Spherical permanent magnet pull force
QuickField simulation example
The permanent magnet sphere is pulled to the steel plate. Calculate the attraction force.
Problem Type
Axisymmetric problem of DC magnetics
Geometry
Given
Permanent magnet grade N42 coercive force is Hc = 910 kA/m, Br = 1.32 T.
Ferromagnetic wall relative magnetic permeability is μ=1000.
Task
Calculate the pull force between the spherical permanent magnet and a ferromagnetic wall.
Solution
This problem can be simulated as a 2D axisymmetric model. The wall dimensions are much larger than the sphere dimensions, and due to fading of the field with distance, most of the magnetic field flux which comes into the wall goes near the sphere. There is no need to simulate an entire wall. We simulate a small piece of the wall located in the vicinity of the sphere.
For accurate calculation, the integration contour is drawn in the air around the permanent magnet. We should preserve a small gap between the permanent magnet and the wall in order to be able to draw a contour.
We use LabelMover parametric tool to calculate the force as a function of the distance between the spherical permanent magnet and the steel wall. Then we will be able to extrapolate the results and find the force when the sphere is in contact with the wall.
The BH-curve of the permanent magnet is linear so we specify a constant value of magnetic permeability instead: Br / Hc / μ0 = 1.15.
Result
Extrapolated value of the pull force when the sphere is in contact with the ferromagnetic wall is 16.1 N. Reference* value is 3.96 lb = 16.8 N.
* Reference: www.kjmagnetics.com.
- Download simulation files (files may be viewed using any QuickField Edition).