What did we do wrong?

[sswee]

I've seen what your describing on parts left in RO rinse water for over 24 hours but not just a few hours. Maybe whatever in the water causing the reaction is more in your water than mine. I stopped leaving parts sitting in rinse water for more than a few minutes after seeing what long term did. I did not want any reaction starting. Glad to see it looks like you figured it out.
SS

[destroyer125]

Desmut will cause large crater pits that you will not be able to directly see until the parts are prepped or attempted to be anodized. It seems to create a bubble pit sort of which doesnt show its ugly head til the top metal has been removed. Ive only seen this happen to parts left in desmutting chemicals overnight though.

[blackcote]

Well we thought we had it figured out. Turns out the desmut rinse water problem was an accidental discovery. We did another batch (careful of the desmut rinse) for the customer including 3 repolished ones. and all new polished pieces had this pitting issue again. the 3 reworked ones didn't... at least not enough that you could immediately see with a thorough glance. all other parts in the batch (fine brushed finishes) came out fine, but maybe we just can't see the pits due to surface finish. The weird thing was that prior to this batch the same day we did 4 batches of parts for another customer which all came out fine. So that scratched the desmut rinse theory. On the this attempt it was right after ano that we notice the pitting. So like throwin a dart blind folded we changed out the acid solution for new. We estimated there was only 150 sq ft on the 20 gallons. Is there any guideline for how much area you can ano on so many gallons of solution? So then we did the reworked parts that were new in the last batch again and we still have this pitting issue, seemingly much smaller and less numerous but still there. I'm totally clueless at this point where the problem could be in the process, especially when we've got other parts from other customers going through just fine using the same exact process.

All clues from what I've seen have been pointing to a material problem, but I don't believe anything was changed in the material used for making these parts. Let's suppose there were non aluminum specs of metal embedded in the parts. What happens in the ano tank to them when electricity is applied. Would the current "gravitate" toward other types of metals and "burn" them out? I've seen something similar on a part we tried to do before where there was a steel part pressed in and another part where someone had broken off a tap in a hole. We got massive fizzing action from those areas on the part when trying to anodize them. But I didn't leave them in long enough to see what would happen. On the piece that had something pressed in, that spot was very discolored (brownish yellowish) while the rest of the part was still bright aluminum. So am I way off on this theory? Should I be looking to change out cleaner and desmut as well and maybe even tear down the ano tank and thoroughly clean it out?