Magnets

[frosch45]

I'm not even sure if this is where this thread belongs, but here goes.

 

A few months ago I baught a Neodium manget. Worked great when I got it, really strong, but now, it can barely lift a pound where as before it could lift 80!

 

I think I remember reading somewhere that magnets lose their power over time? Is there any way that I can recharge my magnet? Its just a cylindrical neodium manget about 2" tall and 1" diameter.

 

I won't pretend to know what I'm talking about though.

[insane_alien]

did you bash it or heat it up a lot? that can cause them to lose power.

 

theres no way to recharge them without melting them down and resolidifying in a strong magnetic field.

[frosch45]

nope, no bashing or anything. It was wierd, it just kinda got weaker over time.

 

I couldn't run a strong current through it or anything?

[Klaynos]

nope, no bashing or anything. It was wierd, it just kinda got weaker over time.

 

I couldn't run a strong current through it or anything?

 

Nope, as IA said the easiest way is to melt down and use a magnetic field or a REALLY powerful magnetic field but it has to be very very strong...

 

It is surprising it's lost it's field so quickly though, what've you used it for?

[frosch45]

well, I got it in like october or something, I used it to help me make ferrofluid and other small projects, other than that, I basically touched it to every single metal within arm's reach for about two weeks...

 

I did notice a slight loss of power after that period, and I guess it just continued.

[Klaynos]

Very odd... I'd only expect it to deteriorate that quick if there was a strong opposing field in the area...

[frosch45]

The wierdest part was that I kept it in a place that was one foot away from any other metallic object.

 

Maybe the paint on my wall has metal in it or something....

[alan2here]

I suspect you heated it up by accident.

 

Maybe you attached to to a radiator when it was on. You can get NIB magnets that are designed to get hot if you need that.

 

Bashing is not generally a problem as by the time you are hitting it hard enough to do any damage you are chipping bits off the outside. Similarly leaving it near another magnet is not a problem unless you are measuring loss of field strength in decades, you should leave them attached with a metal surface on ether side or in the open if you want optimum lifespan.

 

What is that about current?

 

What was the original strength in the measure "N"?

Edited August 12, 2008 by alan2here

[swansont]

I think alan2here is right — from what I can glean the Curie point for this type of magnet can be as low as 80 ºC

[frosch45]

I'm apsolutely positive that I didn't heat it up more than in my pocket, but that was more than 80 degrese...

 

it was rated N45

 

I do remember once I left it stuck to a metal chair all night, and in the morning it was a little bit weaker

 

here is actually the exact place where I got it

 

http://cgi.ebay.com/1-x-2-N45-Rare-Earth-Neodymium-NdFeB-Cylinder-Magnet_W0QQitemZ360077698744QQihZ023QQcategoryZ53142QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Edited August 12, 2008 by frosch45

[insane_alien]

I didn't heat it up more than in my pocket, but that was more than 80 degrese...

 

you're body temperature is more than 80*centigrade??? how are you living? do you notice people burning themselves when they shake your hand?

 

i think you missed the *C part in swansonts post. that and we tend to use SI here, not imperial.

[frosch45]

hahahahahahaha lololol ROFL

 

oops

 

I was thinking about the customary Fahrenheit

[Pete]

Nope, as IA said the easiest way is to melt down and use a magnetic field or a REALLY powerful magnetic field but it has to be very very strong...

Why is that? If it was placed inside a a very strong magnetic field, e.g. inside a coil which when a current is applied, then the it should be possible to magnitize the magnet again. Then again that depends on the hysteresis curve of the material. I imagine that would be very hard to do though given the strength of the field that needs to be applied.

 

This web site - http://www.duramag.com/neodymium.html - states

Most magnet materials are machined in the un-magnetized state. Once the fabrication and cleaning operation are complete the magnet is then magnetized to saturation.

 

Pete

Edited August 15, 2008 by Pete

[Think it thru]

I don't know if you need a certain shape of magnet for your applications but there are strong magnets in computer hard drives which can be gained for free much of the time. They'll certainly bite you if you get skin between two of them.

[Klaynos]

Why is that? If it was placed inside a a very strong magnetic field, e.g. inside a coil which when a current is applied, then the it should be possible to magnitize the magnet again. Then again that depends on the hysteresis curve of the material. I imagine that would be very hard to do though given the strength of the field that needs to be applied.

