At present, many applications of magnets are based on the principle that like At present, many applications of magnets are based on the principle that like poles repel and opposite poles attract and adsorb ferromagnetic substances, such as various magnetic devices, magnetic connection structures, magnetic separation equipment, magnetic transmission equipment, etc.
For magnetic applications, everyone pays great attention to the attraction of magnets. The attraction force of a magnet can be calculated. The following formula can be used for reference. However, it should be noted that the default conditions of the formula are very ideal, that is, the magnetic field distribution is very uniform and the magnetic permeability of the attracted object is very high (weakly magnetic materials such as 300 series Stainless steel and some other ferrous alloys are not applicable), the thickness and adsorption area are sufficient (increasing the thickness and area suction force will not increase, that is, regardless of magnetic leakage), even so the calculated value can only be used as a reference and cannot be used as an accurate calculation .
F(N)=2*S(m²)*B(T)²/μ0
Among them, S represents the adsorption area, B represents the air gap magnetic flux density, and μ0 is the positive air magnetic permeability (which is a constant, μ0=4π*10-7).
How to improve the attraction of magnets?
From the formula, we can see that the attraction of a magnet is proportional to the adsorption area and the air gap flux density. It can be seen that increasing the adsorption area and increasing the air gap flux density are the two major ways to improve the attraction of the magnet.
1. Increase adsorption area
The object to be attracted should at least cover the adsorption surface of the magnet, and the thickness of the object to be attracted can be increased if conditions permit.
When a magnet attracts an iron plate:
🔹 The larger the area of the iron plate, the greater the suction force between the magnet and the iron plate; when the adsorption area is equal to the area of the magnet, the tendency of the suction force to increase will gradually slow down. When the iron plate is large enough, increase the area of the iron plate. The suction power may not be improved;
🔹When the area of the iron plate is the same, when the thickness of the iron plate is thin, increasing the thickness of the iron plate can increase the suction force. When the iron plate is thicker, the increase in suction force by increasing the thickness of the iron plate will gradually level off until there is no increase. .
2. Increase the air gap magnetic flux density
When the adsorption area S remains unchanged, it is a more effective method to increase the suction force by increasing the air gap magnetic flux density and reducing magnetic leakage. Multi-pole magnetization can effectively reduce magnetic leakage.
From the magnetic field simulation diagram, we can see that after the magnet is changed to bipolar magnetization, the magnetic flux leakage is significantly reduced, and a large part of the magnetic field lines form a closed magnetic circuit loop inside the adsorbed iron piece.
If the number of poles is further increased and a magnetic conductive sheet is added to the bottom of the magnet, the magnetic flux leakage will be further reduced and the suction force will be further improved.
The current design trend of magnetic parts is to maximize the utilization of the magnetic field. Through the design of multi-pole magnetic circuits or Halbach magnetic circuits, or with the guidance of some materials with high magnetic permeability, the magnetic field can pass through as much of the object as possible. Attracting objects forms a closed loop of magnetic circuit. Typical applications include:
Rubber magnets are designed for multi-level magnetization, some are double-sided multi-pole, and some are single-sided multi-pole. The magnet performance of rubber magnets is very low, but after multi-pole magnetic circuit design, the magnetic field is densely distributed on the surface. The magnetic leakage is very small during adsorption, resulting in better adsorption effect;
Magnetic devices such as door suction devices are guided by magnetic permeable sheets. When adsorbing, the magnetic circuit is almost formed from the object to be adsorbed. In this way, the utilization rate of the magnetic field is very high. The intuitive experience is that of a small magnetic suction device. (Some still use ferrite), and the suction force is huge when in direct contact.
The design of magnetic parts is inseparable from the consideration of the adsorption distance. The above-mentioned adsorption is based on direct contact. If the distance changes, the suction force often changes greatly. The following figure shows several typical single magnet magnetic attractions. Devices and multi-pole magnetic components have a similar rule. The more poles there are, the greater the suction force is at 0 spacing, but the attenuation becomes more obvious as the spacing increases.