Neodymium magnets, also called NdFeB magnets, are tetragonal crystals formed by neodymium, iron, and boron. According to different production processes, they can be divided into three types: sintered NdFeB magnets, bonded NdFeB magnets, and hot-pressed NdFeB magnets. Due to the different production processes, they have big differences in magnetic properties, post-processing, and applications. In this article, we will take a closer look at these 3 types of neodymium magnets.
Among the three types of neodymium magnets, sintered NdFeB magnets enjoy the largest output and are most widely used. They are produced by powder metallurgy and are divided into 7 series of N, M, H, SH, UH, EH and TH according to the different coercivity of the products.
The sintered NdFeB that has been commercially produced has a remanence of up to 1.45T and an intrinsic coercivity of up to 2786kA/m. The operating temperature is between 80° and 200° depending on the coercivity.
Sintered NdFeB is easy to be oxidized and corroded, so surface treatment is required. According to different requirements of the use environment, surface treatment methods such as phosphating, electroplating, electroless plating, electrophoresis, and vapor deposition can be used. Common coatings are zinc, nickel, nickel-copper-nickel, epoxy resin, and so on.
Sintered NdFeB is difficult to precisely process into a special shape, and problems such as cracking, damage, and difficulty in assembly occur during the process. In order to solve these problems, people tried to crush the permanent magnets and mix them with adhesives, and then press them into a shape in a magnetic field. Thus, bonded NdFeB was developed. It has the advantages of low cost, high dimensional accuracy, a large degree of freedom of shape, good mechanical strength, light specific gravity, etc., and has been widely used in the market.
There are currently 4 processes for forming bonded NdFeB: calendering, injection molding, extrusion, and compression molding, of which calendering and injection are more mainstream. Bonded NdFeB magnets are generally only 80% of theoretical density due to the addition of a large amount of adhesive, so they are weaker than sintered NdFeB magnets in terms of magnetic properties.
Bonded NdFeB is an isotropic magnet with the same magnetism in all directions, so it is convenient to manufacture multi-pole or even countless monolithic magnets. (Bonded NdFeB can also be made into anisotropic magnets)
Hot-pressed NdFeB can achieve magnetic properties similar to sintered NdFeB without adding heavy rare earth elements and has the advantages of high density, high orientation, good corrosion resistance, and high coercivity. However, its mechanical properties are not good, and due to patent monopoly, the processing cost is relatively high. At present, only a few companies on the market have achieved mass production of hot-pressed NdFeB products.
Due to the limitation of the molding technology, the current hot-pressed NdFeB can only be made into a ring shape, and the application range is limited to a certain extent. It is currently mainly used in the fields of automobile EPS motors. The hot-pressed NdFeB magnet has high magnetic performance, and the maximum radial energy product of the magnetic ring can reach 240～360kJ/m3. The magnetic ring is oriented in the radial direction, and the radial magnetic performance is uniform, which can make the motor run quietly and the torque output is smooth. At the same time, it has high heat resistance, and the use temperature can reach 180℃-200℃.
Thank you for reading our article and we hope it can help you to have a better understanding of the 3 types of neodymium magnets. If you want to learn more about neodymium magnets or other types of magnets, we would like to advise you to visit Stanford Magnets for more information.
As a leading magnet supplier across the world, Stanford Magnets has been involved in R&D, manufacturing, and sales of magnets since the 1990s. It provides customers with high-quality permanent magnets like SmCo magnets, neodymium magnets, AlNiCo magnets, and ferrite magnets (ceramic magnets) at a very competitive price.