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Attraction of the ring magnet to the steel plate

QuickField simulation example

Ring magnet is pulled toward the ferromagnetic plate.

Problem Type
Axisymmetric problem of magnetostatics

Geometry
Attraction of the cylindrical permanent magnet to the steel plate Cylindrical permanent magnet is pulled toward the ferromagnetic plate Steel plate Permanent magnet δ l t D1 D2

D1 = 0.5" (12.7 mm) inner diameter of the ring magnet;
D2 = 2" (50.8 mm) outer diameter of the ring magnet;
L = 0.75" (19.05 mm) - thickness of the magnet;
t = 1" (25.4 mm) - plate thickness.

Given
magnet grade N35, Hc = 954930 A/m, Br = 1.26 T;
relative magnetic permeability of the plate μsteel = 1000.

Task
Calculate the pulling force between the magnet and a steel plate.

Solution
To calculate the pull force accurately, and avoid integration along the edge dividing media with large difference in magnetic permeabilities, we place the magnet at a small distance δ = 0.005" (0.127 mm) from the steel plate. Integration contour is drawn in the air around the magnet.

Result
Ring magnet simulation

Pull force
QuickField 608 N
Reference* 556 N (122.4 lb, 1 lb = 4.54 N)

* Reference: www.kjmagnetics.com.