On Sun, Jun 14, 2009 at 11:59 PM, Randall<tr3driver@ca.rr.com> wrote:
>> thus the copper isn't needed unless
>> the metal is badly pitted.
>
> What I was told, long ago, was that it is very difficult to get nickel to
> bond properly to steel. B If it's not done just right (some claim it's
> impossible), then the resulting chrome will eventually peel. B Maybe not
this
> year, maybe not next, but it will peel.
>
>> B They then leave the piece in the nickle for about
>> 45 minutes, vs the usual 5-10.
>
> Sounds kind of haphazard. B For a quality job, there should actually be two
> separate layers of nickel, done under slightly different conditions. B I
> forget the details offhand, but it has something to do with preventing
> dissimilar metal corrosion. B Without the two layers, the part is more apt
to
> rust. B Supposedly the nickel is what provides the corrosion resistance and
> much of the 'shine', the chrome just improves the appearance of the nickel
> and keeps it from tarnishing.
Well, it depends on what you're plating, and why. For something like
a bumper, where you're after the shine, the best process is
copper-coat the bare part, polish the copper to mirror smoothness,
then two layers of nickel, followed by a very thin layer of chrome.
The copper fills the surface of the part, and more readily takes a
polish than steel. The two layers of nickel are called bright and
semi-bright. I think, but can't remember, that the semi-bright goes
first. The bright nickel is a sacrificial coating (galvonically), and
spreads the corrosion forces laterally, instead of through the
coatings.
for a part that's covered in what's called "hard chrome", where the
chrome is a wear preventing surface, there's a slightly different
procedure. (Gun barrels and chambers, hydraulic cylinder bores and
pistons, and the swivel balls of elderly Land-Rovers (LBC content!)
are all hard chromed.) The surface is prepared; typically that
involves grinding it smooth, but sometimes some texture is put into
it, if it's supposed to have it (to keep a film of oil, say). Then
the two (or sometimes three) layers of nickel are put on, followed by
a very much thicker layer of chrome. These parts aren't usually super
shiney, though they can be, if that's useful property.
A part with only one layer of nickel might well look wonderful, but it
won't stay that way.
>> Is there any good
>> way to tell the quality of a re-chroming job?
>
> Not that I know of.
>
> Randall
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David Scheidt
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