Flux is a chemical compound, with a base of potassium tetraborate or potassium fluoride. It can be found in the form of a paste or powder, and it is used to:
1) Facilitate the wetting of the filler metal
2) Dissolve metal oxides that form during heating
3) Protect the joint surfaces from oxidation.
A flux should possess other qualities according to its composition, namely, it should:
- Start to melt at a lower temperature than the solidus of the filler metal used
- Attach itself evenly over the surfaces of the joint
- Not decompose at the maximum brazing temperature. It should be easily removed with water or by brushing.
|Type / Description||Range||Fluidity||Activities||Duration||Available in|
|No. 1 - FLUX 1 F||530 - 750||Excellent||Excellent||Average||Yes||Yes|
|No. 2 - FLUX 1100||550-800||Good||Good||Very long||Yes||Yes|
|No. 3 - BLACK FLUX||600 - 1000||Good||Good||Very long||No||Yes|
|No. 4 - DRY FLUX||550 - 850||Good||High||Very long||Yes||Yes|
|No. 5 - FLUX 751||550-800||Good||High||Average||No||Yes|
|FLUX 707||180 - 350||Good||High||Average||No||Yes|
Here are some solutions that can generally be used depending on the base metal: Copper and its alloys: solutions of sulphuric acid at 10-15%, ferrous metals, nickel and its alloys: solutions of hydrochloric acid at 10-15%. After the chemical treatment, the workpiece must be immediately rinsed with running water and dried. The duration of the treatment will depend on the residue layer and the wetting temperature.