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The Alnico materials (composed predominantly of aluminum, nickel, and
cobalt with minor amounts of other elements including titanium and
copper) permit design latitudes providing high indications, high energies
and relatively high coercivities. They are characterized by excellent
temperature stability and good resistance to demagnetization from
vibration and shock. Alnico offers the best temperature characteristics
of any standard production magnet material available. It can be used for
continuous duty applications where temperature extremes up to 930° F
can be expected.
Alnico material are manufactured through either a casting or sintering
process. Alnico is very hard and brittle. Machining or drilling can not
therefore be accomplished by ordinary methods. Holes are usually cored
in at the foundry. Magnets are cast or sintered as closely as possible
to required sizes so that abrasive grinding to finished dimensions and
tolerances is minimized.
Specialized casting techniques are used to achieve the unique
crystalline
grain orientation found in the Alnico 5 and 8 grades. These anisotropic
grades are designed to produce high magnetic output in a specified
direction. Orientation is achieved during heat treatment, by cooling the
casting from 2000° F at a controlled rate within a magnetic
field which conforms to the preferred direction of magnetization. Alnico 5 and
Alnico 8 are anisotropic and exhibit a preferred direction of
orientation. Magnetic orientation should be specified on your drawing
when you send an order to us.
Cast Alnico 5 is the most commonly used of all the cast Alnicos. It
combines high inductions with a high energy product of 5 MGOe or more and
is used extensively in rotating machinery, communications, meters and
instruments, sensing devices and holding applications.
The higher resistance to demagnetization (coercive force) of Alnico 8,
cobalt content to 35%, allows this material to function well for short
lengths or for length to diameter ratios of less than 2 to 1.
Sintered Alnico materials offer slightly lower magnetic properties but
better mechanical characteristics than the cast Alnico materials.
Sintered Alnico magnets are most suitable in small sizes (less than 1
oz.). In this process, the desired mix of metal powders is pressed to
shape and size in a die, then sintered at 2300° F in a hydrogen
atmosphere. The sintering process is well suited to large volume
production, and results in parts which are structurally stronger than
cast magnets. Relatively close tolerances can be achieved without grinding.
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