Nickel Plating Repair
Q. We are a manufacturer of parts used in the Aerospace industry. My situation is as follows: We have components, (silicon iron substrate), sent out for electroless nickel plating. During final assembly these plated components have a tendency to get damaged or chipped plating because of handling issues. These chips are extremely small, but big enough to expose the substrate material, hence corrosion. I need to repair these chips with brush plating since they cannot be submerged in a bath. I have been experimenting for several weeks now with brush plating and various nickel solutions. I cannot get my experimental parts to pass a salt bath. I have been experimenting with voltage settings, activating solutions, surface preparations with alcohol, plating time etc. I cannot blast the chipped areas either because they are assemblies.
Does anyone have any information or suggestions on what I can try to get this process to work. I am at a loss. I have contacted the companies where I purchased the equipment and have tried what they suggested. Can small chips be repaired with brush plating?
Thanks a lot.
A. I see two different problems. The silicon present in the substrate requires Hydrofluoric acid not found in brush activators that must be safe for hand use (HF is so dangerous that will penetrate skin and destroy bone). The other is the EN itself, which is also very difficult to activate for it tends to develop a dark smut during reverse etch and will never present a grainy microstructure to provide anchorage. My opinion would be to strip the whole plating and do it again, probably using a more ductile plate such as a sulfamate nickel. It will pass a salt test and will not chip. Brush plating companies also offer other chemistries not based on sulfamates.Guillermo Marrufo
Monterrey, NL, Mexico
I really appreciate your response, thank you. I need to find a solution that would allow me to replate the tiny chipped area without stripping the existing EN plating. The brush plating companies are telling me that their products will work, even though I have informed them of the silicon iron substrate. I've even sent them some experimental parts to repair. Is it even possible to repair these parts with brush plating and have them pass a salt fog or salt bath test. Since I do not have much experience in plating yet, I'm not sure I follow exactly what you are saying.
To activate a EN deposit. First no pretreatment steps can be done with a anodic current. Then you use a acid with a anodic current will the EN deposit expose the phosphorus contents. To activate the EN is to use a cathodic current in 30-40 g/l Na Cn for 2 minutes. Rinse in 10 % chloride acid. Cathodic activation for 5-15 sec or to see if the gassing 3,5-4 volts in a clean 30 % sulfuric acid. Activate in a warm nickel activator. With brush nickel method is to use citric acid together with hydrofluoric acid. Remember never a anodic pretreatment.