Quote:
Originally Posted by Xringer
Brazing copper seems to need very high temperatures. What kind of rig would be good for small scale hacker apps?
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I am not a brazing expert, but I will share my very modest experience...
I'm using just a MAPP gas torch, no oxygen. I have tried just propane and it just barely got to cherry red... very frustrating.
When I switched to MAPP, it worked much better.
You probably already have a propane torch, you might try getting a bottle of MAPP gas and running it that way. If it doesn't work, you have a spare bottle of MAPP gas.
Tricky part is that the cherry-red temp is not so far from the slump temp of copper... so you don't want to go too hot.
You may be right, straight MAPP gas might be borderline on larger tube like you have... you'll need to do some tests. Whatever setup you get, you should practice on something that is similar to the piece you're trying to braze. Do several tests... If you use up a whole bottle of gas doing tests, it is money well spent.
> The filler metal used on a lot of those jobs, was 15% silver
> and 85% copper. (Very costly stuff).
You sure don't want to combine plumbing solder & brazing rod, they don't mix, very bad... I know... I tried it once... never again.
I have had the best luck with SilPhos rod. It is self fluxing, flows very nicely.
SilPhos is available in 5% silver (which I use) and 15% silver (which the HVAC trade seems to prefer). I haven't tried the 15% stuff because it's more expensive, but I assume it has a slightly lower melting point, which would be good for you.
Before you braze, you should see if you have any positive pressure in your unit at all. If you don't it means that the R-410a has all leaked out, and you can assume that the unit has been"breathing" (my term) air and moisture in the meantime, so you should pump down and purge with inert gas a few times before you braze (principle of dilution).
If you have any measurable pressure, you can assume you have enough R-410a to prevent "breathing" so you don't need to purge... but you may need to release some pressure...
One of the warnings of running nitrogen (or other inert gas) while you braze is that if your nitrogen pressure is too high,
you will get pin hole leaks. So this may be why you have the pinhole leak you have.
When I braze, I run enough of my inert gas to purge the system, and I provide an escape for the gas, to which I attach a tube that I then insert a few inches into a jar of water. This way, I am assured that I have a continuous flow of purge gas AND I know that I am not building up any significant pressure. I adjust my purge gas flow rate so that I get a bubble every few seconds... so the flow rate is very, very low.
You should ask at a welding shop what kind of rod you should use to fix an existing pinhole leak in a new unit, such as you have. They may even recommend 40% or 60% silver. (If you think 5% or 15% is expensive, wait til you price this stuff!!) BTW, my experience is that the guys who work the counters at welding supply shops (not the big box places) are VERY knowledgeable and helpful, and they understand that the good advice they have is part of their service. Very different from the HVAC trade...
SInce you are not trying to join dissimilar metals, I wouldn't think you'd need flux.
Since the price of rod has gone so high, some places sell what they call "job packs", which is less than a pound, and only has a few sticks (which may be all you'll ever need).
You may also want to isolate the high temperature from the rest of your unit by wrapping wet rags around the tubing. You don't want to get too close to the joint you're working on, you'll make it too hard to heat up.
-AC_Hacker
P.S.: Be aware that brass fittings have a LOWER slump temp than copper...