MadSci Network: Engineering
Query:

Re: Are there any strong, yet thin magnets?

Date: Sun Jul 23 23:48:43 2000
Posted By: Bradley Kelley, Grad student, Mechanical Engineering, Colorado State University
Area of science: Engineering
ID: 964375198.Eg
Message:

Dear Jerry,

There are some very strong magnets out there called "Rare Earth" magnets because 
some of there composition is from very rare metals.  Samarium-Cobalt (SmCo) and 
Neodymium-Iron-Boron (NdFeB) magnets are the most popular.  Neodymium's can be 
made more powerful than SmCo magnets but are very unstable under higher 
temperatures, (well above 100°C, which I'm sure you will not have to deal with). 
 Neodymium magnets tend to oxidize (rust) easily so are usually coated with a 
protective layer.  Therefore I would recommend ordering sizes you can use 
instead of trying to machine or cut them.  Also, order extras because if two get 
away from you they will smash into each other and create an unusable lump.  And, 
keep your fingers out of the way.  Here is a warning I copied from Indigo 
Instruments' website: Neodymium-magnets

Warning!

Do NOT go anywhere near your computer with them or you could damage your monitor 
or hard drive. Keep any other magnetic media away including floppy disks, 
cassette tapes, credit cards, etc.  CD-ROMs are unaffected.

These are not toys and should be kept away from small children. If two of these 
magnets come close enough, they will snap together so quickly they could break a 
bone in your finger or cause a serious blood blister. A pair of the larger disks 
are strong enough to attract each other right through the thickness of a typical 
adult hand.

Pretty cool, Huh!  There are a number of ways to measure magnetic strength, but 
most will say that Neodymium's are by far the strongest at room temperature.  I 
have some 1"x1" by ½" thick Neodymium's left over from an experiment that I can 
barely get off the fridge using my fingers.  Just to warn you, keep them on the 
metal sheet they will likely come with or another piece of metal, or tightly in 
your hand.

There is very little to reference except my experience testing these rare earth 
magnets as mobile composite repair for the Army and what is on the web about 
them.  However, if you want a more detailed explanation of how magnets work or 
how their strength is measured, I am not the one to ask!  Sorry, not my area.

Anyway, Indigo at the above sight has some great small magnets that you will 
likely be able to use.  Use the largest that you can since size and thickness of 
the magnet is the biggest determinate of strength (if made from the same 
material).  Or do any web search for Rare Earth Magnets or Neodymium and you 
will bring up a number of sights that sell these magnets. 

Hope this helps and good luck with the film.

BK


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