Troubleshooting a Nickel Bath: Zinc Contamination

So it’s happened; someone accidentally added zinc anodes to the nickel bath. What can you do? Well, the easiest and most expensive option is to just dump the bath and make it up fresh. While this is a great way to ensure your sales representative remembers you come Christmas time, it won’t put you on your boss’ good side. Instead, you can opt to either dummy plate or complex the zinc metal out of solution.

Dummy Plating

Let’s take a look at dummy plating, and I’m not referring to when you have the new guy try to plate some parts. Dummy plating is a process by which we can remove unwanted metals from a plating solution. In the case of our nickel bath that has been contaminated with zinc, we will need to do some low current density plating. We can achieve this by using a corrugated steel cathode and turning down the amps on the rectifier. I personally would recommend running the dummy plating process at a current density of 2-5 asf. (side note: for help calculating current density, check out our app available on both android and iOS) Once an hour you should increase the current density to about 40 asf for 5 minutes or so. This will “lock” the zinc onto the cathode, and should prevent the bath from stripping the zinc off as fast as it is plated on.

Bear in mind that it is critical that you dummy plate at a low current density (LCD) to remove zinc. Zinc plates at a much lower current than nickel does, and LCD ensures that we plate more of the zinc than nickel. The pulse to high current density (HCD) is to ensure that the zinc is not stripped off by the nickel bath. Without the HCD pulse, you may reach a point in the process where you don’t seem to be removing any more zinc, but still have a lot of zinc contamination.

Complexing the Zinc

Another good option you have is adding a product to the bath to complex out the zinc. When you combine this with dummy plating, you can get your nickel bath back up in running in a very short amount of time. But what does it mean to complex zinc? First, let’s discuss what zinc contamination looks like in a nickel bath. Zinc will plate out in the LCD area of a part, and will have a dark/black appearance. This is unsatisfactory for most people. By complexing the zinc, we remove the dark appearance in the LCD. This is beneficial because it allows us to return to plating production parts without having to remove all of the zinc via dummy plating. While the zinc is still present in the LCD area of the parts, it is not affecting the outward appearance.

If you find yourself dealing with zinc contamination, contact your Asterion sales rep for a quote and operating instructions for the appropriate zinc complexing agent for your process. And remember to check out our app, which includes several useful calculators.