Metal finishing Q&As since 1989

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CLEAR CHROMATE THAT MEETS MIL-SPEC

 

I have posted this question before but never really got definitive answers:

Chromate per MIL-C-5541.

We use the Iridite 14-2 product. We do yellow & clear coatings. The clear is done by applying a light yellow & then bleaching out the color with hot water til we have a totally clear coating.

My boss insists that our clear chromate will not meet the spec & thus we will never certify to it.

My problem, in sales, is that I get lots of rfq's for Clear Chromate per the spec, MIL-C-5541 Class 1A Clear.

Is the solution that clear chromate can be done to meet the spec, BUT, we need to setup a second tank / solution just to do clear chromate coatings?

Bottom line: Is there any product on QPL for Clear chromate that meets the MIL-SPEC? or Is there any product on QPL for Clear chromate that meets the MIL-SPEC & can also be used to meet spec for Yellow chromate?

David A. Kraft
- Long Island City, New York

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Inquire about Alodine 1000L. Dado Macapagal - Toronto   Your boss is your father and as one "son-of-boss" (SOB) to another, listen to your father! In this case he's right. Heating chromates, whether on aluminum or zinc or whatever, above 140 F will degrade the corrosion resistance of the chromate rapidly. We indeed bleach out yellow chromate for many commercial applications but back off that approach when required to meet mil spec. For clear chromate, I'd suggest either Alodine 600 or Oakite's Clear Chromicoat [Chemetall] --- (three numbers that I can't remember! - hey, it's late and you're getting free information so don't complain). If your customers want the real thing, that is certified and tested clear chromate to MIL-C-5541, we'd be glad to do the work. Milt Stevenson, Jr. Syracuse, New York

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Hello David,

I am not going to answer your question as there is no definite answer to it. Class 3 in 5541E is a class where everybody has a lot of confusion about. Now it is up to you how you deal with your customer. First of all there is no word in the spec. itself which tells you that the color should be clear. The spec. only tells that the chem. film should be thinner and excellent in terms of electrical conductivity. Now for this reason I can even go for yellow color under class 3. (As there is no color specification in this spec.). And this yellow color will give me confidence to certify it as I know it will definitely pass 168 hours for salt spray (is not it?, I am sure it even pass 336 hours of salt spray, I tried it once) And as far as electrical resistance test is concerned I think there are as many doubts out there as there are stars in the sky. No body knows how to make the equipment for this. No body knows how to give the exact pressure to the electrode as there is surface porosity.

But again as I said before, there is no regulation which asks you to go for clear color only in class 3. And hey, you can always "EDUCATE YOUR CUSTOMER".

Regards,

Hemant Kumar
- Florida, USA
 

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MIL-C-5541 is quite specific about the color. Paragraph 6.6 states
"...range in color from clear to iridescent yellow or brown." However, Paragraph 3.5 states "Clear(colorless) coating shall only be used when specifically authorized ..."
Therefore, in most cases the color must be iridescent yellow or brown regardless of class.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio