Figure 6-16.Brazing a butt joint.
because abrasive particles or oil might become embed-
ded in the metal.
Mount the work in position on firebricks or other
suitable means of support, and if necessary, clamp it.
This is important because if the joint moves during the
brazing process, the finished bond will be weak and
subject to failure.
The method of application varies, depending upon
the form of flux being used and the type of metal you
are brazing. Refer to the material on fluxes previously
described. It is extremely important that the flux is
suitable for your job.
The next step is to heat the parts to the correct
brazing temperature. Adjust the torch flame (oxygas) to
a neutral flame because this flame gives the best results
under normal conditions. A reducing flame produces an
exceptionally neat-looking joint, but strength is sacri-
ficed. An oxidizing flame will produce a strong joint but
it has a rough-looking surface.
The best way to determine the temperature of the
joint, as you heat it, is by watching the behavior of the
flux. The flux first dries out as the moisture (water) boils
off at 212°F. Then the flux turns milky in color and starts
to bubble at about 600°F. Finally, it turns into a clear
liquid at about 1100°F. That is just short of the brazing
temperature. The clear appearance of the flux indicates
that it is time to start adding the filler metal. The heat of
the joint, not the flame, should melt the filler metal.
When the temperature and alignment are proper, the
filler metal spreads over the metal surface and into the
joint by capillary attraction. For good bonding, ensure
the filler metal penetrates the complete thickness of the
metal. Figure 6-16 shows a good position for the torch
and filler metal when brazing a butt joint.
Stop heating as soon as the filler metal has com-
pletely covered the surface of the joint, and let the joint
cool slowly. Do not remove the supports or clamps or
move the joint in any way until the surface is cool and
the filler metal has completely solidified.
Finally, clean the joint after it has cooled suffi-
ciently. This can be done with hot water. Be sure to
remove all traces of the flux because it can corrode the
metal. Excess metal left on the joint can be filed smooth.
The above described procedure is a general one, but
it applies to the three major types of brazing: silver,
copper alloy, and aluminum. The differences being the
base metals joined and the composition of the filler