Letter 24062

Non-cyanide copper plating thickness limit [Ohio] 

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

Kirk Cooper
- Sidney, OH, USA

Copper electroforms have been built at least 1/4" thick. So one answer is that there is no practical upper thickness limit. Unfortunately your question is cast in the abstract, so there is nothing more I can add.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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, OH

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

No, the key to your question is that it is still abstract :-)

As an engineer I would not be comfortable applying ANY copper unless I understood what it was being applied to, where, and why. After two posts we still don't know whether we can start with pyro and finish with bright acid copper, or whether we can buff in mid-process, and whether we are wasting our time trying to decide whether we can get to 1/4" or only 1/8" when your concern may be whether we can reach .002" or only .001".

We don't know why it's supposed to be cyanide-free--whether a cyanide strike is forbidden on ecological first principles, or it's perfectly acceptable, but you want the 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.

After dealing with more than 24,000 postings here, my feeling is that an inquiry should start: "Here's what I am trying to do: ..." :-)

Ted Mooney, P.E.
finishing.com - Brick, NJ

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, OH

Okay, thanks. You probably realize that acid copper cannot be deposited directly onto steel surfaces. If you can't use a cyanide strike, you would need to try a pyrophosphate copper strike or a nickel strike. Then you could 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 plate .002" of proprietary pyrophosphate copper, but I don't know enough about that to comment either way.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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