Sciencemadness Discussion Board

Plating chromium

Random - 11-6-2015 at 01:21

Has anyone had some experience with chromium plating? How the procedure goes etc...? I read that hexavalent chromium could be used and also trivalent compounds. The parts which I would like to chrome plate are motorbike parts. It's really expensive at my living location so I would like to do it myself.

hyfalcon - 11-6-2015 at 07:22

Here's a couple books on electroplating from another thread.

[Edited on 11-6-2015 by hyfalcon]

WGTR - 12-6-2015 at 14:32

The plating process depends a lot on what the parts are made from. Steel is fairly easy to electroplate, aluminum can be done by platers who are experienced with it. Pot metal, depending on what the alloy is exactly, is something that every plating shop hates. It gives unpredictable results.

Interestingly, what you are referring to isn't necessarily "chromium" plating. The colloquial term is "chrome" plating. It involves not only chromium, but also nickel and usually copper. The chromium layer is on top, but is so thin that it's transparent. It only provides a bluish tint to the nickel layer that is beneath it. The nickel is what gives the characteristic silvery finish. Usually there is also copper underneath the nickel. It's not needed for durability, but is used to provide a surface that can be buffed to a mirror shine. The better plating shops will plate with two different nickel layers. The slight difference in composition and structure between the two provides extra corrosion resistance.

One way that you can save money would be to strip the part yourself. Get out some sandpaper, and wet-sand off the chromium layer, then the nickel, and then the copper. Be prepared to spend a long time doing this. A shop normally uses a grinder for this task, but some times, after the plating is done, faint grinding marks can be seen under the plating. The idea is that the copper and nickel should fill in the rough marks in the base metal, but usually there is no substitute for spending the time to obtain a clean and smooth substrate. Their time is money, so they may cut corners, but your time...?

The copper layer is the next time-consuming part. After striking and building copper on the part, the surface has to be ground and polished to what could be considered a mirror made from copper. Depending on how large the part is, this can take a lot of time and labor. If one grinds into the base metal, the part has to be re-struck and plated with copper again.

If you want to do your own plating, I would recommend stopping after polishing the copper layer. Most of the labor is done by that point. The plating shop should be able to re-activate the copper without too much trouble. Re-activating passivized nickel is a &$*@ though. Nickel plating for "show chrome" is a specialized process, if you want the results to last. Let them do the nickel and chromium plating.

Also, I would practice on unimportant pieces first, and certainly not something that is particularly rare or expensive.