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Steel hardware in re-dipped zinc & clear

We are metal shop in South Jersey. We manufactured some cold-rolled steel trays which then had zinc+clear RoHS compliant plating. After plating we inserted 18 heated-treated carbon steel zinc finished PEM studs. A month after delivery the customer returned items with rust spots and pits. The plater said inadequate plate. One of the trays was given to the plater to be stripped then replated. My question is - will the area around the hardware corrode because of the plater's hydrochloric rinse bath that really can't be rinsed from micro-pores around the hardware insertion area? Is there any guarantee that the hardware attachment areas are ok - or should we just scrap the 15+ pieces which had the hardware installed in them? Thanks for any help.

Cathy Gager
QA in metal shop - Mt. Laurel, New Jersey, USA
February 18, 2011

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Hi, Cathy.

It can be difficult to rinse an assembled component which exhibits capillary action like this, but I don't think it's impossible. Alternating hot and cold rinsing, bicarbonate rinsing, and ultrasonic rinsing are sometimes used. If you do in-line stripping (just running the parts through the plating line again), the first tank the dry parts will see is an alkaline cleaner, so the capillaries will have more tendency to absorb alkalines than acids. However, once parts are severely pitted, especially if heat treated, they're probably history. If not badly pitted, I think the parts can probably be salvaged. Other viewpoints and experiences welcome.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 18, 2011