Making a custom metal shape that will reduce eddy current?

[Blainiac]

Hello all,


I'm looking to start building.  I need to make an interesting shape to guide magnetic flux around, but I am going to have a diametrically magnetized ring magnet spinning inside part of the shape.  I want to reduce any magnetic damping by eddy currents, so I want to stay away from pure steel.  I have looked at ferrite and laminated stuff, but can't find any company or method to make the simple shape I want.  Does anyone have any experience with building custom shapes that have minimal losses for a magnet spinning near the metal?

[energia9]

Hello all,


I'm looking to start building.  I need to make an interesting shape to guide magnetic flux around, but I am going to have a diametrically magnetized ring magnet spinning inside part of the shape.  I want to reduce any magnetic damping by eddy currents, so I want to stay away from pure steel.  I have looked at ferrite and laminated stuff, but can't find any company or method to make the simple shape I want.  Does anyone have any experience with building custom shapes that have minimal losses for a magnet spinning near the metal?

Magnetite powder + Polyester resin= any shape , fair permeability compared to plain steel
or
Magnetite powder + nickel oxide powder + polyester resin = Best properties
ratio must be so that just enough polyester resin added to hold the powder mix together and enough to make it strong too
good luck
Nickel oxide powder:
http://www.ebay.com/itm/Black-Nickel-Oxide-Powder-500g-Free-P-P-/151237457743?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item233674774f
or Cobalt nickel alloy powder
http://www.ebay.com/itm/CoNi-Cobalt-Nickel-Alloy-Spray-Arc-Welding-Powder-By-the-Lbs-/261323764921
and magnetite powder, basic need
http://www.ebay.com/itm/MAGNETITE-500g-Magnetic-non-conductive-COIL-CORE-POWDER-Fe3O4-Ferric-Oxide-/261141008974?pt=LH_DefaultDomain_3&hash=item3ccd37924e

polyester resin (remember not all resins are good for this, this one is great and cheapest per kg
http://www.ebay.co.uk/itm/Polyester-Resin-1kg-Lloyds-Approved-GRP-repairs-/370429558755?pt=LH_DefaultDomain_3&hash=item563f527fe3

[Blainiac]

Thanks for the tips!  Is there any tutorials on how to mix them/ratios?  I'm needing a high permeability/low hysteresis weird shape.  Would you just make a mold, and pour the epoxy/powder mix in and let it harden?  I've never done anything like this before.  How would it compare to a bunch of steel plates cut to shape and pressed together?

Thanks so much for the help, it's very helpful.

[energia9]

Thanks for the tips!  Is there any tutorials on how to mix them/ratios?  I'm needing a high permeability/low hysteresis weird shape.  Would you just make a mold, and pour the epoxy/powder mix in and let it harden?  I've never done anything like this before.  How would it compare to a bunch of steel plates cut to shape and pressed together?

Thanks so much for the help, it's very helpful.

what kind of shape would you like to make?  plain pure iron if annealed with pure hydrogen has second greatest permeability with 200000 ,
metglas has 1000000
you might as well just tell to a local metalcraftsman to cut the required shapes for you from pure iron , since pure iron, (not carbon steel,permeability of only 100)
99.95% iron has a permeability of 5000 untreated.
i dont know the actual permeability of magnetite powder, but i think its way lower than 5000.
but i made powder cores before and they are excellent,   you need to experiment with the ratios, and you make a mold and just pour it in the mold and wait for it to cure and take them out, you can make lots of identical cores if you make a mold which can be dissasembled with a couple of screws.  wear gloves and goggles!

cutting out pure iron sheets and pressing them together is far greatest by the waay..

[Blainiac]

Energia9,


Thank you so much for the wonderful advice.  I've attached the design, basically that, but about an inch thick (2.54 cm).  I would love to do the epoxy/powder stuff.  I think I might give it a try.  Basically a diametrically magnetized ring magnet would be in the circle part, and the flux would need to be able to travel to the bottom prongs when the magnet is in the right position.  The only reason I want as little eddies as I can get is because the only 'cog' on the magnets spinning would be the eddies themselves (magnetic damping), as it shouldn't cog otherwise using the design.  It's based on some older LaFonte Research ideas (the fanner principle and the cogless AC generator ideas they were working on), mixed together.


I was going to have about 8 of these in a row sharing a shaft that 8 magnets would go through, each offset by 45 degrees.  There would be two 'power strokes' per revolution for each of the 8 units, I might have a one way bearing for each of them to capture the powerstrokes.  All of this is just hot air until I can do some tests.  Anyway, the base parts themselves will be based on this advice, so I thank you very much!