# The suction of sintered NdFeB

## What is the suction of sintered NdFeB?

Magnetic attraction refers to the weight of ferromagnetic material that a magnet can absorb. It is affected by the performance, shape, size and adsorption distance of the magnet. There is no mathematical formula to calculate the attraction of a magnet, but we can use it Magnetic attraction measurement device to measure the magnetic attraction value (usually to measure the magnet tension and then convert it to weight), as shown in the figure below. The attractive force of the magnet will gradually decrease as the distance of the adsorbed object increases.

In the application of magnets, magnetic flux or magnetic flux density is an important indicator to measure its performance (especially in motors), but in some application areas, such as magnetic sorting, fishing, etc., magnetic flux is not an effective measure of sorting or The amount of adsorption effect, magnetic attraction is a more effective indicator.

If you search for magnet attraction calculation on the Internet, many websites will write “According to experience, the magnetic force of a neodymium iron boron magnet is 600 times its own weight (or 640 times)”. Is this experience correct? Let’s verify it through experiments just know.
In the experiment, sintered NdFeBN42 magnets of different shapes and sizes were selected. The surface coatings are nickel-copper-nickel, and they are all magnetized in the height direction. The maximum tensile force (N pole) of each magnet was measured and converted into the adsorption weight. The results are as follows:
It is not difficult to find from the measurement results:

• The ratio of the weight that magnets of different shapes and sizes can absorb to their own weight varies greatly, some are less than 200 times, some are more than 500 times, and some can reach more than 3000 times, so the 600 times written on the Internet is not completely correct.
• A cylinder or round cake with the same diameter, the greater the height, the greater the weight that can be sucked, and the suction force is basically proportional to the height.
• Cylinders or round cakes of the same height (blue cells), the larger the diameter, the greater the weight that can be sucked, and the suction is basically proportional to the diameter.
• Cylinders or round cakes (yellow cells) of the same volume and weight have different diameter and height, and the weight that can be sucked varies greatly. Generally, the longer the magnet orientation, the greater the suction.
• Magnets with the same volume may not have the same attractive force. Depending on the shape, the attractive force may vary greatly. The same is true on the other hand. The magnets that hold the same weight of ferromagnetic material may have different shapes, volumes, and weights.
• Regardless of the shape, the length of the orientation direction has the greatest effect on the determination of suction.

## The factor of suction

The attractive force of the NdFeB magnet has a certain relationship with its volume, performance grade and distance.
Volume: the larger the volume, the greater the suction.
Performance grades: The higher the grade, the greater the suction power. For example, for magnets of the same size, N48 has much higher suction power than N35.
Distance: refers to the distance between the magnet and the adsorbed object. The greater the distance, the smaller the suction force.

The attractive force of a neodymium iron boron magnet has a certain relationship with its volume, performance grade, and distance, and there are many specifications and shapes of neodymium iron boron magnets, with holes and special shapes. These are directly related to the attractive force and the calculation is more complicated.
For example: the grade of the square neodymium iron boron magnet is: N35, and the specification is: 30mm×15mm×5mm. Magnet attraction calculation formula: magnet volume × density × 600 (multiple).

• 1. Magnet density: The approximate density of N35 is about 7.5 g/cm3. To understand the density of magnets, it is recommended to read: What is the density of ferrite, injection molded magnet, sintered NdFeB, and bonded NdFeB?
• 2. Magnet weight: volume×density (30mm×15mm×5mm)×0.0075=16.875g
• 3. Magnet attraction: 16.875×600=10125g

It can be seen that a 30mm×15mm×5mm square magnet can absorb approximately 10.125kg of material.
Of course, this is just a theoretical valuation that may not be accurate, and I don’t believe it myself. Accurate data must undergo practical experiments to obtain accurate data.
Attached permanent magnet magnetic force calculation formula: F=BILsinθ
F is the magnetic field force, also called ampere force, B is the magnetic induction intensity, I is the current in the wire, L is the length of the wire, and θ is the angle between B and the wire.
Magnetic pole magnetic field force formula: F=mH, where m is the magnetic pole strength, H is the magnetic field strength, and the magnetic field strength generated by the magnetic pole is inversely proportional to the cube of the distance r.

