In article ,
says...

The geometry and physical arrangement of these pole
pieces is carefully chosen so that there is just sufficient
alternate path (i e leakage flux) to enable the magnet to
operate close to it's maximum energy point when NOT in
contact with an iron surface. This is the BH max point - it
corresponds to the most efficient use of the magnet material
Because of this, the magnet is not degraded when left 'ON'
and not in contact with an iron surface. This deliberate
leakage flux path acts as carefully chosen partial 'keeper'
to protect the magnet from the demagntising effect of a
wholly open magnetic circuit.

When in close contact with an iron surface the overall
magnetic circuit reluctance is very much lower and almost
all the available flux is then diverted away from the
designed in leakage path and now flows through the pole
pieces into the work surface.

Excellent explaination, thank you, Jim.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================