Bonded Mangets

Bonded magnet is a kind of composite material which composed of magnetic powder and binder. Bonded Magnets are distinguished for complex shape, high dimensional precision, tight tolerance, no need for subsequent mechanical machining, integration capability with other functional parts, and suitable for mass production. Magnetic powder, volume fraction of binder and interior porosity plays a decisive role in the magnetic properties of the bonded magnet. Isotropic Neodymium magnet accounts for more than 80% of bonded rate earth magnet market, then other 20% are occupied by anisotropic Neodymium magnets, SmFeN magnets, and Samarium Cobalt magnets. Besides varies choices of magnetic powder, binder with different characters are also adding more diversity to the bonded magnets. The frequently-used binder includes thermosetting and thermoplastic material, thus correspond to compression molding, injection molding, extrusion molding, and calendering molding process. Bonded magnets with different binder also exhibits disparate magnetic properties, shape, and dimension adaptability.

▲ Characteristic Comparison of Different Molding Process:

▲ Product Classifications of Bonded Magnet:

  ● Compression Molded Magnet

Compression molded magnet is mainly composed of isotropic NdFeB powder and thermosetting binder. Compression molded magnet needs to process epoxy resin coating by electrophoresis of spraying to obtain excellent corrosion resistance. Compression molded magnet has relatively higher powder filling ratio and magnetic properties in comparison with injection molded magnet, therefore, it is able to replace sintered ferrite magnet and sintered Neodymium magnet in some applications. Unlike injection molded magnet, compression molded magnet is more adapted to regular shape and low mechanical strength requirements. As isotropic magnet, compression molded magnet can freely select magnetization direction. The most representative application of compression molded magnet is the thin-wall ring magnet. Thin wall magnet can be widely served for variety of stepper motors and brushless direct current (BLDC) motors after multi-pole magnetized.

○ Manufacturing Process of Compression Molded Magnet

○ Magnetic Properties of Compression Molded Magnet

  ● Injection Molded Magnet

Injection molded magnet, often refers specifically to isotropic injection Neodymium magnet, is a kind of composite material produced by mixing isotropic NdFeB powder with the thermoplastic binder and some additives which then allow the magnet to be injection molded just same as any other plastic material would be. For isotropic injection molded neodymium magnet, its magnetic properties are lower than compression molded Neodymium magnet owing to relatively lower filling ratio of isotropic NdFeB powder. The most frequently used thermoplastic binder includes PA12 (Nylon12), PA6 (Nylon6), and PPS, then their maximum operating temperature is 120, 150, 180 degrees Celsius, respectively. Injection molded magnet is praised for its superior dimensional accuracy and mechanical strength. In addition, it also well suited for mass production and integrated ability with other functional parts. Injection molded magnet is broadly applied to household appliances, office automation, consumer electronics, and automotive industry for a long time.

○ Manufacturing process of Injection Molded Magnet

 ○ Magnetic Properties of Injection Molded Magnet

  ● Injection Ferrite Magnet

Injection ferrite magnet is a type of bonded magnet manufactured by mixing ferrite magnetic powder with the thermoplastic binder which then enables the magnet to be injection molded just like any other plastic would be. The maximum operating temperature of PA12 based, PA6 based, and PPS based magnet can achieve 120, 150, and 180 degrees Celsius, respectively. Injection ferrite magnet also has excellent mechanical strength, dimensional accuracy, shape applicability, and integrated ability with other functional parts, which totally same as injection molded Neodymium magnet. Its magnetic performance and cost is significantly lower than injection molded Neodymium magnet and widely served for sensors and low performance motors. Anisotropic injection ferrite magnet need to apply a permanent magnetic field or an electromagnetic field to align molten compound during the injection molding process.

○ Magnetic Properties of Injection Ferrite Magnet

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