Flux and brazing process
The first NB furnace in the world was invented by Alcan company of Canada in 78, and its registered trademark is NOCOLOK.
Flux was developed by Solvay company in 78-79. Flux was mainly a mixture of KF and aif3, namely potassium fluoaluminate (kaif4).
NOCOLOK flux does not react with Al at room temperature and brazing temperature, but only under melting (at least partial melting). After melting, the flux dissolves Al2O3 on the surface of Al, moistens the joint surface, reduces the surface tension of liquid solder, makes the liquid solder flow into the joint surface freely by the action of fine hairs, and prevents the surface reoxidation.
After cooling, the flux forms a layer of 1-2 μ m residue on the surface of the parts (when the flux loading is 5g / m2), with strong adhesion, no moisture absorption, no corrosion, and no fragmentation during the heat exchange process, so it can be directly sprayed with paint.
Flux brazing characteristics:
1. Flux is a mixture of potassium fluoaluminate;
2. The melting point range is 565 ° c-572 ° C, which is lower than the melting point of solder (577 ° C);
3. The particle size range is 0.2-0.5 μ m, and the paste has good properties;
4. Non hygroscopicity, unlimited storage period;
5. No corrosivity;
6. The solubility is 0.2-0.4%, with unlimited shelf life.
The function of flux:
1. Remove the oxide on the surface of base metal and solder to create necessary conditions for liquid filler metal to spread and fill joints on the base metal.
2. The surface of base metal and filler metal is covered with liquid thin layer to isolate air.
3. It can improve the wettability of liquid solder to base metal.
Advantages of the NOCOLOK Brazing process:
1. Flux is inert without corrosion;
2. Larger allowable clearance;
3. Good gap filling performance;
4. Strengthen the corrosion resistance (synthetic aluminum, Zn deposition treatment);
5. The brazed surface is suitable for chromizing / spraying;
6. Allow imperfect cleaning;
7. Do not clean after brazing;
8. The ability of removing oxide film is very strong;
9. Simple storage method;
10. Do not remove brazing residues.