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Lines that appear to be natural grain in clear anodized parts

January 21, 2011

Hi,
We are a precision sheet metal manufacturer and my question is this. We clear anodize(subcontract) .125 thick 5052 H-32 aluminum chassis. The customer requests an orbital finish on the outside and grained finish on the inside.
The parts get a clear chromate, masked, etch and clear anodize.
We are now seeing what appears to be something in the natural grain of the material coming to the surface...it appears as black streaks but as you move around the parts to visually inspect them they disappear and re-appear....any ideas?

Another problem we are experiencing is a textured finish (bumpy) that you can both visually see and feel on the outside of the parts (DA'd finish side). There is no consistency to this.

Thanks,

Russell Koon
Manufacturing - Denver, Colorado, USA

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Russell

Without looking at a pic, my first guess would be the parts are being significantly etched. You should be able to measure the parts before and after to determine how much material is being removed. It is likely that your parts are etched prior to chromate, and again prior to anodize. Excessive material removal will highlight the material grain, and increase surface roughness to a degree.

Willie ALexander
- Colorado Springs, Colorado
January 25, 2011

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January 31, 2011

Hello all,
We finally found the cause of the streaks in the clear anodized parts was in the material itself and the anodize magnified the issue.
Thank you for your responses.
Russ

Russell Koon
- Denver, Colorado, USA

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Another case of GIGO !
And, it was the platers fault.

James Watts
- Navarre, Florida
January 31, 2011