Neodimium magnets

[Nellysdad]

We have a couple of our neodimium magnets plated in Nickel. ASTMB633
We need a test for our receiving inspection other than the std "peel test" to test for adhesion, which does not appear to catch all the discrepant parts. Any ideas are welcome.
Regards

 

[IRstuff]

Could you elaborate as to how they are discrepant?

TTFN

 

[Nellysdad]

Sure,
we have a test where we score the sample part with a knife and press some sticky-tape on there and then we rip the tape off...fairly basic really, but it does identify some bad batches.
Later on,in service, we see peeling occuring, that was not apparent at receiving inspection, even with this test.
regards

 

[MagMike]

Do you know what is causing the parts to peel in service? Is there sub-plating corrosion, or is there something mechanically causing the peeling? Typically if the plating is not disturbed, it will provide sufficient protection.

I've found that nickel, or any metallic plating on Neo magnets, does not have high adhesion strength. Once the surface is scored it tends to peel off fairly easily. I have tried to find a measurement of the adhesion strength, to no avail.

 

[sreid]

I too have experienced "Bad" nickel plating on Neo magnets (and I's not a pretty sight when a motor rotor slings a magnet). In your application could you use a polmer coating as offed by MCE. I've never had a problem with that coating and it costs less.

 

[IRstuff]

The defense industry has had some variable experience with nickel plating of NdBFe magnets. As mentioned above, adhesion requires a buffer layer prior to Ni deposition.

Additionally, the Ni plating is quite tricky. Many plating houses like "shiny" Ni, but that usually implies a harder Ni that tends to crack when the magnet is subjected to temp cycles. You should check to see if there is any hardness variation in the plating.

TTFN

 

[EdStainless]

I believe that what we used was called Paralene. It was developed to protect electronics in severe environments.

We did a lot of Ni work. Ended up with a copper flash and then electroless Ni, with very low P.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[MagMike]

Parylene is a fantastic coating for corrosion protection. I spec it in whenever I can. It is conformal (no "dog bone" effects on the edges) and very, very thin, allowing for tight tolerances on magnet dimensions.

However, it has a low coefficient of friction so it can be a challenge to bond a parylene coated magnet into an assembly.

 

[MagMike]

NellysDad:
Just had a thought: Are you doing your peel test on the parts while they are magnetized? If so, it's possible that the magnetization is helping the otherwise discrepant parts hold onto the plating a bit more strongly (nickel is ferromagnetic and thus attracted by a magnet). It might help improve accuracy to work on parts in the non-magnetized condition.