Metal finishing Q&As since 1989

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Yellow streaks in clear anodizing

Hello,
I am having a problem with anodizing, we are trying to anodize 36 x 83 inch cabinets and after the process there is a yellowish to brown steak running a straight line with the grain of the material, I have tried sanding the cabinets with a thousand grit sandpaper it seemed to help but know I can see the swirl marks of the orbital sander.Any help would be appreciated.
Thanks,

John Jacob
engineer - Colorado
February 26, 2008

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First of two simultaneous responses --

John

What is the alloy? Are the streaks vertical with respect to part racking (drips)? At what step in the process do the flaws become noticeable? Is this a new problem or new part/process?

Willie Alexander
- Colorado Springs, Colorado
February 28, 2008

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Second of two simultaneous responses --

Come back and tell us more: Alloy?, Free acid? Dissolved Aluminum? Are you imbeding foreign material into the soft aluminum with the sanding? Is the sander designated aluminum only.? Surface Prep? What kind and how long in the deoxidizer? Chinese metal? Are you getting the current on the large flat thin part? Thickness measured in the middle?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

February 28, 2008

I can say that this type defect comes from your material. Modifying bath temperatur,electrolyte concentration or current density etc could not solve this problem effectively, but if possible(allowed), you may eliminate the problem by changing the type of electrolyte (from sulfuric to Oxalic) or adding new surface preparation process (for example b-blast).

John Hu
- Singapore
March 3, 2008