A Biblical passage states "there is safety in a multitude of council". In
other words, two heads are better than one.

Ever want to salvage a magnet from a driver?

After seperating the magnet structure from the basket, do you know how to
get the magnet free from the top and bottom plates without destroying it?
( I am talking about ceramic magnets of course. )

I am going to try a few techniques, but I would like to know if there are
others out there who have attempted, successfully or not, the task.

"TC" wrote in message
news
A Biblical passage states "there is safety in a multitude of council". In
other words, two heads are better than one.

Ever want to salvage a magnet from a driver?

After seperating the magnet structure from the basket, do you know how to
get the magnet free from the top and bottom plates without destroying it?
( I am talking about ceramic magnets of course. )

I am going to try a few techniques, but I would like to know if there are
others out there who have attempted, successfully or not, the task.

It sounds impossible to me. Ferrite is a mechanically weak, chemically
active material. It is secured in position by epoxy, which is stronger than
the ferrite.

Standard barium ferrite magnets are not expensive. I would only give it a
second thought if the magnet were strontium ferrite.

"TC" wrote in message
news
A Biblical passage states "there is safety in a multitude of council". In
other words, two heads are better than one.

Ever want to salvage a magnet from a driver?

After seperating the magnet structure from the basket, do you know how to
get the magnet free from the top and bottom plates without destroying it?
( I am talking about ceramic magnets of course. )

I am going to try a few techniques, but I would like to know if there are
others out there who have attempted, successfully or not, the task.


Never tried this task before.

My advice is find some place that does spear repair, and ask them. I think
they probably would have some experience with magnets coming off, so they
likely would have a clue.

My first thought was to apply heat but ceramic might not fare well.

Cut a hole the size of the magnet in a piece of MDF. If the magnet is thick,
then use 2 pieces of MDF stacked together. Make it so it just fits in the
hole. Drop the magnet down into the hole so that only the pole plate is
above the surface of the MDF. Put another piece of MDF on the surface of the
one that the magnet is embedded in so that it is against the side of the
pole piece. With the first piece of MDF, containing the magnet, firmly
shoved against the basement wall or some other non movable barrier, give the
second piece of MDF a good whack with a sledge hammer. You might get lucky
and shear the glue.

James.


"TC" wrote in message
news
A Biblical passage states "there is safety in a multitude of council". In
other words, two heads are better than one.

Ever want to salvage a magnet from a driver?

After seperating the magnet structure from the basket, do you know how to
get the magnet free from the top and bottom plates without destroying it?
( I am talking about ceramic magnets of course. )

I am going to try a few techniques, but I would like to know if there are
others out there who have attempted, successfully or not, the task.

TC wrote:
After seperating the magnet structure from the basket,
do you know how to get the magnet free from the top
and bottom plates without destroying it? (I am talking
about ceramic magnets of course. )

I am going to try a few techniques, but I would like to
know if there are others out there who have attempted,
successfully or not, the task.

First, some comments on the other suggestions.

Epoxy is almost NEVER used in attaching magnets to the
remainder of the structure. It's too expensive and it takes
much to long to cure. The vast majority of ceramic-based
magnet structures are assembled using anaerobic quick-set
adhesives of the type typically known as cyanoacrylates
(sometimes known as "crazy glue"). This is good news, as we
will see in a moment.

Mechanically, the ceramic magnets are quite hard and brittle
and thus prone to cracking and shattering especially if
mechanically shocked. Trying to whack the magnet apart is
almost always a guaranteed way of breaking it.

As to the relative value of barium vs strontium ferrite,
they are equivalent performance and essentially cost wise
and are used interchangeably.

