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Getting Red Rust on Tin Plated Parts

Q. We are tin plating a component,with outer dimensions of Dia. 25 mm X length 35 mm, and with bore region which start from Dia. 20 mm X 9 mm depth,and then M18Thread X 7 mm depth,then further cone region dia 13 X dia. 10 X 5 mm depth, and altogether the total depth the bore region extends around 24 mm deep.

Plating Spec. Base Metal - En1A(L), Undercoating - Cu (min 5 micron), Tin - Min 6 micron

Our Process : Kerosene Cleaning- Alkaline Cleaning - Electro cleaning - Acid picking - cyanide copper - Acid Tin - ovan Drying.

We have severe red rust problem in bore region, at deeper area. What could be the causes?
How those causes would cause red rust? What are recommendation to eliminate this red rust?

S Venkatachalam
auto components - Chennai, India
2006

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A. The rusting is probably the result of no plating coverage in the bore. I would suggest starting by cross-sectioning a sample piece and seeing what kind of plating coverage you have down there.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

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2006

A. Agreed. Acid Tin plating thickness will build up rapidly on the outer surfaces and Acid Tin baths require a lot of care and tweaking in order to plate recesses like these.

You need to also ensure proper fixturing to plate the recesses or may also want to try Alkaline Tin Plating for such parts.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

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Rusting of Cu-Ni-Sn plated steel

Q. My situation: we use cu+ni+tin plating for rust prevention for CRCA.
But after 48 hours it's becoming red rust. Why is this happening?

Muttabattula Kranthi
- Hyderabad. Telangana, INDIA
July 21, 2018

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Ed. note: We're not seeing the rust. Can you tell us where it is and perhaps send a close-up of it?