Choosing Flux for silver brazing
Flux is a chemical compound, and is in most cases made in powder, liquid, slurry or paste. Once the flux is active by temperature increase it has three primary functions:
- Excluding Oxygen during the heating process to prevent oxidation of the metals.
- Assist the flow of the alloy by creating freshly cleaned surfaces for the heated alloy.
- Absorb and dissolve residual oxides on the base metal surface and filler metal.
When silver brazing, there are several flux types that would be suitable however the most important consideration is your base metal, filler metal and brazing processes/heating method. After this choose the correct flux.
AWS (American Welding Society) has developed a handy A5.31 specification to cover the classification of fluxes used for silver-based filler metals.