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How fast can you turn a motor before the magnet powderizes?

  1. Apr 14, 2015 #1
    Assuming the stator and windings won't burn out, how fast can a magnet rotate before it structurally fails?
     
  2. jcsd
  3. Apr 14, 2015 #2
    Depends on the material the magnet is made from, and also the tolerance of bearings that constrain the motion of the magnet.
     
  4. Apr 14, 2015 #3
    So, NIB magnets have a way higher compressive strength (950 MPa) than tensile strength (75 MPa). As you spin it the outer edge is under greater compressive force, while the inner edge is in greater tensile force. So how does it fail at max RPM, by breaking apart or by powderizing itself? Tension or compression? And what about shear?
     
  5. Apr 15, 2015 #4

    Baluncore

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    Science Advisor

    The mode of failure due to over-speed is usually a tensile failure of the armature components with the result that the armature components hit the stator poles and the motor locks.

    If you allow a winch with a DC motor and gearbox to free-run under load without power applied, the rated RPM of the motor can be exceeded. What I have seen happen is the strips of copper commutator being thrown out of the armature taking the attached winding leads and brushes with them. It makes a mess.
     
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