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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation.
August, 2006
Chrome Plating Over a Rough Surface
Q. How does the initial surface roughness effect the outcome of chrome plating? Does it depend on the thickness of the plating? What about surface peaks and valleys -- will the coating always follow the peak and valley or does it smooth them out?
A. Chrome plating does not smooth out peaks & valleys. Nor will it hide scratches or nicks by itself.
For decorative chrome, parts are polished, then coated with a build layer of bright nickel or bright copper/nickel to fill and level peaks & valleys prior to applying the final thin "cap" layer of chrome (0.000020 - 0.000040 thick) hence the bright finish.
For hard chrome, base metal should be ground, smooth, uniform, with no sharp edges. Typically, pre-treatment includes polishing, shot peening, glass bead and/or grit blasting before plating. In the plating process, first step is usually a reverse current chemical etch to enhance adhesion. Evidence of all these pre-treatments can be visible in the finished layer of hard chrome, but is seldom a cause for rejection. Thicknesses ranges from 0.0003 to unlimited.
No substitution for proper base metal preparation in chrome plating. "Chrome is a mirror or what's underneath"
