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Painting The Inside.

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Painting The Inside.

Unread postAuthor: rna_duelers » Wed Sep 19, 2007 3:58 am

With my hybrid that is currently be constructed I have a few issues I need to figure out,and one of them is with the material being used.The chamber is made from Aluminium and I plan to use oxidisers and and many atmosphere shots,the trouble being that some people have had issues with oxides forming on the chamber walls with Aluminium so I plan to paint or coat it some how to prevent the chamber from oxidising.So anyone with some good easy ideas on how to paint the inside of the chamber please fire them off in my direction.

I did have one plan of using an engine enamel and filling the chamber with a lot of the enamel and rolling it around back and forth to coat all walls but I am unsure about how well it will coat the walls,so any ideas would be great.
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Unread postAuthor: psycix » Wed Sep 19, 2007 4:04 am

Maybe you can use some sort of car wax/paint stuffto prevent the oxidizing.
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Unread postAuthor: dwats32 » Wed Sep 19, 2007 4:06 am

Degrease the aluminium first then sandpaper it to prepare to for painting. You'll have to do a bit more than that if you want a really good finish by using powder coating
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Unread postAuthor: rna_duelers » Wed Sep 19, 2007 4:15 am

I cannot get my hand in the chamber the hole is only 40mm,chemically cleaning can be done though.

Powder coating...I'm not made of money.But the problem with using a wax etc would be burnt by the combustion would it not?
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Unread postAuthor: dwats32 » Wed Sep 19, 2007 4:32 am

Engine enamel sounds fine.
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Unread postAuthor: MrCrowley » Wed Sep 19, 2007 4:34 am

Sand paper it by putting some sand paper on a long stick that is similar diameter so it fits inside well.
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Unread postAuthor: rna_duelers » Wed Sep 19, 2007 4:37 am

The chamber is a liquid oxygen bottle so the shape isn't to sanding friendly.Do you think that just degreasing it would be fine or would the sanding be needed?
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Unread postAuthor: MrCrowley » Wed Sep 19, 2007 4:51 am

Fill it up with sand and make it into a sand cloud gun, but that requires you drilling a hole in the chamber and I doubt it would even work :lol:

I say try the enamel idea.
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Unread postAuthor: rna_duelers » Wed Sep 19, 2007 5:09 am

Hahahah any bet my gun has a high ROF then yours....It's in the millions of rounds a second with sand :wink: .

Enamel it is!
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Unread postAuthor: Marco321 » Wed Sep 19, 2007 6:53 am

Do you really need to prevent it from oxidizing? Aluminum is called a passivating metal, which means the oxide it forms protects it from any further corrosion, so its kinda natures way of making a protective barrier on aluminum.

Thats why aluminum is often used in those outboard motor tubby boats, is oxidizes, which makes a protective layer, preventing further corrision.
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Unread postAuthor: SpudBlaster15 » Wed Sep 19, 2007 9:22 am

As Marco said, once an oxide layer has formed on the inside of the chamber, you will not have to worry about further oxidation, even with pure oxygen mixes. The oxide coating that forms on the surface of the aluminum is nearly as hard as high grade tool steel (Rockwell C hardness of ~60), and seals the metal relatively well.

If you wanted extra protection, you could have the tank anodized. Anodizing is a process in which a thicker oxide coating is grown out of the aluminum by means of an electric current passed through a bath of acid in which the aluminum is suspended. This coating is then sealed, and an ultra tough finish is achieved.
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Unread postAuthor: jimmy101 » Wed Sep 19, 2007 11:41 am

Marco321 and Spudblaster are right.

Only a couple minor points. Aluminum oxide is indeed very hard but it adheres to the aluminum pretty poorly. Much better than iron oxide adheres to iron but still pretty poorly. If you take a hunk of aluminum you can use it as a pencil, transfering a gray line of aluminum oxide to a piece of paper. Once the oxide layer is worn off it quits writing. Let it sit for a few days and the layer will reform and it'll write again.

Anodized aluminum is oxidized aluminum that has been carefully treated to maximize the adhesion of the oxide layer to the Al. The anodization coating is pretty strong but smack it with something hard and it will chip off.

I would say that, as long as you are filling the chamber with gases, then the oxide layer that forms just form air exposure will be adequate. If you are doing anything that makes mechanical contact with the oxide layer (like filling with liquid and shaking) then the layer will flake off. This may or may not be a problem since the layer will reform pretty quickly.

The big concern would be exactly what you mean by "oxidizer". Air is fine. Compressed air is fine. Pure oxygen might be another thing. Compressed pure oxygen is definetly another thing, especially at very high pressures. Any stronger oxidizer (hyrogen peroxide etc.) greatly increases the risk that the aluminum will be attacked regardless of the oxide layer.

Of course, strong oxidzers will also attack most paints, so even painting the surface might not protect it.

So, whatever you are up to, be careful.
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Unread postAuthor: psycix » Wed Sep 19, 2007 4:20 pm

rna_duelers wrote:The chamber is a liquid oxygen bottle so the shape isn't to sanding friendly.Do you think that just degreasing it would be fine or would the sanding be needed?


A liquid oxygen bottle?!
Dont you think it can withstand oxidizers then?
Maybe there is already a coating inside.
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Unread postAuthor: DYI » Wed Sep 19, 2007 5:45 pm

A lot of liquid oxygen cylinders only have an operating pressure of about 25psi, not nearly as high as gaseous oxygen cylinders. However, the cylinder is designed to hold pressurised oxygen in the first place, so I fail to see what the problem is. I would hope that you aren't planning on using concentrated H2O2, because that would just be asking for trouble.
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Unread postAuthor: rna_duelers » Wed Sep 19, 2007 11:15 pm

I was thinking the same thing about the oxide layer forming on the inside and making a protective coating.

And it is a liquid oxygen bottle...DAHHHHHHH I'm such an idiot of course it's going to have a protective coating on the inside,why didn't I think of that before...I will how ever paint the other Aluminium fittings and sections that are going to be exposed to oxidisers.

No H202 going to be used but there is going to be 02 and N20 with propane and MAPP etc,it's going to be fun.

Thanks guys.
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