KEVOS® MAKEOS · Manufacturing
Anodizing Time and Coating Thickness
How long must this part anodize to reach the coating thickness, and how much current is needed?
Anodic coating thickness from current density and time by the common “720 rule” for sulfuric acid anodizing of aluminium, the time for a target thickness, the build-up and penetration split, and the rectifier current.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Current density | A/dm² | Anodizing current density (typically 1.2–2 A/dm² for sulfuric acid, higher for hard anodizing). |
| Target coating thickness | µm | Required total coating thickness. |
| Area on the rack | dm² | Total area being anodized. |
| Process efficiency factor | % | Correction from your own process records (100% = textbook rule; alloys, temperature and bath age change it). |
Method and formulas
- 720 rule: thickness (mil) = current density (A/ft²) × time (min) ÷ 720, which in metric is about 0.328 µm per A/dm² per minute.
- Time = thickness ÷ (0.328 × J × efficiency).
- About one third of the coating builds up on the surface and two thirds penetrates into the metal (sulfuric acid process).
- Example: 20 µm at 1.5 A/dm² takes about 40.682 min.
Limitations
- Rule of thumb for Type II sulfuric acid anodizing; hard anodizing and other electrolytes differ.
- High-silicon and high-copper alloys grow coatings more slowly.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set anodizing time for a specified coating
- Size rectifier current for a rack
- Allow for dimensional build-up on toleranced parts
Who it is for
- Finishing supervisors
- Platers
- Design engineers
What you get
- Time to the target thickness
- Build-up per surface and penetration
- Rectifier current
Interpreting the result
- Check thickness with an eddy-current gauge and calibrate the efficiency factor.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1500–1516. Topic reference; no source tables or recommended settings are reproduced.
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