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Bending copper

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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Bending copper

Unread postAuthor: Lockednloaded » Sat Dec 29, 2012 8:23 pm

I want to bend some 1/2" copper tubing into a small "S" shape that will be part of my chamber. I've seen a few how-to's from a quick google search, but I need a method that will be able to hold higher pressures (>300psi)

So does anyone have any experience with "hand bent" copper chambers at significant pressure?
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Unread postAuthor: jrrdw » Sat Dec 29, 2012 9:56 pm

I really can't see the shape making any difference unless the outside curve becomes a stress point from streching it to make the bend. Is that the concern?
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Unread postAuthor: ramses » Sat Dec 29, 2012 11:22 pm

I don't think they would significantly weaken the pipe. In fact, by cold working the copper, you will actually work harden it. Of course, kinks will concentrate stress. The outside of the bend will be thinner, and so will experience slightly less stress. I think you would be save if you took the recommended working pressure of the tube, then cut it in half and took that as your working pressure for the bent pipe.

I believe the recommended method is to fill it with sand or salt, cap the ends (tightly), and then bend, to avoid forming kinks. You should be able to do this cold (more strength), but if you heated it, the pipe would be in its annealed condition, and therefore possibly weaker than when you got it.


If possible, it would be beneficial to buy tube that is designed to be bent, and may even come in the form of a roll.
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Unread postAuthor: jsefcik » Sat Dec 29, 2012 11:59 pm

if you check at your local plumbing stores there is hand benders you can get to do this, in school we did it many times, there is a special grade we used that is softer i cant remember

but try a hand bender
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Unread postAuthor: evilvet » Sun Dec 30, 2012 2:41 am

Buy a plumbers bending spring, the external kind is better for tight radii as it won't get jammed in the pipe.

http://en.wikipedia.org/wiki/Tube_bendi ... ng_springs

Does not mark the pipe or create kinks if done properly. Not sure where you are but Oz gas supply runs at about 8-10 bar and every plumber I work with uses this method.
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Unread postAuthor: Fnord » Tue Jan 01, 2013 12:19 am

Copper tubing (actual ID .5 inches) is annealed and will harden when you bend it. Copper pipe (type k,l,m) is already work-hardened.

I suppose you could calculate the wall thickness difference between straight length of pipe, and a length with a radius bent into it and go from there, but it is unlikely to be a factor at 300 psi.

For very tight radii, heat up the pipe until it has an oxide coating, fill with molten lead, then allow it to cool and bend. Melt the lead back out and clean/flux. I bent some 1/4" tubing into a 1/2" circle like this.
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Unread postAuthor: jsefcik » Tue Jan 01, 2013 3:29 pm

Fnord wrote:Copper tubing (actual ID .5 inches) is annealed and will harden when you bend it. Copper pipe (type k,l,m) is already work-hardened.

I suppose you could calculate the wall thickness difference between straight length of pipe, and a length with a radius bent into it and go from there, but it is unlikely to be a factor at 300 psi.

For very tight radii, heat up the pipe until it has an oxide coating, fill with molten lead, then allow it to cool and bend. Melt the lead back out and clean/flux. I bent some 1/4" tubing into a 1/2" circle like this.



that is an awesome idea, i never heard of it
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