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Fasteners on sheetmetal assemblies won't plate

1998

I am currently experiencing periodic attack on zinc plated steel stamped fasteners,(stand offs) installed into steel sheetmetal parts we nickel electroplate.
It only happens on a hex head shaped fastener with about a .400" - .500" long shaft, and a threaded inner diameter.

Other installed harware, pem nuts and threaded studs are never affected. The stand offs have been case hardened.

After nickel plate the face of the hex is pitted, black and lacks nickel deposit. The OD shaft is also affected, but the internal threads do not appear to have been attacked.

The parts go through a standard Alkaline cleaning, Electrocleaning and HCl dip before Nickel plating.

Has anyone out there had this experience with any electroplating coating, or does anyone care to ponder a theory to its cause.

Any response is welcomed.

Thanks
Juan O.

Juan Ocampo
plating shop - San Jose, California

Are the standoffs cleaned properly before heat treating? It sounds like you may be burning oil in to the metal. If the threads are turned afterward, that might explain it not damaging the threads.

Phil Pace
- Tulsa, Oklahoma
1998

Dear Juan,

The type of parts you describe may result in a lot of dragout and be difficult to rinse. Have you checked the quality of your rinsing?

Good Luck

John Ring
- EnviroPure Solutions
1998

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1998

Jaun,

I remember trying to plate some fasteners many years ago that would not plate right. We later found out they were nitride hardened. Check to see how your parts are heat-treated. It can be a factor, depending on what you are attempting to plate and the process you are using.

Matt

Matt Gazo