45050

Hard chrome cracking over nickel plate "filler" [Georgia] 

May 8, 2007

My shop is having a problem with hard chrome cracking during the machine/grinding process. It appears to be a problem particularly over cylinder O.D.'s that have been grinded and filled with nickel plate, machined flush, then hard chrome plated. I realize that the machine process can have a great influence on this, but it seems to be primarily on the cylinders that have patches of nickle plate.

I'm stumped, any information will be helpful.

Dennis Parham
Plating shop employee - Atlanta, GA, USA

You need to grind the parent metal so you can have about a 0.003" per side of nickel after the nickel is machined. Then you clean,activate and chrome plate.
Otherwise you have a product that will not hold up during the chrome grind/use.

James Watts
- FL

After you have straightened and rounded the surface, just before the chrome, you must give the part an activation in an acidic Woods strike for the chrome bath to work over a uniform metal (in this case a very thin nickel film). There should be no delay form activation to chrome and no reverse etch in the chrome. Otherwise it will passivate again w/o adhesion.

Guillermo Marrufo
Monterrey, NL, Mexico