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Ferrite
General Information
Ferrite magnets are sintered
permanent magnets composed of Barium or Strontium Ferrite.
This class of magnets, aside from good resistance to demagnetization,
has the popular advantage of low cost.
Ferrite magnets are very hard and brittle, and require
specialized machining techniques. Moreover, they should
be machined in an unmagnetized state. We are equipped
to machine these materials to specifications.
Anisotropic grades are oriented in the manufacturing direction,
and must be magnetized in the direction of orientation.
Isotropic grades are not oriented and can be magnetized
in any direction, although some degree of greater magnetic
strength will be found in the pressing dimension, usually
the shortest dimension.
Due to their low cost, Ferrite magnets enjoy a very wide
range of applications, from motors and loudspeakers to
toys and crafts, and are the most widely used permanent
magnets today.
Manufacturing Methods
Pressing and Sintering:
Pressing and sintering involves pressing very fine ferrite
powder in a die, and then sintering this pressed magnet.
All fully dense Ferrite magnets are produced this way.
Ferrite magnets can be wet pressed or dry pressed. Wet
pressing yields better magnetic properties, but poorer
physical tolerances. Generally, the powder is dry for
grade 1 or 5 materials, and wet for grade 8 and higher
materials. Sintering involves subjecting the material
to high temperatures to fuse the pressed powder together,
thus creating a solid material. Magnets produced through
this process usually need to have some finish machining,
otherwise surface finishes and tolerances are not acceptable.
Some manufacturers extrude instead of press wet powder
slurry and then sinter the material. This is sometimes
done for arc segment shapes, where the arc cross-section
is extruded in long lengths, sintered, and then cut to
length.
Injection Molding:
Ferrite powder is mixed into a compound and then injection
molded in the same way as plastic.
Tooling for this manufacturing process is usually very
costly. However, parts produced through this process can
have very intricate shapes and tight tolerances. Injection
molded ferrite properties are either lower or about the
same as grade 1 Ferrite.
Assemblies
We are able to manufacture metal and other components
of finished sub assemblies using our CNC machining facilities.
Assemblies using metal or other components and magnets
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.
Surface Treatments
The corrosion resistance of Ferrite is considered excellent
, and no surface treatments are required. However, Ferrite
magnets may have a thin film of fine magnet powder on
the surface and for clean, non-contaminated applications,
some form of coating may be required.
Machining
Ferrite is brittle, and prone to chipping and cracking.
Special machining techniques must be used to machine this
material. We are fully equipped to machine these materials
to your blueprint specifications.
Magnetizing and
Handling
Ferrite magnets require magnetizing fields of about 10
kOe. They can be magnetized with multiple poles on one
or both pole surfaces. No special handling precautions
are required, except that large blocks of Ferrite magnets
are powerful, and care should be taken to ensure that
they do not snap towards each other.
Temperature Effects
Up to about 840F, changes in magnetization are largely
reversible, while changes between 840F and 1800 F are
re-magnetizable. For all Ferrite magnets, the degradation
of magnetic properties is essentially linear with temperature.
At 350 F, about 75% of room temperature magnetization
is retained, and at 550 F, about 50% is retained.
Common Applications
for Ferrite Magnets
Ferrite magnets are widely used in motors, magnetic couplings,
for sensing, loudspeakers, holding-magnet systems, crafts,
magnetic therapy, novelties, and toys.
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