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Premium electromagnet core material

  1. Nov 21, 2008 #1
    I'm trying to get feedback on electromagnet design and specifically sourcing premium core material for a pulse coil electromagnet. I have seen this question asked a few times on this forum, but doesn't appear to have really been answered.

    What is THE BEST core material and where to source small quantities? Links? Suppliers?

    To make the most efficient and strongest electromagnet I am wondering what I should be looking for in core material. The cores will be 3/8" x 2" wrapped with 1200 turns #24 AWG magnet wire. This will be a DC circuit with voltages around 3volts @ .5 amps.
    Hysteresis and eddy currents aren't an issue as it is a low-cycle application. Strongest electromagnet per watt is the primary goal.

    Currently I am using a grade 2 hex bolt, permeability of 50-100u, so I'm looking to increase efficiency by upgrading core material.
    99.99% iron and electrical steel are two possible choices I have considered (2000u?), but are difficult to source in small quantities.
    Does anyone have links/suppliers for these?
    (http://www.surepure.com/products.php?ID=7&meas1_ID=41&subCat=23 @ $96!!)

    What about 1018 cold-rolled steel?

    I have also tried 2000u ferrite rods with very poor results - you would think the high permeability would make a good core - but it seems to just 'suck up' the flux rather than transmitting it.
    Mu-metal, Somalloy, Permalloy, Powdered Iron cores etc. seem as though they would perform like the ferrite rods - high permeability but low performance? Due to low saturation points?
    And these high u materials seem to be used mostly as shielding etc. not cores.

    Please help me figure on the best core material and where to source it in small quantities!


    Last edited: Nov 21, 2008
  2. jcsd
  3. Nov 21, 2008 #2
    Try soft grain oriented silicon steel alloy, laminated into leaves.

    I dunno. Buy a bunch of Is for transfromer EI cores and stack them into a square crossection core if you can.

    Hmm. A little research shows the relative permeability, u/u_0, of grain oriented silicon steel at 40,000, and supermalloy at 1^10^6. :surprised
    Last edited: Nov 21, 2008
  4. Nov 21, 2008 #3
    Hi Phrak - thanks for the reply!

    The problem is how to source a premimum material in small quantities, that is fully annealed and doesn't totally break the bank...

    Carpenter Steel offers some great (expensive) stuff and good info.
    This is a great read on core materials:
    Sound like their Vacumet Core Iron or the Silicon Core Iron C would be EXCELLENT cores.
    (if one could get a small quantity AND it was fully annealed )
    They only offer large orders directly and all the materials need further final annealing.
    edfagan.com and frysteel.com were offered as small suppliers when I spoke to them, but they don't offer the premimum em core materials and still not annealed.
    Frysteel: $30 per ft. plus $40 packing cost plus $9 per cut (1' to 6' rods) plus shipping
    (think I'll call Carpenter Steel again about suppliers - it seems their stuff rocks!)

    Surepure offers .5" x 1' rods of 99.9% iron at $96

    CMI (http://www.cmispecialty.com/index.cfm )
    Their min. order is $250 (50 lbs) plus shipping (alot for 50 lbs.) and all their stuff then needs to be further annealed to realize it's full magnetic properties....... (yeeessh)
    And getting them on the phone or their material spec. sheets is like pulling teeth!

    I guess a visit to junkyard for some microwave laminations to hack apart is on the list for next week......
  5. Nov 21, 2008 #4
    no problem, glad to help.

    I used to obtain prototype size orders directly from Toshiba America. Same story from a small time distributor working out of his garage. Things have changed. Have you tried Digikey? They sell electronics parts. I don't know about core material.

    From what I gather, you don't have a target minimum permeability or flux density--just the maximum that you can practically get.

    Your target dimensions of 3/8 by 2" is kind of slender for off-the-shelf EI core leaves. Too bad. Could you series the I's to make them twice as long? If that's the case, you might look for some scrap transformers about an inch and a half on a side.
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