Information
Magnet Types
Ferrite Magnets or Ceramic Ferrite Magnets are manufactured
from strontium ferrite, usually die pressed and sintered. Sintering
is when a mass of metal particles bonded and partly fused by
the use of pressure and heat below the melting point. Due to
good machining properties, these magnets can be cut and magnetized
to virtually any size or shape required. Due to their high coercively
and low cost, they are used in a wide range of applications.
Stable up to a maximum temperature of 120°C, by weight they
are stronger than steel, but less so than neodymium or Rare
Earth Magnets. Like all ceramics, they are quite brittle and
will easily break if dropped onto a hard surface. They are the
most economical choice for magnetic strength.These magnets
are also made in different grades. Ceramic-1 is an isotropic
grade with equal magnetic properties in all directions. Ceramic
grades 5 and 8 are anisotropic grades. Anisotropic magnets are
magnetized in the direction of pressing. The anisotropic method
delivers the highest energy product among ceramic magnets at
values up to 3.5 MGOe (Mega Gauss Oersted). Ceramic magnets
have a good balance of magnetic strength, resistance to demagnetizing
and economy. They are the most widely used magnets today.
Ferrite magnets are generally the best choice for doing repulsion
and attraction experiments since some of the rare earth magnets
may be too strong and bar magnets will demagnetize. Ferrites
come in blocks/slabs, disks and rings.
Attributes of Ceramic Magnets
- High intrinsic coercive force.
- Least expensive material compared to alnico and rare
earth magnets.
- Limited to simple shapes due to manufacturing process.
- Lower service temperature than alnico, greater than
rare earth.
- Finishing requires diamond cutting or grinding wheel.
- Lower energy product than alnico and rare earth magnets.
Neodymium Magnets or Rare Earth Magnets are manufactured
from sintered neodymium iron boron. They possess the most powerful
magnetic properties in relation to volume and can lift up to
1000 times their own weight. However they do not possess strong
heat resistant qualities usually remaining stable up to 80°C,
although SH grades of the compound are available which are stable
up to 120°C. For higher temperature applications, rare earth
samarium cobalt is recommended. Also due to their corrosive
nature, neodymium is usually supplied nickel coated. These magnets
are magnetized through their thickness, and are often used when
space is limited and you need a lot of sticking power. Neodymium
Magnets or Rare Earth Magnets can be used for demonstrating
attraction and repulsion, for science, engineering, research &
development, education, industry and magic, but the larger ones
are exceptionally strong and should be used with caution.
Neodymium Magnets or Rare Earth Magnets are available in disks,
slabs/blocks and rings.
What is the difference between Ferrite Magnets and Rare
Earth or Neodymium Magnets?
The biggest differences between ferrite magnets and rare
earth magnets is that rare earth magnets are much stronger.
The intensity of magnetization and the coercive force are elements
determining the performance of permanent magnets. Since rare
earth magnets contain iron and cobalt in the state not containing
oxygen, their magnetization is large. In addition, magnetization
of rare earth magnets has a strong force (coercive force) aligning
the magnetism in one direction, so they are much stronger magnets
than ferrite magnets. Since they have about 7 times the performance
of ferrite magnets in total energy per volume, rare earth magnets
are used for powerful magnetic circuits that could not be conceived
of until now, space-saving magnetic circuits, etc.
What are the primary applications for Rare Earth or Neodymium
Magnets?
The primary application, for rare earth magnets, is the voice
coil motors that are a part of computer hard disk drives. Other
applications include various industrial motors, sensors, consumer
electronics, office equipment, musical instruments, and cellular
phones. Recently, rare earth magnets have been used in products
that help protect the environment and save energy such as electric
vehicle motors, wind powered generators, and air conditioner
compressors.
Attributes of Rare Earth or Neodymium Magnets
- Very high resistance to demagnetization
- High energy for size
- Good in ambient temperature
- Moderately priced
- Material is corrosive and should be coated for long
term maximum energy output
- Low working temperature for heat applications, but higher
levels of heat resistance materials are being introduced
periodically.
Bar Magnets are used in physics education labs to show
magnetic fields when used with compasses, iron filings or light
metal objects such as paper clips. If a bar magnet or
horseshoe magnet is stored properly, with its keepers, it can
have a shelf life of at least 20 years.
Flexible magnets are very similar to the injection
moulded magnets but are produced in flat strips and sheets.
These magnets are lower in magnetic strength and very flexible
depending on the materials that was used in the compound with
the magnetic powders. Vinyl is often used in this type of magnet
as the binder.
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