fluxless brazing of aluminum

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Has anyone had much experience with the fluxless brazing rods for aluminum?
Are they as good as what's been claimed on the websites?  What are the
recommended limitations in gage thickness for brazing aluminum with propane?
I'm planning to work with 22 gauge alum.  I've read that brazing with
thicker aluminum sheets will work better if you use higher temps that you
get from from oxy-acetylene tanks.



Re: fluxless brazing of aluminum
wrote:

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I don't think the "miracle rod" is much better than epoxy.   Joints
made with it tend to be brittle and crack easily.  

However, brazing aluminum with flux about requires special goggles
that block the sodium flare from the flux so you can see what you're
doing.

I think the issue with propane vs O/A is more the chemistry of the
flame than a matter of temperature.   A propane flame has ample heat
to braze (or melt) aluminum, but  O/A with a reducing flame  works a
lot better for me.  



Re: fluxless brazing of aluminum
On Mon, 13 Jun 2005 12:33:18 -0500, Don Foreman

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I've built canoe racks, bicycle carriers, and other such stuff using
the "miracle rod" and 6061T6 and have never had a joint crack. I've
also used it with "utility grade" aluminum with good results.
TIG welding is definitely better - and now that I have TIG available
to me, I generally have things welded instead of "brazed" when working
with aluminum.
I usually used oxy-acetelene with the "miracle rod" because aluminum
is such a good conductor of heat it is difficult to get things hot
enough with propane.

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Re: fluxless brazing of aluminum
I've used these rods quite a bit since the mid-80s, and I think might more
accurately be described as "aluminum repair rods". They appears to have a
high zinc content, and I can't say that I've felt sick after using them, but
others may have different sensitivities, so take any precautions you feel
are neccessary.

The first ones I got were being marketed by Mesa Foundry, and the last ones
I got from a tractor supply store, are branded U.S. Forge.

For small thin pieces, a common propane torch will work, but for pieces with
more mass, only the higher output of a MAPP torch is adequate (the type with
a swirl-combustion chamber torch style) using MAPP gas, of course.
I haven't used these rods with an O/A torch, as most of the parts I've done
are small and MAPP has been adequate. As an example, 1/8" x 1" angle or flat
aren't difficult.

The claims that the rod won't "stick" to steel is not entirely correct..
I've found that it sticks to some alloys when you don't want it to.
The claims that it works well with non ferrous materials seems to be
accurate.

The main preparation is to clean the repair areas. Aggressive scratching
with a clean SS brush is recommended, just before the repair. Removal of
anodizing and other contaminants will be required.

If you're familiar with soft soldering, this product doesn't work the same,
so don't be expecting it to.
Initially, the same adequate heating of the parts before adding the rod is
about the same (heat the work, not the rod), but then you need to start
scratching the rod into the joint.

At this point, you can observe the oxide layer breaking up, while the rod
begins to fuse/blend with the aluminum or aluminum alloy parts.
If this doesn't occur (with aluminum work/parts), then the work isn't hot
enough.

The sign that I see that let's me know that the joint area is hot enough, is
that the workpiece(s) will appear to be forming small bumps (like
goosebumps) when the heat in the work material is sufficient. I've observed
this with nearly all of the aluminum that I've joined, whether it's been
billet/bar stock or cast alloys.

This repair rod product isn't perfect for any type of part. The aluminum
alloys that I've worked with are soft in the heat zone after repairs. A
repaired part shouldn't be subjected to high stresses.
Some hardness may return with aging, but I'm ignorant as to how this takes
place.. maybe someone else can offer some insight into this.

I would consider some repairs to be very good, and while I might use it to
repair a small boat prop, I wouldn't attempt to repair a plane prop (even
for a model plane).

There are numerous sources for other types of similar (and also better)
products, look up The Tinman, and Postle for other examples.

WB
..................

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aluminum?
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propane?
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