|
|
Neodymium Iron Boron
General Information
Collectively known as Rare Earth
magnets, Neodymium Iron Boron (NdFeB) and Samarium Cobalt
(SmCo) magnets are alloys of the Lanthanide group of elements.
Rare Earth magnets are the most advanced commercialized
permanent magnet materials today. NdFeB magnets are available
in a number of different grades that span a wide range
of properties and application requirements.
NdFeB magnets are available in sintered as well as bonded
forms. The bonded form of the material can be produced
with close tolerances off tool, with little or no finishing
required. The energy product of the bonded form is much
lower than that of the sintered form - up to 10 MGOe.
The sintered form usually requires some finishing operations
in order to hold close mechanical tolerances.
NdFeB magnets are brittle (though not as brittle as the
SmCo types), and machining operations should be performed
prior to magnetization, using diamond tools. We are equipped
to fabricate these materials to blueprint specifications.
All NdFeB magnets, except the bonded NdFeB B10N material,
are anisotropic, and can only be magnetized in the orientation
direction. B10N material is isotropic and can be magnetized
in any direction, and with multiple poles, although special
magnetizing fixtures are required for this. In general,
magnetizing fields of about 30 KOe are required to saturate
NdFeB magnets, with high coercivity grades requiring
about 40 KOe.
Manufacturing Methods
NdFeB magnets are manufactured in the 4 following forms:
Sintered
- fine NdFeB powder is compacted in a die and then sintered,
fusing the powder into a solid material. There are 2 forms
of pressing: die pressing (which involves a hard die into
which the powder is placed and then pressed), and isostatic
pressing (involving a special "rubber" die into
which powder is placed and then pressed with equal force
in all directions on the powder). Die pressed parts are
usually made smaller than isostatically pressed parts.
Although the magnetic properties of isostatically pressed
parts are higher, the uniformity of magnetic characteristics
is usually lower than that of die pressed parts. Sintered
parts normally need some finish machining in order to
meet final tolerances.
Compression Bonded
- this is a technique whereby a special form of NdFeB
powder is blended with a plastic carrier material, die
pressed and then heated. Parts made in this way can be
of complex shapes and come off the tool with close tolerances,
requiring no further finish machining. They have lower
energy products than sintered materials - in the range
of 10 MGOe. The Bonded NdFeB materials are isotropic -
i.e. they can be magnetized in any direction.
Injection Molded
- NdFeB powder is blended with a plastic material and
injection molded. The resulting parts have energy products
in the 5 MGOe range, but can be made with extremely intricate
shapes.
Extruded
- though not popular at present, NdFeB based flexible
magnets can be made by binding NdFeB powder with a carrier
material and extruding the material in sheet or strip
form. Energy products up to about 6 MGOe have been achieved
in this way.
Comparison of NdFeB and SmCo Magnets
| Material |
NdFeB |
SmCo |
| Energy
Products (MGOe) |
10 to 55 |
15
to 32 |
| Mechanical
Strength |
Medium |
Low |
Density
(lbs/in3 - gm/cm3) |
0.275
- 7.5 |
0.300
- 8.3 |
| Corrosion
Resistance |
Low |
High |
| Temp
Stability |
Low
to Medium |
High |
| Cost |
Lower |
Higher |
Assemblies
We are able to manufacture metal and other components
of finished sub assemblies using our CNC machining facilities.
Assemblies can be fabricated by adhering magnets with
adhesives to suit a range of environments, by mechanically
fastening magnets, or by a combination of these methods.
Due to the relatively brittle nature of these magnet materials,
press fits are not recommended.
When multiple magnets are assembled in repelling positions,
it is advisable to use mechanical fastening in addition
to adhesives, since if adhesives were to give way, repelling
magnets may dislodge and endanger personnel using them.
Our design engineering team will be happy to assist you
in designing housings for your magnet assemblies.
Surface Treatments
The corrosion resistance of SmCo is considered good while
that of NdFeB is considered poor. Painting, coating, or
plating is therefore highly recommended for NdFeB. Plating
NdFeB is a difficult process, and commercial plating houses
are unlikely to be able to achieve plating with good adhesion.
Nickel, Zinc, or Tin plating provides good corrosion resistance
for NdFeB magnets. We are also able to cadmium chromate
or aluminum chromate plate NdFeB using vacuum deposition
techniques. A variety of organic coatings have also been
successfully developed for NdFeB, exhibiting good corrosion
resistance characteristics. For especially harsh environments,
it may be advisable to use a combination of coating techniques,
or to encapsulate the material in a sealed housing.
Machining
Some machining operations may be performed on NdFeB materials
using carbide tools, although surface finishes thus obtained
may be less than optimal. In general, NdFeB magnets must
be machined using diamond-grinding techniques.
We are fully equipped to machine these materials to your
blueprint specifications.
Bonded NdFeB is easily machined. Coolants must be used
while machining this material in order to avoid spontaneous
combustion of powder. Machining this material removes
a layer of protective coating, and re-coating for corrosion
resistance may be necessary.
Magnetizing and
Handling
All Rare Earth magnets require extremely high magnetizing
fields and special consideration must be given to this
when designing complex assemblies, if it is intended to
magnetize after assembly. Consult us if you foresee any
problems.
Rare Earth materials are mechanically weak, and magnetically
very strong. They must therefore be handled very carefully
to avoid damage and injury to personnel handling the magnets.
Receiving and assembly personnel should be warned about
the dangers of handling magnetized Rare Earth magnets.
Isotropic bonded NdFeB materials can be magnetized in
any direction, or with multiple poles. Special magnetizing
fixtures are required in order to achieve multiple pole
magnetization. Such multiple pole fixtures may cost several
thousand dollars depending on complexity of design and
production rate requirements.
Temperature Effects
Magnetic properties of NdFeB deteriorate rapidly above
about 140° C, depending on the grade of material,
and the permeance coefficient of the magnet in operation.
The higher the permeance coefficient the magnet operates
at, the higher the temperature it will withstand. High
Hci NdFeB materials operating at a high permeance coefficient
can operate to about 210° C.
Common Applications
for Neodymium Iron Boron Magnets
Holding systems requiring very high holding forces, high
field yoke magnets, high performance stepper, DC, servo,
linear, and voice coil motors, magnetic bearings, magnetic
couplings, loudspeakers, Halbach arrays, headphones, microphones,
magnetic separation, instrumentation, switches, relays,
magnetic resonance, sputtering, vacuum deposition, charged
particle beam guidance, particle accelerators, undulators,
wigglers, and others.
Shapes, Sizes,
and Grades Available
In addition to the stock shapes, sizes, and grades listed,
others are available. Please inquire. Non-standard shapes
and sizes can be fabricated to blueprint specifications
from raw stock. Isotropic bonded NdFeB can be specially
formulated to meet special requirements, with energy products
from 1 to 10 MGOe, as required.
|
|
