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Anodizing that fades
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I am a quality control manager working with type II anodizing for the first time. Some of our parts, after being in the field for three months or so, get a lighter color to them going from their original black to a brownish orange color. I believe the problem to be ultra-violet bleaching and I know that it is from a problem in the anodizing process. Is their a cheap and easy to perform test that would readily find the defective anodizing?
Kenneth J. Winward- Kennewick, WA, U.S.A.
First of two simultaneous responses -- ++
The problem is more likely with the sealing than with the actual anodizing (although it is also possible that a poor quality dye was used, the sealing issue is more likely). ASTM B 136 describes a dye stain test to use to check seal quality on a pass/fail basis. The test requires Nitric Acid (40%) for two minutes and blue dye for 5 minutes, if there is a color change the parts fail (check out the spec for more detailed instructions, make sure to rinse and dry the part in between steps).
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Jim Gorsich Accurate Anodizing Inc.  Compton, California, USA |
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Second of two simultaneous responses -- ++
Use the dye stain test on your parts.. its a very easy one. All it takes (in the case of dyed parts) is a 50% (vol) solution of nitric acid. Place a drop on the surface, and allow it to remain there for 2 min. Rinse thoroughly. If a spot remains after rinsing, the part is not sealed adequately, which is what I suspect the problem may be. In the case of clear (natural, for the purists out there) anodizing, one would follow up the nitric acid with a drop of Blue 2LW dye for a period of 5 min, followed by a rinse. If the blue spot remains..then, once again the part has failed. Abrading the spot with Pumice [linked by editor to product info at Amazon] is allowed in both tests. If the spot does not show after a light pumicing, then it has passed.
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Marc Green anodizer - Boise, Idaho |