salt allows water to become colder. Salt water can go below freezing point without becoming ice.


that still didn't answer the question no it doesn't make dry ice, dry ice is solid CO2, ice is just solid H2O and NaCl is salt. not exactly sure what happens but its makes a chemical burn, like it melts your skin or something, i would look into it but i got homework
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Unread postAuthor: dgr-c » Fri Jan 05, 2007 7:23 am

Deko wrote:...did salt and ice make dry ice or was it some other kind of reaction?


Salt had little or nothing to do with it -- it was simply sudden freezing.

Water ice is less dense than liquid water, i.e. it expands as it freezes. Dry ice quick-froze the water in the skin cells (probably several layers deep). The frozen intracellular water burst the cell membranes. As soon as the dry ice was gone, general body heat blood flow re-thawed the spot, which now had no structural integrity. The general trauma brought extra blood to the afflicted area, causing redness and swelling in the surrounding tissue.

While the cells were destroyed by freezing, not burning, the result was much the same. A region of necrotic cells and a physiological response. Hot, cold, chemical reaction -- your body's response to suddenly dead skin always looks pretty much the same. But hey, it's all fun and games until someone loses an eye.
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Unread postAuthor: Deko » Fri Jan 05, 2007 7:37 pm

ok thanks dgr-c

i didnt think it made dry ice at first but when singularity made the comment that dry ice can burn you i thought of the time that happened so thats why i asked.

and can dry ice really burn you? because ive handled it bared handed and nothing happened, or does it have to say in contact with your skin for so long for it to burn you?
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Unread postAuthor: frankrede » Fri Jan 05, 2007 8:15 pm

It does burn, its so cold , i cantr imagine you holding it when it stings me through my gloves/
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Unread postAuthor: Bluetooth » Fri Jan 05, 2007 8:49 pm

I held a piece of dry ice for over 10 sec without it burning me.
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Unread postAuthor: benstern » Fri Jan 05, 2007 9:18 pm

thats bullshit. thats not possible.
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Unread postAuthor: Bluetooth » Fri Jan 05, 2007 10:00 pm

With tweezers it is :wink: . Actually once I touched a piece of dry ice too long so I don't have feeling in the edge of my index finger. I wasn't really holding it, I was just touching it by accident and didn't notice.
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