What’s the difference between bonded NdFeB magnets and sintered NdFeB magnets？

Is bonded magnet better or sintered magnet better? In fact, both types of magnets belong to NdFeB. The two types of magnets are distinguished according to their production processes. The bonded NdFeB magnet is formed by injection molding, while the sintered NdFeB magnet is formed by evacuating and heating at high temperature.

What is a bonded NdFeB magnet?

Bonded neodymium iron boron magnets are generally molded by injection molding. Injection molding is a process of mixing magnetic powder and binder to granulate, and then making permanent magnets through injection molding process called injection molded magnets. Compared with other manufacturing methods of permanent magnets, injection molding has unique and irreplaceable advantages. The injection molding process makes the product have better consistency in size and performance. During the molding process, the material completely fills the mold cavity with the highest concentration under the strong injection pressure, and the material contains thermoplastic binder, so that the magnet has good physical and mechanical capabilities.

What is a sintered NdFeB magnet?

Sintered NdFeB magnet is an anisotropic magnet produced by powder sintering. Generally, only a blank can be produced after sintering, and then through mechanical processing (such as wire cutting, slicing, grinding, etc.) to become magnets of various shapes.

Bonded NdFeB magnets vs sintered NdFeB magnets

Sintered magnets are more magnetic: the bonded NdFeB magnets are molded by injection molding, so they contain adhesives, and the density is generally only 80% of the theoretical value. The sintered neodymium magnet is heated at a high temperature through a complicated process. Therefore, the bonded NdFeB magnet is attenuated by about 30% compared with the sintered NdFeB magnet. For example, the coercivity of our sintered magnet has reached 33AH. Therefore, sintered NdFeB is generally used in a wider range than bonded NdFeB.

Temperature characteristics: The maximum operating temperature of a bonded magnet depends on the magnetic powder and binder used. For example, a combination of ferrite powder and nylon 6 or PPS can pass the 180°C test. Nylon 12 melts when the temperature is above 170°C, so if the design temperature of the magnet exceeds 150°C, nylon 12 is not recommended. Take the neodymium iron boron magnetic powder with higher magnetic energy product as an example. If its intrinsic coercivity is 9500 oersteds (760kA/m), no matter what kind of binder is used, the There will be significant irreversible loss of magnetic properties. In addition, the shrinkage of the binder in the material during cooling will also cause the size of the product to change. The degree of shrinkage depends on the thickness and shape of the product. The typical dimensional tolerance is: ±0.05mm. Therefore, the application range of sintered magnets is wider than that of bonded magnets.

Bonded neodymium iron boron magnets have better corrosion resistance: due to the high content of polymer binder in injection molded magnets, the magnet itself has strong corrosion resistance and usually does not require surface coating protection. Sintered neodymium magnets is a hard and brittle material that is difficult to process. It has high loss during processing, high cost, poor dimensional accuracy, and poor corrosion resistance. The surface requires electroplating.

Bonded magnet injection molding has higher dimensional accuracy: Since the injection molded product is consistent in size with the injection mold cavity, the product dimensional accuracy can be controlled relatively high. The magnetization direction of the magnet can be selected arbitrarily, and the shape of the magnet can be made complex.

Bonded magnets are cheaper：have less materials, fewer processes, and simple processes. But the magnetic performance is low, and the highest performance of the isotropic bonded magnet is only one-fifth of the sintered NdFeB magnet.

Application 

Bonded NdFeB magnets do not require mechanical processing to obtain the final size magnets, which can save materials. The product has high dimensional accuracy and is suitable for mass production. But the magnetism is weak. The bonding is suitable for some thin, small and irregular products. Bonded magnets are often used in: magnetic stators of low-power DC motors, multi-pole magnetic rotors of brushless DC and stepping motors, magnetic transmission devices, automotive and other industrial sensors and other products. For any specific application, the choice of binder depends on many factors, including: temperature characteristics, strength, water absorption, solvent resistance, complexity of the magnet shape, and compatibility with magnetic powder.

Sintered magnets are more widely used，Sintered magnets are widely used in different applications, such as electronics, electrical appliances, packaging, motors, toys, leather goods, automobile machinery,  loudspeakers, magnetic hooks, magnetic holder, filters automobiles etc.