What do the different product grades of sintered NdFeB mean?
NdFeB strong magnetic grades are in contact with friends in the magnetics-related industries every day, so what is behind these complex grades? What are the differences between different grades of NdFeB magnets? How to choose the appropriate NdFeB magnetic material by grade? Today I will give you a systematic explanation.
Magnetic Characteristics of Sintered NdFeB Magnets
| Grade | Remanence | Coercive Force | Intrinsic Coercive force | Max Energy Product | Max Working Temp. | |||||
| Br | Hcb | Hci | (BH) max | |||||||
| KG | T | KOe | KA/m | KOe | KA/m | MGOe | KJ/m | ℃ | °F | |
| N35 | 11.4-11.8 | 1.18-1.28 | ≥ 10.8 | ≥ 836 | ≥ 12 | ≥ 955 | 33-36 | 263-287 | 80 | 176 |
| N38 | 11.8-12.3 | 1.18-1.28 | ≥ 10.8 | ≥ 860 | ≥ 12 | ≥ 955 | 36-39 | 287-310 | 80 | 176 |
| N40 | 12.7-12.9 | 1.27-1.29 | ≥ 11.0 | ≥ 876 | ≥ 12 | ≥ 955 | 38-41 | 303-326 | 80 | 176 |
| N42 | 12.9-13.3 | 1.29-1.33 | ≥ 10.5 | ≥ 836 | ≥ 12 | ≥ 955 | 40-43 | 318-342 | 80 | 176 |
| N45 | 13.3-13.8 | 1.33-1.38 | ≥ 9.5 | ≥ 756 | ≥ 12 | ≥ 955 | 43-46 | 342-366 | 80 | 176 |
| N48 | 13.8-14.2 | 1.38-1.42 | ≥ 10.5 | ≥ 835 | ≥ 12 | ≥ 955 | 46-49 | 366-390 | 80 | 176 |
| N50 | 13.8-14.5 | 1.38-1.45 | ≥ 10.5 | ≥ 835 | ≥ 11 | ≥ 955 | 47-51 | 374-406 | 80 | 176 |
| N52 | 14.3-14.8 | 1.43-1.48 | ≥ 10.8 | ≥ 860 | ≥ 11 | ≥ 876 | 50-53 | 398-422 | 80 | 176 |
| 33M | 11.4-11.8 | 1.14-1.18 | ≥ 10.3 | ≥ 820 | ≥ 14 | ≥ 1114 | 31-33 | 247-263 | 100 | 212 |
| 35M | 11.8-12.3 | 1.18-1.23 | ≥ 10.8 | ≥ 860 | ≥ 14 | ≥ 1114 | 33-36 | 263-287 | 100 | 212 |
| 38M | 12.3-12.7 | 1.23-1.27 | ≥ 11.0 | ≥ 876 | ≥ 14 | ≥ 1114 | 38-41 | 303-326 | 100 | 212 |
| 40M | 12.7-12.9 | 1.27-1.29 | ≥ 11.4 | ≥ 907 | ≥ 14 | ≥ 1114 | 38-41 | 303-326 | 100 | 212 |
| 42M | 12.8-13.2 | 1.28-1.32 | ≥ 11.6 | ≥ 923 | ≥ 14 | ≥1114 | 40-43 | 318-342 | 100 | 212 |
| 45M | 13.2-13.8 | 1.32-1.38 | ≥ 11.8 | ≥ 939 | ≥ 14 | ≥ 1114 | 43-46 | 342-366 | 100 | 212 |
| 48M | 13.6-14.0 | 1.36-1.40 | ≥ 11.8 | ≥ 939 | ≥ 14 | ≥ 1114 | 46-49 | 366-390 | 100 | 212 |
| 50M | 14.0-14.5 | 1.40-1.45 | ≥ 13.0 | ≥ 1033 | ≥ 14 | ≥ 1114 | 48-51 | 382-406 | 100 | 212 |
| 30H | 10.8-11.4 | 1.08-1.14 | ≥ 10.2 | ≥ 812 | ≥ 17 | ≥ 1353 | 28-31 | 223-247 | 120 | 248 |
| 33H | 11.4-11.8 | 1.14-1.18 | ≥ 10.6 | ≥ 844 | ≥ 17 | ≥ 1353 | 31-33 | 247-263 | 120 | 248 |
| 35H | 11.8-12.3 | 1.18-1.28 | ≥ 11.0 | ≥ 876 | ≥ 17 | ≥ 1353 | 33-36 | 263-287 | 120 | 248 |
| 38H | 12.3-12.7 | 1.23-1.27 | ≥ 11.2 | ≥ 890 | ≥ 17 | ≥ 1353 | 36-39 | 287-310 | 120 | 248 |
| 40H | 12.7-12.9 | 1.27-1.29 | ≥ 11.5 | ≥ 915 | ≥ 17 | ≥ 1353 | 38-41 | 303-326 | 120 | 248 |
