Bonded neodymium iron boron magnets are a type of permanent magnetic material produced by mixing neodymium iron boron magnetic powder with a binder through a special process. They are widely applied in many fields due to their low cost and flexible shaping advantages.
Definition of Bonded Neodymium Iron Boron Magnets
Bonded neodymium iron boron magnets utilize neodymium iron boron (NdFeB) alloy powder as the magnetic functional phase, typically using magnetic powders prepared through rapid quenching processes, which possess a nanocrystalline structure. A polymer binder (such as epoxy resin, nylon, or polyphenylene sulfide) serves as the matrix phase, helping to fix the magnetic powder particles and provide mechanical strength and shaping properties.
The magnetic powder is mixed with the binder in proportion, and through processes such as molding, injection molding, and rolling molding, it is directly formed into the desired shape within a mold. The final magnet is then cured or cooled to achieve its final form.
Performance Characteristics of Bonded Neodymium Iron Boron Magnets
| Magnetic Properties: The residual magnetic flux density (Br) typically ranges from 5.0 to 8.0 kG (0.5 to 0.8 T), which is about 50%-70% that of sintered neodymium iron boron magnets. The intrinsic coercivity is generally between 8-15 kOe (640-1200 kA/m), offering good resistance to demagnetization, though it is lower than sintered neodymium iron boron magnets. The maximum magnetic energy product (BH_max) usually falls between 5-12 MGOe (40-96 kJ/m³), significantly below the 30-52 MGOe of sintered neodymium iron boron magnets.
| Low Eddy Current Loss: The binder increases the electrical resistivity of the magnet, resulting in low eddy current losses in high-frequency or high-speed applications. This is beneficial for increasing motor efficiency and stability.
| Processing Performance: Because bonded neodymium iron boron magnets are made using molding and injection processes, their dimensional accuracy can reach ±0.05mm or even smaller, eliminating the need for secondary processing and making them suitable for mass production. They can also be shaped into thin walls, gears, rings, and complex shapes to meet specific design requirements.
| Limited Temperature Resistance: Binders are prone to aging, softening, or degrading at high temperatures, which limits their operational temperature. The maximum working temperature is usually no more than 150°C, while some high-performance binders can withstand up to 180°C. However, prolonged use at high temperatures may lead to decreased magnetic properties or reduced mechanical strength.
| Corrosion Resistance: The magnetic powder is encapsulated by the binder, which has good corrosion resistance. Consequently, bonded neodymium iron boron magnets generally do not require additional protection in normal environments. However, they may need surface coatings in strong acids, strong alkalis, or high-humidity environments.
| Difficult Recycling: The close bonding of the binder and magnetic powder makes separation challenging during recycling. Removal of the binder typically requires methods such as high-temperature pyrolysis or chemical dissolution, which are complex and may lead to a decline in the performance of the magnetic powder, resulting in higher recycling costs.
Grade of Bonded Neodymium Iron Boron Magnets
| Property Grade | Br (mT) | Br (Gs) | Hcb (kA/m) | Hcb (kOe) | Hcj (kA/m) | Hcj (kOe) | (BH)max (kJ/m 3) | (BH)max (MGOe) | Tw/ °C |
| BNP-3 | 450-510 | 4500-5100 | 199-263 | 477-597 | 6.0-7.5 | 24-32 | 24-32 | 3.0-4.0 | 120 |
| BNP-6 | 590-650 | 5900-6500 | 302-374 | 597-796 | 7.5-10.0 | 44-53.6 | 44-53.6 | 5.5-7.0 | 120 |
| BNP-8 | 620-670 | 6200-6700 | 390-454 | 636-796 | 8.0-10.0 | 60-68 | 60-68 | 8.0-9.5 | 120 |
| BNP-8SR | 620-660 | 6200-6600 | 405-470 | 955-1114 | 12.0-14.0 | 65.6-72 | 65.6-72 | 8.2-9.0 | 160 |
| BNP-9H | 650-700 | 6500-4000 | 421-484 | 915-1034 | 11.5-13.0 | 72-80 | 72-80 | 9.0-10.0 | 160 |
| BNP-10 | 680-720 | 6800-7200 | 413-477 | 636-796 | 8.0-10.0 | 76-84 | 76-84 | 9.5-10.5 | 120 |
| BNP-11 | 700-740 | 7000-7400 | 430-493 | 636-796 | 8.0-10.0 | 80-88 | 80-88 | 10.0-11.0 | 120 |
| BNP-12L | 730-770 | 7300-7700 | 366-430 | 517-637 | 6.5-8.0 | 84-92 | 84-92 | 10.5-11.5 | 110 |
Applications of Bonded Neodymium Iron Boron Magnets
| Automotive: Bonded neodymium iron boron magnets are primarily used in motors for electric tailgates and electric latch doors, driving the opening and closing mechanisms. They provide stable magnetic performance, making them suitable for motors that require compact size and high torque. Additionally, these magnets are used in motor systems for car seat adjustments, including forward/backward, height, and reclining adjustments, ensuring smooth and precise operations to enhance passenger comfort.
| Power Tools: In the field of power tools, bonded neodymium iron boron magnets are widely applied due to their high dimensional accuracy, design flexibility, good mechanical strength, lightweight, and relatively low cost. For instance, in the motors and transmission systems of electric wrenches, these magnets help improve motor efficiency, enabling the wrench to deliver significant torque in a compact size, meeting the demands for tightening or loosening bolts and nuts.
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Image Source: Couragemagnet & Maglastic & Magnaworkstechnology & Mdpi & Miknatisavm
