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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
840 F, 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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