Printable View
So I have a project on the go..... I need to bend some 40mm copper pipe into a tight 'u' to make a wet back for a 'rocket stove' I have built.
It needs to be a tight bend, as the rocket stove is made from two D size oxygen bottles welded together.
I have acouple of copper 90° elbows to use, but thought it might be better to bend it... am I being paranoid about the brazing in the hot box?
Any of you clever shooters happen to be a plumber?
You can fill it with sand and heat and bend, or use a plumbers spring if yo can find one of that diameter
Copper tig welds really well, but welding with silfoss will be fine. If you get it hot enough in use to melt silfoss you’ll have other problems to worry about.
Ok, I thought as much.Quote:
Originally Posted by 2post
Will run with the elbows, as I reckon a 180° bend will be a mission.
Thanks guys.
+1 for the silfoss, just make sure the copper gets to cherry red in colour when you're heating it with the torch.
All wetback units I have seen have been bits of straight pipe with the corners done using two 90degree elbows, all silfos'd together. As long as the copper pipe is always full of water the silfos should not be able to get hot enough to melt.
....Let the water boil dry though, and all bets are off!
P.S. if you need a stick or two of 15% sending up give me shout.
Make sure the sand is DRY:)Quote:
Originally Posted by 40mm
My dad made a 1/2” copper coil about 4 foot long to fit in an 8” flue to heat water using the sand. He was one clever bugger. Fitted to a small chip heater, fired with waste oil. Emery thing glowed orange, down to the feet, when it was fired upQuote:
Originally Posted by 40mm
I bent some 25mm steel tube for a motorbike into a tight U bend a number of years back. I flattened and folded over one end, packed the tube as full as possible with sand (like compress it in there as much as possible as you add it) then flattened and folded over the other end until I could not fold it any more and the whole thing was tight. I then made a former for the shape I wanted from MDF scraps, clamped one end of the tube down and bent it around by hand. It held its shape perfectly and I could tweak it to exactly the bend I wanted. I then cut the ends off, got the sand out and trimmed it to final length. Great way to do one or two bends in a pinch, prob easier to pay a fella for more than that.
The sand or plumbers spring method is the classic one. I can remember dad doing this I got to hold the blowlamp to heat the section, the colour changes on the pipe when the flame was on it fascinated me.
Just use the pre bent piece. most plumbing pipe is hard drawn and requires annealing by getting cherry red and then cooling. Otherwise bending is nigh impossible.
unless you have a hard round surface it is difficult to bend 40mm pipe.
use plumbers silphos as it is cheaper than fridgie stuff.
@2post what would you recommend I use to clean up the 40mm pipe? It is old stuff, so pretty tarnished etc.Quote:
Originally Posted by 2post
I was thinking of a wire wheel and sand paper before some kind of acid flux etc? Am I on the right track?
Cheers
@40mm Normal household vinegar will do the trick after a quick buff with a wire brush.
@2post, so with the vinegar flux, do I need to rinse it off with water before welding?Quote:
Originally Posted by 2post
I do have some 'spirits of salts' on the shelf if that is better? Also, I suppose it will need to be rinsed off prior to welding??
Cheers, 40mm
Clean it after welding it, just use emery where you want to weld. If you heat it and quench it most of the scale will fall off.
Are you after function or form? As in are you wanting to clean it up only so it weld well or is it to be a beautiful thing?
Yes wash it with water and dry it off before welding. What welding stick are you using. Ezyflow needs a flux but silfoss should be ok without if it’s clean enough. @40mm
@2post, I have silfos. ANd I dont care what it looks like, just so long as it works!
So, I have the 'spirits of salts' is that better than vinegar?
I’d give it a go if that’s what you have
@40mm have you considered other options aside from a in-fire wet back considering you have quite a small firebox? I would go with either a Yunca style water jacket heater that sits above the fire box or wrap 1/2 " copper around the flue as a heat scavenger but not welded to it. A tiny little pump can be used to push the water and circulate to a radiator. A friend who is a plumber has this set-up in his own house
Oh.... the fittings are quite expensive, being 40mm. I will do more research. Cheers though.Quote:
Originally Posted by 2post
The heat exchanger is 1.2m long and 40mm pipe, so wont fit anything else.... I have made a 'rocket stove' which is a very efficient type of fire.Quote:
Originally Posted by Moa Hunter
It is made from two D size oxygen bottles welded together at a right angle.
The burn chamber is horizontal (on the ground and insulated) while the flue is vertical as usual.
Will burn bark and all the scesps from the wood pile etc without smoking the place out or choking.
Might even try some coal in it.
I think photos are required of this wondrous creation.
Here you go.Quote:
Originally Posted by Sidetrack
I will make a post for the home builds thread when I get some more pictures and progress.
Attachment 200399
Attachment 200400
Awesome! There's heaps of simple build rocket stoves designs now that use square tube. I've been tempted to build one for while with some leftover steel fence post I've got laying around. Will be watching this thread with interest!
https://www.google.com/search?q=rock...active&ssui=on
Go to to pit stop and see if they will bend it for you
They have hydraulic pipe benders
Would deal with copper like butter as Designed for steel and stainless
Probably only take them a couple of minutes and im sure they could be bribed with cold green glass or brown glass bottles :)
Make sure you have no airlocks, hahaha
Cheers for the advice mate, I think the copper might be a bit soft and crease/ fold up? Maybe not.Quote:
Originally Posted by rambo-6mmrem
Anyway, I have gone with two 90' bends as I already had them...
Will be making a thread about this project when I get back into it.
not this project mate!Quote:
Originally Posted by Maca49
But I have my eyes on a mates old hot water cylinder....
Thinking of capping off all the safety valves etc and putting a bit of petrol inside it, then hard wire the heater.
A mattress bag or two full of oxygen taped to the outside and a couple road flares or something that will burn for a good while.
Just gotta find a paddock far enough from any stock, buildings, bush or houses and roads..... Not actually that easy in Auckland.
Should be an interesting 'science experiment'
Copper to copper joints only need to be clean (no flux) if using silphos. Is that a copper to steel joint at the open end? Copper to mild steel with silphos ( eziflo is better) will need braising flux and very clean steel, dont get the steel red hot.
Thanks for the advice @musket.Quote:
Originally Posted by musket
There is copper/copper and copper/brass joints to make.
copper to brass can use silphos. just don't get brass hot. if it is pink it is going to melt. Needs flux too. idk if it is helpful but pink flux is shit. white flux works effectively.Quote:
Originally Posted by 40mm
ok, dam. I have a big jar of pink flux powder...Quote:
Originally Posted by Russian 22.
If you are using silphos, just get it 'Bright' with sand-paper, wipe with clean-cloth, dont touch it with fingersQuote:
Originally Posted by 40mm
