Additional Considerations: Tank Liners: For large steel tanks, use PP, PVC, or rubber linings. Heating/Cooling Coils: Use titanium or PVDF for acidic baths. Support Frames: Use PP, PVC, or fiberglass for chemical resistance.
Author: Robby
Selecting the right tank material for each stage of the anodizing process is critical to ensure chemical resistance, durability, and process stability. Below is a detailed breakdown of recommended materials for each tank in a typical sulfuric acid anodizing line (Type II/III), including cleaning, etching, anodizing, dyeing, and sealing.
Process: Removes oils, grease, and light oxides.
Chemicals Used:
Alkaline cleaners (pH 10–14)
Acid cleaners (e.g., nitric-hydrofluoric mix for descaling)
Recommended Tank Materials:
Polypropylene (PP) – Good for mild alkaline cleaners.
PVC (Type I or II) – Economical for weak acids/alkalis.
Polyethylene (HDPE) – Resistant to many chemicals.
Stainless Steel 316L (for heated alkaline tanks) – Only if passivated; avoid for HF acid.
Avoid:
Carbon steel (corrodes in acids/alkalis).
Uncoated stainless steel 304 (pits in chlorides).
Process: Removes surface oxides and smoothens or textures the metal.
Chemicals Used:
Sodium hydroxide (NaOH, 5–10%, 50–70°C)
Mixed acid etch (e.g., HNO₃ + HF for titanium)
Recommended Tank Materials:
Polypropylene (PP) – Best for hot NaOH (up to 80°C).
PVC (for lower temps <50°C) – Cheaper but less durable.
PVDF (Kynar®) – Superior for high temps and strong acids.
Fiberglass Reinforced Plastic (FRP) – With vinyl ester resin for NaOH.
Avoid:
Metals (SS, Ti, Al) – NaOH attacks most metals.
Process: Electrochemical oxide layer formation (15–25°C for Type II, 0–10°C for Type III).
Chemicals Used:
Sulfuric acid (H₂SO₄, 15–20%)
Possible additives (oxalic acid, organic acids for hardcoat)
Recommended Tank Materials:
PVC (Type I or II, ½"–¾" thick) – Most common for small tanks.
Polypropylene (PP, welded seams) – Better for larger tanks.
PVDF (for high-purity or heated tanks) – Best chemical resistance.
Lined Steel Tanks (rubber or PP-lined) – For very large industrial tanks.
Avoid:
Unlined steel (corrodes rapidly).
Stainless steel (unless passivated, but not ideal).
Process: Coloring the anodized layer (50–70°C for some dyes).
Chemicals Used:
Organic dyes (pH 5–6, 50–60°C)
Inorganic dyes (metallic salts, room temp)
Recommended Tank Materials:
Stainless Steel 316L (for heated dye baths) – Smooth surface, easy to clean.
Polypropylene (PP) – For non-heated or acidic dyes.
PVC – Economical for room-temp dyes.
Avoid:
Carbon steel (rust contamination).
Process: Hydrating the oxide layer to seal pores.
Chemicals Used:
Deionized water (90–100°C)
Nickel acetate (pH 5.5–6.5, 80–90°C)
Recommended Tank Materials:
Stainless Steel 316L – Best for hot sealing (corrosion-resistant).
Polypropylene (PP, for non-metallic option) – Good for <90°C.
PVC (for lower temps) – Not ideal for boiling water.
Avoid:
Uncoated carbon steel (rust stains anodized parts).
Process: Removing residual chemicals.
Chemicals Used:
Deionized (DI) water (room temp or heated).
Recommended Tank Materials:
PVC (most common) – Cost-effective, corrosion-proof.
Polypropylene (PP) – More durable than PVC.
Stainless Steel 304/316 (for heated rinses) – If DI water is maintained properly.
Avoid:
Low-grade plastics (can leach contaminants).
| Process Tank | Recommended Materials | Avoid |
|---|---|---|
| Cleaning (Alkaline) | PP, PVC, HDPE, SS 316L (if passivated) | Carbon steel |
| Etching (NaOH/Acid) | PP, PVDF, FRP (vinyl ester) | Metals |
| Anodizing (H₂SO₄) | PVC, PP, PVDF, rubber-lined steel | Unlined metals |
| Dyeing | SS 316L (heated), PP/PVC (room temp) | Carbon steel |
| Sealing (Hot Water/NiAc) | SS 316L, PP (for <90°C) | Uncoated steel |
| Rinse (DI Water) | PVC, PP, SS 304/316 | Low-grade plastics |
Tank Liners: For large steel tanks, use PP, PVC, or rubber linings.
Heating/Cooling Coils: Use titanium or PVDF for acidic baths.
Support Frames: Use PP, PVC, or fiberglass for chemical resistance.