Letter 24062

Non-cyanide copper plating thickness limit  

+++

What is the practical upper thickness limit for a functional copper plating on mild steel using a non-cyanide process?

Kirk Cooper
- Sidney, Ohio

Hi, Kirk. Copper electroforms have been built at least 1/4" thick. So the answer is that there is probably no practical upper thickness limit to copper plating. Unfortunately your question is a bit abstract, so I don't know exactly what else to add. Please try to phrase the question in terms of your own situation and maybe we can help. Good luck.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Ted is correct. The question is so broad. When you say non-cyanide, you open the door to several chemistries (sulphate, pyrophosphate, fluoborate). Of those, the one most used to develop thick plates is the sulphate. A practical limit could be how much roughness can be tolerated on the outer surface. Without additives, which tend to increase stress and can lead to cracks, thus limiting thickness, 1/8" can be done with no more roughness than a piece of coarse emery paper. Beyond that, you can go up and end with something that resembles a coral or a sponge.

Guillermo Marrufo
Monterrey, NL, Mexico

The key to my question is non-cyanide plating. For a commercial plater, plating a steel part which will be torch-brazed, what is the thickest copper plate you would feel comfortable putting on using a non-cyanide process?

Kirk Cooper
- Sidney, Ohio

Your question is still abstract, Kirk :-)

We still don't know whether we can start with copper pyrophosphate and finish with bright acid copper, or whether we can buff in mid-process, to smooth it back up. And are we wasting time debating whether we can get to 1/4" or only 1/8" when your concern may be whether you can reach .002"?

An often used approach in some fields is to nickel plate first, then you can directly plate a simple copper sulphate solution quite thick. But is nickel objectionable in your application for any reason?

We don't know why it's supposed to be cyanide-free--whether a cyanide strike is forbidden on ecological or safety principles, or it's perfectly acceptable, but you want the larger grain structure of a non-cyanide as the final plate. We don't know if the copper is supposed to be bright for decorative purpose as well as functional application, whether it needs to be uniform grain, hard, a good wear surface, etc.

I guess I'm saying that I wish your inquiry would start: "Here's what I am trying to do: ..." :-)

Good luck and thanks.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

OK - I consider myself sufficiently chastised for lack of detail :-) Here's what I am trying to accomplish: copper plate a mild steel part which will later be brazed to another part. For environmental and process flexibility reasons, I desire to minimize or eliminate use of cyanide in the strike or the plating bath. Desired plating thickness ranges up to 0.002". Aesthetic function of the plating is secondary, but it should have a surface finish (Ra) not exceeding 0.0005". Brightness is not critical, but consistency of appearance is. Hardness should be similar to that of a cyanide-based process. Thank you.

Kirk Cooper
- Sidney, Ohio

Thanks, Kirk. You probably realize that acid copper cannot be deposited directly onto steel surfaces because it will "immersion deposit" and offer no adhesion.. If you can't use a cyanide strike, you would need to try a pyrophosphate copper strike or a nickel strike.

Then you can finish with an acid copper (sulphate or fluoborate). I don't think .002" is a technological hurdle as, when I was involved in the stripping of the copper from the William Penn city hall tower in Philly, we discovered that they had plated copper 20 times as thick as what you want more than 100 years ago.

It may be possible to directly plate .002" of a proprietary pyrophosphate copper, but I don't know enough about that to comment; you could inquire of a supplier of that process like EPI. Good luck!

Ted Mooney finishing.com Brick, New Jersey