Metal finishing Q&As since 1989

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Lifting hard anodize

2002

Dear Sirs,

We are having a problem with blistering/ lifting layer of hard anodize on a batch of material (L111 T6 condition bar)the parts are 60 mm dia. 40 mm in length, hollowed out to leave a 20mm spigot in the middle. A number of the parts have a light patch with a hard anodize patch which lifts on some, and burning on others. The program used is pre-set using a micro processor and works fine on all other work of the same L111 material. The only difference is the T6 condition but is within the material spec. We are hard anodizing to 50 microns. The solution used is 240-260g/l sulfuric acid running at 0C with plenty of air agitation. We do a large number of parts using L111 material with no problems? We have carried out checks to eliminate hot spots. can you suggest the likely cause.

John Camfield
- Southampton, England

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2002

1. Too much air hitting the parts may be displacing solution which will cause a "burn" and later flake off.

2. Increase the strength and the time in the deoxidizer.

3. Ramp up slower

4. Increase the area of contact.

5. Watch for under solution sparks or arcs which are burns of a sort and will also later flake off.

6. Commercial additives are helpful.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina