A 7-tank cold phosphating process is a metal surface pretreatment system used before powder coating or painting. Its purpose is to clean the metal, improve paint adhesion, and increase corrosion resistance.
* Typical 7-Tank Cold Phosphating Process
Tank 1 → Degreasing
Tank 2 → Water Rinse
Tank 3 → Derusting / Pickling (if required)
Tank 4 → Water Rinse
Tank 5 → Phosphating
Tank 6 → Water Rinse
Tank 7 → Passivation / Final Rinse.
* Tank-by-Tank Explanation
Tank Process Purpose
1 Degreasing Removes oil, grease, dirt, and shop contaminants. Usually alkaline cleaner.
2 Water Rinse Removes cleaner carryover.
3 Derusting / Pickling Removes rust, scale, and oxides using acid-based chemicals.
4 Water Rinse Removes acid residues.
5 Phosphating Forms a phosphate conversion coating that improves paint adhesion and corrosion resistance.
6 Water Rinse Removes unreacted phosphate chemicals.
7 Passivation Seals the phosphate layer and improves corrosion resistance before drying and coating.
