magnet in harddrives

C

Chiropter

Guest
If you have taken an old harddrive into parts, you probably found
magnetic plates which are a part of the mechanism to control pickup
arms. I found them carrying extremely strong magnetism for their small
size. I never saw such a strong magnet before. Can somebody tell what
kind of alloy they are made of?
 
If you have taken an old harddrive into parts, you probably found
magnetic plates which are a part of the mechanism to control pickup
arms. I found them carrying extremely strong magnetism for their small
size. I never saw such a strong magnet before. Can somebody tell what
kind of alloy they are made of?
Click to expand...
They're probably of the sort known as "rare earth" magnets, which
incorporate lanthanide metals along with others. See the page at
http://www.rare-earth-magnets.com/magnets.htm for some further
information.

They are indeed very strong for their size and weight. They can tend
to be brittle and prone to chip (an especial problem given how readily
they can fly towards the nearest piece of sheet steel and pinch the
^%X$& out of your fingers!).

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
 
I checked out this site, about rare earth magnets. This is a very
interesting one!

--

Jerry G.
=====


"Dave Platt" <dplatt@radagast.org> wrote in message
news:10b0dflp8hjsmc8@corp.supernews.com...
If you have taken an old harddrive into parts, you probably found
magnetic plates which are a part of the mechanism to control pickup
arms. I found them carrying extremely strong magnetism for their small
size. I never saw such a strong magnet before. Can somebody tell what
kind of alloy they are made of?
Click to expand...
They're probably of the sort known as "rare earth" magnets, which
incorporate lanthanide metals along with others. See the page at
http://www.rare-earth-magnets.com/magnets.htm for some further
information.

They are indeed very strong for their size and weight. They can tend
to be brittle and prone to chip (an especial problem given how readily
they can fly towards the nearest piece of sheet steel and pinch the
^%X$& out of your fingers!).

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
 
dplatt@radagast.org (Dave Platt) wrote in message news:<10b0dflp8hjsmc8@corp.supernews.com>...
If you have taken an old harddrive into parts, you probably found
magnetic plates which are a part of the mechanism to control pickup
arms. I found them carrying extremely strong magnetism for their small
size. I never saw such a strong magnet before. Can somebody tell what
kind of alloy they are made of?

They're probably of the sort known as "rare earth" magnets, which
incorporate lanthanide metals along with others. See the page at
http://www.rare-earth-magnets.com/magnets.htm for some further
information.

They are indeed very strong for their size and weight. They can tend
to be brittle and prone to chip (an especial problem given how readily
they can fly towards the nearest piece of sheet steel and pinch the
^%X$& out of your fingers!).
Click to expand...
At least with the rare earth magnets used in small stepper motors, if you
disassemble the magnet assembly then a good amount of the magnet's strength is
lost. You need a "keeper" in the magnetic circuit to prevent this strength
loss.

I do not know if the same principle applies to the voice coil magnets in
current hard drives, but I'm guessing that it does.

Tim.
 
At least with the rare earth magnets used in small stepper motors, if you
disassemble the magnet assembly then a good amount of the magnet's
strength is
lost. You need a "keeper" in the magnetic circuit to prevent this
strength
loss.
Click to expand...
No, you don't.
Rare earth magnets will eventually loose their strength (and the earth will
eventually stop spinning), but the "keeper" won't make any difference that
you'll live to see.

None of the suppliers and manufacturers talk about any decay rate, or using
a "keeper".
Of course it won't harm anything either.
 
Tim Shoppa wrote:
dplatt@radagast.org (Dave Platt) wrote in message news:<10b0dflp8hjsmc8@corp.supernews.com>...

If you have taken an old harddrive into parts, you probably found
magnetic plates which are a part of the mechanism to control pickup
arms. I found them carrying extremely strong magnetism for their small
size. I never saw such a strong magnet before. Can somebody tell what
kind of alloy they are made of?

They're probably of the sort known as "rare earth" magnets, which
incorporate lanthanide metals along with others. See the page at
http://www.rare-earth-magnets.com/magnets.htm for some further
information.

They are indeed very strong for their size and weight. They can tend
to be brittle and prone to chip (an especial problem given how readily
they can fly towards the nearest piece of sheet steel and pinch the
^%X$& out of your fingers!).


At least with the rare earth magnets used in small stepper motors, if you
disassemble the magnet assembly then a good amount of the magnet's strength is
lost. You need a "keeper" in the magnetic circuit to prevent this strength
loss.

I do not know if the same principle applies to the voice coil magnets in
current hard drives, but I'm guessing that it does.

Tim.
Click to expand...
One of the notable properties of rare earth magnets is their very high
magnetizing force, meaning they don't need keepers.

Are you sure you're not thinking of AlNiCo magnets, which are really
nice magnets but most certainly require keepers?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Sat, 22 May 2004 23:42:06 -0500, Chiropter <chiropter@cox.net> wrote:

If you have taken an old harddrive into parts, you probably found
magnetic plates which are a part of the mechanism to control pickup
arms. I found them carrying extremely strong magnetism for their small
size. I never saw such a strong magnet before. Can somebody tell what
kind of alloy they are made of?
Click to expand...
They are Neodymium Iron Boron (NIB)
 
Tim Wescott <tim@wescottnospamdesign.com> wrote in message news:<10b2sbhepqh6lc7@corp.supernews.com>...
Are you sure you're not thinking of AlNiCo magnets, which are really
nice magnets but most certainly require keepers?
Click to expand...
That seems likely. Are AlNiCo's more common in stepper motors?

Tim.
 
Tim Shoppa wrote:

Tim Wescott <tim@wescottnospamdesign.com> wrote in message news:<10b2sbhepqh6lc7@corp.supernews.com>...

Are you sure you're not thinking of AlNiCo magnets, which are really
nice magnets but most certainly require keepers?


That seems likely. Are AlNiCo's more common in stepper motors?

Tim.
Click to expand...
I wish I knew. DC motors can come with ferrite (cheap), AlNiCo
(middling) or rare earth (expensive). The biggest problem with AlNiCo
in a DC motor is that over-enthusiastic application of current
demagnetizes the field magnets, so you only see them in applications
where the driver electronics can be trusted to limit the current. This
wouldn't be nearly as much of a problem in a stepper since the coil
resistance limits the current, so I would expect that AlNiCo magnets
would be much more common.

Ferrite magnets are that hard, nearly black material. It's what you
find in toy motors. They are moderately strong, not being able to
generate as much field as an AlNiCo but they have much higher
magnetizing force than AlNiCo so they loose very little if any field
without a keeper.

AlNiCo is silvery, it usually breaks cleanly with a distinct grain
that's between 1/32 and 1/16th inch grain size, and it has the renowned
need for a keeper. These are usually cast and are often magnetized in
place, and often have a very nice shiny as-cast surface.

Rare earth materials are usually a dull gray, they tend to shatter with
a very fine grain, they are WAY STRONG, and just to confuse things they
are often gold or chrome plated (because they corrode like anything).
They are usually sintered, and in their as-formed state they have a
smooth but slightly porous surface.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
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