The pressed bonded NdFeB magnet is a type of bonded NdFeB magnet, and the main topic of this article.
Definition of Pressed Bonded NdFeB Magnet
A pressed bonded NdFeB magnet is a permanent magnetic material formed by mixing rapidly quenched NdFeB magnetic powder with a binder and then shaping it under pressure.
Rapidly quenched NdFeB magnetic powder is a high-performance NdFeB alloy powder produced through a rapid quenching process, giving it a specific crystal structure and magnetic properties. The binder serves to bond the magnetic particles together. The magnetic powder and binder are mixed in a particular ratio, granulated, and combined with a coupling agent to produce the final product. Finally, coating protection is applied through methods such as cathodic electrodeposition, spraying, or vapor deposition.
Characteristics of Pressed Bonded NdFeB Magnets
| Corrosion Resistance: The polymer binder forms a protective film on the magnet’s surface, isolating the magnetic powder from the external environment and preventing direct contact with corrosive agents, thereby enhancing corrosion resistance. Additionally, the rapidly quenched NdFeB powder exhibits nano-sized grains and isotropic properties, which contribute to enhanced chemical stability and further improve corrosion resistance.
| Magnetization Properties: Being isotropic, these magnets exhibit the same magnetic properties in all directions, making them suitable for multi-pole magnetization and various magnetization orientations.
| Magnetic Performance: Due to the addition of the binder, the density typically falls to about 80% of the theoretical value, resulting in lower magnetic performance compared to sintered NdFeB magnets.
| Dimensional Accuracy: High dimensional accuracy with minimal deformation, allowing direct molding into various permanent magnet components without secondary processing.
| Shape Flexibility: High design freedom, enabling the production of magnets in various shapes such as strips, sheets, tubes, rings, or other complex geometries based on application requirements.
Grades of Pressed Bonded NdFeB Magnets
| Grade | Br (KGs) | Hcb (Koe) | Hcj (Koe) | (BH)max (MGOe) | Temp.Coeff.(%/°C) | Curie Temp.(°C) | Max.Op.Temp.(°C) |
|---|---|---|---|---|---|---|---|
| TN-2M | 2.5-3.5 | 2.0-3.0 | 3.0-4.0 | 2.0-3.0 | -0.1 | 320 | 160 |
| TN-2 | 2.5-3.5 | 2.0-3.0 | 5.0-7.0 | 2.0-3.0 | -0.1 | 320 | 160 |
| TN-3M | 3.5-4.5 | 2.5-3.5 | 3.5-4.5 | 3.0-4.0 | -0.1 | 350 | 160 |
| TN-3 | 3.5-4.5 | 2.5-3.5 | 6.8-7.3 | 3.0-4.0 | -0.1 | 350 | 160 |
| TN-4M | 4.0-5.0 | 2.5-4.0 | 4.5-5.5 | 3.5-4.5 | -0.11 | 350 | 160 |
| TN-4 | 4.0-5.0 | 2.5-4.0 | 7.3-7.9 | 3.5-4.5 | -0.11 | 350 | 160 |
| TN-5M | 4.5-5.5 | 2.5-4.0 | 4.5-5.5 | 4.5-5.5 | -0.11 | 350 | 160 |
| TN-5 | 4.5-5.5 | 2.5-4.0 | 7.4-8.0 | 4.5-5.5 | -0.11 | 350 | 160 |
| TN-6M | 5.5-6.0 | 3.5-4.0 | 5.5-6.0 | 5.5-6.5 | -0.11 | 350 | 160 |
| TN-7M | 5.5-6.0 | 4.0-4.5 | 6.5-7.0 | 6.5-7.0 | -0.12 | 320 | 160 |
| TN-7 | 6.0-6.5 | 4.0-5.0 | 7.5-8.5 | 7.0-8.0 | -0.12 | 320 | 160 |
| T N-7H | 6.0-6.5 | 5.0-6.0 | 12.0-14.0 | 7.0-8.0 | -0.11 | 350 | 180 |
| TN-8M | 6.0-6.5 | 4.0-5.0 | 7.5-8.5 | 7.5-8.5 | -0.12 | 320 | 160 |
| TN-8 | 6.0-6.5 | 4.5-5.5 | 8.5-9.5 | 7.5-8.5 | -0.12 | 320 | 160 |
| TN-8H | 6.0-6.5 | 5.0-6.0 | 10.0-12.0 | 7.5-8.5 | -0.11 | 350 | 180 |
