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Samarium Cobalt
General Information
Collectively known as Rare Earth
magnets, Samarium Cobalt (SmCo) and Neodymium Iron Boron
(NdFeB) magnets are alloys of the Lanthanide group of
elements. Rare Earth magnets are the most advanced commercialized
permanent magnet materials today. SmCo magnets are available
in a number of different grades that span a wide range
of properties and application requirements.
SmCo magnets are brittle and machining operations should
be performed prior to magnetization, using diamond tools.
We are equipped to fabricate these materials to blueprint
specifications.
SmCo magnets are anisotropic, and can only be magnetized
in the orientation direction. In general, magnetizing
fields of about 35 to 45 kOe are required to saturate
SmCo materials.
Manufacturing Methods
SmCo magnets are manufactured in the following forms:
Sintered
- fine SmCo powder is compacted in a die and then sintered,
fusing the powder into a solid material. There are two
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 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 usually need some finish machining in order to meet
final tolerances.
Compression Bonded
- this is a technique whereby a special form of SmCo 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 - currently in the range of 15
MGOe.
Comparison of NdFeB
and SmCo Magnets
| Material |
NdFeB |
SmCo |
| Energy
Products |
10 to 55 |
15 to 33 |
| 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. Coatings for corrosion
resistance are therefore not generally required for SmCo
magnets.
Machining
SmCo is extremely brittle, and highly prone to chipping
and cracking. Special machining techniques, involving
diamond-grinding techniques, must be used to machine this
material.
We are fully equipped to machine these materials to your
blueprint specifications.
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.
SmCo materials are mechanically very 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.
Temperature Effects
SmCo magnets can operate at temperatures up to 350C ,
depending upon the grade and permeance coefficient. Sm2Co17
materials exhibit superior temperature characteristics
as compared to the Sm1Co5 types.
Common Applications
for Samarium Cobalt 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.
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