1 Alkaline Degreasing Removes oil, grease, dirt
2 Water Rinse Removes alkaline cleaner
3 Derusting / Pickling Removes rust and mill scale, if required
4 Water Rinse Removes acid residues
5 Phosphating Creates a phosphate conversion coating on steel
6 Water Rinse Removes excess phosphate solution
7 Passivation / Final Rinse Improves corrosion resistance and paint adhesion.
* What happens in the phosphating tank?
- In cold phosphating, the metal part is immersed or sprayed with a phosphate-based chemical solution, commonly based on iron phosphate or zinc phosphate.
- The chemical reacts with the steel surface and forms a thin, adherent phosphate layer. This layer:
1. Improves paint/powder-coating adhesion
2. Gives some corrosion resistance
3. Provides a better surface for subsequent painting
4. Helps reduce paint peeling and under-film corrosion
