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. Anistropic 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.
- Tooling is expensive.
- 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.
- Most common grades of ceramic are 1, 5 and 8 (1-8 possible).
- Grade 8 is the strongest ceramic material available.
Neodymium Magnets or Rare
Earth Magnetsare 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
10 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 molded 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.
|
