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Approximative pull force of a permanet magnet

  1. Aug 4, 2010 #1
    Hello

    1. The problem statement, all variables and given/known data

    A disc magnet of radius R and height H attracts a mild steel plate.
    Coercive force Hc, Remanence Br and Bhmax are known.
    Main problem is to find an approximative formula that gives the pull force of the magnet at a given distance x. :shy:

    I have found a formula that gives the force (eq.2), but the results are 4 times smaller then the experimental results. :confused:
    [PLAIN]http://img293.imageshack.us/img293/2019/clipboard01aj.jpg [Broken]


    2. Relevant equations
    Eq.1 [PLAIN]http://img707.imageshack.us/img707/1124/img0028144742812.png [Broken]

    Eq.2 [PLAIN]http://img833.imageshack.us/img833/730/img0017144742796.png [Broken]

    3. The attempt at a solution
    Experiment:
    Neodymium magnet N48
    @0mm - F=42N
    @0.1mm - F=33N

    Next step it will be to try the FEA analysis with Quickfield, but I need tiny analytical relations

    Thank you!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
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