The Attraction of NdFeB Magnet

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 measure the magnetic attraction value through a magnetic attraction measurement device (generally measuring the pulling force of the magnet and then converting it into weight), as shown in the figure below. The attraction of a magnet will gradually decrease as the distance from the adsorbed object increases.

If you search for magnet attraction calculations online, many websites will say "According to experience, the magnetic force of NdFeB magnets is 600 times their own weight (some say 640 times)". Is this experience correct? We can verify it through experiments.

The experiment selected sintered NdFeB N42 magnets of different shapes and sizes, with Ni-Cu-Ni coatings on the surface, and magnetized in the height direction. The maximum pulling force (N pole) of each magnet was measured and converted into adsorption weight. The measurement 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

For cylinders or round discs with the same diameter, the greater the height, the greater the weight that can be absorbed, and the suction force is basically proportional to the height

For cylinders or round discs with the same height, the greater the diameter, the greater the weight that can be absorbed, and the suction force is basically proportional to the diameter

For cylinders or round discs with the same volume and weight, the diameter and height are different , the weight that can be sucked up varies greatly. Generally, the longer the orientation direction of the magnet, the greater the suction force.

Magnets of the same volume do not necessarily have the same suction force. Depending on the shape, the suction force may vary greatly.

The same is true in reverse. The shape, volume and weight of magnets that suck up the same weight of ferromagnetic materials may be different.

No matter what the shape, the length of the orientation direction has the greatest influence on the suction force.

The above is a suction force test for magnets of the same grade. We will do more tests and comparisons later to see how the suction force of magnets of different grades differs.