Scope of this guide
This intermediate guide goes into diagnosis: reading symptoms, isolating the variable that changed, and fixing it with data you can collect on the line.
Process: Anodizing. Figures in this guide are industry-standard starting ranges; confirm against your supplier TDS before locking settings.
Working ranges and control points
The table below is the daily reference for a anodizing line. Set by the card, verify by the control point column.
| Parameter | Typical range | Control point | Watch out |
|---|---|---|---|
| Sulfuric acid | 150–200 g/L | Titration daily | Low acid softens film |
| Current density | 1.2–1.8 A/dm² | Amp-min per area | Burns at high spots |
| Bath temperature | 18–21 °C | Chiller alarm active | Warm bath gives soft film |
| Film thickness | 8–15 µm decorative; 20–25 µm hard | Eddy current per batch | Thin film fades fast |
| Sealing | 95–100 °C water, 20 min | Seal quality dye test | Poor seal stains |
Diagnose It Fast: the intermediate view
Beyond the basic card, this is the layer that matters at your level:
| Symptom | Likely variable | Confirm by | First fix |
|---|---|---|---|
| Dull or hazy finish | Bath chemistry drift | Hull cell panel | Rebalance per test |
| Defects cluster on one rack position | Contact or current map | Position thickness map | Repair contact / re-map amps |
| Good-bad-good pattern | Loading or cycle drift | Time-stamped samples | Standardise load weight |
| Defect appears after maintenance | Work just done | Revert one change | Restore and re-verify |
Standard routine
- Etch and desmut before anodizing
- Rack tight — contacts carry full current
- Hold bath within ±1 °C through the run
- Eddy-current check thickness per load
- Seal immediately after rinse; never leave films dry overnight
Engineer notes
- Contacts leave bare marks — place them on non-visible edges
- Alloy composition changes colour; 6063 vs 6061 need separate colour standards
- Dye baths live or die by pH 5–6 control
- Cold sealing needs different time rules than hot water sealing
- Record amp-min per area; thickness follows it almost linearly
Safety: Anodizing buses carry high current. Confirm bus off before racking; wet acid mist needs ventilation and eye protection.
FAQ
Why does the same batch show two colours?
Alloy mix or temperature drift. Separate alloys and log chiller performance.
How do I verify sealing quality?
Dye stain test per batch; unprotected films absorb dye visibly.
What thickness is enough for indoor hardware?
8–12 µm decorative is standard; outdoor needs 15 µm or more.