magnets are manufactured by a die pressing and
sintering process which allows economic
production of components in a varied array of
sizes and shapes.
Ferrite magnets may be either strontium
ferrite (SrO.6Fe2O3) or barium ferrite
(BaO.6Fe2O3) and can be produced with isotropic
or anisotropic magnetic properties. Anisotropic
properties are derived from the high
magneto-crystalline shape anisotropy of the
ferrite particles. These particles can be
envisaged as hexagonal platelets with
perpendicular magnetic preference (c ¨C axis).
Physical orientation of the ferrite particles is
necessary in the pressing process to achieve
magnetic alignment. Ferrite magnets have
excellent corrosion resistance and have normal
operating capabilities between - 40¡ãC and +250¡ãC.
As temperature increases remanence decreases by
0.2 %/¡ãC whereas coercivity increases by 0.3 %/¡ãC.
At very low temperatures there is a risk of
permanent de-magnetisation in magnet systems
with low working points.
Processing begins with granulation or drying of
the ferrite powder raw material before axial
pressing to form compacts of the required shape.
Isotropic ferrite magnets are produced by dry
pressing of granulated ferrite raw material
using mechanical or hydraulic presses.
Anisotropic magnet properties are achieved by
pressing in a magnetic field. In this case,
pressing may be carried out using dry powder or
wet slurry dependent upon the level of
anisotropic properties required. Specially
designed electromagnetic tools are employed to
produce the anisotropic grades. With all
pressing techniques, continuous in-process
monitoring techniques ensure consistent green
density is maintained on all products.
After pressing the compacts are sintered in
air at high temperature to consolidate them,
thereby giving their definitive shape and
Grinding and/or other finishing operations
can be used to achieve very close dimensional
tolerances if necessary.
Components may be magnetised before final
inspection, packing and despatch.