An 8-tank chemical process is commonly used in metal finishing to clean metal parts, remove rust, prepare the surface, and apply a chemical treatment before painting or powder coating.
The exact chemicals depend on the metal type (MS, GI, aluminium, etc.) and the final coating process. Below is a typical example for mild steel (MS) components before painting or powder coating.
1. Typical 8-tank process
Tank 1 — Degreasing
Purpose: Remove oil, grease, and machining residues.
Typical chemical: Alkaline degreaser.
Tank 2 — Water rinsing
Purpose: Wash off degreaser residue.
Typical chemical: Clean water.
Tank 3 — Derusting / pickling
Purpose: Remove rust and scale from steel.
Typical chemical: An approved acid-based deruster or pickling solution.
Tank 4 — Water rinsing
Purpose: Remove residual acid and dissolved contamination.
Typical chemical: Clean water.
Tank 5 — Surface conditioning or activation
Purpose: Prepare the surface for uniform conversion coating, if required.
Typical chemical: Surface conditioner or activator appropriate to the coating system.
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Tank 6 — Phosphating
Purpose: Improve paint adhesion and corrosion resistance.
Typical chemical: Iron phosphate or zinc phosphate, depending on the process.
Tank 7 — Final rinsing
Purpose: Remove residual treatment chemicals.
Typical chemical: Clean water, sometimes demineralized water
Tank 8 — Passivation or final treatment
Purpose: Provide additional surface protection where specified.
Typical chemical: Compatible passivation or post-treatment chemical. Some lines instead use this stage for another rinse.
