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Unorthodox Joint Advice

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unorthodox Joint Advice

Unread postAuthor: skyjive » Wed Nov 04, 2009 12:30 pm

So I need to put a 1/2" copper pipe through a hole drilled through the middle of an iron endcap in such a way that the joint between the outside of the copper pipe and the inside of the hole in the endcap is pressure tight. Suggestions? The joint would have to take in the ballpark of 100 psi, and more importantly be able to withstand fairly high temperatures, on the order of magnitude of a propane torch. Luckily the OD of 1/2" copper pipe is exactly 5/8", so if I drilled a 5/8" hole it would fit fairly snugly, but how to make it pressure tight at high temperature? Thanks in advance for you advice.
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Unread postAuthor: Technician1002 » Wed Nov 04, 2009 12:47 pm

Brazing with a torch and a flux coated brazing rod comes to mind.

This IS how the copper tube goes through the steel case of a refrigerator compressor shell.
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Brazing job on my 2 inch valve.
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Unread postAuthor: jrrdw » Wed Nov 04, 2009 12:50 pm

Your asking a lot from your materials. The copper has to have a faster expansion rate then the rest, further as well. You can get the fit it together by chilling the copper and heating the end cap, then slide the copper through.

Will it give you what you want? I dought it.
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Unread postAuthor: Moonbogg » Wed Nov 04, 2009 1:35 pm

Well, this might sound kinda lame, but you could use a press fit steel pin going through both parts for mechanical strength andthen seal everything with JB weld. That would be pretty strong.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 04, 2009 1:37 pm

Unorthodox Joint Advice


Maybe the Dutch can help :D
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Unread postAuthor: psycix » Wed Nov 04, 2009 3:45 pm

Incoming dutchman! (not flying today)

You mention an iron endcap. Do you have to use that endcap?
What about replacing that for a threaded reducer/bushing, and brazing a threaded fitting onto the copper pipe?
Detachable, sturdy and leak-free.
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Unread postAuthor: skyjive » Wed Nov 04, 2009 5:19 pm

Image

Maybe this will help clarify. I can't use standard fittings because I need a sort of coaxial setup with the space between the copper and iron pipes pressurized. The crack between the edges of the endcap hole and the copper pipe outer wall needs to be pressure tight, but not particularly strong since there will be no axial force on the copper pipe trying to push it through the hole. Also the joint will be exposed to prolong high temperatures (think holding a propane torch up to it for a while) so it needs to be heat resistant, which makes me wary of trying brazing or JB weld, although that might end up working ok. So I need a joining method that can resist pressure (~100 psi) and heat (propane flame) but doesn't need to be at all mechanically strong.
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Unread postAuthor: POLAND_SPUD » Wed Nov 04, 2009 5:35 pm

what temperature are we talking about ?? in Celsius??
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Unread postAuthor: skyjive » Wed Nov 04, 2009 6:57 pm

According to Wikipedia, the maximum propane flame temp is 2k Celsius, but in reality would probably be a bit less.
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Unread postAuthor: twizi » Wed Nov 04, 2009 8:46 pm

are u makeing a steam gun
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Unread postAuthor: Lentamentalisk » Wed Nov 04, 2009 9:23 pm

Is there a reason why you haven't already decided on welding? That is the only way I really see possible. You just need something that requires a hotter flame than what ever flame you will be using on it. I don't understand what your question is.
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Unread postAuthor: hi » Wed Nov 04, 2009 9:34 pm

I agree on brazing. its just like soldering and you can buy kits at lowes/home depot.
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Unread postAuthor: Technician1002 » Wed Nov 04, 2009 9:45 pm

Not to pick on anyone, but just to educate the general public.

Is there a reason why you haven't already decided on welding?


Welding is the melting of two pieces of the same metal with or without a filler of the same material. Most welding is in the iron and steel family of metals.

Brazing is a high temperature soldering type process where two pieces of metal the same or different are joined with a 3rd metal to bind them together without melting either. Due to the copper/iron joint, it can't be welded, but it can be brazed. Most brazing is for joining dissimilar metals or metals of vastly differing thickness where welding would melt one away.
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Unread postAuthor: skyjive » Wed Nov 04, 2009 9:51 pm

Right, welding wouldn't work, and I don't have the knowledge or equipment for it anyway. I'm thinking maybe I could just compress a neoprene washer or something onto the top of the end cap to seal off the crack, or use some similar mechanical method, since like I said it doesn't have to withstand a large force.

Brazing is certainly an attractive option, but I'm not sure the applied heat wouldn't just remelt the joint.

And yes, good guess, this is a steam-related idea.
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Unread postAuthor: hi » Wed Nov 04, 2009 10:21 pm

but I'm not sure the applied heat wouldn't just remelt the joint.


???

you just heat the metal until it cherry red, then you apply the braze. when you are done you just let it sit until its cool.

Are you worried about when you use steam and heat it up? water boils at 212 degrees, its going to take around 1000 degrees to melt the braze. it melts a lot hotter than solder.

the mythbusters made a steam gun and used regular solder and didnt have a problem. like i said, the braze has to be bright cherry red to melt it.
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