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Each month the Copper Development Association of South Africa (CDAA) brings insight into the dos and the don’ts of copper soldering.

Brazing is the second most commonly used method for joining copper tube. Making brazed joints is similar to making soldered joints with respect to measuring, cutting, reaming, cleaning, assembly, and support. As for soldering, the brazing filler metal is melted by the heat of the tube and fitting, and is drawn into the joint by capillary action.

The major differences between soldering and brazing are:

  • Type of flux used;
  • Composition of filler metal; and
  • Amount of heat required to melt the filler material.

 Applying flux
The fluxes used for brazing copper joints are different in composition from soldering fluxes; the two types cannot and should not be used interchangeably.

Brazing fluxes are water based, whereas most soldering fluxes are petroleum based. Similar to soldering fluxes, brazing fluxes dissolve and remove residual oxide from the metal surface; protect the metal from re-oxidation during heating; and promote wetting of the surface to be joined by the brazing filler metal.

Fluxes can also provide the artisan with an indication of temperature. Application of the flux is the same as when soldering.

If the outside of the fitting and the heat-affected area of the tube are covered with flux (in addition to the end of the tube and the cup), oxidation will be prevented and the appearance of the joint greatly improved.

We will look at brazing filler materials in the next issue.

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