Pull Force of Magnet

Significance of Pull Force to Magnet

For permanent magnet, its comparative measurement method of magnetic property contains magnetic moment, magnetic flux and magnetic field strength. But in fact, pull force also can be used as a comparative measurement method of magnetic property, and much more acceptable by civil use.

Calculation and Influence Factors of Pull Force

Welcome to use our pull force calculators!

Relevant literatures indicates that pull force of simple shape magnet to its surrounding large enough ferromagnetic material can be calculated by below formula:

Where B_g is the surface gauss of attracted ferromagnetic material, the unit is kGs; A_g is the polar area, the unit is cm²; F is the pull force, the unit is the gram.

The calculation can be also described as below:

The unit of pole face area and the attractive force is in² and pound respectively.

Actually, the flux generated by the magnet is in non-uniform distribution on the surface of ferromagnetic material, then the estimated value of A_g and B_g will have a certain bias. It should be noted that more accurate and complex calculation should utilize FEM simulation software.

Many magnet distributors have launched their own online calculation tools based on above calculation formulas. Different calculators also have different computing results for the same magnet, and almost all calculators exaggerate the actual pull force of the magnet. The deviations between these computing results are mainly caused by different B_g value.

The pull force of magnet is significantly dependent on below influence factors:

1. Type and grade of magnet.

2. Polar area of the magnet.

3. Air gap between magnet and test plate. As we can see from below FEM simulation results, the pull force decreased with increasing air gap. Even small air gap will have a dramatic effect on the pull force in the theoretical calculations.

4. Test plate conditions:

The condition of the test plate can refer to Test Method for Determining Breakaway Force of A Magnet which developed by representative members of the Magnet Distributor and Fabricators Association (MDFA).

a. Material and composition. 1018 cold rolled steel has been adopted, other high permeability low carbon steel also suitable.

b. The test plate should be thick enough to carry all flux, or result in the low pull force due to saturation of the test plate. The surface gauss value on the opposite surface should not be more than 5 Gauss.

c. Flatness and roughness. The 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.

5. Operating temperature.

If you any questions or comments regard pull force of magnet, please feel free to contact with SDM team.