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.rizinia.com