How to evaluate and limit the remanent force of a solenoid actuator ?

Question

How to evaluate and limit the remanent force of a solenoid actuator ?

Matschef (Aeronautics)

(OP)

27 Nov 23 15:00

Hi,

I am designing a solenoid actuator that is similar in size to this one :

https://cdn.norgren.com/pdf/en_6_6_009_FLATPROP_EQ...

One key requirement is that the actuator shall have a low remanent force (i.e. remaining magnetic force once the coil is de-energized). The material I plan to use for the core and plunger is the good old AISI 430FR solenoid quality. My guess is that remanent force is not going to be an issue because everyone use the 430 FR, but I would like to be sure that I am not missing anything. I also do confess that I am not very familiar with magnetic hysteresis.

Is there a way to evaluate the remanent force that does not rely on some very expensive FEA software like ansys maxwell ? For now I have to use FEMM 4.2 or analytical calculus.

In datasheets it is shown that the remanence of the 430FR is around 0.6 Tesla. I did compute that some parts of my core are going to be higher than that, even close close to the saturation. If flux density is going to stay at 0.6 T, would'nt that create a significant remanent force ? I think there is something that I did not get. I would be grateful if someone could point where I am wrong.

Beside limiting local magnetic flux saturation in the core and making sure that the material is properly annealed, is there something more than I can do ? I did some search on this forum and found those posts that deal with magnetic annealing :

https://www.eng-tips.com/viewthread.cfm?qid=356538
https://www.eng-tips.com/viewthread.cfm?qid=374799

Is transverse magnetic field annealing something that is done on the 430FR? At first glance it looks promising : I could lower hysteresis at the price of permitivity. but so far I have found nothing on it. it seems only used on nanocrystalline alloys.

Thanks for the help!

MagBen (Materials) · Answer 1 · 2023-12-05 21:22:07

I guess you will live with the high Br from ferritic 430, which could be over 0.8T, half of Bs. Fortunately, the material has a low coercivity, still categorized as a soft magnetic material, and so it is easily to de-mag. A capacitor could do the trick (a small reverse field or decreasing AC fields). If corrosion is not a concern, you may choose other soft magnetic materials, say Mu-metal, with much smaller Br or Hc, or even low carbon steel with a large range and randomly distributed grain structure, and so smaller Br.

Matschef (Aeronautics) · Answer 2 · 2023-12-06 13:00:32

thank you for your answer.

If I do understand correctly, I should place a capacitor very close to the core of the solenoid. The capacitor is wired in parallel to the coil. When the coild is energised, the capacitor B field is in the same direction than the coil's field. When it is de-energised the magnetic field is going in the reverse direction and should be enough to cancel the coercitivity of the material ?

I wish I could use some nicer material like Mu-metal but corrosion is a major issue. So stainless steel it is

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How to evaluate and limit the remanent force of a solenoid actuator ?