10.4.6. Brazing
As brazing requires sophisticated techniques and experiences, it must be performed by a qualified person.
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.
<Brazing Method for Preventing Oxidation>
1.Attach a reducing valve to the nitrogen gas cylinder.
2.Apply a seal onto the clearance between the piping and inserted pipe for the nitrogen gas in order to prevent the nitrogen gas from flowing backward.
3.When the nitrogen gas is flowing, be sure to keep the piping end open.
4.Adjust the flow rate of nitrogen gas so that it is lower than 0.05 m3/h, or 0.02 MPa (0.2 kgf/cm2) by means of the reducing valve.
5.After taking the steps above, keep the nitrogen gas flowing until the piping cools down to a certain extent (i.e. temperature at which pipes are touchable with finger).
6.Completely remove the flux after brazing.
Fig. 14 Prevention of Oxidation during Brazing
Cautions during brazing
1.General Cautions
a.The brazing strength should be high as required.
b.After operation, airtightness should be kept under pressurized condition.
c.During brazing do not allow component materials to become damaged due to overheating.
d.The refrigerant pipe work should not become blocked with scale or flux.
e.The brazed part should not restrict the flow in the refrigerant circuit.
f.No corrosion should occur from the brazed part.
2.Prevention of Overheating
Due to heating, the interior and exterior surfaces of treated metal may oxidize. Especially, when the interior of the refrigerant circuit oxidizes due to overheating, scale occurs and stays in the circuit as dust, thus exerting a fatally adverse effect. So, make brazing at adequate brazing temperature and with minimum of heating area.
3.Overheating Protection
In order to prevent components near the brazed part from overheating damage or quality deterioration due to flame or heat, take adequate steps for protection such as (1) by shielding with a metal plate, (2) by using a wet cloth, and (3) by means of heat absorbent.
4.Movement during Brazing
Eliminate all vibration during brazing to protect brazed joints from cracking and breakage.
5.Oxidation Preventative
In order to improve the brazing efficiency, various types of antioxidant are available on the market. However, the constituents of these are widely varied, and some are anticipated to corrode the piping materials, or adversely affect HFC refrigerant, lubricating oil, etc. Exercise care when using an oxidation preventive.
10.4.7. Servicing Tips
The drier must also be replaced whenever replacing the refrigerant cycle parts. Replacing the refrigerant cycle parts first before replacing the drier. The drier is supplied in a vacuum pack. Perform brazing immediately after opening the vacuum pack, and then start the vacuum within two hours. In addition, the drier also needs to be replaced when the refrigerant has leaked completely. (Applicable for drier models only)
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