Q. We plate brake pistons with nickel (sulfate/chloride) followed by chromium. Some of the parts have “voids” and “nodules” in the nickel-plated layer. Any suggestions?—B.S.
A. Based on the additional information you provided me, I suggest you consider a number of things to try to solve the problem. I would start out by trying to get better control of your bath. I believe that testing once a month is not adequate for good nickel plating. For example, the bath analysis results you sent me show your pH to be on the high side and most of the bath components to be on the low side, so I suggest more frequent testing.
I also recommend that you start using a Hull cell if you are not already doing so. Hull Cell panels can be very helpful in diagnosing the “health” of the bath. In addition, thesel panels will help you “forecast” what may go wrong in the bath if you don’t make corrections.
The solution to your specific problem most likely has to do with cleanliness of the substrate surface and your bath. “Voids” in the plated surface are usually caused by the surface not being as clean as it should be. While your cleaning process sounds more than adequate, your problem could very well be small amounts of oil on the surface of your plating bath. Sometimes this oil is camouflaged when you have a layer of foam on the surface. You should revisit your cleaning process. If you are plating cast iron or materials of this type, you can have problems if you take short cuts in
The nodules you describe may be caused by particulate matter suspended in the plating bath. This problem usually can be resolved by improving your filtration process.
Finally, I recommend you start keeping simple written records of when your problem occurs. This will help you determine any patterns to your problems.