[Miguel58rt]

Hello,

Recently we recived a costumer complaint regarding contamination in an aluminum part that is anodized (we bought this part), this contamination was detected in an inspection under black light (UV).
We are having a hard time to find the root cause of this issue and I would like to know if anyone here have some expirence with this type of issues.
Until know we have identified some conditions that change in the current process of these pieces:

The contaminated pieces were finished using a sand blasting process. the normal process should be polishing.
Contamination can not be removed from the parts.
This part are covered to be protected with a blue film, one of the teories is that the contamination came from the adhesive of the blue film, this happened due the surface after the sand blasting is more abrasive and the adhesive of the film came into the porous crated by this process.
I don´t know if this sound logical to you guys I´m not an expert on this area but what we know is the pieces leaves our company in good conditions, we have several inspections to validate this conditons and we never detect this issue.


Attached is a picture from the issue that we have, I really apreciate your help to get information about sanding process, anodizing on aluminum and contamination.

[awerby]

It's probably oil from the compressor used for the sandblasting, which can escape through the rings and get into the air stream. If the parts need to be pristine, you might look for an oil-less compressor to do that with (divers use them to fill their tanks). Aluminum usually comes with that blue plastic on it; if that was a problem for anodizing, they wouldn't use it. Polishing often will leave residues as well, from the grease-based compounds used. But those can usually be removed by cleaning the parts afterwards.

[Miguel58rt]

Thanks a lot for your response, I will review your comments with our supplier.

[dharmic]

It's probably oil from the compressor used for the sandblasting, which can escape through the rings and get into the air stream. If the parts need to be pristine, you might look for an oil-less compressor to do that with (divers use them to fill their tanks). Aluminum usually comes with that blue plastic on it; if that was a problem for anodizing, they wouldn't use it. Polishing often will leave residues as well, from the grease-based compounds used. But those can usually be removed by cleaning the parts afterwards.

Just FYI SCUBA compressors are anything but oil free, in fact Bauer compressors (one of the most popular brands) rely on oil mist in the airstream being compressed to lubricate one or more stages.

What they do have that's different is multiple cyclone separators to spin the oil and condensation out of the air between the final stages and after the final stage, as well as one or more filters combining activated charcoal and a molecular sieve to remove all traces of moisture, oil and any hydrocarbon byproducts from the oil getting hot in the compressor (carbon monoxide, carbon dioxide etc).

Nothing stopping you from banging a cyclone separator and filter on the outlet of a shop compressor apart from the heinous price tag on the filtration media which needs changing fairly frequently.

[mactec54]

I does not matter how much oil is on the parts before anodizing, the part is stripped of all contaminates before anodizing, if there is any oil present the part will not anodize very well at all

If this is happening at the color stage then the parts have not gone through a good enough acid neutralizer and wash before the color process

If this is happening after the color process, the anodizer needs to use a better sealing process, if the parts are not sealed correctly after the color, then the parts can pick up any contamination they come in contact with

[Miguel58rt]

Mactec54 thanks for your comments.

What do you think about the preparation process that the pieces have before the anodizing process, our supplier use sanding process (polishing) but they also were using sand blasting during one month, apparently this pieces are the ones that have contamination. Do you think that the roughness of the sand blasted pieces can allow more adherence of contamination (in this case adhesive from the blue film that we use to protect the final assembly)?

[mactec54]

Mactec54 thanks for your comments.

What do you think about the preparation process that the pieces have before the anodizing process, our supplier use sanding process (polishing) but they also were using sand blasting during one month, apparently this pieces are the ones that have contamination. Do you think that the roughness of the sand blasted pieces can allow more adherence of contamination (in this case adhesive from the blue film that we use to protect the final assembly)?

It sounds like they are doing a poor sealing of the parts, are they using nickel acetate for sealing, there could be contamination in the sand blasting process, but if they have proper prep after, before anodizing it should not matter how you finish the parts, color can change when a part is sand blasted, most use glass beads for blasting, this should not be as aggressive as sand