I don't know why anyone quotes pulling force, it is confusing and unless you are designing a lifting magnet it is useless.
I don't even know what they mean in this case. For a properly designed lifting magnet I would take it to mean the force needed to pull the assembly from a thick smooth steel plate.
For a single magnet I have no idea what form of magnetic circuit they are claiming this figure for. I would guess that it is the force needed to pull a single magnet off a thick smooth steel plate when it is stuck on with its active face on the disc.
The pulling force depends entirely where the flux goes when the magnet is in contact and changes in the magnetic circuit have dramatic effects. One thing is certain, this force relates to the case when the magnet is in contact with the plate. Any air gap reduces the force more or less as the inverse square so a 1mm gap would drop this force to a fraction of the no air gap case.
If you put your dual rotors together with no gap the force needed to separate them will be incredible, in fact they will smash themselves as they come close together and if they don't smash you won't separate them by pulling.
The force drops rapidly with increase in air gap and with a gap of 1" between them the force will be quite modest. I suspect at 2" gap you could separate them by hand ( don't try such things! )
For the usual rectangular magnets and 12 per disc as used in the 10ft machine when you are jacking the discs apart you can usually pull them apart when the gap gets to about 1". I have never measured such things but I guess 50lbs at this point.
You will have a stator between your magnets and I advise that you never try without one or some similar thickness of non magnetic material between them. If you jack them together with no stator you will probably reach a point where you bend the discs when the gap gets under 1/4".
Make sure that under no circumstances the discs come together and just as important make sure they never come into contact with thick steel plate. You need your wits about you when handling these things.
The normal operating forces are not large but with no air gap the things are deadly.
Flux
