Flux

7.3.2.4. Solder Joints

  1. In making a soldered joint the surface to be soldered shall be cleaned bright and the joint shall be properly fluxed, made with solder and thoroughly cleaned of all residue


7.2.9.2.(3) Solders and flux having a lead content in excess of 0.2 per cent shell not be used in a portable water system.


Flux exists as one of three substances:

a gas, liquid or solid. Corrosive and non-corrosive are the two main types of flux. Non-corrosive (or non-active) flux is used primarily on clean metal surfaces.


This type of flux acts as a shield or cover, preventing oxidation. Tallow and resin are two types of non-corrosive flux.

Corrosive flux are used in conditions where the metals are oxidized. Hydrochloric acid is an example of a corrosive flux. Another type of corrosive flux is chloride of zinc, also known as "killed spirits". The most commonly used type of corrosive flux is the solder paste. It is composed of a variety of substances, such as resin and acid. As acidic flux leave a residue behind, they should be burnt or washed away. Pipe and fittings should be cleaned prior to application of paste.