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Cadmium Plating specification for clear chromate

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Current postings:

March 22, 2022

Q. This is an old thread, but it is the first topic I came across that seems to be in line with my question. Per QQ-P-416, Paragraph 3.2.9.1, Type II should yield a part having a color that is "...distinctly colored iridescent bronze to brown, including olive drab, yellow, and forest green". It seems to me that this statement would not permit the use of a clear chromate. We recently received some parts from a plater that we rejected because there is no perceivable coloration (the parts look silver). The supplier has stated that a clear chromate was used. Historically, any parts we have had plated Type II are almost always gold/yellow/olive drab - but always "distinctly colored" (not silver). Am I misinterpreting something?

M Miller
Quality Engineer - Goldsboro North Carolina



March 2022

A. Hi M. You appear to be 100% correct, and I have removed my earlier mistaken claim to the contrary; I do not see any sign that QQ-P-416 ever allowed clear chromate.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



March 22, 2022

A. Hi M
Generally you are right. Chromate treatment should produce a distinctive colour (iridescent gold/brown/olive drab...). AMSQQP416 [affil. link to spec at Techstreet] revision F (2021) requires such colour for type II A treatment (Chromate treatment). AMS2400Y [affil. link to spec at Techstreet] (2020) requires similar color as well.

As much as I know, distinctive colour is not required in 2 cases:
AMS-QQ-P-416 Type II B (WITHOUT hexavalent Cr) - "...some treatments may not produce a distinct color change after the coating is applied"
AMS2400Y - treatment with Chromic Acid (if approved by cognizant engineering organization).

Probably an origin of this "color" issues is proprietary "clear" treatment. Such treatments may be marketed as "CLEAR Chromate" because they contain chromates, but it is actually mainly Chromic acid with some minor amount of chromate salts...

Leon Gusak
- Winnipeg, Canada





Closely related Q&A's, oldest first:

2003

Q. We have several "old" drawings that specify the following finish over a brass machined part. The drawing note reads: CAD Plate per QQ-P-416 [link by ed. to spec at Defense Logistics Agency, dla.mil] , Type 2, Class 3, CLEAR. Is this a correct callout? I'm especially interested in the "Clear" part of the callout as I've never seen clear CAD plate.

Bob Diamond
mechanical engineer - Hauppauge, New York, USA



2003

A. Cadmium plating which is not to be painted is almost always topped with a chromate conversion coating which can be clear, yellow, or olive drab. Although yellow is probably more common for cad, clear is perfectly valid. This spec means that the cadmium plating is topped with a clear chromate conversion coating.

Update: Sorry, I made an assumption that Bob's spec would be okay, apparently based on my misreading of a reference which I thought was to QQ-P-416 but was not, instead of carefully actually reading QQ-P-416 (we never learn, do we). QQ-P-416 has been canceled since 2002, but as far as I can see going back as far as 1956, it did NOT ever allow for clear chromate.

I believe that it is valid to add additional requirements to a spec ("... per QQ-P-416, but it is additionally required that ..."), but not to dilute or contradict it ("... per QQ-P-416, but it is not necessary that ..."); therefore this appears to NOT be a valid callout.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


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