Topic: Help with aluminum round anodizing problem!

We are having a whole host of aesthestic problems with clear anodizing small aluminum round pieces, including  (i) pitting or machining marks showing trough on the final product, (ii) a tan discoloration, (iii) die marks running the entire length of the piece that were not visible prior to anodizing, (iv) water marks or white discoloration blotches on the pieces which are sometimes in limited spots and sometimes effect an entire rack.  The most frustrating thing is these problems come and go and are not consistent even when we identify the process.  

We are using Mil Spec 8625, Type II, Class I decorative with 201 called out (15 minute anodize time).  We have tried a deep etch, but are now trying either a 1 minute etch or just a soap and deox process, but it doesn't seem to make a difference.  In an ideal world, we'd prefer to use a chemical pre-treatment to remove the pitting or machining marks.  We have tried 6063-T6 alloy and 6061-T52 alloy 1'' aluminum rounds as the base material, and have had marginally better results with the 6063, but are having a whole host of problems.  In general, we have been machining a .010 dia skin cut from the diameter of the piece to clean up the outside.  Also, we have tried a few different anodizers with similar results.  

Does anyone have any thoughts on the right mechanical surface conditioning of the pieces prior to anodizing (e.g. 180 grit then 320 grit paper) or better yet, a chemical alternative?  Am I doing something wrong in the anodizing process?  Has anyone ran across the problem of pitting showing up after anodizing?


Re: Help with aluminum round anodizing problem!

This is a link to some photos of the types of problems we are encountering as well as to a PDF file showing some of the processes we have tried next to a control sample of the clear anodized finish we are trying to match.


  Blotching on Part.JPG
  Die Marks - Grooves Running Entire Length.JPG
  Dings & Handling Marks.JPG
  Discoloration - Tinting.JPG
  No Anodize on Edge.JPG
  White Film - Chalkiness.JPG
  Discoloration from Centerless Grind.JPG