Now to the problem at hand: how to separate the parts. As
mentioned, these days the magnets are generally adhered
used anaerobic adhesives. This is good news for two reasons:

1. If you know at least tje approximate formulation of the
adhesive, there exist "solvents" that can break it down.

2. MOst of these adhesives fail at elevated temperatures.

The trick is to find a temperature that's high enough to do
the job, but low enough not to do other damage. ANd that
higher temperature is determined by what you want the out-
come to be. There are two clear choices:

1. You want the magnet to remain magnetized,

2. You don't care.

What you choose determines whether you limit the heating to
well below the material's Curie temperature (where magnetism
will be lost). Generally, a temperature of 400-450 F is
sufficient to break the adhesive but not loose magnetism.
This is achievable in conventional ovens.

However, mind you that doing this is likely to give off pretty
nasty fumes, which are likely to be harmful to one degree or
another.

I have taken a pile of magnet structures and put them in a
ceramic kiln and run it up to maybe 1000 degrees F
with the result that the structures fell apart very nicely.
There was no residual magnetism, but that was not my goal at
the time (don't worry about physically damaging the ceramic,
they are cured at a temperature MUCH higher than this).

I have also taken magnets and run them in an oven at 475 F
for about 2 hours, and 80% of them had sufficient adhesive
failures that, with some effort against the magnetism, they
came apart cleanly.

An alternative: if your goal is to get a collection of magnetized
ceramic ring magnets, and you're not particular about the size,
consider salvaging old microwave ovens. Pull out the magnetron,
and it's usually very easy to get the magnet off of it with
no damage.

Dick, those were precisely my thoughts as well, vapourizing the glue with
heat.

A few weeks ago I bought a good sized toaster oven at a garage sale for this
purpose.

I concluded a cast ceramic magnet could withstand very high temperatures,
greater than the toaster oven could produce but yet not so great as to cause
energy loss in the magnet.

I'll set it up in the back yard and let them bake for a while. Kind of like
an easy-bake oven for speaker techs!

I thank all who provided input in this thread...

wrote in message
ups.com...

TC wrote:
After seperating the magnet structure from the basket,
do you know how to get the magnet free from the top
and bottom plates without destroying it? (I am talking
about ceramic magnets of course. )

I am going to try a few techniques, but I would like to
know if there are others out there who have attempted,
successfully or not, the task.

First, some comments on the other suggestions.

Epoxy is almost NEVER used in attaching magnets to the
remainder of the structure. It's too expensive and it takes
much to long to cure. The vast majority of ceramic-based
magnet structures are assembled using anaerobic quick-set
adhesives of the type typically known as cyanoacrylates
(sometimes known as "crazy glue"). This is good news, as we
will see in a moment.

Mechanically, the ceramic magnets are quite hard and brittle
and thus prone to cracking and shattering especially if
mechanically shocked. Trying to whack the magnet apart is
almost always a guaranteed way of breaking it.

As to the relative value of barium vs strontium ferrite,
they are equivalent performance and essentially cost wise
and are used interchangeably.

Now to the problem at hand: how to separate the parts. As
mentioned, these days the magnets are generally adhered
used anaerobic adhesives. This is good news for two reasons:

1. If you know at least tje approximate formulation of the
adhesive, there exist "solvents" that can break it down.

2. MOst of these adhesives fail at elevated temperatures.

The trick is to find a temperature that's high enough to do
the job, but low enough not to do other damage. ANd that
higher temperature is determined by what you want the out-
come to be. There are two clear choices:

1. You want the magnet to remain magnetized,

2. You don't care.

What you choose determines whether you limit the heating to
well below the material's Curie temperature (where magnetism
will be lost). Generally, a temperature of 400-450 F is
sufficient to break the adhesive but not loose magnetism.
This is achievable in conventional ovens.

However, mind you that doing this is likely to give off pretty
nasty fumes, which are likely to be harmful to one degree or
another.

I have taken a pile of magnet structures and put them in a
ceramic kiln and run it up to maybe 1000 degrees F
with the result that the structures fell apart very nicely.
There was no residual magnetism, but that was not my goal at
the time (don't worry about physically damaging the ceramic,
they are cured at a temperature MUCH higher than this).

