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Bitter Magnet Construction

  1. Nov 22, 2014 #1
    Evening, gentlemen!

    Just a quick question for you guys... maybe more, if anyone's seriously interested. I've got a project going on at the university that I hope to get funding for in the future, which is the construction of a relatively small Bitter electromagnet. I say 'relatively' because the thing is still going to be entirely liquid cooled and the whole nine yards.

    Anyway, my problem is sourcing the Bitter plates that are going to to form the inner and outer cores of this magnet. We have a small CO2 cutting laser that would probably punch through a 20-mil copper sheet, but I'd need to print out roughly 2000 of these, which would take forever. I'm flipping through the internet right now looking for a prototyping / metal stamping service that would be able to manufacture these, but I'm having trouble turning up anything reasonable.

    Other than that, the ceramic core(s) I'll be using shouldn't be too hard to find, though they might be a bit expensive, nor should the housing and plates that will seal each end of the unit. Cooling will be easily handled by some common copper plumbing hardware (might be too hot for PVC), a radiator, reservoir, and small pump. I'm actually a computer engineering student, so the whole thing will ultimately be controlled by an STM32F microcontroller which will handle a small display for temperature, voltage, and some various other safety readouts along with the power controls themselves. I still need to work out some sort of low-voltage-with-f***all-amperage power supply, but that won't be too tough.

    Any thoughts on sourcing about 2000 each of copper and insulation plates? No way could I effectively laser-cut each one of these on my own, and I only have a relatively small amount of personal funding for this. Thoughts are welcome! I'll probably stick some design files from AD-Inventor up here as a preview once I get them thrown together.

    Much appreciated,
    - Matt
  2. jcsd
  3. Nov 22, 2014 #2
    For the copper, your cost will vary mostly by whether the geometries to be punched are standard and can be soft tooled from plate. If you need hard tooling then the investment price goes up.
    It's best to negotiate geometries and needs with the directly with the shop as they can identify means of saving you cost. Also, it never hurts to arrange a meeting in person and have your drawings second checked for errors and inconsistencies before the meeting.
  4. Nov 22, 2014 #3

    Doug Huffman

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    Gold Member

    Be careful, Bitter plates must be strong too, to resist the resultant magnetic forces.

    My switchboard reverse power detectors used Eddy Current motors just barely powerful enough to keep the contacts shut, and blistered my fingers when I grabbed one too soon.
  5. Nov 22, 2014 #4
    Yep - what I'm going to end up with should be fairly small scale, but unfortunately scaling magnets down comes with a few problems regarding non-linearity - luckily we're not shooting for anything too impressive. The entire core is going to be held together by eight insulated bolts arranged in an octagon, similar to just about any other bitter magnet out there. I might do a redesign into a nested three-core design in order to make the plates a bit thicker to help keep things together.

    I'm a bit worried about what thermal expansion might do to this, so I'll have to make sure our current solution doesn't turn into an impromptu bolt cannon. There was originally a lot of alumina-based ceramic in the design to avoid the use of a lot of insulating sheaths, but that fell through when I realized that expansion combined with fairly low tensile strength wouldn't exactly be a good plan.

    We'd looked into aluminum or some alloy thereof to use in the plate design for cost, but the amount of heat dissipation needed to get a similar field would be absurd. I'll have to set up a meeting with one of the metal fabs that our university's had previous dealings with... they might be willing to knock a few cents off, and I'm certainly open to lowering cost as much as possible.
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