Letter 15083

ASTM-B-633 [Texas]  

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I have used yellow zinc electroplate ASTM B-633 [link is to info about 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, TX, USA

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.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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.

Tim Neveau
- Rochester Hills, MI

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.)

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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