7-Tank Process for Phosphating (Chemical Treatment Line)
- The 7-tank phosphating process is a standard surface preparation method used to improve corrosion resistance, paint adhesion, and surface cleanliness of metal components.
Tank 1: Degreasing (Alkaline Cleaning)
Purpose: Remove oil, grease, dirt, and contaminants
Chemicals Used: Alkaline degreaser
Temperature: 50–70°C
Time: 5–10 minutes.
Tank 2: Water Rinse 1
Purpose: Remove residual degreasing chemicals
Type: Overflow rinse (fresh water)
Time: 1–2 minutes
Tank 3: Derusting / Pickling
Purpose: Remove rust, oxide scales
Chemicals Used: Acidic solution (HCl or H₂SO₄-based)
Time: 5–10 minutes
Tank 4: Water Rinse 2
Purpose: Remove acid residues from pickling
Time: 1–2 minutes.
Tank 5: Phosphating
Purpose: Create a protective phosphate coating
Types: Zinc phosphating (most common), Iron phosphating
Chemicals: Phosphate solution with accelerators
Temperature: 50–70°C (zinc), ambient for iron
Time: 5–10 minutes.
Tank 6: Water Rinse 3
Purpose: Remove unreacted phosphate chemicals
Time: 1–2 minutes.
Tank 7: Passivation / Final Rinse
Purpose: Enhance corrosion resistance and seal coating
Chemicals Used: Chromate / non-chrome sealers
Time: 1–2 minutes.
