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Trivalent chromium reacting with cutting fluids.



September 21, 2010

Question: Has anyone had issues with trivalent chromate reacting with residual cutting fluids in holes?
Background: We have an aluminum casting with a couple machining operations (surfacing, several drill & taps). It is being produced overseas and the supplier has delivered over 1k units with no (major) issues. The part was changed to include a trivalent chromate finish. We now have issues with installing the threaded fasteners in the tapped holes (torque out too soon, not starting, cross threading, ect).
Inspection of the holes showed small crystals (what looks like table salt)inthe hole.

Any ideas?

Thanks

Gary McGuire
Product Designer - Portland, Oregon, U.S.A.





September 21, 2010

Hi, Gary.

Any possibility that the "salt" could be aluminum corrosion? This sounds more like a case of under protection than over protection. Are you sure it was chromate treated? It can be hard to see a TCP treatment, and that can be sufficient grounds for "some" overseas suppliers to try to get away with simply omitting the treatment.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



September 23, 2010

Gary

If the processing chemistry was not properly rinsed from the threaded holes, and allowed to dry, it would not surprise me if a 'salt' formed. Try cleaning/rinsing with warm water and drying.

Willie Alexander
- Colorado Springs, Colorado



September 25, 2010

To expand on a previous post. It should not be the end user's responsibility to fix this issue. If there is chemical residue/solids around the holes from the coating treatment, this issue should be addressed with the coating vendor, and have them improve their rinsing techniques.

Marc Green
Marc Green
anodizer - Boise, Idaho


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