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May 2003

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 2 May 2003 13:42:10 -0700
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George: Type III chromate conversion coatings really don't offer much
environmental protection.
However they do offer some protection as opposed to straight zinc. Are the
fingerprints reacting and etching into the zinc plating or do they just show
up on the surface of the coating? I would expect a properly applied coating
to resist some handling.

Obviously a Salt Fog or Salt Spray test would help to give you some
quantitative indication of the quality of the coating, but that takes time
and equipment.

You can also do a weight loss test by weighing the part, stripping the
coating and re-weighing. I've used this method on aluminum with class 1A
coatings with success. However the accuracy of this for very thin coatings
is not the greatest and may be difficult for stripping the coating from a
zinc substrate.

A spot test can also be done. This is strictly a qualitative test but has a
very high sensitivity to the presence of Chromate. It will not tell you the
quality of the coating but it will definitely tell you if any Chromate is
present. Make a solution of 0.1% B.W. diphenylycarbazide to reagent grade
methanol. Place a drop on the suspect part. If there is Chromate present it
will turn a brilliant violet color.

                                                                Good Luck

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076



-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Friday, May 02, 2003 12:26 PM
To: [log in to unmask]
Subject: [TN] Type 3 Chromate Conversion Coating


If a cold rolled commercial quality steel (per ASTM A366) assembly that is
zinc plated (0.0002" min per ASTM B633 Type 3) and supposed to be colorless
chromate conversion coated begins to show finger prints and surface tarnish
in a relatively benign environment, should you suspect that the chromate
conversion coating is missing or improperly applied?  And secondly, is there
an analytical method to determine the presence and quality of the coating or
would one have to resort to Salt Fog testing

Regards,
George

George M. Wenger (908)-546-4531
Reliability Engineer
RF Power Amplifier Group
Andrew Corporation,  40 Technology Drive, Warren, NJ 07059
[log in to unmask]


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