Thin Dense Chrome

Letter 1003

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We have a specification (Thin Dense Chrome) that requires suppliers to run salt spray tests on coupons for acceptance. The specification does not allow any undercoats.Salt spray is in accordance with Federal Standard 151, Method 881.1

The test is as follows:

Type I - 4130 coupon plated to 0.0003-0.0005 - the salt spray is run at 24 hours.
Type II - 4130 coupon plated to 0.0003-0.0005 - The salt spray is run at 48 hours.

The problem is that 50% of our suppliers pass these requirements and the other half say that its impossible to pass the salt spray tests. I know the reason is the density of the chrome, and that a undercoat is required. What I want to know is:
1)Is this reasonable requirement?
2)Does anyone have more information on thin dense chrome?

Garry Pickett
aerospace - Los Angeles, California

Gary, If half of your vendors can pass the test (honestly), the other half should be able to also. Half a thou is not much thickness for corrosion protection, but 24 hours is not that long either.

Is it failing in a particular area, such as dead center or near the edge?In the center, they may not have the minimum thickness and the edge may be stress cracking.

Is everybody running annealed sample panels or are some of the failures running hardened panels?

Have panels from everybody been run by a neutral lab on a regular basis? Temperature, % salt pH and quantity of condensate could easily affect the results if it was close.

My guess is the failures are getting macro cracking rather than microcracking.

James Watts
- Navarre, Florida

James, I'm as honest as I can be, but then again were not talking about a lot of vendors. The coupons are failing at the 48 hour salt spray, and they are failing at the edges. Everybody is running annealed panels, and all plating labs have been sending their coupons to neutral labs. Those results are then sent back to us for review. You maybe right about the cracking problem. Do you know of any specifications on Thin Dense Chrome?

Garry Pickett
boeing

COULD YOU PLEASE TELL ME WHAT THE CHEMICAL CONTENTS OF THIN DENSE CHROME IS? I WOULD LIKE TO KNOW THE SPECIFICS IN PERCENTAGES.

THANKS,

MARK CRETNEY
- GARDEN CITY, MI