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


Magnetic attraction refers to the weight of ferromagnetic substances that a magnet can absorb. It is affected by factors such as the performance, shape, size, and adsorption distance of the magnet. There is no mathematical formula that can calculate the attraction of a magnet, but we can use it the magnetic attraction measuring device is used to measure the magnetic attraction value (usually measuring the pulling force of the magnet and then converting it into weight), as shown in the figure below. The attraction force of the magnet will gradually decrease as the distance of the attracted object increases.

If you search for magnet suction calculations on the Internet, many websites will write "According to experience, the magnetic force of NdFeB magnets is 600 times their own weight (some also write 640 times)". Is this experience correct? We will verify it through experiments. Just know.


The experiment selected sintered NdFeB N42 magnets of different shapes and sizes. The surface coatings are all nickel-copper-nickel, and they are all magnetized in the height direction. The maximum pulling force (N pole) of each magnet was measured and converted into adsorption weight. The result is as follows:

It is not difficult to find from the measurement results:

The ratio of the weight that can be picked up by magnets of different shapes and sizes 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 cakes with the same diameter, the greater the height, the greater the weight that can be absorbed, and the suction is basically proportional to the height.


 For cylinders or round cakes (blue cells) of the same height, the larger the diameter, the greater the weight that can be sucked up, and the suction is basically proportional to the diameter.


Cylinders or round cakes (yellow cells) with the same volume and weight have different diameters and heights, and the weight that can be picked up varies greatly. Generally, the longer the orientation direction of the magnet, the greater the suction force.


Magnets with the same volume do not necessarily have the same suction force, depending on the shape, the suction force can vary greatly; the same is true in reverse, magnets that attract the same weight of ferromagnetic substances may have different shapes, volumes and weights.


 Regardless of the shape, the length of the orientation direction has the greatest effect on determining the suction force

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