Newbie Q regarding electromagnet cores

[ArcadeJ]

Is there any real advantage to using very high permeability materials as the core of a cylindrical shaped electromagnet versus an iron core?

In particular, I am interested in generating an attraction (or repulsion) force between a permanent magnet and an electromagnet separated by about 1/4 inch.

I was under the impression that the core of the electromagnet is not critical unless saturation of the core may be a problem. Is that correct?


Thanks,
AJ

 

[UKpete]

For the greatest force you want the highest flux density, so I would say that you want a core material with a high saturation flux density rather than high permeability. Up to a point the two usually go hand-in-hand, but when you get to the really high permeability materials their saturation flux density is not so good.

The very highest saturation flux density is obtained from cobalt alloys which are expensive e.g. Vacoflux from Vacuumschmeltze, Bsat approx. 2.2T (22000gauss). That is only about 10% higher than mild steel, so you may as well just use steel.

Hopefully someone else can recommend a suitable grade of iron or steel, I assume you are in the US and I'm not familiar with the grades over there.

 

[israelkk]

10% Higher flux density gives 21% more attraction force!!!

 

[ArcadeJ]

Thanks for the help!

What if I don't have enough amp-turns to saturate even the iron core? (Currently using about 900 Amp-turns as I am very space and power limited)

In that case is there any advantage to using a more exotic core?

Also, can anybody reccommend a good reference book for electromagnet design?

Thanks,
-AJ

 

[MJR2]

If the core is not saturated more expensive cores will have little or no value. Type 1020 low carbon material is generally readily available.

Electromagnetic Devices - Herbert Rooters is one

 

[UKpete]

Well, it depends on the relative dimensions i.e. the total flux path length cf the airgap. The gap often dominates the total reluctance regardless of the finer details of the core. But of course it is worth at least a calculation.