Ring magnet is pulled toward the ferromagnetic plate.
Axisymmetric problem of magnetostatics
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.
magnet grade N35, Hc = 954930 A/m, Br = 1.26 T;
relative magnetic permeability of the plate μsteel = 1000.
Calculate the pulling force between the magnet and a steel plate.
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.
556 N (122.4 lb, 1 lb = 4.54 N)
* Reference: www.kjmagnetics.com.