Bitter magnets

Discussion in 'General Electronics Chat' started by teratron, Sep 24, 2008.

  1. teratron

    Thread Starter New Member

    Sep 22, 2008
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    I want to build a bitter plates magnet for 1 or 2 teslas. I looked at the web site of the University of Florida, the magnet laboratory are doing experiments with bitter plate up to 100 teslas. There are some drawings and texts, but don't tell you how to build a small scale, like 1 or 2 teslas. The pictures are not clear how the plates are put together, and how they are connected together to work like a coil. Are they a flat discs or spiral shaped discs that are connected in the ends? You can see both pictures in the web sites. Also, what is the purpose of the rods that goes through the plates. You can check the web sites for better understanding. www.hfml.run.nl/20t-magnet.html. also www.magnet.fsu.edu/education/tutorials/magnetacademy/magnets/fullarticle

    I need your help with the specifications for a small scale size for 1 or 2 tesla bitter magnet: size of the discs, how many discs, insulation material, and be able to work with 12vDc.,how many amps?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Your links don't work. This one does - http://www.hfml.sci.kun.nl/20t-magnet.html.

    Field strength is directly related to current through the structure. The "rods" through the plates are clearly the bolts holding the structure together.

    You may have to do some more research and experimenting to complete your project.
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I hope these bolts are not conductors, eventhough they look metallic and they didn't mention the need to use a non-conductor.

    I wonder of a good cost-effective way to make such a thing. Waterjetting? Laser cut? Punch (only good for 1000+ parts probably, because of NRE)

    Steve
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Given the forces, the bolts must be very strong.

    As far as construction, some trials with cardboard might show how to mark holes for passage of bolts. Then all you need is a drill press and patience. This is a one-off project, or so it seems.
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
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    beenthere,

    What forces are you refering to? The laminations are copper, which do not contain ferrous material.

    Steve
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Did you follow my link? Those are great big grade 7 bolts. All those force line exert an huge repulsive force.
     
  7. scubasteve_911

    Senior Member

    Dec 27, 2007
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    So, the necessity for strong bolts is due to the fact that the bolts are ferrous? Why not due away with the steel and use nylon or something?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    No, the whole thing will fly apart if not held together with bolts. The total force may amount to tens of tons. Steel may not be the ideal, but strength is what is needed.
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
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    Looks like about 26 gauge (US Standard) to me. (based on the one 32mm measurement given, a paper card, and some math. I could be wrong.) For a one-off hobby or class project, they could be cut with snips and perforated with a punch.
     
  10. scubasteve_911

    Senior Member

    Dec 27, 2007
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    384 to 512 sheets is a lot of manual labour.. laser cutting is relatively cheap these days, I would attempt that first.

    I designed a magnetic bearing and had 100 complex stator laminations cut out of a stack of 50 blanks, only set me back 200$ with shipping :D One of the downfalls is slag produced.

    I wonder if waterjetting is any cheaper?

    Steve
     
  11. teratron

    Thread Starter New Member

    Sep 22, 2008
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    I thank you all to discuss the ways to deal with the bitter plates. I will read more carefull all the suggestions. The applications for the bitter magnets, that are my projects in the paper; build a powerfull coilgun and a magnetic launcher, with several coils in parallel ( similar to what are used nowdays, to launch jets, in the new aircraft carriers ). I intend to build just a model in scale.
     
  12. thingmaker3

    Retired Moderator

    May 16, 2005
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    Seems to me the bolts would need insulating sleeves on them. Otherwise, one would have to be super careful when assembling to avoid shorting across some of the plates.
     
  13. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Is the force on the bolts because they are from magnetic material, or is it because of the layers repelling?

    I thought that in a solenoid the trurns of the coil are attracting each other. Is that true?
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
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  15. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I agree, I mentioned this concern earlier. This is without question, because it's a clear electrical path and bolts would cause a short for this path.

    I am a bit unclear about the lorentz force. The definition:

    F = q( E + ( v X B) )

    F is the force (in newtons)
    E is the electric field (in volts per meter)
    B is the magnetic field (in teslas)
    q is the electric charge of the particle (in coulombs)
    v is the instantaneous velocity of the particle (in meters per second)
    × is the vector cross product
    ∇ and ∇ × are gradient and curl, respectively

    But, B = uH

    So, we can see, that permeability of the material is a bit factor to the above equation. Something with a high permeability will create more force. Copper has a permeability of about 800 times less than steel, so it is confused why they would want to use steel bolts. Maybe because of the orientation?

    The electric field contribution will be much less than the magnetic field, because of the much higher current density.

    Maybe what is normally insignificant is made to be appreciable at that high of a current. It would be fun to experiment with anyways.

    Steve
     
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