When using the insert method, insert a strip of the
the time to start adding the filler metal (silver solder).
silver-base filler metal in the joint before assembly.
If the temperature and alignment are proper, the filler
Before brazing the parts, clean them with emery cloth,
metal spreads over the metal surface and into the joint
steel wool, or an acceptable cleaning solvent. Apply
by capillary attraction. Make sure the filler metal
flux with a brush. Next, fit the two parts together and
penetrates the complete thickness of the metal for good
align them. Then light the torch and direct the heat on
bonding. Stop heating as soon as the filler metal has
the tube or thinner portion, as shown in figure 3-46.
completely covered the surface of the joint. Then allow
The lines drawn on the tube indicate the path of the
the joint to cool before moving, so the filler metal
torch while heating the tube.
Heat applied to the tubing causes it to swell and
bring the surface of the tube into contact with the inside
surface of the fitting. This closes the clearance area,
forcing the flux from either end of the joint. Be sure to
heat the entire circumference of the tube until flux
begins to flow. Flux flow tells you that the tube has
expanded sufficiently. This is the signal to proceed to
the second phase of heating. As soon as the flux flows
freely, about 6 seconds after you see the fluid, direct
the flame to that portion of the fitting hub farthest from
the junction of the tube and the fitting. Rotate the flame
over the joint segment until brazing filler metal
appears at the junction of the pipe and fitting. At that
moment, flick the torch away so the flame wipes
toward the pipe. This completes one segment of the
joint. This procedure is repeated until all segments are
completed. A satisfactory joint has a continuous ring
of filler metal at the end of the fitting. The ring must
also be smooth and concave.
A number of different types of equipment are used
in silver brazing. In your work, silver brazing can be
accomplished by the use of methylacetylene
propadiene (MAPP) cutting/welding equipment.
A commonly used oxygas welding outfit (fig. 3-
47) consists of a cylinder of acetylene or MAPP gas or
a cylinder of oxygen, two regulators, two lengths of
hose with fittings, and a welding handle with tips. An
oxygas outfit also is called a welding rig.
In addition to the basic equipment mentioned
above, numerous types of auxiliary equipment are
used in oxygas welding. A very important item is the
spark igniter that is used to light the torch (view A, fig.
3-48). Another item you will use a lot is an apparatus
wrench, the same or similar in design to that shown in
view B, figure 3-48. The apparatus wrench is
sometimes called a gang wrench because it fits all
the connections on the welding rig. Note that the
wrench shown has a raised opening in the handle that
serves as an acetylene tank key. Other common
accessories include tip cleaners, cylinder tracks,
clamps, and holding jigs. Safety apparel, such as
goggles, face shields, gloves, leather aprons, sleeves
and leggings, also is essential and should be worn as
required for the job at hand.
With the feed-in method, the parts are heated to
the correct temperature. Watching the behavior of the
flux is the best way to determine the temperature of the
joint as the heating progresses. First, the flux dries
out as the moisture (water) boils off. Then the flux
turns milky and starts to bubble at about 600°F.
Finally, it turns into a clear liquid at about 1100°F.
This last temperature is just short of the brazing
temperature. The clear appearance of the flux indicates
Figure 3-46.Applying heat for brazing a tube and fitting.
Oxygas welding equipment may be stationary or
portable. A portable oxygas outfit, such as that shown
in figure 3-49, is advantageous where the equipment
must be moved around from one job to another.
To carry out your welding duties, you should
understand the purpose and function of the basic pieces
of equipment that make up the welding outfit. Before
discussing the apparatus, look at the gases used in gas
welding, particularly MAPP gas and oxygen.
MAPP GAS.MAPP gas is an all-purpose
industrial fuel that has the high-flame temperature of
acetylene and the handling characteristics of propane.