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Neodymium Iron Boron Permanent Magnet Material Technical Specification Manual (Version 2026)
Detailed Overview of Neodymium Iron Boron (NdFeB) Permanent Magnet Grades, Magnetic Properties, Temperature Characteristics, and Dimensional Tolerances Neodymium Iron Boron (NdFeB), also known as Neo magnets or N42 magnets, is the strongest type of permanent magnet commercially available. It is widely used in electric motors, generators, hard disk drives, magnetic resonance imaging (MRI) machines, and various consumer electronics. Below is a detailed technical breakdown of its key parameters. ### 1. Grades (牌号) The grade of an NdFeB magnet indicates its maximum energy product ($BH_{max}$). The naming convention typically consists of the letter "N" followed by a number representing the maximum energy product in MGOe (Mega-Gauss Oersteds). * **Standard Series:** N30 to N52 * **N30 – N38:** Lower cost, suitable for general applications where extreme strength isn't critical. * **N40 – N48:** High performance, commonly used in automotive sensors, wind turbines, and high-efficiency motors. * **N49 – N52:** Maximum energy density. Used in space-constrained applications requiring peak magnetic force (e.g., aerospace, high-end speakers). * **High-Temperature Series (H, SH, UH, EH):** * These grades have the same base number but are designed to withstand higher temperatures without losing magnetism. * **N35H:** Max operating temp ~100°C * **N35SH:** Max operating temp ~150°C * **N35UH:** Max operating temp ~180°C * **N35EH:** Max operating temp ~200°C * **Low-Cobalt / Cobalt-Free:** Newer formulations aim to reduce reliance on cobalt while maintaining performance. ### 2. Magnetic Properties (磁性能) Key metrics define the magnet's ability to generate a magnetic field and resist demagnetization. | Parameter | Symbol | Unit | Typical Range (N42 Standard) | Significance | | :--- | :--- | :--- | :--- | :--- | | **Residual Induction** | $Br$ | Gauss (G) / mT | 12,000 – 14,000 G (1.2 – 1.4 T) | Strength of the magnetic field when no external field is applied. Higher is better. | | **Coercivity (Intrinsic)** | $H_{cj}$ | Oe (Oersted) / kA/m | 10,000 – 16,000 Oe (800 – 1270 kA/m) | Resistance to demagnetization by opposing fields. Critical for stability. | | **Coercivity (Normal)** | $H_{cb}$ | Oe / kA/m | 10,000+ Oe | Resistance to partial demagnetization. | | **Maximum Energy Product** | $(BH)_{max}$ | MGOe / kJ/m³ | 38 – 52 MGOe (300 – 410 kJ/m³) | Overall magnetic strength. Determines how small a magnet can be for a given application. | | **Reversible Temp Coeff.** | $\alpha(Br)$ | %/°C | -0.09 to -0.12 %/°C | Rate at which magnetic strength drops as temperature rises. | | **Remanence Temp Coeff.** | $\beta(H_{cj})$ | %/°C | -0.4 to -0.6 %/°C | Rate at which coercivity drops with temperature. | ### 3. Temperature Characteristics (温度特性) NdFeB magnets are sensitive to temperature changes. Performance degrades as heat increases, and they suffer irreversible losses if the Curie temperature is approached or exceeded. * **Operating Temperature Range:** * Standard grades (N): Up to 80°C * H Grade: Up to 100°C * SH Grade: Up to 150°C * UH Grade: Up to 180°C * EH Grade: Up to 200°C * **Curie Temperature ($T_c$):** Typically 310°C – 380°C. Above this point, the material loses all magnetic properties permanently. * **Irreversible Losses:** Even below the max operating temperature, exposure to high heat causes temporary loss of flux. If cooled down, some strength may not return. This is why derating factors are applied in motor design. * **Thermal Expansion:** Low coefficient of thermal expansion, but mechanical stress due to thermal cycling can cause cracking in brittle NdFeB materials. ### 4. Dimensional Tolerances (尺寸公差) Due to the sintering process, precise control over dimensions is challenging but achievable with secondary machining (grinding, cutting, EDM). * **Standard Tolerances (Per ISO 9001 / Common Industry Standards):** * **Diameter (for discs/cylinders):** ±0.05 mm to ±0.10 mm * **Thickness/Height:** ±0.05 mm to ±0.10 mm * **Length/Width (Rectangles):** ±0.05 mm to ±0.10 mm * **High-Precision Tolerances:** * Achievable via precision grinding: ±0.01 mm to ±0.02 mm. * Requires additional cost and time. * **Angle Tolerance:** Perpendicularity usually within 0.05 mm over the face diameter. * **Surface Finish:** Ra 0.8 μm to 1.6 μm after grinding. Polishing can achieve smoother finishes but adds cost. ### 5. Other Technical Considerations * **Corrosion Resistance:** NdFeB is highly prone to oxidation and rust. * **Coatings Required:** Nickel-Copper-Nickel (Ni-Cu-Ni), Zinc, Epoxy, Gold, or Parylene. * Without coating, the magnet will degrade rapidly in humid environments. * **Brittleness:** Sintered NdFeB is ceramic-like. It is strong magnetically but mechanically weak; it chips and cracks easily under impact or tensile stress. * **Demagnetization Curve:** The shape of the B-H loop determines suitability for dynamic applications (motors) vs. static applications (holding latches). A square loop is preferred for holding, while a rounded loop aids in motor efficiency.
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