| 42H | 12.8-13.2 | 1.28-1.32 | ≥ 12.0 | ≥ 955 | ≥ 17 | ≥ 1353 | 40-43 | 318-342 | 120 | 248 |
| 45H | 13.2-13.5 | 1.32-1.38 | ≥ 12.0 | ≥ 955 | ≥ 17 | ≥ 1353 | 42-46 | 335-366 | 120 | 248 |
| 46H | 13.3-13.8 | 1.33-1.38 | ≥ 12.2 | ≥ 972 | ≥ 16 | ≥ 1274 | 44-47 | 350-374 | 120 | 248 |
| 48H | 13.6-14.3 | 1.36-1.43 | ≥ 12.5 | ≥ 995 | ≥ 16 | ≥ 1274 | 46-49 | 366-390 | 120 | 248 |
| 30SH | 10.8-11.4 | 1.081.14 | ≥ 10.0 | ≥ 796 | ≥ 20 | ≥ 1672 | 28-31 | 223-247 | 150 | 302 |
| 33SH | 11.4-11.8 | 1.14-1.18 | ≥ 10.5 | ≥ 836 | ≥ 20 | ≥ 1672 | 31-34 | 247-276 | 150 | 302 |
| 35SH | 11.8-12.3 | 1.18-1.23 | ≥ 11.0 | ≥ 876 | ≥ 20 | ≥ 1672 | 33-36 | 263-287 | 150 | 302 |
| 38SH | 12.3-12.7 | 1.23-1.27 | ≥ 11.4 | ≥ 907 | ≥ 20 | ≥ 1972 | 36-39 | 287-310 | 150 | 302 |
| 40SH | 12.5-12.8 | 1.25-1.28 | ≥ 11.8 | ≥ 939 | ≥ 20 | ≥ 1972 | 38-41 | 302-326 | 150 | 302 |
| 42SH | 12.8-13.2 | 1.28-1.32 | ≥ 11.8 | ≥ 939 | ≥ 20 | ≥ 1672 | 40-43 | 320-343 | 150 | 302 |
| 45SH | 13.2-13.8 | 1.32-1.38 | ≥ 12.6 | ≥ 1003 | ≥ 20 | ≥ 1592 | 43-46 | 342-366 | 150 | 302 |
| 30UH | 10.8-11.4 | 1.08-1.14 | ≥ 10.2 | ≥ 812 | ≥ 25 | ≥ 1990 | 28-31 | 223-247 | 180 | 356 |
| 33UH | 11.3-11.7 | 1.13-1.17 | ≥ 10.7 | ≥ 852 | ≥ 25 | ≥ 1990 | 31-33 | 247-263 | 180 | 356 |
| 35UH | 11.7-12.1 | 1.17-1.21 | ≥ 10.7 | ≥ 852 | ≥ 25 | ≥ 1990 | 33-36 | 263-287 | 180 | 356 |
| 38UH | 12.1-12.5 | 1.21-1.25 | ≥ 11.4 | ≥ 907 | ≥ 25 | ≥ 1990 | 36-39 | 287-310 | 180 | 356 |
| 40UH | 12.5-12.8 | 1.25-1.28 | ≥ 11.4 | ≥ 907 | ≥ 25 | ≥ 1990 | 38-41 | 302-326 | 180 | 356 |
| 28EH | 10.5-10.8 | 1.05-1.08 | ≥ 9.5 | ≥ 756 | ≥ 30 | ≥ 2388 | 26-29 | 207-231 | 200 | 392 |
| 30EH | 10.8-11.4 | 1.08-1.14 | ≥ 9.5 | ≥ 756 | ≥ 30 | ≥ 2388 | 28-31 | 223-241 | 200 | 292 |
| 33EH | 11.3-11.7 | 1.13-1.17 | ≥ 10.2 | ≥ 812 | ≥ 30 | ≥ 2388 | 31-33 | 247-263 | 200 | 392 |
| 35EH | 11.7-12.1 | 1.17-1.21 | ≥ 10.2 | ≥ 812 | ≥ 30 | ≥ 2388 | 33-36 | 263-287 | 200 | 392 |
| 38EH | 12.1-12.5 | 1.21-1.25 | ≥ 11.4 | ≥ 907 | ≥ 30 | ≥ 2388 | 36-39 | 287-310 | 200 | 392 |
| 30AH | 10.8-11.3 | 1.08-1.13 | ≥ 10.2 | ≥ 812 | ≥ 35 | ≥ 2785 | 28-32 | 223-255 | 220 | 428 |
| 33AH | 11.2-11.7 | 1.12-1.17 | ≥ 10.2 | ≥ 812 | ≥ 35 | ≥ 2785 | 31-34 | 247-271 | 220 | 428 |
First, the common sintered NdFeB grades can be divided into seven categories: N, M, H, SH, UH, EH and TH. Except for the N type, every other type will appear at the end of the product brand. For example, N38M is M series, N38TH is TH series, and if there is no letter after “N38”, then it is N series. (Of course, there are some uncommon and higher-performance grades in the back.
