Nickel Sulfamate Plating Problem: Adhesion Is Poor

A. Jennifer,

Could you describe the cleaning steps prior to the Woods strike and also the current density and time in the strike? Also if you had access to some ferroxyl solution apply some with Q-tips ⇦ this on eBay or Amazon [affil links] to an area that peeled and if it turns blue that will tell you the adhesion failure is between the base metal and the Woods strike. If it doesn't that will tell you the failure is between the strike and the sulfamate tank. Other things to look at would be stress in the sulfamate deposit. Is there excessive transfer time between the strike and the sulfamate bath? I personally don't think the high metal is the problem. There are test strips for Nitrate contamination that most good lab supply companies have. Hope this helps.

A. Tank 1 is too high in chloride which causes the metal to dissolve too fast and increase in concentration, also high chloride cause high stress (which in the case of poor surface preparation will peel right off)

Tank 2 you got too hot, that caused the sulfamate radical to break down and form ammonium ions which cause brittleness which in the case of poor surface preparation will flake right off.

I suspect your "Woods Strike" has crept up in nickel concentration because you do not remove the anodes when not in use. As the metal rises in a low efficient hydrogen scrubbing nickel strike bath it converts to a high efficient nickel plating solution and will not activate stainless steel. Dump it and start over with 32 av oz per gallon of Nickel Chloride plus 32 fluid ounces of Hydrochloric acid AND TAKE THE ANODES OUT WHEN NOT IN USE !

A. Two excellent advises. I would only add that, if you're not doing it yet, you should analyze stress in the plate with a contractometer. Inner diameter needs a slightly compressive stress to push a little bit against inner walls, while the outer one would benefit if slightly tensile. This can be tailored in your same bath with a little experience. For more details, you may want to contact the Nickel Development Institute. They can send you copies of very informative technical papers.

A. Jennifer,

Mr. Probert is certainly right, but check also your cleaning and activation processes. Out of my experience, when one has trouble with adhesion, the culprit lies in most of the cases in the preparation, especially when plating turbine shafts.

A. You left out a few things. what temp and ASF are you striking and plating at? How high did tank two get? Tank makeup / limits is governed by the OEM who built the part and has the repair process. Having three OEM's to placate, I combined the three and took the resulting most critical (restrictive)limits. I assume that you are waxing this part. Will it pass a water break test after the caustic clean rinse? Are you using pumice? If so are you getting it all out of the edges of the wax. If there are a few particles left and you are doing a heavy build, it will grow huge nodules. If you have huge nodules and the machinist cuts from the outside in, you have a good probability of tearing the plate. This force combined with a poor or marginal adhesion is enough to make it come off as a ring. The machinist can help by taking smaller cuts, working from the center to the outside until the bulk of the nodule is removed. Another evil that the nodules cause is an interrupted cut. This is a high demand on the plate.

Next, what are you using for anodes in the Woods Nickel. I had adhesion problems using nickel rounds, especially when the tank started to smell. My preference was for rolled depolarized nickel anodes which do not have to be pulled from the tank except in several days of projected non use. I found that my nickel growth rate in the woods tank increased as the amount of nickel increased. I did my makeup with near the low end of my range of nickel and used 3/4 of my allowable HCl range. The high acid low nickel worked the best for me. This affected how well the strike held and sure seemed to make the sulfamate stick better to the strike. This may be because it made me feel good and was not a reality. I tried to strike at 80 ASF as the optimum is 100 ASF, but falls like a rock above 110 ASF.

You do not mention your acid etch or the type of SS. That makes a huge Difference. If it is not activated, it can not stick! Reduce your transfer time from the strike to the sulfamate nickel.