Neville,
Unless how it's magnetized (axially, diametrically, etc
http://www.kjmagnetics.com/magdir.asp) is standard on microwave
magnetron magnets, I don't know how you can tell gauss. I have a large
(10" diameter) thick (1.25") speaker magnet that's hollow in the
middle. My compass nor my +/- magnets are much help in determining
which way things flow so I leave it on the dryer with the berkey on top.
There is a magnetic viewing film
(http://www.kjmagnetics.com/products.asp?cat=154) that would allow you
to see the direction of magnetization. Perhaps measuring pull would give
you a clue about the gauss. There's some interesting reading regarding
gauss at K & J. http://www.kjmagnetics.com/FAQ.asp
Yes, there are other magnet companies, I just happen to have read the
info from this company.
Saralou
other interesting links....
http://www.kjmagnetics.com/blog/index.php/2010/01/04/surface-fields-101/
http://www.freepatentsonline.com/5177403.html
http://www.repairfaq.org/REPAIR/F_micfaq2.html
Don't know how accurate this is
http://www.sas.org/E-Bulletin/2002-10-25/labNotes/body.html
25 October 2002
*Sources of Extremely Powerful Magnets*
Source: Sam's Gadget FAQ
<http://www.repairfaq.org/sam/gadget.htm#gadsep>
Two excellent sources of magnets are described below. These are at
least as strong as the more well known speaker types, possibly much
stronger, and generally easier to remove:
* Microwave oven magnetron tubes. Go to your local appliance
repair shop and ask - they just toss bad ones. Each one has
two ring shaped ferrite magnets about 2-1/4" in diameter with
a 7/8" hole, magnetized N-S on the faces.
Surplus places typically charge $3 to $6 each for one of these
magnets.
Note: A few older magnetrons used AlNiCo magnet assemblies or
even possibly electromagnets which are not nearly as
interesting. However, you probably won't see any of these.
* Large hard disk drives - especially full height 5-1/4" high
performance types - e.g., Seagate WREN series or Micropolous
boat anchors (the rare earth magnets in these are wicked). The
magnets in small drives are even stronger but are, well, much
smaller. :-) A typical size for a large drive is about 1" x
1-1/4" by 1/2". Since almost no one wants such large slow
drives anymore, they are often found at swap meets or yard
sales for next to nothing. These magnets are a few thousand
Gauss compared to 10 to 15 K Gauss (1 to 1.5 Tesla) for a
medical MRI scanner (of course, the field of the MRI scanner's
superconducting magnet is uniform over a volume of several
cubic FEET! The disk drive magnet's field decays quickly as
you move away from it.)
Surplus places may charge $12 or more for ONE of the magnets
from a large disk drive (there are typically 2 to 6 such
magnets in a disk drive)!
I have a monolithic clump of 40 or 50 of the magnets from full
height 5-1/4" SCSI drives. I figure there is a black hole
growing inside but haven't dared to look. :) The only way I
was able put the clump together with minimal damage to flesh
was by using a hard wood ramp to gently guide each new magnet
into place. I haven't figured out how I'll ever get them apart
though!
Here is a quick easy experiment to try with these powerful
magnets: Slide one such magnet over a thick aluminum plate.
What do you feel? Or, let a 1/8" x 2" x 12" aluminum plate
drop through the intact yoke from a Seagate WREN series 5-1/4"
full height hard drive positioner. What happens? Why? What
material might produce an even more pronounced effect? Why?
For more things to do with these neat magnets, see:
Neodymiumarium <http://www.netcomuk.co.uk/%7Ewwl/neodym.html>.
CAUTION: Both these types are powerful and will squash flesh as they
suck all the bits off of your magnetic media! I am not kidding about
the part about squashed flesh - with some you actually need a small
crowbar to pry the assembly apart!
You will find that some of these magnets are painted. This provides
some resistance to chipping though this material may be on the verge
of flaking off or has already done so in spots. In any case, I
further recommend that you add additional layers of a tough enamel
(e.g., Rustoleum) or the plastic/rubber dip used to coat tool
handles. Otherwise, chipping damage (at least) will result all too
easily and the chips are just as powerful as the rest of the magnet.
Additional Disclaimer: I will not be responsible when your spouse or
parents come home to find the microwave or PC missing some key
components and as dead as a brick!
(From: Terry Sanford (tsanf...@nf.sympatico.ca).)
Magnets salvaged from scrapped computer drives are strong!
* We use them to hold old blankets that cover a vintage car
stored in garage.
* Useful for finding nail locations in plasterboard walls.
Strong magnet will 'stick' to wall at the nail location.
better than those weak magnet 'dippy indicator' things! You
can leave magnet parked on the nearest nail head after each use!
* Use magnet to pick up wrench/spanner dropped off boat wharf
into ten feet of sea water! Also fished wrench out from under
patio deck other day; main problem was finagling wrench
through the gap between the deck boards. Used bent coat hangar
which kept sticking to the magnet; darn!
