plated vs. unplated thread wear

[adtchad]

Hello all,
We have a number of brass (half hard)nuts that have been nickel plated that do not meet specs. We can re-tap them to meet those dimensions, but during that process the nickel platting will be removed. Does anybody have any data, or a reference, as to what the wear rate would be for both brass and nickel plated brass. I am trying to justify not throwing these nuts away. They cannot be re-plated because they have a plastic handle overmolded on them already.

Thanks in advance for your help.
Alfonso Del Toro
Chad Therapeutics, Inc.
Chatsworth, CA

 

[metengr]

What is the mating stud/bolt material? Also, the application?

 

[adtchad]

The nut is use in a compressed oxygen gas application and is a CGA-540. Its mating part is a CGA-540 Nickel plated brass male thread.

 

[metengr]

adtchard;
I believe the nickel plating is to reduce the chances for galling since you are joining like materials. The nickel plate is softer than brass and would deform to the thread profile during installation. Re-tapping the nuts sound like a good idea but re-using them without thread protection will probably result in galling over time.

For the re-tapped brass nuts can you use Teflon tape on the male threads to reduce galling? I am not sure if you have any specific requirements that force you to revert to using Nickel plating. Also, have you checked or confirmed with an electroless plating company that re-plating cannot be done after tapping? I have seen electroless nickel plating kits.

 

[adtchad]

metengr:
Thanks a lot for your inputs. Unfortunately, we cannot use teflon tape since this nut handles are designed for multiple engagements. I will contact our supplier about electroless plating and see if that is a viable route. Again, thanks a lot for your help.

 

[israelkk]

You should use oversized taps that are designed such that the added thickness of the coating will not make the thread smaller than it should be.