Metal finishing Q&As since 1989

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Creating a spec for RoHS compliant finishes

2007

Hello,

I hope this isn't too abstract of a request, but I am in need of considerable guidance.

I have been given the assignment of creating/finishing a spec, to be referenced on our drawings, regarding RoHS compliant surface coatings. I have never written a spec, let alone for something I know nothing about.

I am looking for a format to follow. Is there generic verbiage that I should use? What information should be given, besides thicknesses, so that I am not too vague or overly wordy. I will find out what specific coating materials are to be used, as of this writing, I only know the powder coating material.

Our product is x-ray equipment in an office environment, so corrosion isn't an issue. The bulk of our components are presently anodized aluminum and painted/plated steel. We are also currently investigating powder coatings.

Thank you in advance for any assistance.

Best regards,

Richard Spencer
Mechanical Designer - Hatfield, Pennsylvania, USA

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First of two simultaneous responses --

If I were you, I'd focus on where ROHS non-compliant materials might creep in.

Though it is not common, steels occasionally contain lead to improve machinability. This would likely make them non-compliant.

The other possibility I see is a hexavalent chromium conversion coating used in conjunction with zinc plating applied for paint prep. or as a stand alone finish on internal parts. That would also make them non-compliant.

Dave Wichern
Consultant - The Bronx, New York
2007

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Second of two simultaneous responses -- 2007

Hi Richard,

The specification is there to inform the manufacturer that you are aware of current legislation and that you wish him to conform to its requirements.

I think what legislation is trying to achieve is that when your item becomes surplus to requirements and sent away for recycling it will not create problems to the environment due to unacceptable high heavy metal content.

Here are the parameters according to European legislation:

To comply with EU directive 2002/95/EC requires that the homogeneous material does not contain more than:

0.1% of Pb, Hg, Cr(Vi), PBB (polybrominated biphenyls), PBDE (polybrominated diphenyl ethers) per substance and per homogeneous material and less than:

0.01% Cd per homogeneous material.

Terry Hickling
Birmingham, United Kingdom

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2007

"It means just what I choose it to mean -- neither more nor less"

-- Humpty Dumpty in Lewis Carroll's "Through the Looking Glass"

Thanks, Terry. But readers should be warned never to use that word "homogeneous" in their own specs, but rather to always refer back to what the EU Directive chooses that word to mean, because the EU Directive plays Humpty Dumpty to their Alice, and their meaning of "homogeneous" is not logically deducible.

The EU chooses "homogeneous" to mean complete nonsense like --

• zinc plating is not homogeneous with the substrate (although it can't be removed with a chisel and the substrate it is supposedly not "homogeneous" with is often zinc); but
• chromate conversion coating is homogeneous with the plating (although it is a hundredth as thick as the plating, is easily rubbed off with a pencil eraser, and there would be no such thing as white rust on plated steel parts were they not so obviously wrong).

So don't use the word "homogeneous" in your spec, Richard; put the EU interpretation of what it means in your spec.

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

Theoretically, specifications may contain whatever the writer wants to, but in order to be respectful and respected they must be deeply informed, informative, well structured, congruent and in accordance with higher level regulations and specifications. They should be prepared and revised by experienced people. It seems quite a disproportionate task for a person that declares to know nothing about it. Why don't you tell your boss to assign someone else with more experience. That would be very honest. If doing so might risk your job, you have a long way in front. Get as many books and specs as you can about the subject and study them. Also ask for very close help.

Guillermo Marrufo
Monterrey, NL, Mexico
2007

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Although your conclusion is a bit harsh, I thought your description of the properties and requirements of a specification was terrific, Guillermo. Thanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007