 

This web site - http://www.duramag.com/neodymium.html - states

 

 

Pete

 

You alter the hysterisys loop when you heat it so you need a less powerful field to flip all the domains.

 

So doing it at home where nice big electromagnets are hard to come by heating and doign it is better, if you melt and solidify in a magnetic field you get alignment far easier.

[Pete]

You alter the hysterisys loop when you heat it so you need a less powerful field to flip all the domains.

From the OP's comments it doesn't appear that it was heated to an extent that would alter it to a significant extent.

So doing it at home where nice big electromagnets are hard to come by heating and doign it is better, if you melt and solidify in a magnetic field you get alignment far easier.

Seems to me that melting and solidifying a magnet in that way is just as unpractical.

 

Pete

[Klaynos]

From the OP's comments it doesn't appear that it was heated to an extent that would alter it to a significant extent.

 

Seems to me that melting and solidifying a magnet in that way is just as unpractical.

 

Pete

 

Melting yes but heating no.

 

And as to your first point we were talking about ways to remagnitise it.

[Pete]

I never assumed that heating it would present a problem (depending on what temperature it melts at that is). Its the melting that can be difficult since it'd have to be melted and poured into a mold, each of which would have to be able to withstand the heat.

 

As far as how to remagnetize then one can do so using a a very strong electromagnet. That's how they are magnetized in the first place, i.e. after the magnets are created/formed they are then magnetized. What advantage to do think there is in melting it first??

 

But it'd be much much easier to simply buy a new one.

 

Pete

[insane_alien]

handling extremely hot liquids isn't so difficult with a bit of practise, i've learned a lot about it from my volcano.

 

as for the advantages of melting it, it allows easier alignment of the crystal structure than forcing them to realign when solid. this means your electromagnet doesn't need to be as powerful for the same effect.

[swansont]

Melting wouldn't be necessary.

 

Heating with the proper thermal cycle so the best crystalline structure is formed to allow the domains to add most efficiently.

[Pete]

Melting wouldn't be necessary.

 

Heating with the proper thermal cycle so the best crystalline structure is formed to allow the domains to add most efficiently.

I imagine that was already done when the magnet was created in the first place.

 

insane_alien - What kind of temperatures are you talking about? What is the melting temperature of the material that a neodium magnet is made of?

 

... this means your electromagnet doesn't need to be as powerful for the same effect.

I can't see how you'd magnetize the magnet to a particular field strength unless you have a magnetic field that is at least that strong (usually stronger is required).

 

Pete

[swansont]

I can't see how you'd magnetize the magnet to a particular field strength unless you have a magnetic field that is at least that strong (usually stronger is required).

 

Pete

 

If you're heating the material you don't have to do as much work to "unstick" some domains, since the thermal energy has done that for you.

[insane_alien]

I can't see how you'd magnetize the magnet to a particular field strength unless you have a magnetic field that is at least that strong (usually stronger is required).

 

yes, you do need a magnet at least that strong but the difference is in you need a magnet say 20% stronger for a liquid and for making it with a solid you need it 60% stronger than your target.

[Pete]

yes' date=' you do need a magnet at least that strong but the difference is in you need a magnet say 20% stronger for a liquid and for making it with a solid you need it 60% stronger than your target.

[/quote']

I'd like to read more about this. Where did you obtain this information?

 

Reagarding what I quoted above

Most magnet materials are machined in the un-magnetized state. Once the fabrication and cleaning operation are complete the magnet is then magnetized to saturation.

Why would manufactures do it this way if they can obtain a stronger field otherwise?

If you're heating the material you don't have to do as much work to "unstick" some domains' date=' since the thermal energy has done that for you.

[/quote']

I was speaking about a magnet which was already manufactured and magnetized, as is the present situation. How would the domains because "stuck" in the 'wrong' position after manufacturing and magnetization? How are they aligned when melted? I assumed that domains are aligned when the magnet is magnetized. Is that not true?

 

Pete

[insane_alien]

I'd like to read more about this. Where did you obtain this information?

 

i made those numbers up to illustrate my point that liquids align easier and to get the same field strength in the same amount of time you need a stronger magnet when it is solid.

 

Why would manufactures do it this way if they can obtain a stronger field otherwise?

 

i believe there are physical limits to the strength of permanent magnets and it is really difficult to machine already magnetised parts as the shavings stick to everything.