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Plating specifications

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When requesting material certifications from plating suppliers, specifically zinc plating w/ chromate w/ sealer, what information would you expect to see and is there a standard form that is used in the industry.

Peter Woodworth
consumer security containers - Rochester, New York, USA


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This answer probably won't help you too much, Peter, but the thing is, it's the product designer's job to specify the plating; it's not the plating shop's job. The plating shop simply certifies that it has done the plating that was requested.

Here is a real-world example of what I am talking about, and it happens all the time: a part is plated and it fails because it was not given a hydrogen embrittlement relief baking. The designer says "you didn't bake it and you were supposed to". The shop says "no, soft steel doesn't need baking and baking was not done; if this was hardened steel, you should have specified baking and we would have charged you to do it".

Aerospace manufacturers, automobile manufacturers, and medical instrument manufacturers tell the plating shop exactly what to do--the plating shop doesn't tell them what they're going to provide. Smaller manufacturers, working with less critical parts, are less familiar with plating and tend to rely on the expertise of the plating shop. But this is dangerous because the shop knows the customer will usually go with the cheapest source, so they are not going to volunteer themselves into the cost of complying with a spec that their competitors won't be including in their bid :-(

Another thing that can happen is the customer specifies something vague like "commercial zinc plate" expecting this to mean a minimum of .0002" because one shop tells them that's what it means; and another shop then plates .0001" and claims "commercial zinc plate" just means "complete coverage" :-)

The sad news is that you have to specify the coatings and the performance criteria. If you don't have enough experience with plating to do that, you have to call in a finishing consultant to sit down with the product designer and educate him/her sufficiently to get a good spec written, or at least work with several plating shops to write a spec. Then the certs that the shop supplies will certify compliance with the spec you told them to plate to.

Good luck!

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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In regards to corrosion resistance. Is there a good guide book or reference manual, that could be used as a guide for understanding corrosion and subsequent plating alternatives with performance specifications such as hours of salt spray resistance or high alkalinity resistance.

Peter Woodworth
- Rochester, New York, USA


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Between your first question and the second, it truly sounds like your organization is really in need of someone who knows the surface finishing field. For a start, you might try searching on this website for some education/training outfits, or at least look at the library recommendations here.

totter James Totter, CEF
- Tallahassee, Florida



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Zinc finishes are specified in ASTM B633 [link is to spec at TechStreet] Types I-IV. Check out this cool link which lists free of charge most common surface finishing specs: http://www.engineers edge.com/finishing.htm.

Process suppliers of Zinc Chemistries and many plating shops have established recipes that pass a multitude of accelerated life tests such as salt spray, etc., and will certify to it.

These certifications are generally traceable to an independent testing lab.

Dave Kinghorn
     Chemical Engineer
SUNNYvale, California



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That's a great link, Dave--thanks. But I have to disagree with its preface that "Often MIL, AMS, and other controlled specifications are not required...". Metal finishing should always be done to a specification. Undocumented metal finishing like "commercial zinc plate and yellow" are meaningless, and don't save time or effort . . . they just lead to trouble nearly every time.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
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