* Also you can 'feel' if current is actually flowing to an
electrical appliance by holding a strong magnet next to the
wiring! It detects 'flow' not the presence of voltage.
PS: After WWII, strong horseshoe ex radar magnetron magnets were
sold surplus for about two and sixpence each. Someone took his into
a pub on way home and everyone had a great time with it until people
starting checking their (then magnetic) watches. He wasn't too
popular after that I can tell you!
Other Sources of Fairly Powerful Magnets
The following are other possibilities. However, they are not likely
to be nearly as strong!
* Spent laser printer toner cartridges where the entire
developer assembly is part of the cartridge (e.g., EPS-2 for
Canon engines). These include a page-width ferrite magnet.
However, expect to make a mess disassembling the cartridge as
there will still be considerable toner remaining inside.
WARNING: The toner is a possible health hazard. A good dust
mask should be used while working on these. Also, do not
vacuum what remains - static can set off a dust explosion -
use wet rags or paper towels to clean up the mess! The coating
on the photosensitive drum may also be a hazardous material.
* Loudspeakers.
o Smaller or older speakers use AlNiCo type magnets which
are usually in the form of a cylinder (about as tall as
it is wide). AlNiCo is an extremely hard metal alloy.
AlNiCo magnets are not as powerful as ferrite or rare
earth types and are easily demagnetized (but just as
easily remagnetized). Passing a stack of these through
the center hole of a strong ferrite magnet will increase
their strength dramatically - until they are separated
from each other!
o Modern loudspeakers use ring shaped ceramic ferrite
magnets (similar to those in a microwave oven magnetron)
glued to the pole piece (yoke) assembly within which the
voice coil moves. The ferrite is extremely hard but very
brittle so care must be used to extract these from the
yoke assembly - see the section: Disassembling
Loudspeakers to Get at the Magnets
<http://www.sas.org/E-Bulletin/2002-10-25/labNotes/body.html#gaddlm>.
* Permanent magnet stepper and servo motors. These will use
ferrite or rare earth magnets usually in strange shapes. Note:
Removing the magnets may result in partial demagnetization
(reduction in magnetic strength) as the rotor is part of the
magnetic circuit. Therefore, I do not recommend this source.
There is generally no practical way of remagnetizing the
strange shapes involved.
* Optical (laser) pickups from CD players, CDROM drives, and
other optical data storage devices. These may have some very
tiny, but strong, rare earth magnets in the focus and tracking
actuator. However, it seems a shame to sacrifice the beautiful
mechanics in such a device just to get the magnets! CAUTION:
Tiny magnets even more fragile than bigger ones!
Disassembling Loudspeakers to Get at the Magnets
For small speakers with AlNiCo type magnets (the magnets usually
look like metal cylinders), careful prying with a sturdy screwdriver
will usually break the adhesive bond and/or free them from the yoke
assembly. Note: Use the proper tool for the job - not your dad's
prized screwdrivers!) Unlike the ceramic magnets described below,
AlNiCo types are metal and quite sturdy.
(From: Arie de Muynck (ad...@pi.net).)
For the normal black ceramic ring shaped magnets (and likely for
some Ticonal 'iron colored') the trick is: heat the complete
assembly slowly using a paint-stripper gun, or in an oven (thermal,
not microwave!). The glue will weaken and with a screwdriver you can
SLOWLY work them loose. Protect your fingers with an old cloth.
Never apply too much force, the ceramic would chip or break.
Do not overheat them above the so-called Curie temperature or the
magnet will loose it's power irreversibly. That temp depends on the
material but should be way above the 120 C or so to soften the glue.
If you want to experiment with this effect: use a piece of iron
attracted towards a magnet, heat the iron with a flame and above a
rather sharply defined temperature it will not be attracted anymore.
The effect is used in some Weller soldering irons to stabilize the
temp.
Note that the force of a bare ceramic magnet is not as strong as you
might expect, the magnetic lines of the large area of the ring have
to be bundled and guided though iron to a narrow gap to provide a
proper magnetic field.
------------------------------------------------------------------------
Copyright (c) 1994, 1995, 1996, 1997, 1998 by Samuel M. Goldwasser.
All Rights Reserved.
------------------------------------------------------------------------
On 11/16/2010 7:29 AM, Neville Munn wrote:
Anyone know anything about the Gauss measurement of magnets?
Specifically, magnets out of a microwave magnetron. As one would be
aware if familiar, those magnets are like a donut, or a very thick
washer in shape.
I'm interested in the Gauss measurement of the *inside* of the hole in
the centre. Don't know if that measurement would be the same
as either the north or south pole of the faces of the magnet.
Secondary to the above...would the centre hole be distinctly north or
south in polarity, or would that be impossible to determine due to the
fact that it's a hole, or circular in shape? Or a combination of both
in such a restriced area?
Anyone got any idea of what the Gauss meter reading would be?
My query *IS* in relation to EIS/CS by the way...{experimental}.
N.
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