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Permanent Magnets  (Text Version)

Permanent Magnets (Text Version)

Posted by L.E. Carlson on Aug 18th 2021

About Permanent Magnets

What is a permanent magnet?

A permanent magnet is an object made from a material that is magnetic and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door.

Permanent Magnets Materials

AlNiCo

Ceramic

SAMARIUM COBALT

NEODYMIUM

Some of the shapes of permanent magnets come in:

Ring Magnets

Bar Magnets

Disc Magnets

Cylinder Magnets

Cube Magnets

Magnetic Balls

Block Magnets

Horseshoe Magnets

Pyramid Magnets

Rod Magnets

Wedge Magnets

Alnico Magnets Characteristics

Excellent temperature stability, high residual induction, and relatively high energies characterize Alnico materials, composed primarily of alloys of Aluminum, Nickel, and Cobalt. They are manufactured through either a casting or sintering process. Cast magnets may be manufactured in complex shapes, such as horseshoes, not possible with other magnet materials. Sintered Alnicos offer slightly lower magnetic properties but better mechanical characteristics than cast Alnicos.

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 er magnet should be about 1.250" long. Because of its higher coercivity, Alnico 8 may be used in shorter lengths and in disc shapes.

Ceramic Magnets

Attributes of Ceramic Material

High intrinsic coercive force

Tooling is expensive

Least expensive material compared to alnico and rare earth magnets

Limited to simple shapes due to manufacturing process

Lower service temperature than alnico, greater than rare earth

Finishing requires diamond cutting or grinding wheel

Lower energy product than alnico and rare earth magnets

Most common grades of ceramic are 1, 5 and 8 (1-8 possible)

Grade 8 is the strongest ceramic material available

Applications of Ceramic Magnets

Speaker magnets

DC brushless motors

Magnetic Resonance Imaging (MRI)

Magnetos used on lawnmowers and outboard motors

DC permanent magnet motors (used in cars)

Separators (separate ferrous material from non-ferrous)

Used in magnetic assemblies designed for lifting, holding, retrieving and separating

Rare Earth Magnets (Samarium Cobalt & Neodymium)

Collectively known as Rare Earth magnets, Samarium Cobalt (SmCo) and Neodymium Iron Boron (NdFeB) magnets are alloys of the Lanthanide group of elements. Rare Earth magnets are the most advanced commercialized permanent magnet materials today. SmCo magnets are available in a number of different grades that span a wide range of properties and application requirements. SmCo magnets are brittle and machining operations should be performed prior to magnetization, using diamond tools. We are equipped to fabricate these materials to blueprint specifications.

Samarium Cobalt

Attributes of Samarium Cobalt Material Applications of Samarium Cobalt Magnets

Computer disc drives High resistance to demagnetization

High energy (magnetic strength is strong for its size)

Good temperature stability

Expensive material (cobalt is market price sensitive)

Computer rigid disc drives, printers and speakers

Neodymium Magnets

Neodymium magnets (Nd-Fe-B) are composed of neodymium, iron, boron and a few transition metals. These magnets are extremely strong for their small size, metallic in appearance and found in simple shapes such as rings, blocks and discs.

Attributes of Neodymium Material

Very high resistance to demagnetization

High energy for size

Good in ambient temperature

Low working temperature for heat applications, but higher levels of heat resistance materials are being introduced periodically

Sensors

Traveling wave tubes

Linear actuators

Satellite systems

Motors where temporary stability is vital

Samarium cobalt magnets SmCo) are composed of samarium, cobalt and iron.

Samarium Cobalt

Attributes of Samarium Cobalt Material Applications of Samarium Cobalt Magnets

Applications of Neodymium Magnets

Magnetic separators

Linear actuators

Microphone assemblies

Servo motors

DC motors (automotive starters)

Attributes of Samarium Cobalt Material Applications of Samarium Cobalt Magnets

Rare Earth Magnets (Samarium Cobalt & Neodymium)

Collectively known as Rare Earth magnets, Samarium Cobalt (SmCo) and Neodymium Iron Boron (NdFeB) magnets are alloys of the Lanthanide group of elements. Rare Earth magnets are the most advanced commercialized permanent magnet materials today. SmCo magnets are available in a number of different grades that span a wide range of properties and application requirements. SmCo magnets are brittle and machining operations should be performed prior to magnetization, using diamond tools. We are equipped to fabricate these materials to blueprint specifications.

Computer disc drives High resistance to demagnetization

High energy (magnetic strength is strong for its size)

Good temperature stability

Expensive material (cobalt is market price sensitive)