"Steve W." wrote in message
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"Proton Soup" wrote in message
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On Sun, 20 Feb 2005 14:54:51 -0500, "Lee Michaels"
wrote:


While we're on the subject of chromed bars, I've got one (just happens
ot be for standard sized weights), and the chrome is starting to wear
away where the clips to hold the weights slide on and off. And oddly
enough (to me at least), the metal underneath the chrome appears to be
copper, not steel. Now I'm pretty damn sure the bar isn't solid
copper (it'd be too expensive and bendy), so it must be a plating that
is applied before the chrome. But why? Is it to help the chrome
better adhere (decent chrome job, btw, no flaking) or some other
purpose, like limiting the aforementioned hydrogen embrittlement?

-----------
Proton Soup

"Thanks for noticing that I didn't actually say anything." - Mike Lane

There are a LOT of different types of "chrome" plating.

What most folks see as Chrome plating is AKA Triple Chrome Plating. It
is a layered process. The part is ground and buffed to a high polish.
However this surface may still have small imperfections. So it is plated
with a layer of copper. This copper does two things, one it fills the
imperfections and it conducts electricity better than the steel, both of
which gives you a better and more even layer of plating. The part is
then buffed again to a very high polish. (ANY imperfections must be
taken out NOW) then the part is cleaned and plated in a nickel bath.
Then it is buffed again and finally plated with a very thin chromium
layer. The chromium layer is for wear resistance, it is the nickel that
makes the finish bright and shiny. It wears pretty well BUT the
copper/steel interface area is very fragile, any oil/rust or other
contaminant will cause plating failure.

Then you have "hard chroming" That is an entirely different process. In
HC you polish the part to a finished size smaller than required and then
plate chromium onto the part until it is built up over the required
size, then ground and polished back to the correct spec.

"Flashed" chrome is another different process that is done in a vacuum
chamber and is basically vacuum deposited onto a surface that either
doesn't conduct electricity or has a complex shape that plating in a
tank cannot handle. (tight interior corners are hard to plate due to
faradaic rejection in the tight angles. (same problem with powder coat
in tight areas)

Hydrogen embrittlement is a real problem in high strength materials
(steel, aluminum alloy,titanium alloys), subjected to high loading
(suspension parts, stressed bars). The plating currents cause the
hydrogen to be absorbed into the material and this weakens it. It is
possible to correct the problem though. You need to follow each step of
plating with a bake in the oven (375-450 depending on HRc of the steel)
to remove the hydrogen from the item.

So it's the same problem that may occur when using an electrolytic process
to derust?