How to clean anodized parts?

A. Two things. One, I suggest you do all of your mechanical finishing prior to anodizing. I'm not sure what to recommend, because I don't know the size or configuration of the part. However, I think the most important item, or #2 is that you should ultrasonically clean your parts prior to anodizing.

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

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A. 1. Kenton above is absolutely 100% on the mark. Get all the burrs off BEFORE anodizing either mechanically or by etching.

2. Then understand that anodizing (Aluminum Oxide) is very hard, very brittle, and builds in a perpendicular plane from the substrate. On the inside of the bottom of a thread the adjacent planes in the deep acute angle build out 90 degrees until the oxide from each plane crashes into each other, cracks, flakes, and falls out. Conversely, on the top of the threads, where the substrate is very very thin, the very point is open because of the 90 degree phenomena, but also very brittle because the point itself is pure aluminum oxide
- look at it straight and it will crack off.

Your options include, (1) Higher temperature anodizing which produces a slightly softer coating (2) Sealing to the maximum which slightly softens the coating, but most of all reducing thickness which will limit the two planes crashing into each other.

A. Your parts don't sound like they should be a problem. I think you must have a chemical contamination problem. The only other thing I can suggest is to clean in D.I. water. Normally ultrasonics don't work well in D.I., but that is the best I can come up with.

A. Anodized surfaces can be hard to clean. I believe that acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! is a good approach, but you've tried that. IPA may work, but if acetone didn't it's not likely unless the particular polymer is alcohol soluble. Pending my becoming better informed, I don't quite share your concern about ultrasonic cleaning. I did see a NASA report of 7075 parts damaged by ultrasonic cleaning and IPA, but there seemed to be a strong possibility that those parts were not anodized right such that they have been damaged by the next process solution they saw, no matter what it was :-)

A. Although I cannot state the source(s), as it's confidential, I've seen data from 2 major Semiconductor OEM's that shows ultrasonic cleaning to be detrimental to the anodize coating.

A. You need to remove both the metal and polymer stains without damaging your Aluminium anodize. The questions would be, is the anodize sealed or not sealed? Did the stain occur before or after the seal?
If the part is sealed and the stains occurred after the seal, then Nitric acid would remove the stains without damage to the sealed anodize.
If the part is not sealed, Nitric acid may still remove the stains.
If Stains occurred before the part became sealed, there is little or no chance stains can be removed without stripping the anodic layer.

Good lock.

Ed. note: More about nitric acid cleaning of aluminum can be found on thread 32785, "Post-anodize cleaning with nitric acid"

A. If your cleaning solution is between pH 6.5 and 7.5, and the swab picks up dye, then the incoming dyed anodizing was not sealed. You need to implement an ASTM seal test program and reject incoming anodizing that does not pass the tests.

A. 1. The temperature alone will fade the black dye.
2. The black dye was not completely sealed.