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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Decorative chrome plating to meet 500h red rust salt spray?
We have a brush guard we build for a customer, and they want decorative chrome plating, and they are asking us to meet 500h red rust salt spray. Our coater has gone above the original dip times quoted and is currently at 2 min copper 60 min nickel and 1 min chrome, and is only getting 264 hrs before red rust. Talking to the coater they have said they feel this is the best they can achieve, and longer dip times and the chrome will become brittle and shatter; they have suggested a tin-chrome alloy but said its hard to find anyone doing that in the southeast US. So we're stuck between a rock and a hard place. Is our customer asking for an unreasonable request or is our plater just not up to the task?
Michael Donnelly Jr- Chattanooga, Tennessee, USA
August 31, 2011
September 1, 2011
Hi, Michael.
There is much written between the lines, or assumed, so this threatens to be a long thread.
First, designing to an accelerated corrosion test is very questionable. These tests are for the purpose of QA (to check that your process didn't deteriorate). They are not for design, because the corrosion mechanism is so fundamentally different that a salt spray test cannot predict real life. For example, powder coating outperforms galvanizing in a salt spray test, but doesn't hold a candle to it in real life.
Secondly, salt spray is not the appropriate test for nickel-chrome plating. CASS or Corrodkote would be better.
To address the question of whether your plater is up to the task, I would ask how much automotive plating they do. If it is a mainstay, they probably are.
The most direct way to pass the test would probably be to do electroless nickel plating in place of the copper plating, or before it, but there are many possible tweaks to the nickel-chrome plating process including duplex or triplex nickel plating, and an improved proprietary chrome plating. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
I am greatly bothered by the use of "min" for the thickness of each coat.
Do you mean mil or is it the time in each tank. If it is time, the chrome time is extremely too low for a coating that to me is extremely too little as my guess is that this part is going to see a good bit of wear.
- Navarre, Florida
First of two simultaneous responses -- September 2, 2011
Just to clarify what Ted said. By "automotive" plating, he means plating of OEM parts for car manufacturers, not replating of auto parts for the restoration/hobby business.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
Second of two simultaneous responses -- September 2, 2011
Q. Is there a table for time/rust and chrome plating thickness. We would like to get a 5yr or more time period before rust is exhibited on our chrome plated products both dipped and plated.
Charles Geurts- Cottage Grove, Wisconsin, US
June 1, 2012
A. Hi Charles.
Actually, there is no distinction between chrome plating and chrome dipping; they are both actually nickel plating followed by chrome plating. If you can find a copy of a plating spec from any automobile manufacturer, it will easily go five years, probably a lot more. But poor chrome plating would be worse than no plating at all :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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