electromagnet

Discussion in 'General Electronics Chat' started by wes, Jan 21, 2008.

  1. wes

    Thread Starter Active Member

    Aug 24, 2007
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    hi i was wondering what would make for a good electromagnet that when the power is on it can build up a strong magnetic field and when it is off it has almost no magnetic field would a solid steel bar make a good one, it's supposed to be for a motor i am making that has to go from low power to high power
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Kinda hard to guess about power levels, but the softer the steel, the better it will work as the core in an electromagnet. It will become magnetized as you use it, so the residual field may be a problem. If you don't mind a buzz, use AC out of a transformer to drive the coil, and the steel won't get magnetized.
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Wes,

    beenthere is correct about using soft steel for the core. The less carbon the material has and more iron, the better! Common materials that are used are 1008 and 1018 cold or hot rolled steel. You can simulate easily and for free in two dimensions by use of a program called "Femm". Just google it, it's an easy to use software package that works exceptionally well.

    If you are changing fields quickly, then you should consider using laminations. Laminated materials reduce eddy current losses significantly, which could be a factor in your application.

    You need to understand relationships between geometry, number of turns, current, saturation and etc. to make your electromagnet as suitable as possible for what you're trying to accomplish. I would need to know exactly what you were trying to accomplish, before recommending a particular geometry or coil construction.

    Steve
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    There is "soft" and there is "soft."

    Carburized & hardened 1018 has a Rockwell C hardness of 13. But so does spheroidized 1095. Annealed 416 drops off the bottom of the Rockwell C chart, but would be a poor choice for this application due to permeability of a pathetic 1.008.

    What is needed here is a magnetically soft steel, regardless of what the Rockwell or Vickers machine says. A material with "low reluctance" is needed. That means "high permeability." 1018 and 1008 are indeed acceptable choices, regardless of heat-treatment. Not great, but acceptable. Electrolytic iron is even better for this application.

    Since reluctance is inversely proportional to permeability, something like Permalloy or Nylomag would be vastly better. Such things are hard to find in small quantity, though.

    If the part is to be scrounged, look for "mild steel." If you've got big budget and contacts, look for "Goodfellow Magnetic Shielding Alloy," or "Nylomag 77."
     
  5. techroomt

    Senior Member

    May 19, 2004
    198
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    i think the magnet design is just as important as the material it is made of. a friend makes an electro-magnet for mill working machines powered by a 9v battery that clamps the steel unbelievably well, and when switched off the steel can be lifted off easily.
     
  6. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
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    Don't use any kind of steel. Steel will be able to maintain a magnetic field after the power is turned off. Use pure iron.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Agreed, soft iron is the thing to make a magnet core from. But how much of it is available from the local hardware, as opposed to cheapo carriage bolts (my favorite).
     
  8. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    First of all, in most electromagnet applications, the ratio of holding force when activated versus the residual isn't absolutely critical. When energized, the electromagnet may be able to lift a ton of material, then the residual magnetization may amount to a 0.5lb force. Pure iron is hard to come by and will rust faster than any grade of steel.

    Steve
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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