Clear Anodizing Producing Poor Finish

[zoltecrules]

Greetings-

I recently recieved some samples of 6061-T6 Aluminum from a anodizer that were given this military specification: MIL-A-8625F Type II Class I. They showed up like this:

http://www.ziptied.com/Coppermine/albums/userpics/11079/Photo_091608_009.jpg

If you can't see, the finish is very bad. Basically it has these water spots that my customer will NOT accept. What I was wondering is:

1. Is finish typical for the spec I called out above?

2. If so, is there an additional etching spec I should be calling out to prevent this?

Thanks in advance

 

[yank38]

Class I of the spec you refer to i9n section 3.5 states: "Any natural
coloration resulting from anodic treatment with the various alloy compositions
shall not be considered coloration. The characteristic color Imparted by the
sealing process shall also be considered as non-dyed."

I would argue that the part meets the spec. For true color control class 2 should have specified.

 

[skylerf]

We anodize Type II, class 1. After examining the pictures, I would say that it looks pretty bad. I don't think it is a material problem. 6061-T6 is very common to anodizer, and anodizes well. It could be a surface contaminent that is interfering with the finish. Maybe their pretreament or cleaning processes did not remove the contamient. Sometimes the pretreatment system itself can also cause similiar issues if not properly managed.

After machining, we normally do some type of surface conditioning to remove machine marks or to give a bighter finish. You might want to consider the same to improve the overall appearance. But I think we would both agree that it must be reworked. If the anodizer it not successful in fixing this problem, I would take my business somewhere else.

 

[zoltecrules]

Thanks for the suggestions guys. I had the anodizer redo it and it came back much better than before. No water spots, just some marks due some physical marks on the existing extrusion when we sent it to them.

Skylerf-

You spoke about some surface conditioning. Can you elaborate? I was going to sand off the scratches before I send them out but if you know something better....

 

[skylerf]

Sanding is not bad, but you should know that sometimes the anodizer's pretreatment system will bring out or highlight the stratches. Its important to work your way into the finer grits of sandpaper. Don't jump from rough grit straight into a super fine grit.

We use vibratory tumbling with plastic media, which does an excellent job of removing machine marks (lathe or milling).

For a rough/satin finish, beadblasting is excellent.

For a mirror finish, buffing with a cotton wheel and polishing compound is excellent. Anodizing will actually give a slightly frosted finish (with a short hot etch cycle time).

There are a lot options out there to look at.