Demagnetisation of ferrite magnets
Cristian, Wed Jun 21 2017, 05:22AMHi!
I'm not able to find big ferrite cores in my country (Chile) and now import of other country is not an option, so i'm courious if it's posible to demagnetise the ferrite magnets (for example, heating up to the courie point) and use it as normal ferrite core.
I found this video http://www.youtube.com/watch?v=ZcLSLdd3Q5w
Testing the heating in neodimiun magnets, when they glow red, they lose its magnetics propieties, and can't return if you try to use a coil to that.
But i'm not sure if that lost of magnetics properties is permanent. So, you can't no longer use as magnet and still like ferrite core?, or it's mean that it's internal composition changed and can't be use neither like a magnet nor like a normal ferrite core ?
Here is the biggest ferrite core that i have found until now, and a ferrite magnet that i want as core
Thanks for help!
Re: Demagnetisation of ferrite magnets
johnf, Wed Jun 21 2017, 06:33AM
no
Even demagnetised magnets do not have the same properties of power ferrites.
To get some for your projects you need to find an aircon company and befriend them.
Modern aircon (inverter type) have a host of good ferrite cores in the control electronics.
Other good things include solid state motor drives again a good source of unobtainium
johnf, Wed Jun 21 2017, 06:33AM
no
Even demagnetised magnets do not have the same properties of power ferrites.
To get some for your projects you need to find an aircon company and befriend them.
Modern aircon (inverter type) have a host of good ferrite cores in the control electronics.
Other good things include solid state motor drives again a good source of unobtainium
Re: Demagnetisation of ferrite magnets
Dr. Slack, Wed Jun 21 2017, 12:47PM
The key difference is that transformer ferrites are 'soft', they have a small hysteresis loop, the smaller the better, and a lot of research goes into making it small, smallest loop materials command a premium price. Small loop is necessary as the energy lost per cycle of magnetisation appears as heat in the core.
Magnet ferrites are 'hard', they have a very large area hysteresis loop, the bigger the better, and a lot of research goes into making them big, big loop materials command a premium price. Big loop is necessary so that they continue to generate a magnetic field, even in the face of a large demagnetisation field. Having demagnetised a ferrite magnet, it's possible to remagnetise it again. The largest loop materials will take the most energy to remagnetise.
Dr. Slack, Wed Jun 21 2017, 12:47PM
The key difference is that transformer ferrites are 'soft', they have a small hysteresis loop, the smaller the better, and a lot of research goes into making it small, smallest loop materials command a premium price. Small loop is necessary as the energy lost per cycle of magnetisation appears as heat in the core.
Magnet ferrites are 'hard', they have a very large area hysteresis loop, the bigger the better, and a lot of research goes into making them big, big loop materials command a premium price. Big loop is necessary so that they continue to generate a magnetic field, even in the face of a large demagnetisation field. Having demagnetised a ferrite magnet, it's possible to remagnetise it again. The largest loop materials will take the most energy to remagnetise.
Re: Demagnetisation of ferrite magnets
kimbomba, Thu Jun 22 2017, 04:06AM
One of the best answers I've read in the forum
kimbomba, Thu Jun 22 2017, 04:06AM
One of the best answers I've read in the forum
Dr. Slack wrote ...
The key difference is that transformer ferrites are 'soft', they have a small hysteresis loop, the smaller the better, and a lot of research goes into making it small, smallest loop materials command a premium price. Small loop is necessary as the energy lost per cycle of magnetisation appears as heat in the core.
Magnet ferrites are 'hard', they have a very large area hysteresis loop, the bigger the better, and a lot of research goes into making them big, big loop materials command a premium price. Big loop is necessary so that they continue to generate a magnetic field, even in the face of a large demagnetisation field. Having demagnetised a ferrite magnet, it's possible to remagnetise it again. The largest loop materials will take the most energy to remagnetise.
The key difference is that transformer ferrites are 'soft', they have a small hysteresis loop, the smaller the better, and a lot of research goes into making it small, smallest loop materials command a premium price. Small loop is necessary as the energy lost per cycle of magnetisation appears as heat in the core.
Magnet ferrites are 'hard', they have a very large area hysteresis loop, the bigger the better, and a lot of research goes into making them big, big loop materials command a premium price. Big loop is necessary so that they continue to generate a magnetic field, even in the face of a large demagnetisation field. Having demagnetised a ferrite magnet, it's possible to remagnetise it again. The largest loop materials will take the most energy to remagnetise.
Re: Demagnetisation of ferrite magnets
klugesmith, Thu Jun 22 2017, 05:57PM
My words exactly. Kimbomba beat me to it. Hats off to Dr Slack.
Back to OP.
Both classes of ferrite will be demagnetised by a temperature excursion above the curie point. As Dr Slack said, back at room temperature they will be just as softly or hardly magnetisable as before.
At some point, excess temperature and time will make permanent changes to the material properties. We can be sure the changes are not in a desirable direction. Otherwise they would be made at the ferrite factory, in a deliberate heat treatment process.
OP seeks a change that would generally be undesirable. But I agree with Dr Slack: it's hard to imagine a permanent magnet ferrite composition becoming magnetically soft enough to be good for transformers.
Among permanent magnet materials, NdFeB magnets have the widest BH loops and the lowest curie points of all. It makes the video demonstration (link in OP) very easy -- they start temporarily losing magnetic hardness long before the Curie point. It's one reason some electric motors use samarium-cobalt instead of NIB.
klugesmith, Thu Jun 22 2017, 05:57PM
My words exactly. Kimbomba beat me to it. Hats off to Dr Slack.
Back to OP.
Both classes of ferrite will be demagnetised by a temperature excursion above the curie point. As Dr Slack said, back at room temperature they will be just as softly or hardly magnetisable as before.
At some point, excess temperature and time will make permanent changes to the material properties. We can be sure the changes are not in a desirable direction. Otherwise they would be made at the ferrite factory, in a deliberate heat treatment process.
OP seeks a change that would generally be undesirable. But I agree with Dr Slack: it's hard to imagine a permanent magnet ferrite composition becoming magnetically soft enough to be good for transformers.
Among permanent magnet materials, NdFeB magnets have the widest BH loops and the lowest curie points of all. It makes the video demonstration (link in OP) very easy -- they start temporarily losing magnetic hardness long before the Curie point. It's one reason some electric motors use samarium-cobalt instead of NIB.
Re: Demagnetisation of ferrite magnets
Cristian, Thu Jun 22 2017, 08:38PM
Thanks to all, I had not thought about the BH curves and the specific use of both types of ferrites
I'll try to scavenge some electronics and try to be lucky to find ferrite cores
I want to make an induction heater with resonance in series, so I need a coupling transformer with the inner diameter biger than the working coil pipe (approximately 7 mm in diameter). Perhaps one possibility is to use the flyback ferrite core, but the disadvantage is that between the core and the pipe will be a large space, and that could affect the coupling factor
it would works?
Cristian, Thu Jun 22 2017, 08:38PM
Thanks to all, I had not thought about the BH curves and the specific use of both types of ferrites
I'll try to scavenge some electronics and try to be lucky to find ferrite cores
I want to make an induction heater with resonance in series, so I need a coupling transformer with the inner diameter biger than the working coil pipe (approximately 7 mm in diameter). Perhaps one possibility is to use the flyback ferrite core, but the disadvantage is that between the core and the pipe will be a large space, and that could affect the coupling factor
it would works?
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