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Regular wavy stripes after anodizing

Sir,

We have recently anodized 3mm thick grade 3003 H14 aluminium sheets to NA25 (in China) The resultant finish is an even and consistent wavy stripe effect all in the same direction.It would appear to be possibly related to electrical current(?) as the markings are so regular.The surface finish of the anodizing appears smooth and normal. I have not experienced this before and would be grateful if you could advise whether this is a common phenomenon and its cause.

Regards and Thanks,

Matthew Wan
Civil - Sha Tin, Kowloon, Hong Kong
2004

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You may have stresses in your sheet before or during anodizing.

Good luck

Khair Shishani
aircraft maintenance - Al Ain, UAE
2004

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Good Morning Matthew,

It is possible stresses come into effect. I am more inclined to think that 'Pickling' or the pre-anodise solution could be to blame as rolled aluminum should show defects prior to processing.

Hope this helps.

ALLAN GIBBON
- KITCHENER, ONTARIO, CANADA
2004

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Hello all experts,

I have a batch of extruded aluminum profile (6063) just got anodized by our supplier and also found the same black stripes, if they were caused by stress of the original extruded material, how I can get rid of the black stripes.

I have tried polishing the material before anodizing, but it didn't work.

Can anybody help me ?

Kenneth Wong
- Hong Kong
2004

Do you have a picture of each problem that both of you have mentioned? I just posted a similar question above this question. I too have 3003 AL, that sounds like the exact same thing. Is it cold mill banding? I will post a picture of mine when I get the battery in the camera charged.

Michael Balda
- Prophetstown, Illinois, USA
2004

Ed. note: Mr. Balda's posting, now with pictures, is letter 31757.