44041

Nickel or Copper plating of internal threads [UK] 

February 16, 2007

One of our Graduate Engineers has been set the task of evaluating whether the internal threads of steel fasteners could be built up by plating in Nickel and Copper, and then machined back to the required thread form while retaining sufficient strength to achieve a set pull out test.
Internal diameters are in the order of 17mm.
I understand that proximity to the electrodes determine the amount of deposit, so do you think this is possible?
How would the plating contractor achieve as uniform a coat as possible so as to reduce the necessary machining to a minimum? or would the deposit be concentrated on the thread crowns etc? Could he shape the electrode, or would adjusting the voltage etc be of benefit?
Regards,

Martin Rich
Ship Repair - Plymouth UK

I am very confident that very substantial pull out strength could be achieved with electrolytic sulphamate nickel plating. But the "then machined back" proviso of your inquiry is critical. There is no way to not substantially distort the threads in this plating process. The critical thing would seem to be that you must plate thick enough to achieve at least the required root diameter on the thread. Whether your tap could then follow that root diameter to restore the original thread is a question though.

Ted Mooney, P.E.  finishing.com Brick, NJ

Steel, copper and a marine environment is a very bad combination.
Both electroplated copper and nickel will build up on the thread points and jigging an internal anode on each 17mm part will be costly and not solve the problem.
The answer seems to be electroless nickel. Good corrosion resistance, no build up and the thickness can be controlled so machining back may not be needed.
There should be a plating shop in your area with this process.

Geoff Smith Hampshire, England

There is no doubt that electroless nickel would be much easier and would deposit much more evenly than electrolytic nickel, Geoff. But the same could be said for painting the holes or chocolate dipping them :-)

The thing is, electrolytic nickel has been long and widely used for load-bearing repairs of all sorts, and to fabricate load-bearing electroforms. And my question is whether we can trust electroless nickel plating as a load bearing element? I personally don't know and would appreciate hearing if anyone has experience in this.

Ted Mooney, P.E. 
finishing.com
Brick, NJ

Electroless nickel is widely used in the offshore oil and aerospace industries, particularly on threaded parts. It can be hardened to 1000VPN. The geometry of a threaded joint imposes mainly compressive stress to any coating.
On the other hand - chocolate tastes much better.

Geoff Smith Hampshire, England

A good one this. One of the problems is getting adequate adhesion of the plating material onto the threads; since it is the internal thread of the fastener, I presume we are talking about the nut and not the bolt. The first stage is to ensure the thread is adequately cleaned - this could be a problem if the nuts are well used. Secondly, you need sufficient adhesion and pull strength; this will be dependent on the level of cleanliness achieved as well as the type of metal being deposited. Finally, there is the problem of getting the thread to be an exact replica of the orginal and to do this you will need to retap the thread. If you decide to go on an electrolytic route, you will need an internal anode to ensure good enough distribution - you will also need very good agitation to get the deposit in the bottom of the threads. However, if you use electroless nickel, you won't have these problems. It will be difficult to retap copper without some galling and retapping nickel can be horrendous - have you ever tried to saw through a lump of nickel- it work hardens at an alarming rate. Nickel will also gall. I do not knwo if electroless nickel is easily machinable as I have never tried it, but all things considered, I would have my first go with that - probably medium phos nickel. You could also try an electroless nickel-PTFE composite to give it some lubricity.

Trevor Crichton R&D practical scientist - UK

Threaded inserts are sounding better and better :-)

Ted Mooney, P.E. 
finishing.com
Brick, NJ

Hi,
I know that some of the companies who were originally using hard chrome on cylindrical parts now use electroless nickel. They were grinding off hard chrome to get to the right dimensions so same may be true about electroless nickel.
I think electrolyte sulphamate would serve the purpose but then you will have highs and lows of thicknesses on tips and bottoms of the internal threads. Getting auxiliary anodes for a 17mm part will be tough.
Electroless nickel with PTFE should be the first call...

Thanks

Hemant Kumar
- Florida, USA

Certainly electroless nickel is the right choice for the job under reference. We can have uniform build up of the thickness.areas where where the coating is not required also can be masked. no buisiness of auxilary anodes. also upon baking the hardness also will be incresed and is on par with the hard chrome plating. electroless nickel is replacing hard chrome in many load bearing applications. we practically used electroless nickel for salvaging applications and the machinability is quite good.

STG.S. RAMANUJAM
- Hyderabad, A.P, INDIA