[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.