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Parts that rust before assembly

The issue I have is parts that rust in an assembly cell. They are machined in various workcenters in our shop, and require no plating as they are used internally for generator engines. The parts are submersed after they are installed, but we have issues with rust both before and after assembly, and any surface rust at all is a non-conformance. After several attempts, the problem persists. Does anyone have any suggestions? The steel is 1215 and all parts except one are machined in oil, and that change is under way.

William Elliott
Manufacturing Engineer - Bluffton, Indiana
2007

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Flash rusting is a common problem. It is unlikely that you will find it practical to revise the whole environment of your shop to make it dry enough and clean enough that flash rusting can be stopped, William. So your choices are to speed the parts though so quickly that they rust less, or to pretreat them. If keeping them oiled doesn't do it, you may need to phosphatize or black oxide the parts -- but it's possible that a simple dip in a proper rust preventative compund rather than machining oil may solve the problem. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December , 2007

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Based on your description, your problem most likely is from the processing fluids that are being used for manufacturing the parts. A quick test is to take a clean steel panel, place several drops of each of the fluids on the panel and allow to dry. (Also put a couple of drops of DI water on the panel as well). What you'll likely see is significant corrosion on the areas where the process fluids were.

Oiling a dirty part doesn't really gain you much, just a slight delay in the onset of rusting. If the contaminate is already on the part surfacem it'll eventually pull in enough water for corrosion to begin.

Terry Natale
- Beachwood, Ohio
2007

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Flash rusting may be avoided by dipping or wiping the parts with specially formulated rust-preventive oils(proprietary rust-preventive oils are available).Another method is using VPI paper to cover the parts.However the second method is not cost-effective.Another alternative is to do Zinc phosphating and dipping in rust-preventive oil.
Ramajayam,Bangalore

Subramanian Ramajayam
consultant - Bangalore, India
January 12, 2009