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Pull force of a permanent magnet on an iron sheet

Posted Mar 10, 2019, 8:29 p.m. EDT Low-Frequency Electromagnetics, Parameters, Variables, & Functions, Equation-Based Modeling 2 Replies

Owen Day
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Hi all,

I am currently trying to model the pull force of a permanent magnet when attached to the surface of an iron sheet.

I have currently used the 'force calculation' in the mfnc set up, and I am getting a value for the force which is definitely in the right ball park.

However, I have a couple of issues. One being that I do not know how to model an infinite plate. In reality the plate will be much greater in length than the magnet. However, increasing the length, considerably increases the run time and therefore I was wondering if there was a way to do so without having to actually model a very large plate.

The second issue is that the force calculated is very low when the magnet is actually touching the surface. It provides a much more realistic value when there is a small gap, however the value changes significantly with the size of the gap. I am not sure if this is because I need to add something to the model or whether or not it is down to me using the wrong method and actually calculating the pull force of the magnet incorrectly.

Any help would be much aprreciated, thanks in advance!

Owen

2 Replies Last Post Mar 11, 2019, 11:01 p.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 6 years ago Mar 11, 2019, 6:02 a.m. EDT

Owen,

this blog contribution by Nirmal Paudel: https://www.comsol.de/blogs/modeling-magnetic-bearings-in-comsol-multiphysics may be helpful. Specifically read the part 'Magnetic Force/Torque' approximately in the middle of the text.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Owen, this blog contribution by Nirmal Paudel: https://www.comsol.de/blogs/modeling-magnetic-bearings-in-comsol-multiphysics may be helpful. Specifically read the part 'Magnetic Force/Torque' approximately in the middle of the text. Cheers Edgar
Owen Day
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Posted: 6 years ago Mar 11, 2019, 11:01 p.m. EDT

Edgar,

Thank you very much for your help,

I have implimented the low permeability gap condition, however the issue remains that I am unsure of what size gap I should specify. It offers the same result as it did when i had just left a normal air gap previously, ie the force continues to increase significantly as the gap is reduced. I was just wondering if there was a standard distance which is usually recommended or if I need to carry out some experimental data to verify the correct distance for my model. Or whether it is just simply the smaller the gap is made, the more accurate the result is liekly to be.

I am also still looking for help as to how to model an infinite iron plate/sheet if anyone has any ideas.

Thanks, Owen

Edgar, Thank you very much for your help, I have implimented the low permeability gap condition, however the issue remains that I am unsure of what size gap I should specify. It offers the same result as it did when i had just left a normal air gap previously, ie the force continues to increase significantly as the gap is reduced. I was just wondering if there was a standard distance which is usually recommended or if I need to carry out some experimental data to verify the correct distance for my model. Or whether it is just simply the smaller the gap is made, the more accurate the result is liekly to be. I am also still looking for help as to how to model an infinite iron plate/sheet if anyone has any ideas. Thanks, Owen

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