Sintered NdFeB Magnet
Sintered NdFeB Magnet
Remanence, coercivity, Curie temperature, and BH energy product properties of sintered NdFeB magnets characterize this type of magnets as those that have high strength and general application potential. The remanence of a ferromagnetic material is the magnitude of the magnetic field that the material can sustain when it is no longer subject to an external magnetic field. The coercivity of a permanent magnet is its ability to maintain its magnetic field in an external field applied in the reverse direction. As the temperature of a material increases, the particles begin to excite and move randomly; this effect can destroy the magnetic properties of a permanent magnet. The temperature at which the magnet loses its properties is different for each material and is called the Curie temperature. The BH product is the multiplication of the remanent magnetic field and the coercive magnetic field that are required to reduce the remanence to zero. This quantity describes the energy of a volume of magnetic material.
NdFeB magnets are manufactured using a power metallurgy production process. After sintering the material should be sliced to required size for coating and magnetization. Sintered NdFeB magnets offer the highest energy per unit volume among any other permanent magnet materials, it can lift up to 1000 times its own weight. It is manufactured in numerous energy and temperature grades: current energy levels start at 33 MGO with up to 52 MGO. The intrinsic (jHc) coercive force determines the maximum operating temperature, however, it should be noted that even with the SH (high coercivity) of 150oC degree, materials still have a poor temperature coefficient, which means that an open circuit magnet can lose about 0,10% of remanence per oC. These losses are called reversible losses and the remanence will recover as the temperature falls.
A vast choice of magnets with standard disk, cylinder, block shapes are available; non standard shapes can be manufactured by using diamond slicing or grinding techniques. Apart from temperature difficulties, due to the high Iron content in NdFeB magnets, they also suffer from corrosion that is why magnets are normally supplied coated; moreover, particular care must be taken in order to prevent from Hydrogen or salt water environments. Although Neodymium offers 30-40% higher energy levels than SmCo alloys and is considerably lower in cost and less brittle, SmCo magnets should still be considered your first choice if either high temperatures and or hostile environments are to be encountered within your application.
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