Secondly, there are four main indicators for measuring the performance of sintered NdFeB products.
- Br remanence: the unit is Tesla (T) and Gauss (Gs), 1Gs = 0.0001T. It refers to the magnetic induction intensity of a sintered neodymium iron boron magnet when a magnet is magnetized by an external magnetic field in a closed circuit environment until the technology is saturated and then the external magnetic field is cancelled. In layman’s terms, it can be temporarily understood as the magnetic force of the magnet after magnetization.
- Hcb Coercivity: The unit is Oersted (Oe) or Ampere/meter (A/m), 1A/m=(4π/1000)Oe, 1 Oe=(1000/4π) A/m. When the magnet is magnetized in the reverse direction, the value of the reverse magnetic field strength required to reduce the magnetic induction intensity to zero is called the magnetic coercive force. But at this time, the magnetization of the magnet is not zero, but the applied reverse magnetic field and the magnetization of the magnet cancel each other out. At this time, if the external magnetic field is removed, the magnet still has certain magnetic properties.
- Hcj Intrinsic coercivity: The strength of the reverse magnetic field required to reduce the magnetization of the magnet to zero. We call it the intrinsic coercive force. Its unit of measurement is the same as the coercive force. The classification of magnetic grades is based on their intrinsic coercivity. Low coercivity N, medium coercivity M, high coercivity H, ultra-high coercivity UH, extremely high coercivity EH, highest coercivity TH. The intrinsic coercivity of NdFeB magnets will decrease as the temperature rises. Therefore, when choosing to use NdFeB magnets, you must choose the grade that suits us. The next issue will be further introduction
- (BH)max Maximum magnetic energy product: represents the magnetic energy density established in the space between the two magnetic poles of the magnet, that is, the static magnetic energy per unit volume of the air gap, which is the maximum value of the product of B and H, and its size directly indicates the performance of the magnet . The numbers in the magnetic grades represent the theoretical maximum energy product of the product.
Again, we can see that there are two measurement units for each performance index. This is because they use different unit systems— SI system and CGS system, that is, the international system of units and the Gaussian system of units, which are like length units. The difference between “m” and “li”. There is a certain conversion relationship between the International System of Units and the Gaussian System of Units, but it is more complicated, so we won’t introduce it.
Finally, it is not difficult to find that the performance of sintered NdFeB products under each brand is not a unique fixed value, but a numerical range. The performance ranges of products from different manufacturers are not completely the same. You should pay special attention to whether the performance of the supplier’s products can meet your requirements when purchasing.
