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Letter 15083
ASTM-B-633
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I have used yellow zinc electroplate ASTM
B-633 [link is to spec at TechStreet] Type II (5 um)on
sheetmetal enclosures for indoor applications. The enclosure has
numerous spot welds. My new customer does not like the look of the
yellow plating (and the rainbow effect)and wants to use a clear
plating. For indoor applications is it OK to use the clear zinc
electroplate ASTM-B-633 Type III (5 um)? I have heard that the clear
is less corrosion resistant than the yellow. Would I need to increase
thickness of clear plating to compensate? Enclosures would experience
typical assembly handling.
Thanks,
Mike McLaughlin
- Richardson, Texas
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Yes, the clear chromate is less corrosion resistant. No, you do
not need to increase the zinc thickness. Yellow chromate is rapidly
joining the dinosaurs. Make the change.
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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FYI Ted, I think he is considering moving from yellow hexavalent
to clear hexavalent. In any case it is hexavalent. Since he's not in
the automotive industry, he probably has years and years before his
company will see any hexavalent chrome regulation deadlines. You
could get progressive and switch to a clear trivalent, but who wants
to change if they don't have to, since it costs more?
You may be fine switching from yellow to clear. The decrease in
corrosion performance may not even be a problem for your customers.
Do you use salt spray testing on your current product? If I were you,
I would have a few samples plated with the clear chromate and put it
in salt spray and see if it will give you enough hours resistance to
white and red corrosion. Or, you can ask the plating chemical
supplier to provide some information on the difference.
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Tim Neveau
Rochester Hills, Michigan
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Tim:
I wouldn't claim, short of reading the particular spec sheet, that
a given clear chromate is necessarily hex-free. But some are, and
almost all have far less hex chrome than a yellow chromate (which is
why they're not yellow).
Since he is not in the auto industry and not subject to the
requirement that the replacement coating meet the identical
performance specs as the original, the clear chromate will simply be
a clear chromate, with no extra steps, and will cost him nothing
extra. A few shops even charge marginally less for clear than yellow.
As for when to make a change, it depends on where on the curve he
wants to be. It doesn't pay to be the cannon fodder of the first
charge unless he has to be; but bringing up the rear, especially when
the change will cost little, would make no sense. It would leave him
out of the loop, racing to catch up on the technology when nobody is
interested in it or talking about it any more, and being marked by
the customers as unprogressive.It leaves one a straggler in the herd,
to be picked off by the jackals. The jackals may be personal injury
lawyers suing for skin cancer, etc. (We get a kick out of mixed
metaphores in this office, and I want to see Tom Pullizzi top this
one, with its buzy field full of cannons, infantry, automobiles,
chromate vats, lawyers, jackals and gazelles.)
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Ted Mooney
finishing.com
Brick, New Jersey |
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