"LLBrown" wrote in message
...

"DoN. Nichols" wrote in message
...
On 2008-11-11, Don Young wrote:

wrote in message
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Here is what goes on.... I bend a thin wall brass tube to shape then I
have
to melt the bending medium out of the pipe with a torch. This causes a
black scaling to show up on the outside of the pipe. To remove this I
dip
the pipe in a 50/50 mix of muratic acid and water. This in turn plates
the
pipe with very thin copper that I have to buff off.

Would a paint stripping gun get hot enough to remove your bending
medium without producing scale?
--Glenn Lyford
I bet it would. My heat gun works great for mass de-soldering of old
circuit
boards. I can just melt the solder, whack the board against something
solid,
and all the components fall off.

I'm surprised that I haven't seen mention of Cerrobend here. It
is a low melting point alloy designed for the purpose. IIRC, it melts
below the boiling point of water, so you can extract it without getting
hot enough to generate scale. The one disadvantage to Cerrobend (and
several other Cerro alloys) is that they are quite expensive, so if you
need a large amount for your support, it will not be cheap. (However,
it is infinitely reusable -- just make sure that you melt it in a
non-metalic container -- porcelain, quartz, anything which will handle
boiling water and not be likely to form an alloy with your bending
support.

As for the solder melting -- that may be well below the melting
point of the alloy which you are using for bend support. *Good* solder
is (or was) something like 38/62 (I forget which side was tin) but that
was the percentage for the eutectic alloy -- the one with the lowest
melting point.

Enjoy,
DoN.

I have never tried Cerrobend but other builders have warned me that
getting it out of the pipe is a pain sometimes because it almost acts as a
solder and binds to the brass. I am not sure what coating the pipe with
oil would do to the Cerro... if it would be good for more than one use.
LLB

Oil is the traditional barrier for bending tubing with Cerrobend, but NOT
detergent motor oil.

Here's an old technical report on bending tubing with Cerrobend:

http://www.canadametal.com/pdf/cerro_bending.pdf

It also mentions limitations with using pitch, lead, and sand as
alternatives.

I have a four-pound block of Cerrobend that I haven't used for years, but
one thing I remember from using it is that it is unusually liquid for a
metal when it's melted. Stainless steel containers are recommended for
melting it, although the low temperatures involved would allow the use of a
wide variety of materials. As you say, it will solder itself to some metals
unless you oil the surface first.

--
Ed Huntress