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Can inspection methods affect a passivated component?





February 8, 2012

Q. We've manufactured some pistons from AMS5629 stainless steel. Would it make any difference if we did our final conformance inspection after the part has been passivated or would it be better to inspect the part prior to passivation? I understand that the passivation process forms a thin, transparent oxide film. No further machining is required on the parts. Measuring equipment will include comparators, height gauge, DTI etc...

Alan Dodd
Engineer - Merseyside, England



February 11, 2012

A. Hello Alan!

My company, and every other one I know, does the final inspection after passivation. The passivated layer isn't affected by measurement equipment.

Have fun!

lee gearhart
Lee Gearhart
metallurgist - E. Aurora, New York



February 15, 2012

A. Final inspection means just that - but any measuring or other operations that could lead to a legitimate rectification op. should be carried out earlier in the process. If any op is required later, the part will require re-passivation. Any non rectifiable fault after means a wasted passivation op.
Passivation leaves a surface that will never be cleaner. I would like to keep inspector's dirty fingers as far away as possible. Yes, I know they all wear gloves but I have seen too many gloves that make fingers look very clean indeed!

geoff smith
Geoff Smith
Hampshire, England



February 16, 2012

A. My understanding of the passivation process is to remove free iron from the surface of the part. Free iron is usually picked up from the machining operations. Also the passivation process will accelerate the chromium oxide layer that will occur naturally anyway. Therefore doing testing on the finished product using mics or other measuring devices should not leave any free iron on the surface. With that being said you should be able to do "Final testing" as your last operation before packing the parts for sale. I would disagree with Geoff's statement that the passivation process is a cleaning operation unless by "Clean" he means free of iron contaminates. Respectfully.
Kevin...

Kevin W. Gallich
- Freemansburg, Pennsylvania, USA



February 16, 2012

A. Thanks, Kevin; but Geoff knows what passivation is. The passivation step per se may not be what metal finishers usually identify as a "cleaning" step, but a component which has gone through a proper passivation sequence will be very clean as Geoff says. Thanks again.

Regards,

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




May 16, 2013

Q. We have a part that is 17-4PH calling out passivate per AMS2700 [affil. link]. The parts are returned very dirty. Is that common - the nature of the beast or are the parts being mishandled?
The passivator told us we could clean with a heavy duty degreaser. Is that proper?

Karen Mason
- Cleveland, Ohio



May 21, 2013

A. Hi Karen. A judge has to hear both sides before rendering a verdict, and before offering my two cents worth I suppose I should hear the other side . . . but this sounds crazy. The parts were clean when they left the passivation tank, and they should have gotten back to you clean. Good luck.

Regards,

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


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