Brazing is started by applying heat to the
parts to be joined. The preferred method is by oxyacetylene flame.
Propane and other gases are sometimes used on smaller sizes. A slightly
reducing flame should be used, with a slight feather on the inner
blue cone; the outer portion of the flame, pale green. Heat the
tube first, beginning at about one inch from the edge of the fitting.
Sweep the flames around the tube in short strokes up and down at
right angles to the run of the tube. It is very important that the
flame be in continuous motion and should not be allowed to remain
on any one point to avoid burning through the tube. Generally, the
flux may be used as a guide as to how long to heat the tube, continuing
heating after the flux starts to bubble or work, and until the flux
becomes quiet and transparent, like clear water. The flux will pass
through four stages:
At 212oF (100oC) the
water boils of.
At 600oF (315.6oC)
the flux becomes white and slightly puffy and starts to work.
At 800oF (426.7oC)
it lays against the surface and has a milky appearance.
At 1100oF (593.2oC)
it is completely clear and active and has the appearance of water.
Now switch the flame to the fitting at the
base of the cup. Heat uniformly, sweeping the flame from the fitting
to the tube until the flux on the fitting becomes quiet. Avoid excessive
heating of cast fittings.
When the flux appears liquid and transparent
on both the tube and the fitting, start sweeping the flame back and
forth along the axis of the joint to maintain heat on the parts to
be joined, especially toward the base of the cup of the fitting. The
flame must be kept moving to avoid burning the tube or the fitting.
Apply the brazing wire or rod at a point where
the tube enters the socket of the fitting. The temperature of the
joint should be hot enough to melt the brazing alloy. Keep the flame
away from the rod or wire as it is fed into the joint. Keep both the
fitting and the tube heated by moving the flame back and forth from
one to the other as the alloy is drawn into the joint. When the proper
temperature is reached, the alloy will flow readily into the space
between the tube outer wall and the fitting socket, drawn in by the
natural force of capillary attraction. When the joint is filled, a
continuous fillet of brazing alloy will be visible completely around
the joint. Stop feeding as soon as the joint is filled.
NOTE: For tubing one inch and larger, it is difficult
to bring the whole joint up to heat at one time. It frequently will be found
desirable to use a double-tip torch to maintain the proper temperature over
the larger area. A mild pre-heating of the whole fitting is recommended.
The heating then can proceed as in steps 7, 8, 9, and 10. If difficulty
is encountered in getting the whole joint up to heat at one time, then when
the joint is nearly up to the desired temperature the alloy is concentrated
in a limited area. At the brazing temperature the alloy is fed into the
joint and the torch is then moved to an adjacent area and the operation
carried on progressively all around the joint.
水平连接 - 在进行水平连接时，最好是在相当于时钟5点钟指针位置处开始进行铜焊合金作业，然后移到7点钟指针位置，随后移到连接部位的顶部，确保铜焊作业位置交迭进行。
HORIZONTAL JOINTS - When making horizontal joints,
it is preferable to start applying the brazing alloy at the 5 o'clock position,
then move around to the 7 o'clock position and then move up the sides to
the top of the joint, making sure that the operations overlap.
VERTICAL JOINTS - On vertical joints, it is immaterial
where the start is made. If the opening of the cup is pointed down, care
should be taken to avoid overheating the tube, as this may cause the alloy
to run down the tube. If this condition is encountered, take the heat away
and allow the alloy to set. Then reheat the solder cup of the fitting to
draw up the alloy.
After the brazing alloy has set, remove residual
flux from the joint area as it is corrosive and presents an unclean appearance
and condition. Hot water or steam and a soft cloth should be used. Wrot
fittings may be chilled; however it is advisable to allow cast fittings
to cool naturally to some extent before applying a swab. All flux must be
removed before inspection and pressure testing.
If the alloy fails to flow or has a tendency
to ball up, it indicates oxidation on the metal surfaces, or insufficient
heat on the parts to be joined. If work starts to oxidize during
heating, it indicates too little flux, or a flux of too thin consistency.
If the brazing alloy refuses to enter the joint and tends to flow
over the outside of either member of the joint, it indicates this
member is overheated, or the other is underheated, or both. In both
cases, operations should be stopped and the joints disassembled,
recleaned and fluxed.