Metal finishing Q&As since 1989

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Seeking Opinion on Anodic and Cathodic cycles involved with Cleaning and Material activation

October 23, 2008

I am involved in a Nickel Sulfamate plating process. The base materials over which this nickel plate is applied is an configuration of two Inconel flanges welded to a ferrous steel tube bonding the flanges together.

Cleaning: The part is immersed in a cleaning bath where we apply an electrical charge in both an anodic and cathodic cycle. My question is there a recommended sequence for these anodic and cathodic cycles?

Activation: The part is immersed in a Sulfuric acid bath where we apply an electrical charge in both an anodic and cathodic cycle. My question is there a recommended sequence for these anodic and cathodic cycles?

Joe Burns
Plating shop employee - Euclid, Ohio, USA

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October 23, 2008

Hi, Joe.

Electrocleaning: When the work is cathodic, the scrubbing bubbles are hydrogen; when it is anodic, the scrubbing bubbles are oxygen. There is twice as much hydrogen produced as oxygen, so the cathodic cleaning action is better, but it raises the possibility of hydrogen embrittlement and the deposition of metallic smuts on the work. So cathodic followed by anodic may be best.

Electroacid: The important rule here is that you can only properly plate on an activated surface, so you do not want to end the acid cycle on a phase where the part may be passive. I think that means the work should be cathodic.

However, don't forget that electroplating is an incredibly complicated process if you try to scientifically take every little detail into account. So there is a lot of empirical knowledge involved in the process. You may never resolve the science of how many seconds of this and how many seconds of that; you may have to just go with what works, and just hold those parameters.

Regards,

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

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You can get some guidance from books on plating that include prep steps.
I think that you have a poor engineering setup with Inconel being considerably more difficult to activate than the steel.
You run the risk of over activating the steel or under activating the Inconel.
I like ending on cathodic as the tank retains a charge after the current is shut down and actually reverses and the part become anodic for a second or two. The use of current requires that you have a much less contaminated tank than a simple no current or it will deposit trash during the cathodic cycle. I would experiment with a scrap part to see what might work best for you.

James Watts
- Navarre, Florida
October 24, 2008