## Performance parameters of NdFeB magnets

 Brand Remanence Coercivity Intrinsic coercivity Magnetic energy product Working temperature Br Hcb Hcj (BH)max Tw mT kA/m kA/m kJ/m3 [kGs] [kOe] [kOe] [MGOe] N35 1170-1220 ≥868 ≥955 263-287 80° [11.7-12.2] [≥10.9] [≥12] [33-36] N38 1220-1250 ≥899 ≥955 287-310 80° [12.2-12.5] [≥11.3] [≥12] [36-39] N40 1250-1280 ≥907 ≥955 302-326 80° [12.5-12.8] [≥11.4] [≥12] [38-41] N42 1280-1320 ≥915 ≥955 318-342 80° [12.8-13.2] [≥11.5] [≥12] [40-43] N45 1320-1380 ≥923 ≥955 342-366 80° [13.2-13.8] [≥11.6] [≥12] [43-46] N48 1380-1420 ≥923 ≥955 366-390 80° [13.8-14.2] [≥11.6] [≥12] [46-49] N50 1400-1450 ≥955 ≥876 382-406 80° [14.0-14.5] [≥12.0] [≥11] [48-51] N52 1430-1480 ≥876 ≥876 398-422 80° [14.3-14.8] [≥11.0] [≥11] [50-53] N54 1450-1500 ≥876 ≥876 414-438 70° [14.5-15.0] [≥11.0] [≥11] [52-55] 35M 1170-1220 ≥868 ≥1114 263-287 100° [11.7-12.2] [≥10.9] [≥14] [33-36] 38M 1220-1250 ≥899 ≥1114 287-310 100° [12.2-12.5] [≥11.3] [≥14] [36-39] 40M 1250-1280 ≥923 ≥1114 302-326 100° [12.5-12.8] [≥11.6] [≥14] [38-41] 42M 1280-1320 ≥955 ≥1114 318-342 100° [12.8-13.2] [≥12.0] [≥14] [40-43] 45M 1320-1380 ≥955 ≥1114 342-366 100° [13.2-13.8] [≥12.5] [≥14] [43-46] 48M 1370-1430 ≥1027 ≥1114 366-390 100° [13.7-14.3] [≥12.9] [≥14] [46-49] 50M 1400-1450 ≥1033 ≥1114 382-406 100° [14.0-14.5] [≥13.0] [≥14] [48-51] 35H 1170-1220 ≥868 ≥1353 263-287 120° [11.7-12.2] [≥10.9] [≥17] [33-36] 38H 1220-1250 ≥899 ≥1353 287-310 120° [12.2-12.5] [≥11.3] [≥17] [36-39] 40H 1250-1280 ≥923 ≥1353 302-326 120° [12.5-12.8] [≥11.6] [≥17] [38-41] 42H 1280-1320 ≥955 ≥1353 318-342 120° [12.8-13.2] [≥12.0] [≥17] [40-43] 45H 1320-1370 ≥973 ≥1353 342-366 120° [13.2-13.7] [≥12.3] [≥17] [43-46] 48H 1370-1420 ≥995 ≥1353 366-390 120° [13.7-14.2] [≥12.5] [≥17] [46-49] 35SH 1170-1220 ≥876 ≥1592 263-287 150° [11.7-12.2] [≥11.0] [≥20] [33-36] 38SH 1220-1250 ≥907 ≥1592 287-310 150° [12.2-12.5] [≥11.4] [≥20] [36-39] 40SH 1250-1280 ≥939 ≥1592 302-326 150° [12.5-12.8] [≥11.8] [≥20] [38-41] 42SH 1280-1320 ≥963 ≥1592 318-342 150° [12.8-13.2] [≥12.1] [≥20] [40-43] 45SH 1320-1380 ≥979 ≥1592 342-366 150° [13.2-13.8] [≥12.3] [≥20] [43-46] 28UH 1040-1080 ≥764 ≥1990 207-231 180° [10.4-10.8] [≥9.6] [≥25] [26-29] 30UH 1080-1130 ≥812 ≥1990 223-247 180° [10.8-11.3] [≥10.2] [≥25] [28-31] 33UH 1130-1170 ≥852 ≥1990 247-271 180° [11.3-11.7] [≥10.7] [≥25] [31-34] 35UH 1170-1220 ≥860 ≥1990 263-287 180° [11.7-12.2] [≥10.8] [≥25] [33-36] 38UH 1220-1250 ≥899 ≥1990 287-310 180° [12.2-12.5] [≥11.3] [≥25] [36-39] 40UH 1240-1280 ≥939 ≥1990 302-326 180° [12.5-12.8] [≥11.8] [≥25] [38-41] 28EH 1040-1080 ≥780 ≥2388 207-231 200° [10.4-10.8] [≥9.8] [≥30] [26-29] 30EH 1080-1130 ≥812 ≥2388 223-247 200° [10.8-11.3] [≥10.2] [≥30] [28-31] 33EH 1130-1170 ≥836 ≥2388 247-271 200° [11.3-11.7] [≥10.5] [≥30] [31-34] 35EH 1170-1220 ≥876 ≥2388 263-287 200° [11.7-12.2] [≥11.0] [≥30] [33-36] 38EH 1220-1250 ≥899 ≥2388 287-310 200° [12.2-12.5] [≥11.3] [≥30] [36-39] 28AH 1040-1080 ≥787 ≥2624 207-231 230° [10.4-10.8] [≥9.9] [≥33] [26-29] 30AH 1080-1150 ≥819 ≥2624 223-247 230° [10.8-11.3] [≥10.3] [≥33] [28-31] 33AH 1130-1170 ≥843 ≥2624 247-271 230° [11.3-11.7] [≥10.6] [≥33] [31-34]

## Physical properties of NdFeB magnets

 Parameter Company Index Density g/cm3 ≥7.3 Curie temperature ℃ 310-340 Br reversible temperature coefficient ℃/% -0.100~-0.130 Hcj reversible temperature coefficient ℃/% ﹣0.40~﹣0.70 Compressive strength N/mm2 1050 Bending strength N/mm2 250 Tensile strength N/mm2 80 Vickers hardness 600 Coefficient of thermal expansion (20 to 200 ℃) 10-6/k ∥5⊥-1.5 Specific heat J/(Kg.K) 460 Thermal conductivity W/(m.K) 9 Resistivity μΩ.cm 150

## Surface coating of NdFeB magnets

 Surface Coating Coating method Coating thickness (μm) Coating color Description of coating characteristics Nickel Electroplate ≥ 5 Silvery It has strong corrosion resistance and outstanding high temperature and humidity resistance. Zinc Electroplate ≥ 5 Silvery white It has strong corrosion resistance and salt spray resistance. Gold Electroplate ≥ 5 Golden It has outstanding high temperature resistance, strong corrosion resistance and good anti discoloration ability. Nickel copper nickel Electroplate 15-30 Silvery Strong corrosion resistance. Epoxy Electrophoresis 15-20 Black/grey Strong corrosion resistance, outstanding salt spray resistance, high temperature and high humidity resistance.

Source: China Permanent Magnet Manufacturer – www.ymagnet.com