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General purpose specification to replace ASTM B633

My problem with trivalent chrome is that the standards bodies seem to have completely failed in coming up with suitable specifications. I know that every car company has their own proprietary specs & every plating company has their proprietary blend of wiz bang chemicals. None of that is particularly useful to those of us in smaller industries. I try to use industry standard specifications that are widely available and recognized. What I need is a general purpose specification to replace ASTM B633. I do not want to use a GM, Ford, or other proprietary spec.

Is any standards body even addressing this problem?

David R Gallup
- Greenville, South Carolina
April 11, 2008

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Hi, David. As I think you recognize, we have several different technologies for trivalent chromating today (thin film/thick film, topcoat/no topcoat, different types of topcoats) and their performance is fundamentally different one from the other in many respects (adhesion of paint, resistance to pretreatment chemicals, salt spray performance, conductivity, temperature resistance, etc). And at the same time, we have a number of non-chromate alternatives being promoted.

We're early in the lifecycle for what you want, unfortunately. By which I mean the vendors and shops are still in the mode of trying to recapture their investment in the new technology by claiming the proprietary advantages of their own approach. Such that, even if the standards bodies spent a small fortune on testing and classification of all of the types of trivalent chromating, I think you'd still find that shops and vendors would be unwilling to disclose which classification their trivalent chromate fell into because their competitors' technologies would have some advantages over theirs ;-)

I personally believe, based on several projects where trivalent chromates caused paint and powder adhesion problems, or failed during subsequent pretreatment for painting, that for right now you are stuck with specifying a particular brand of trivalent chromate that works for your needs, and only letting shops who use that brand quote on your parts. This is a pain, and it certainly will change as the coatings become "commodities", but it will take time.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 14, 2008