Nitrogen gas
cylinder
Pipe
Flow meter
M
Stop valve
From Nitrogen cylinder
Nitrogen
gas
Rubber plug
3-5-3. Brazing
As brazing work requires sophisticated techniques,
experiences based upon a theoretical knowledge, it
must be performed by a person qualified.
In order to prevent the oxide film from occurring in
the pipe interior during brazing, it is effective to
proceed with brazing while letting dry Nitrogen gas
(N2) flow.
Never use gas other than Nitrogen gas.
1. Brazing method to prevent oxidation
1) Attach a reducing valve and a flow-meter to
the Nitrogen gas cylinder.
2) Use a copper pipe to direct the piping mate-
rial, and attach a flow-meter to the cylinder.
3) Apply a seal onto the clearance between the
piping material and inserted copper pipe for
Nitrogen in order to prevent backflow of the
Nitrogen gas.
4) When the Nitrogen gas is flowing, be sure to
keep the piping end open.
5) Adjust the flow rate of Nitrogen gas so that it
is lower than 0.05 m
3
/Hr or 0.02 MPa
(0.2kgf/cm
2
) by means of the reducing valve.
6) After performing the steps above, keep the
Nitrogen gas flowing until the pipe cools down
to a certain extent (temperature at which
pipes are touchable with hands).
7) Remove the flux completely after brazing.
Fig. 3-5-1 Prevention of oxidation during brazing
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