In the application of magnets (especially in motors), magnetic flux or magnetic flux density is an important indicator to measure its performance, but in some applications (such as magnetic separation, fishing, etc.), magnetic flux is not an effective measure of separation or the amount of pull force, magnetic attraction is a more effective indicator. Magnetic attraction refers to the weight of the ferromagnetic material that the magnet can absorb. It is affected by the performance, shape, size and adsorption distance of the magnet. The attraction of the magnet will gradually decrease as the distance of the adsorbed object increases. There is no mathematical formula to calculate the attractive force of a magnet, but we can measure the magnetic attractive force with a magnetic attractive force measuring device (usually measuring the magnet's tensile force and then converting it into weight). In the experiment, sintered NdFeB N42 magnets of different shapes and sizes were selected. The surface coatings are nickel-copper-nickel, which are magnetized in the height direction. The maximum tensile force (N pole) of each magnet is measured and converted into the adsorption weight. The measurement result shows that 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. Cylinders or discs of the same diameter, the greater the height, the greater the weight that can be pulled, and the pull force is basically proportional to the height. The cylinders or discs of the same height, the larger the diameter, the greater the weight that can be pulled. The diameter is basically proportional tp te pull force. When the diameter and height of the cylinder or round disc of the same volume and weight are different, the weight that can be pulled varies greatly. Generally, the longer the magnet magnetization direction, the greater the pull force. For the same volume magnet, the pull force is not necessarily same, depending on the shape, the pull force may vary greatly. The opposite is also true, the shape, volume, and weight of a magnet that pulls the same weight of ferromagnetic material may be different. No matter what shape, the length of the magnetization direction has the main effect on pull force.
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