I have also taken magnets and run them in an oven at 475 F
for about 2 hours, and 80% of them had sufficient adhesive
failures that, with some effort against the magnetism, they
came apart cleanly.

An alternative: if your goal is to get a collection of magnetized
ceramic ring magnets, and you're not particular about the size,
consider salvaging old microwave ovens. Pull out the magnetron,
and it's usually very easy to get the magnet off of it with
no damage.

TC wrote:
I concluded a cast ceramic magnet could withstand very
high temperatures, greater than the toaster oven could
produce but yet not so great as to cause energy loss in
the magnet.

FYI, the temperature data from the various ferrite manu-
facturers suggest that this is precisely the case. Typical
Curie temperature is in the realm of 842F or 450C, with the
maximum recommended operating temperature being 480F or
250C.

The big question is whether the adhesives will withstand
450F. Many don't, some might.

But your "experiment" is probably easy and safe enough to
find out. Just for laughs, keep a fire extinguisher handy.

wrote:
TC wrote:

I concluded a cast ceramic magnet could withstand very
high temperatures, greater than the toaster oven could
produce but yet not so great as to cause energy loss in
the magnet.


FYI, the temperature data from the various ferrite manu-
facturers suggest that this is precisely the case. Typical
Curie temperature is in the realm of 842F or 450C, with the
maximum recommended operating temperature being 480F or
250C.

The big question is whether the adhesives will withstand
450F. Many don't, some might.

But your "experiment" is probably easy and safe enough to
find out. Just for laughs, keep a fire extinguisher handy.

I've never had much difficulty simply prying them off with a wood
chisel...or similar thin, sharp tool.

Now, why would anybody want to? The magnet is pretty much useless
without the focusing effect of the iron poles anyway.....

jak

jakdedert wrote:
I've never had much difficulty simply prying them off with a wood
chisel...or similar thin, sharp tool.

Well, I have to say having been in the driver manufacturing
business and having had to do this probably on a couple of
hundred magnets of all different sizes, my success rate
given the two methods I proposed have been 100%, while
the method you suggest has worked (i.e., resulted in an
undamaged magnet) maybe 50% of the time.

Now, why would anybody want to? The magnet is pretty
much useless without the focusing effect of the iron
poles anyway.....

One may need a source of magnetized ferrite rings for,
say, cancelling the external leakage field of an existing
driver.

wrote:
jakdedert wrote:

I've never had much difficulty simply prying them off with a wood
chisel...or similar thin, sharp tool.

Stanley makes a tool, shaped something like a putty knife, much thicker
however. It's got a sharply beveled knife or chisel edge and is about 2
1/2" wide. It's strong enough to slam it with a hammer...good for all
kinds of things. Once the initial bond is broken, the metal can be
pried off with only magnetic attraction keeping it in place.

Well, I have to say having been in the driver manufacturing
business and having had to do this probably on a couple of
hundred magnets of all different sizes, my success rate
given the two methods I proposed have been 100%, while
the method you suggest has worked (i.e., resulted in an
undamaged magnet) maybe 50% of the time.

I only salvage cheap drivers, which could account for my success rate.

Now, why would anybody want to? The magnet is pretty
much useless without the focusing effect of the iron
poles anyway.....


One may need a source of magnetized ferrite rings for,
say, cancelling the external leakage field of an existing
driver.

In that case, a little 'chippage' shouldn't be a problem....

jak

Nitromethane will vigorously attack many if not most anaerobic
adhesives. Drag race places sell it. Last price I paid was around $50 a
gallon-but they usually will sell a pint or so.

Hi Bret,

Have you tried using this nitromethane on any magnets to see if it works?

If you can, give it a whirl and let us know.

I am going to see about the availability of it round these parts.

"Bret Ludwig" wrote in message
oups.com...
Nitromethane will vigorously attack many if not most anaerobic
adhesives. Drag race places sell it. Last price I paid was around $50 a
gallon-but they usually will sell a pint or so.