Q. Our company does a lot of bright nickel plating. One area that we have problems with is the barrel nickel plating of parts that have somewhat complex geometries. For example, the nickel plating on the inside of some parts becomes dark after drying. Raising the current density and reducing the load sizes seems to reduce but not eliminate the darkening. Another problem is the formation of a yellow film on the walls of the plating tank. Can you comment on these issues? M.L.
A. After receiving your question, I remembered that I answered a similar question a number of years ago (To be exact: 1996). All this demonstrates that many plating problems are not one-time events but are cyclical in nature! Here is what I wrote:
There are a number of areas to investigate in trying to solve your problem. The area of the part that becomes dark after drying is a low current density area. Usually this is a sign of metal impurities such as zinc, copper or lead in your bath. Is there anyway these metal ions could get into the plating bath? The best way to remove these impurities is to dummy the bath with corrugated cathodes at 3–5 amps/sq ft for at least eight hours.
You also mention the problem of a yellow film being present on the walls of the plating tank. This could very well be iron, which can also give the same symptom. The best way to remove iron is to raise the pH (5.2–5.6), treat with nickel carbonate, add peroxide (one mL per L of 30% peroxide), agitate for two hours at 120°F and then filter. Readjust the pH after filtration. Before trying this procedure on the entire plating bath, test it with a small sample.
You do not mention anything about performing chemical analysis of the plating bath. This is something that is an absolute must in today’s world of electroplating. You should be analyzing for “tramp” heavy metals on a regular basis.
Another thing to consider: Your brightener system may be present in excessive concentration. Sometimes this will cause dull, dark deposits in low current density areas. Yes, there can be differences in performance between different brightener systems, but I doubt changing brightener systems will make a dramatic difference.
If iron is the problem, putting the barrel in “hot” may also help.
I have e-mailed you a copy of the Nickel Tank Doctor, which should help you with troubleshooting your nickel plating baths. Note to our readers: If you are interested in receiving a copy of this troubleshooting guide for bright and Watts nickel plating baths, e-mail me at firstname.lastname@example.org.