[Shop-talk] (no subject)

[David Scheidt]

On Sun, Jun 14, 2009 at 11:59 PM, Randall<tr3driver at 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
> _______________________________________________
> Support Team.Net B http://www.team.net/donate.html
>
> You are subscribed as dmscheidt at gmail.com
>
> Shop-talk mailing list
>
> http://autox.team.net/mailman/listinfo/shop-talk
>
> http://www.team.net/archive
>



--
David Scheidt
dmscheidt at gmail.com