Summary for flash chrome plating Discussion
Flash chrome plating on C-276 Hastelloy threads was failing because the alloy likely passivates very quickly, not simply because of its nickel content. Brian Terry said the issue sounds like activation: after acid activation, plating must begin within about 2 minutes, and changing to nickel plating would not solve that if activation is still poor. He also warned that electroplated nickel can create galling problems, so medium- or high-phosphorus electroless nickel is preferable. SK Cheah agreed that high-nickel alloys need activation and suggested a Woods nickel strike before flash chrome; he also explained that any plating will change thread dimensions, with major and minor diameters increasing by about twice the coating thickness and pitch diameter by about four times. James Watts recommended electroless nickel for threaded parts, noting low-phos EN may be harder and can give good thread coverage with proper barrel agitation.
Q. Attempting to flash plate threads of a 2″ nut made from c-276 Hastelloy Stainless Steel and running into issues. When trying to flash them in house the plating would visibly flake off of the metal leaving nothing adhered. I sent it out to a local plating company, after three attempts and three failures I’ve been informed they cannot get the job done, sighting the nickel content of the metal may be too high. Does that make sense?
The alternative I have would be to Nickel Plate the piece. Does Nickel Plating alter the thread dimensions in any way? I.e. after plating will I still be able to thread the nut unto it’s mating part, I am dealing with a .03″ tolerance at best before running into sealing issues.
Any ideas/thought will be greatly appreciated.
–Dan
Dan Brueggemann
– Waukesha, Wisconsin
October 29, 2014
A. Hi Dan,
Sounds like you have an activation issue rather than a nickel content issue. High nickel alloys have a tendency to “passivate” very quickly, so after the acid activation step the plating will need to begin within 2 minutes.
If you were to change to nickel plating you would still have the same issue if the base material has not been activated properly and then processed within a couple of minutes of activation.
Nickel will build up just the same as chromium, so whatever thickness you specify for chrome should be the same as you would call up for nickel. The problem you will have is that if you call up electroplated nickel you will run into galling issues, you would probably need to call up as a minimum a medium phosphorus electroless nickel, or more preferably a high phosphorus electroless nickel.
Brian Terry
Aerospace – Yeovil, Somerset, UK
October 30, 2014
A. Dan,
1. High Nickel alloys need activation before any plating is done.The activation method is similar when plating on SS. You would have better results with a woods nickel strike before the flash chrome.
2. The screw thread dimensions will change once plating thickness covers the original surface. Theoretically, the major and minor diameter will increase by 2 times the plating thickness. The pitch diameter will increase by 4 times the plating thickness.
Good Luck.
SK Cheah
– Penang Malaysia
October 30, 2014
A. When dealing with threads, I would certainly go with EN.
Low Phos EN might be an option as it comes out of the tank harder than the other ENs do. You may be able to skip the bake, depending on the hardness of the nut.
You can get good coverage in the threads with EN run in a barrel with the holes in the drum enlarged for better solution flow and with heavy air agitation
⇦ huh?
directly under the drum.
James Watts
– Navarre, Florida