The initial and general knowledge of the permanent magnet in most people includes attractive or repulse force between the magnetic pole and the attractive force between magnetic field and ferromagnetic objects. Pull force also can be utilized as a comparative measurement method in some specified circumstances besides conventional surface gauss, magnetic flux, and magnetic moment. Some formulas can roughly calculate the pull force of the permanent magnet. Then many magnet distributors have launched their online calculators based on relevant formulas. Our calculators are also available now. The complex case can be resolved by Finite Element Analysis (FEA).
Pull force of permanent magnet is significantly dependent on below factors:
- Type and grade of magnet.
- Polar area of the magnet.
- Operating Temperature.
- Air gap between magnet and test plate. FEM simulation results showed that force decreased with increasing air gap, and even very small air gap has a huge impact on the force.
- Test plate. The requirement with regard to the test plate can refer to Test Method for Determining Breakaway Force of A Magnet developed by representative members of the Magnet Distributor and Fabricators Association (MDFA).
a. Material and composition of the test plate. Both 1018 cold rolled steel and other low carbon steel with high permeability can be adopted.
b. Thickness of the test plate. Test plate should be thick enough to carry all flux or result in the low pull force due to magnetic saturation. Surface gauss value on the opposite surface should be less than 5 Gauss.
c. Flatness and roughness of the test plate. Flatness and roughness of the test plate have a powerful effect on the pull force of the magnet, and this variable has been neglected for a long time. There is a neglected air gap between the magnet and unqualified test plate and further got a relatively low pull force.