4 ms·

How large of a magnet are we talking, and what were you doing with it? So I know what to be terrified of, for future reference.

• jacquesm 4y ago
  The ceramic one was a 2x2" square 1/4" thick one that had one stuck corner, trying to remove it shattered it, the other was a neo that accidentally jumped up when I put down a heavy piece of steel and that in turn allowed the magnet to start flying towards it, it shattered on impact. That one was a lot larger (2"x2"x1"), and neos are a lot more powerful for the same size as ceramics. In both cases it was to test sets of magnets under controlled circumstances to see which ones I would order in bulk for the rotor of a windmill. Lessons learned: make no assumptions on whether or not a magnet really is free to be released, do not place magnets loose on a workbench even if they are far away from your work area because when the friction unexpectedly disappears you are going to be in for a surprise. Don't mess around with very large neos unless you know what you are doing, they can really hurt you. (And when you do know what you are doing: observe safety precautions religiously and always wear safety glasses until your whole rig is assembled and the magnets are safely enclosed). Something like this just scares me: https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-magnet https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-mag...
  • willis936 4y ago
    I saw a PPPL group propose the use of permanent magnets to assist in stellarator geometry. My first and continued thought has been "this is completely insane". Permanent magnets are fragile, violent, and cannot be turned off. All engineering challenges aside, they propose making an industrially sized death machine that cannot be turned off.
    • jacquesm 4y ago
      You actually can turn them off. You can use mu-metal to short circuit the magnetic field. https://en.wikipedia.org/wiki/Mu-metal https://en.wikipedia.org/wiki/Mu-metal
      • willis936 4y ago
        That can provide shielding, but how does that turn off the permanent magnetic field when a human considers working on (maintenance or decommissioning) the machine?
        • jacquesm 4y ago
          Well, during decommissioning that would be a tricky thing to do, but during maintenance I could image a way to slide the mu metal in front of the magnets shunting the field away in a safe way. But you are right, working on such gear requires strict precautions and attention to safety detail. Let me give you one example of how hard it is to work with these: while building the windmill I had decided on an 'inside out' model where the rotor rotates around the stator, this has a bunch interesting properties, such as pushing the magnets onto the drump while they rotate instead of trying to eject them from the rotor in the normal designs. And because magnets get hot any kind of glue or other adhesive would be subject to all kinds of thermal stresses, might let go or melt. So that was a pretty neat solution. My rig for installing the drum was a half ton crane over a very heavy steel workbench that had the stator mounted to it. As I lowered the rotor suddenly the whole assembly, table and all lifted off the ground and perfectly centered itself around the rotor. I swear I never ever saw that one coming and it really scared the crap out of me because only minutes before then I was still fiddling with pushing some wires in place inside the stator while the rotor was already floating above it. A bit earlier and I could have easily gotten pinched, in spite of all my precautions.