magnetize ferrite with rare earth PM - energy? 4

[RyreInc]

We're looking at magnetizing a small bonded ferrite magnet using sintered neodymium magnets. It looks doable, but I'm confused about the energy aspects of this system.

Looking at the max energy products, bonded ferrites are roughly 1.5MGOe, while N52 magnets are 52MGOe. Multiplying through their respective volumes I get energies of 7mJ for the ferrite part and 13J for the neo magnets, a ratio of about 20kJ/J.

Of course this is a simplification as neither will be operating at their maximum energy potentials, but what else is missing here? Does this imply that this system will demagnetize the neo magnets over (very roughly) 20k parts?

The magnetizing system I've drawn up in FEA utilizes a steel yoke and has a relatively small air gap, and it appears that the neo magnets are operating at a good permeance coefficient and are not at risk of demagnetizing... is this not the case?

 

[MagMike]

Don't go by energy product. The magnetic field output of the N52 magnets in the magnetizing fixture (as an assembly) needs to be compared to the coercivity of the bonded ferrite material. As a general rule of thumb, the magnetic field produced by the magnetizing fixture needs to be at least 3x the coercivity.

BTW: NdFeB magnets are oftentimes used to magnetized flexible ferrite strip material. With the correct configuration, it should work for your bonded ferrite magnet.

 

[RyreInc]

I understand that I need to generate a certain field strength to saturate the ferrite.

My question is essentially, where does the energy come from? Does the energy transfer from the magnetizing system to the part as it's magnetized? (It has to come from somewhere...) Does this energy transfer slowly demagnetize the neo magnets?

 

[ndsram]

Try to place the bonded ferrite magnet on one pole of the N52 and try to impact other N52 magnet onthe other pole of the ferrite magnet so you do like some impulse flux flow through the ferrite magnet.

I have never done this, but I feel this shuould work to magnetize the ferrite magnet. Take care that your impact should not physically damage neither of the magnet both ferite and NdFeB

 

[RyreInc]

ndsram, that would not work, and is unnecessary anyways. Also, it doesn't address my questions.

I already have a solution to create the necessary field strength from PMs, just wondering about energy and longevity.

 

[MagMike]

You will not slowly demagnetize the Neo magnet. The NdFeB produces a magnetic field, not energy. The energy transfer comes from the motion of bringing the Neo magnet close to the ferrite.

 

[IRstuff]

MagMike already addressed your concerns. There is no conservation of magnetism involved. Unless you have an antagonistic field opposing your PMs, or your whack them or have them in a high temperature environment, they should have no problems. The energy product is a measure of how much energy it would take to demagnetize the magnetic, but you need to have an opposing field to make that happen. Your ferrite will never be configured to oppose the PM's field, and even if you do, the PM's field would override that of the ferrite, since the PM's field is much stronger.

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[MagBen]

Thanks MagMike for your answer.
I had the same confusion as RyreInc did not long time ago.

b.t.w., permeance coefficient is unlikely a factor to affect demagnetization for RE magnets since normally the B-H curve is a straight line. It does matter for AlNiCo magnets where the intrinsic and normal B-H curves are similar, and non-linear.

 

[ndsram]

You need not to worry about the longevity of the NdFeB Magnet (magnetic field). Because you need 3x times the Coercivity of the NdFeB magnet to demagnetize. Here the energy of the N52 magnet will also remain undisturbed.

On the Ferrite magnet, the impact of the magnetic field of NdFeB magnet will influence. If you place the ferrite magnet between 2 magnets of 2 pole of N52, you can see the impart of magnetism in the ferrite magnet however it may not be saturated.

While you give some dynamism for the N52 magnet and subject your Fe magnet in the field of N52 dynamism, then your Fe magnet would magnetize sooner.

If you compare the spec of BH of Fe & N52, you may see Fe magnet is much lower (around 30 times) to N52 magnet.
On the Ferrite magnet under magnetized condition, and if you disturb the Fe magnet with N52, your magnetism of Fe will be disturbed.

 

[RyreInc]

Thanks everyone, especially MagMike, for your replies. In hindsight is seems almost obvious that it is the physical movement of the part into the magnetic field that provides the source energy to magnetize the part.

MagBen's comment is enlightening as well, but I will have to take some more time to fully wrap my head around that.