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Q. We have had a problem with our acid nickel bath for more than a year. What was once a bright nickel color is now a gray color, although it still looks bright. When we set the rectifier to the correct amperage for the load, the parts appear to burn. Also, we can only leave the parts in for about 1 to 3 min or they will start to turn black and smoky-looking. Any suggestions as to what the problem might be? S.B.
A. There are a number of possible reasons for the problems with your bright nickel plating bath, including:
- The current is too high for your plating load.
- Zinc, copper or lead is present in your plating bath.
- Iron is present in your plating bath.
First, check the current density for a given load of parts. It never hurts to recheck your calculations. Then perform a complete analysis of the bath, paying particular attention to heavy metals: zinc, copper, lead and iron. If any of these metals are present, you should dummy the plating bath, which will remove the zinc, copper and lead. You should dummy the plating bath on a regular basis.
Removing iron from the bath is a little more complicated. Although this is a somewhat messy process, iron can be removed by raising the pH of the bath using nickel carbonate, adding peroxide and filtering. It is critical that you completely remove the solid material that forms after this treatment. Adjust the pH of the bath after the filtration and see if your results have improved.
I always suggest that before you add any new chemicals to your plating bath you perform this test on a small amount of material. In a case like this, I suggest you plate a Hull cell panel with a sample of the plating bath prior to treating the bath. After performing the treatment and re-acidifying the sample, perform an-other Hull cell test to see if your results have improved. If the sample now gives you a bright deposit that meets your specs, you should proceed to do your entire plating solution.