| TN-9M | 6.5-7.0 | 4.5-5.5 | 7.5-8.5 | 8.5-9.5 | -0.12 | 320 | 160 |
| TN-9 | 6.5-7.0 | 4.5-6.0 | 8.5-9.5 | 8.5-9.0 | -0.12 | 320 | 160 |
| TN-10 | 6.5-7.0 | 4.5-6.0 | 8.5-9.5 | 9.0-10 | -0.12 | 320 | 160 |
| TN-10H | 6.5-7.0 | 5.5-6.0 | 11.0-13.0 | 9.0-10.0 | -0.11 | 350 | 180 |
| TN-12 | 7.0-7.5 | 5.0-6.0 | 8.5-9.5 | 9.5-10.5 | -0.12 | 320 | 160 |
| TN-13 | 7.0-8.0 | 5.5-6.5 | 8.5-9.5 | 10.5-11.5 | -0.12 | 320 | 160 |
Manufacturing Process of Pressed Bonded NdFeB Magnets
| Mixing: Magnetic powder and binder are blended in a mixer at a specific ratio to ensure uniform distribution. A coupling agent may be added to enhance adhesion between the powder and binder.
| Pressing: The mixture is placed into a mold and compacted under pressure. The pressing force affects the magnet’s density and performance, requiring adjustment based on size and shape.
| Curing: The pressed magnet is placed in a curing oven at 120°C–150°C to solidify the binder, firmly bonding the magnetic particles and forming a magnet with sufficient strength and magnetic properties.
| Grinding: If high-dimensional accuracy is required, grinding is performed to improve precision and surface quality.
| Coating: The magnet is coated (e.g., spraying, electrodeposition) to enhance corrosion resistance and insulation properties.
| Magnetization: The coated magnet is placed in a magnetizer to achieve the desired magnetic performance.
Types of Coatings for Pressed Bonded NdFeB Magnets
| Epoxy Coating: Offers excellent waterproofing, chemical resistance, and adhesion, with minimal absorption and permeability. Applied via spraying or electrodeposition, it effectively protects the magnet from corrosion, making it suitable for use in industrial equipment, automotive parts, and other applications.
| Polyurethane Coating: Offers excellent wear resistance, weather resistance, and flexibility, thereby extending the magnet’s lifespan in demanding environments, such as outdoor equipment and automotive interiors.
| Teflon Coating: Known for its non-stick properties, corrosion resistance, and high-temperature stability, it also offers excellent electrical insulation, making it ideal for high-end electronics and electrical devices.
| Nickel Plating: The nickel layer has a stainless-steel-like appearance, resists oxidation, and maintains a glossy finish. It can pass 12–72-hour salt spray tests and is commonly applied in a Ni-Cu-Ni multilayer structure for enhanced corrosion resistance, used in high-end electronics and automotive components.
| Chrome Plating: Highly corrosion-resistant and chemically inert, but due to high costs, it is rarely used except in highly acidic or alkaline environments.
Magnetization Direction of Pressed Bonded NdFeB Magnets
As isotropic magnets, they exhibit uniform magnetic properties in all directions, allowing for flexible magnetization orientations.
Applications of Pressed Bonded NdFeB Magnets
| Office Products: Drive motors for printers, scanner motors, copier synchronous feed motors (STP), etc.
| Automotive Motors: Window lift motors, seat adjuster motors, etc.
| Industrial & Household Motors: Servo motors, power tool motors, air conditioning refrigeration motors, etc.
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