Another Visit to RoHS

Ask an Expert From: Products Finishing, ,

Posted on: 6/1/2005

Question: Our company is a manufacturer and distributor of fasteners and electronic components that are sold throughout North America and Europe.

Question:

Our company is a manufacturer and distributor of fasteners and electronic components that are sold throughout North America and Europe. Many of these components are zinc plated and chromated after the plating step. Most of these zinc plated components contain less than 1,000 ppm of hexavalent chrome. We have assumed that these components would be compliant with the RoHS directive. A number of our customers now state that these parts are not compliant because the hexavalent chrome is intentionally added in a final processing step. Can you shed any light on this issue? C. S.

Answer:

Your question is extremely important but I don’t think I have a definitive answer at this time. For those who have not been initiated into this latest set of regulations, RoHS is the acronym for “The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment Regulation 2004. It will take effect on July 1, 2006. The regulations will regulate the amount of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) that can be present in products sold after the July 1, 2006 date.

The maximum concentration value is 0.1% or 1,000 ppm by weight in homogeneous materials for lead, mercury, hexavalent chromium, PBB and PBDE. The limiting value for cadmium is 0.01%.

What is the definition of a homogeneous material? The definition used is that a material that cannot be mechanically separated or disjointed is a homogeneous material. The term also means uniform composition throughout the part. A piece of steel would be homogeneous as would be individual plastics, resins and coatings.

Mechanically disjointed or separation is taken to mean materials that can be separated by cutting, unscrewing, grinding, etc.

A key question is a zinc plate with a chemical conversion coating a homogeneous material with a uniform composition throughout the entire layer. The answer is no. The chromate conversion process is primarily a surface phenomenon. The “interior” of the zinc layer will not contain any hexavalent chrome. If you look at the zinc and chromate layers as separate layers, you will have a high level of hexavalent chromium in the chromate conversion layer. “Classical” yellow and darker chromates will have very high concentrations of hexavalent chromium.

Okay then, what’s the solution? You must change to the trivalent chromate conversion coatings. This does not appear to be a problem with the clear coatings but poses difficulty with the heavier chromate conversion coatings.

I personally would appreciate any input from our readers regarding the issues involved with the RoHS regulations.

 


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