Custom Cast Alnico Disc Magnets

Custom Cast Alnico Disc Magnets

Alnico magnet is hard and brittle. Machining or drilling cannot therefore be accomplished by ordinary methods. Holes are usually cored in at the foundry, and magnets are cast close to final size and then finish machined to closer tolerances.

Alnico disc magnet has a low coercive force, and is easily demagnetized if not handled with care. For optimum performance of Alnico 5 magnets, the magnetic length should be approximately 5 times the pole diameter or equivalent diameter. For example, a 0.250" diameter magnet should be about 1.250" long. Because of its higher coercivity, Alnico 8 may be used in shorter lengths and in disc shapes.

Manufacturing Methods

Alnico magnets are manufactured through either casting or sintering processes.

Cast alnico magnets are manufactured by pouring a molten metal alloy into a mold and then further processing it through various heat-treat cycles. The resulting magnet has a dark gray exterior appearance, and may have a rough surface. Machined surfaces have a shiny appearance similar to steel.

Sintered alnico magnets are manufactured by compacting fine Alnico powder in a press, and then sintering the compacted powder into a solid magnet.

Surface Treatments

The corrosion resistance of Alnico is considered excellent , and no surface treatments are required. However, Alnico magnets are easily plated for cosmetic reasons if required.

Magnetizing and Handling

Alnico magnets require magnetizing fields of about 3 kOe. Because of their relatively low coercivities, special care should be taken to assure that these magnets are not subjected to adverse repelling fields, since these could partially demagnetize the magnets. Magnetized magnets should be stored with keepers to reduce the possibility of partial demagnetization. If Alnicos are partially demagnetized, they may be easily remagnetized.

Application

Cast Alnico 5 magnet is the most commonly used of all the cast Alnicos. This material is used extensively in rotating machinery, meters, instruments, sensing devices, and holding applications.