Neodymium permanent magnets (Nd-Fe-B) are composed of neodymium, iron, boron and
a few transition metals. These magnets are extremely strong for their
small size, metallic in appearance and found in simple shapes such as
rings, blocks and discs.
Attributes of Neodymium
Very high resistance to demagnetization
High energy for size
Good in ambient temperature
Material is corrosive and should be coated for long term maximum energy
Low working temperature for heat applications, but higher levels of
heat resistance materials are being introduced periodically.
Applications of Neodymium
Magnetic separators, linear actuators, microphone assemblies, servo motors,
DC motors (automotive starters), computer rigid disc drives, printers
For as pressed material, tolerance on the thickness (direction of magnetization)
is ± .005. Other dimensions are ± 2.5% or ± .010,
whichever is greater. According to IMA standards, visual imperfections
such as hairline cracks, porosity and minor chips are commonly found in
sintered metallic magnets. A chipped edge is considered acceptable if
no more than 10% of the surface is missing. Cracks are acceptable as long
as they do not extend across more than 50% of pole surface.
Typical Magnetic and Physical Properties of Neodymium Magnet Material
Maximum energy Product
Residual induction Br
Coercive Force Hc
Intrinsic Coercive Force
Magnetizing and Handling
Neodymium magnets are very brittle and very strong magnetically. Therefore,
it is crucial to handle these magnets with extreme care to avoid personal
injury and damage to the magnets. Fingers can be severely pinched between
attracting magnets. Magnets can chip if allowed to jump at
an attracting object. It is highly recommended that when constructing
rare earth magnetic assemblies, they be magnetized after assembly.
Since neodymium magnet material is prone to chipping and cracking, it
does not lend itself to conventional machining methods. It can, however,
be abrasively ground, but only with the use of liberal amounts of coolant.
The coolant minimizes heat fracturing and the risk of fires caused by
oxidized grinding dust.