Where the
world gathers for metal finishing
Q&As since 1989


-----

Zinc plating of case hardened steel

I am an engineer at Mallory Ignition/Erson Cams. We produce race/performance automotive components. One of our popular line of products is our adjustable fuel pressure regulators. We use 12L14 steel to make the seat and the plunger (which slides on the seat). To reduce wear, we case harden both components. Then, to reduce corrosion, we send the parts out for Type II zinc plating with gold/yellow dichromate. The problem is, when you take a handful of these parts out of the box, you will find that your hands will have "glitter" on them as if small pieces of the plating is coming off the parts. Sometimes you can even see blistering of the plating. In these cases, you can scratch the plating off with your fingernail. Those small pieces of plating cause problems when they get into the fuel injectors. I have called both of the platers we have tried and got no real concrete answers. Is there a different type of plating that I should use or are the platers just doing something wrong?

I would really appreciate any help.

Robb McMackin
Mallory Ignition/Erson Cams - Carson City, Nevada, USA
 

See letter 13357.

James Watts
- Navarre, Florida
 

---

Leaded materials in sulfuric forms lead sulphate which will smut up the part and result in adhesion failure whether it's lead in steel, brass or a tin-lead soldered joint! Fluoboric acid may not be as common as sulfuric, hydrochloric or nitric, but it's well known to anyone whose ever dug below the surface of a plating adhesion problem on lead bearing materials!

The other problem with hardened steel is that exposure to any acid may result in a carbon smut on the surface. There is nothing more difficult to remove chemically than carbon smut. Therefore, we often use mechanical preparation such as glass bead blasting only and then directly into the plating bath.

Milt Stevenson, Jr.
Syracuse, New York