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After some experiments, I had some NdFeB permanent magnets "contaminated" with iron filings, sticking to it's poles surfaces/edges - you may have seen that before.

There are some working ways to remove them*; But I am wondering whether they can be collected using a stronger magnet.

I tried to collect the filings from a magnet (NdFeB, N35) using a smaller magnet of stronger magnetisation (N52).

When I tried, it seemed to work better than with a magnet of the same strength, but not much, and not in an obvious systematic way.
Also, I tried a larger magnet of equal magnetisation, which is stronger based on it's size - with no relevant results.

Of course, the situation is way more complicated than it looks in terms of "how strong are the magnets". I assume what is relevant is only the strength of the field locally to the particles to be moved. I think this depends much on the geometry of the whole magnetic circuit. Maybe it would need suitable pole pieces to concentrate the flux of the second magnet?

So what I'm trying to understand is:

  • What needs to happen at the location of an iron particle to lift it from a magnet by magnetic forces?

And with that, I'd like to understand

  • how to create that situation

even if it's not practicable. I think the effects making it difficult would be very interesting to understand.

(The same problem as described often occurs with debris of NdFeB magnet ceramics, when magnets collide hard, are of delicate geometry - or just not correctly sintered.
Would that change the situation in an interesting way?)



*) The practical problem of removing iron filings from magnets can be solved by touching the magnet with sticky tape; some kind with thick glue layer, like Gaffer tape, works best. It works even better when there is a magnet pole of the right kind near the non-sticky side of the tape.

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  • $\begingroup$ It is the gradient of the field that attracts filings. The gradient is max at edges or points. Can you use the corner or edge of one magnet to pick up filings from a flat surface of another? $\endgroup$ – Keith McClary Sep 25 '15 at 3:05
  • $\begingroup$ Oh, that works indeed! I used a cylindrical magnet diam 10mm x 30mm to pick up filings from the pole centre of a diam 25mm x 20mm magnet, both of same magnetisation. I had tried similar things, did not notice because the magnets were smaller before. $\endgroup$ – Volker Siegel Sep 25 '15 at 4:04
  • $\begingroup$ I can confirm it works even when picking up particles from magnets with stronger magnetisation. I could collect iron particles with a diam 4mm x 20mm N35 magnet from a 5mm cube magnetized N53. Obviously, you have a valid answer! $\endgroup$ – Volker Siegel Sep 25 '15 at 4:16

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