Neodymium Magnets
Neodymium Magnet Overview
Neodymium permanent magnets (NdFeB) are made of Neodymium, Iron and Boron. They are from the Rare-Earth magnet family and have the highest magnetic energies of any material available today. Grades up to N53 with 15,000 Gauss (1.5 Tesla) are available. NdFeB magnets can now be used at operating temperatures up to 220C.
In addition to magnetic holding applications, Neodymium magnets are used in brushless DC motors, contactless sensors, medical devices, magnetic resonance imaging equipment, wind turbines, generators, electric vehicles, and many types of electronic devices.
There are three types of Neodymium Magnets: Sintered Neo, Bonded and Hot-pressed.
Sintered NdFeB
Sintered Neodymium magnets produce the highest magnetic properties. However, the complexity of the shape and magnetic field configuration is limited. Sintered Neodymium magnets are brittle and also sensitive to heat and corrosion. Therefore, careful consideration should be given to temperature and protective coating requirements.
Bonded Neodymium Magnets
Bonded NdFeB Overview
Compression Bonded NdFeB
Bonded Neodymium magnets are manufactured by combining NdFeB powders with an epoxy binder. Although weaker than sintered Neo, complex magnetizing patterns, shapes and over molding can be done with Bonded Neodymium. They are available as the stronger Compression Bonded Neo or more versatile Injection Molded Neo.
Hot-Pressed NdFeB
Hot-pressed Neodymium magnets are fully dense radially oriented NdFeB rings. The orientation is achieved by mechanically pressing Rare Earth powders through a process called Backward Extrusion. This technique is used to produce high-performance rings with small diameters. Hot-Pressed NdFeB has superior corrosion resistance to sintered magnets, with the added advantage of Unipolar, Multipole and skewed multipole magnetization options.
Radial Oriented Neodymium Ring Magnets
Radial Oriented NdFeB Overview
Radially magnetized neodymium magnets are the perfect solution for high-performance permanent magnet motors and sensors that require precise and stable operation.
While more costly to manufacture than traditional neodymium magnets, radial oriented ring magnets can reduce the expense of assembling arc segments. Radial oriented ring magnets are also dimensionally superior, reduce cogging and noise in motor applications.
Radially Oriented Ring magnets can be magnetized as unipolar, multi-pole, and skewed magnetization patterns to meet a wide range of application requirements.
Ceramic Ferrite Magnets
Ferrite Magnet Overview
Hard Ferrite Magnets, aka Ceramic Magnets, are permanent magnet materials composed of Iron Oxide (Fe2O3), Barium (Ba) or Strontium (Sr) or any combination of the two. Ceramic magnets are the lowest cost permanent magnet, while providing good resistance to demagnetization.
Ferrite C5 and Ferrite C8 are the most widely used Ceramic Magnet Grades. Due to their low cost, Ferrite magnets are used in a wide range of applications, including motors, loudspeakers, and industrial applications. They are the most widely used type of permanent magnet.
How Ferrite Magnets are made:
Ferrite magnets are formed by a compression molding technique, which is then followed by sintering. Finish grinding or shaping, when necessary for better control of dimensions, is normally done by diamond grinding wheels.
The material to be molded can be either a dry powder or wet slurry form. Magnetic performance can be increased in a preferred direction by applying a magnetic field in that direction during the molding process.
Mechanical Characteristics
Hard Ferrite magnets should not be used for structural purposes, since they are low tensile and flexural strength. Small imperfections are common in sintered ceramic magnets. These do not affect magnetic performance.
Samarium Cobalt Magnets
Samarium Cobalt Overview
Samarium Cobalt magnets are the second strongest rare earth magnet compared to Neodymium magnet material. Samarium Cobalt magnets, also known as SmCo, have better temperature stability and are extremely resistant to demagnetization. However, they are brittle, and prone to cracking and chipping.
Samarium Cobalt magnets are mainly used in the high-end applications which require high operating temperature between 250° and 350°C, such as aerospace and medical applications.
Alnico Magnets
Alnico Magnet Overview
Alnico magnets are composed of aluminum, nickel, and cobalt. The main advantage of Alnico is its’ low temperature coefficient and the wide operating temperature range from – 273°C to 400°C.
Alnico 5 and 8 are anisotropic grades, designed to produce high magnetic output in a specified direction. The magnetic orientation is achieved during heat treatment.
How Alnico Magnets are made:
Alnico magnets are manufactured through one of two processes; casting or sintering. Because Alnico is very hard and brittle, machining and drilling cannot be accomplished by ordinary methods.
Alnico magnets are cast or sintered close to the required size, so that grinding to the finish dimensions and tolerances can be minimized.
Cast Alnico 5 and Alnico 8 grades are used extensively in rotation machinery, communications, meters, instruments, sensing devices and holding applications. Alnico 8 offers higher resistance to demagnetization (coercive force).
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 of less than 1oz.
During processing, the mix of metal powder is pressed into shape and size inside a die, then sintered at 2300 F in a hydrogen atmosphere.
The sintering process is well suited for large volume production, and parts that are structurally stronger than cast magnets. Relatively close tolerances can be achieved without grinding.