Thermal Characteristics of Sintered NdFeB Magnets
| Neodymium Material Type | Maximum Operating Temp | Curie Temp |
| N | 176°F (80°C) | 590°F (310°C) |
| M | 212°F (100°C) | 644°F (340°C) |
| H | 248°F (120°C) | 644°F (340°C) |
| SH | 302°F (150°C) | 644°F (340°C) |
| UH | 356°F (180°C) | 662°F (350°C) |
| EH | 392°F (200°C) | 662°F (350°C) |
| AH | 428°F (220°C) | 662°F (350°C) |
Physical and Mechanical Characteristics of Sintered NdFeB Magnets
| Density | 7.4-7.5 g/cm3 |
| Compression Strength | 950 MPa (137,800 psi) |
| Tensile Strength | 80 MPa (11,600 psi) |
| Vickers Hardness (Hv) | 560-600 |
| Young’s Modulus | 160 GPa (23,200 ksi) |
| Recoil Permeability | 1.05 μrec |
| Electrical Resistivity (ρ) | 160 μ-ohm-cm |
| Heat Capacity | 350-500 J/(kg.°C) |
| Thermal Expansion Coefficient (0 to 100°C) | 5.2 x 10-6 /°C |
| parallel to magnetization direction | |
| Thermal Expansion Coefficient (0 to 100°C) | -0.8 x 10-6 /°C |
| Perpendicular to magnetization direction |
Plating Characteristics of Sintered NdFeB Magnets
| Plating Type | Overall Thickness | Salt Spray Test | Pressure Cooker Test |
| NiCuNi (Nickel Copper Nickel) | 15-21 μm | 24 hours | 48 hours |
| NiCu + Black Nickel | 15-21 μm | 24 hours | 48 hours |
| NiCuNi + Epoxy | 20-28 μm | 48 hours | 72 hours |
| NiCuNi + Gold | 16-23 μm | 36 hours | 72 hours |
| NiCuNi + Silver | 16-23 μm | 24 hours | 48 hours |
| Zinc | 7-15 μm | 12 hours | 24 hours |
Each individual layer of Nickel and Copper are 5-7 μm thick. The Gold and Silver plating layers are 1-2 μm thick. Test results shown to allow comparison between plating options. Performance in your application under your specific test conditions may vary. Salt Spray testing conducted with a 5% NaCl solution, at 35°C. Pressure Cooker Test (PCT) conducted at 2 atm, 120°C at 100% RH.
Measurement Systems of Sintered NdFeB Magnets
| Unit | cgs System | SI System | English System |
| Length (L) | centimeter (cm) | meter (m) | inch (in) |
| Flux (ø) | Maxwell | Weber (Wb) | Maxwell |
| Flux Density (B) | Gauss (G) | Tesla (T) | lines/in2 |
| Magnetizing Force (H) | Oersted (Oe) | Ampere turns/m (At/m) | Ampere turns/in (At/in) |
| Magnetomotive Force (mmf or F) | Gilbert (Gb) | Ampere turn (At) | Ampere turn (At) |
Conversion Between Systems of Sintered NdFeB Magnets
| CGS System to SI system |
| 1 Oe = 79.62 At/m |
| 10,000 G = 1 T |
| 1 Gb = 0.79577 At |
| 1 Maxwell = 1 Line = 10-8 Wb |
| 1 G = 0.155 lines/in2 |
How to distinguish between sintered NdFeB magnet and bonded NdFeB magnet?
Neodymium magnet is the industry name for neodymium iron boron powerful magnets. Its chemical formula is Nd2Fe14B. It is a man-made powerful magnet and has the strongest magnetic force so far. The material grades of NdFeB magnets are N25-N52EH; the shapes can be processed into different shapes according to specific requirements, including round, diamond, square, perforated, magnetic tile, racetrack, convex, concave, trapezoidal or Semicircle etc.
How to distinguish bonded NdFeB and sintered NdFeB? In fact, both of these magnetic materials belong to NdFeB. The difference between these two types of magnets is based on their production process. The bonded neodymium iron boron magnet is actually formed by injection molding, while the sintered neodymium iron boron magnet is formed by evacuation and then high-temperature heating and pressing.
The bonded neodymium iron boron magnet is formed by injection molding, so it contains an adhesive, the density of which is generally only about 75% of theoretical. The sintered NdFeB magnet is heated at a high temperature through a complicated process. Therefore, the bonded NdFeB magnet is attenuated by about 25% compared to the sintered NdFeB magnet.
Sintered NdFeB 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. Sintered NdFeB is a hard and brittle material that is difficult to process. It has high loss during processing, high cost, poor dimensional accuracy, poor corrosion resistance, and the surface needs to be electroplated. But the advantage is that it has higher performance, and it has achieved N52H at present.
In summary, the magnetic properties of bonded NdFeB magnets are only about 6% of that of sintered. At present, the energy product of sintered NdFeB magnets can reach above N52H, while the bonded magnets are generally below 10T, and the best is only 12M. The performance of the magnetic powder used in the bonded magnet is generally 15T, and the bonded magnet is only 10.5T at most. Therefore, sintered NdFeB is generally used in a wider range than bonded NdFeB.
Source: China Permanent Magnet Manufacturer – www.rizinia.com
