Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation
Q. I have several problems in my hard chrome plant with the control of the temperature in the process.
I have prepared a tank with an external bath of water to cool the chrome process fluid when it exceeds 60° C. Due to the fact that the chromic acid is corrosive to the metal, the metallic walls are protected by glass fiber, which reduces heat transmission, so I can't work with high amperes. What can I do to have major efficiency in my exchange of heat? It is not possible to build a titanium tank because it’s really expensive. Can you send me a basic diagram about tank construction with a flow cooling system? I don't know if it is necessary to control the flow of the water in the cool tank or not.
Another problem: In several pieces after the hard chrome process, pitting ( holes) appears in the piece so I have to strip the hard chrome and start again and again. What is causing this and how can I correct it.
A. Emilio, on your question about cooling systems? Try this website for starters ! http://www.nmfrc.org/pdf/crtext.htm
Pits are often a regular issue when it comes to hard chrome. Although pitting can have numerous causes, let me take this opportunity to talk about "part prep".
I've seen the best and the worst preparations for hard chrome. The worst I've seen is the practice of "no preparation". Let's not go there at this time.
To be sure, the key steps to preparing a surface for hard chrome are; 1.) remove all previous coatings, rust, organic and other blemishes, 2.) polish, remove, blend nicks, scratches, pits, tool marks, and other surface imperfections. 3.) it is customary for most metals to further clean and prepare the surface by grit blasting with a suitable media 4.) there's even a final pumice scrub and water rinse to ensure readiness for plating.
The real trick is getting the well prepared part into the chrome bath without getting it dirty again. This requires well designed tooling and good handling practices. With a well maintained plating bath, low in contaminants and free from floating debris, anodes in good condition and well placed and a proper pre-etch and start up plating procedure, you should produce a very smooth chrome deposit free from pits.
Chrome is a mirror of what's underneath. The better you prepare the base metal, the better the finish.