I'm trying to curl up some small copper pipe (or tube, if you prefer) to make a toy boat along this line:
Is it worth trying to anneal a piece with a blowtorch? If so, what's the best procedure?
I just bropught some of this for a studetn project.
Fill with fine dry sand, seal the ends and bend. The sand "should" stop the walls of the tube collapsing.
Heat to cherry red, then plunge into cold water.
To be sure, fill the annealed tube with Wood's Metal, bend to shape, then melt the Wood's Metal out by placing the tube in boiling water.
Colin Bignell
Woods Metal not cheap
Copper is very easy to anneal. Heat until the copper is a uniform dull red colour and then either quench in water or just leave to cool. Keep moving the flame around so as not to overheat or burn any particular area. A dimly lit room makes the colour easier to see. Unlike ferrous metals which harden with a fast quench and anneal with a slow cool, copper also anneals with a fast quench. Because copper work hardens so quickly if you bend or hammer it you may need to anneal it multiple times as you work it into the desired shape but you can do so as often as you like without harming the material.
Most of the copper pipe you buy is in hard or "half hard " condition. Makes it stronger. You can anneal it by heating to red heat and letting cool. It will then bend better but will have reduced pressure rating.
Annealed pipe can be bought, it usually comes in a coil and is thicker guage hence more expensive.
One thing you might do if it is a project is consider automotive hydraulic copper brake pipe if you need a really high pressure.
To stop it from kinking, you can buy and external spring,fits over the pipe while you bend it.
Get it glowing cherry red green tinge to flame and then drop it in a bucket of water. Fine pipe may throw a jet of hot water out so wear eye protection. Dry sand in the tube and ends sealed with wax or tape before you try to bend it will make it keep its shape.
You only need to anneal the part you will be bending.
For a pop pop boat? I think that might be overkill. ;-)
Tim
That would leave a residue inside the tube, which Wood's metal usually does not. As the application seems to involve heating the coil, that may be important.
Colin Bignell
In principle, but would it be likely to matter for this low-tech application? In my experience, without flux the solder just won't wet the oxidised bore.
I think annealing might be enough with thick-wall tube, but I'd be nervous about modern tube kinking without internal support. The sand method is good, but is it easily removed from a relatively tight set of coils?
I'll try it.
Let me put it this way: I spent less than £2 on the hull *and* I got to eat the kippers.
To be powered by a candle or alcohol lamp, so as someone else has said, this is a low-tech application.
Nice project method, including the bending.
Thanks for dragging it in. :)
Try copper brake pipe.
OK but £13 for a kilo of Woods metal when you need less than 100 grams. An engineer is someone who can do for a shilling what any fool can do for a pound.
The cadmium puts me off a bit...
Normal brake pipe is plated steel, top quality brake pipe is a copper nickel alloy of some sort. Both of these have lower thermal conductivity than copper, and will be significantly thicker than you need for your working pressures.
I used 3mm OD pipe (or thereabouts) and wrapped it around a bit of dowel to get the coil. No woods metal, no sand, no solder, nothing.
The former helps a lot.
Andy
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