Magnetizing & Handling

Temperature Effects

Cast Properties

ALNICO Magnets and Assemblies

General Information

ALNICO remains the workhorse of the permanent magnet industry and can be relied upon to deliver impressive flux density at an economical price.  ALNICO has excellent temperature stability, high residual induction, and relatively high energies.  These magnets are composed primarily of alloys containing Aluminum, Nickel, and Cobalt.

ALNICO magnets are manufactured through either a casting or sintering process. Cast ALNICO magnets may be manufactured in complex shapes, such as horseshoes, not possible with other magnet materials. Sintered ALNICO magnets offer slightly lower magnetic properties but better mechanical characteristics than cast Alnicos.

Cast Alnico 5 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, to name a few.

Alnico 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 has a low coercive force, and is easily demagnetized if not handled with care. For optimum performance of Alnico 5, 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 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 magnets are manufactured by compacting fine Alnico powder in a press, and then sintering the compacted powder into a solid magnet.

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

Machining

Alnico is hard and brittle, and prone to chipping and cracking. Special machining techniques must be used to machine this material. Holes must be made by EDM methods. We are fully equipped to machine these materials to your blueprint specifications.

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 steel shunts or "keepers" to reduce the possibility of partial demagnetization. If ALNICO magnets are partially demagnetized, they may be easily remagnetized.

Temperature Effects

Changes in magnetization are largely reversible up to about 1,000°F.  Temperatures above this level affect the magnets intrinsic properties and the magnetization is not fully reversible. Approximately 90% of room temperature magnetization is retained at temperatures of up to 1,000°F.