Fw: <VV> Oxy Acetylene Torch Brazing Procedure

Sun Feb 20 17:04:21 EST 2005

At the request of John Beck, I am copying the group...

----- Original Message -----
From: "Garth Stapon" <stapon1 at earthlink.net>
To: "John McMahon (by way of "Harry Jensen, CORSA Executive Secretary"
<corsa at corvair.org>)" <jmac2112 at adelphia.net>
Sent: Sunday, February 20, 2005 4:04 PM
Subject: Re: <VV> Oxy Acetylene Torch Brazing Procedure

> John:
>
> The definition of brazing is that it is a process that takes above 800
> degrees F, but below the melting point of the material.  (In the case of
> mild steel, this is in the 2,500 degree range and will vary depending on
> carbon content). Below 800 degrees F is considered soldering.
>
> Most bronze alloys bond in the 1,600 - 1,800 degree F range.  The
exception
> to this is with silver alloys which can bond as low as 1,200 degrees F.
>
> There are several tricks that can help to make brazing more successful.
>
> 1) Clean the base metal of contamination as well as possible. Use a # 5
> shade lens so that you have good visibility.  DO NOT BRAZE WITHOUT EYE
> PROTECTION! Anything darker makes it difficult to see what you are doing.
>
> 2) Use oxy / acetylene as the preferred fuel gas. (oxy-propane, oxy mapp
as
> well as propylene tend to yield oxidizing flames, and are not great for
> brazing).
>
> 3) Set a 3 X carburizing flame.  Basically the combustion ratio for a
> neutral flame is 1.4 parts oxygen to one part acetylene.  We want to add
> additional acetylene in the flame in order to produce a reducing
atmosphere.
> This will help the wetting action of the alloy immensely.
> Most people try to braze with a neutral or oxidizing flame - this is not
the
> preferred setting and can be determined by a very tight blue cone with
more
> noise coming from the brazing tip.
>
> 4) The outside flame envelope should be set at a distance of 3 X the
> distance of the inner cone.  This will soften the flame, lower the
> temperature slightly and provide the "best" flame condition for the braze
> operation. Be sure to match the size of the tip to the job at hand.  A
size
> 1 tip should be adequate for sheet metal.
>
> 5) Use a flux coated electrode with an auxiliary flux. Heat the tip of the
> bronze rod slightly and dip it in the auxiliary flux jar.  If the rod is
not
> hot enough, flux will not adhere to the rod.
>
> 6) Lay the bronze rod on the joint and melt some of the auxiliary flux off
> the rod into the joint area.  Keep the torch moving (like you are painting
> the car with a spray gun) as overheating the base metal is likely the
> primary cause of your problem. Do not melt the rod until the auxiliary
flux
> has been applied along the entire length of the joint.  The auxiliary flux
> performs two functions. It is an anti oxidizer and will indicate when you
> are close to the braze alloy bonding temperature.  It will actually go
clear
> and start to flow easily when the correct brazing temperature has been
> reached. You may not be using enough flux. More auxiliary flux is better
> than not enough flux.
>
> 8) Melt a small amount of the bronze filler metal on top of the substrate
> (base metal).
>
> 9) Keep the torch moving and do not bring it closer than 3 inches from the
> base metal as you come up to brazing temperature, as this will help you to
> control over heating. When the small amount of bronze filler on the
> substrate starts to flow, add more rod as required.  If the puddle gets
too
> large and becomes difficult to control, increase the distance to the base
> metal by backing off with torch. Six to eight inches torch to work
distance
> is not uncommon once the bonding temperature has been reached.
>
> 10) Braze the joint with continuous movement of the torch, in and out,
back
> and forth. Do not stop the movement of the torch as this will cause over
> heating and excessive oxidation on the substrate. Work slowly across the
> material with the torch heating a six inch distance at the braze deposit
as
> well as in front of where you want to add alloy.
>
> 11) Let the residual heat in the base metal melt the filler rod. Do not
> apply heat directly to the rod as you may oxidize the alloy.
>
> 12) Once the braze joint is completed, allow to cool to room temperature
and
> remove excessive flux with a water soaked rag as most fluxes are easily
> removed with water.
>
> Note - There are nickel and silver enhanced brazing rods that bond at
lower
> temperatures, but also cost more $$$'s when compared with conventional
> alloys.
>
> There is another option that is an electric arc process known as mig
> brazing, but this is a topic for another post.
>
>
> Hope this helps.
>
> LATE CANADIAN POWER GLIDE SEDANS RULE
> ----- Original Message -----
> From: "John McMahon (by way of "Harry Jensen, CORSA Executive Secretary"
> <corsa at corvair.org>)" <jmac2112 at adelphia.net>
> To: "Virtual Vairs" <virtualvairs at corvair.org>
> Sent: Sunday, February 20, 2005 2:47 PM
> Subject: <VV> question for Garth Stapon
>
>
> > Garth,
> >
> > My name is John McMahon, and I'm piecing together a 1965 Monza that has
a
> > lot of rust.  I've been using an oxy-acetylene mini-torch (Meco Midget),
> > and I've gotten pretty good at welding sheet metal with it, but I've
been
> > having a heck of a time with brazing.  I've got some 1/16" bronze
brazing
> > rod, and I've been heating it gently and dipping it in the flux, but I'm
> > having a very hard time getting it to start flowing.  Even if I take a
> > scrap piece of sheet metal and heat it up and try to make a pool on it,
I
> > have to heat the steel up until it is *almost* melting before the
brazing
> > rod will start to flow, and then sometimes I get the silly situation
where
> > the two metals melt into one another.  Anyway, the books make it sound
so
> > easy, like you can just heat the steel until it's a deep cherry red and
> > then touch the rod to it and it will start flowing, but that has NOT
been
> > my experience.  If you can think of something that I'm doing wrong, or
if
> > there is a better type of rod to use for sheetmetal, please let me know!
> >
> > Thanks,
> >
> > John
> >  _______________________________________________
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