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Searching for soft iron core

  1. Apr 9, 2015 #1
    Hi, I am planning to conduct an experiment using electromagnet but I could not find the soft iron core.

    My school lab doesn't have it, and I tried asking around in shops which sell electrical appliances and shops which sell science apparatus but nobody seems to sell it. Does anyone know where can I get one? And how many tesla should be sufficient for experiments involving magnetic levitation?
     
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  3. Apr 9, 2015 #2
    And also, I'd appreciate it if somebody knows anything that I could use to substitute soft iron core. Is it wise to use hard iron instead?
     
  4. Apr 9, 2015 #3

    jim hardy

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    "soft" probably refers to its magnetic property, meaning it is not easy to permanently magnetize it.

    You can experiment with scrap iron like a bolt or railroad spike, or take apart an old transformer.

    Here's a link to a manufacturer of iron cores with educational material.
    http://mag-inc.com/company/company-information-learn-more-about-magnetics

    just one source , of many returned by a google search:
    https://www.surplussales.com/Inductors/FerPotC/FerPotC-2.html


    one Tesla is a pretty strong magnet.
     
  5. Apr 9, 2015 #4

    davenn

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    did you try a hardware shop, they would have all sorts of things made out of sort iron rod that you could put into use
    or go to a building site and grab a 0.5 metre length of scrap reinforcing rod

    Dave
     
  6. Apr 10, 2015 #5

    tech99

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    A traditional method is to heat up a mild steel bolt or nail to cherry red using a Bunsen Burner and plunge it into water. It should look black.
     
  7. Apr 12, 2015 #6
    Thank you for all of your replies.

    I am planning to try using iron nail to see if it works, as the school can easily provide me with that. Unfortunately I don't have an old transformer.. :(
    Thank you for the links, I will check them out! :)

    Oh yea, I did not think of hardware shop! :D Is reinforcing rod soft iron tho?

    I did not know you could make your own soft iron core that way. Thank you for the tips!
     
  8. Apr 12, 2015 #7

    sophiecentaur

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    If you want the 'best' iron for experiments then you can do a lot worse than get an old transformer and saw it apart. You may need to struggle to get all the windings and the potting compound but the iron in the laminations is specially selected! Good luck and mind your fingers.
    PS You could just use the transformer as it is - treat it like a lump of iron and forget about the windings - it's even good for AC as long as you don't connect the ends of the wires to each other.
    If you try to do things with steel, you usually find that it has remnance and will not lose its magnetism once it's been touched with a strong magnet. This happens with nails, which are not chosen for their 'softness'.
     
  9. Apr 12, 2015 #8

    jim hardy

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    Just beware of microwave oven transformers (aka MOT's). They have a high voltage winding that's dangerous. Saw the high voltage windings off a MOT first thing..
     
  10. Apr 13, 2015 #9

    sophiecentaur

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    It's strange but there are fewer and fewer actual transformers in equipment these days. It's all switch mode PSUs and high frequencies. Shaded pole motors would be a good source of Iron but everyone uses brushless PM motors these days. But powerful magnets abound - hard drives and small motors are full of 'em.
     
  11. Apr 13, 2015 #10

    davenn

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    easily bent by hand
     
  12. Apr 14, 2015 #11

    sophiecentaur

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    Reinforcing rod???
    It's made of steel, to be as strong as possible, surely. Likely to have high hysteresis. Soft Iron is pretty rare - except where it is used for its magnetic properties (e.g. in School Labs).
    It used to be easy to buy kits for winding your own transformer. All I could find (a quick search) was this, which is a bit expensive but it has E and I laminations and you could make up your own core.
    It is possible that Iron wire (v. soft) could be obtained from gardening stores. I did have a reel of it, a while ago.
     
  13. Apr 14, 2015 #12

    jim mcnamara

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    The usual definition of soft iron - low carbon content iron. Annealing will make it easier to bend. Bendability - I do not think it has a lot to do with the softness of iron in this context.
     
  14. Apr 14, 2015 #13

    tech99

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    I have two sets of nails for making electro magnets for school pupils, which I call steel and soft iron. The soft iron ones are annealed as I described, and they lose magnetism when the current is switched off. They are not actually soft physically. You will find the idea of annealing to make soft iron in old electricity books.
     
  15. Apr 14, 2015 #14

    jim hardy

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    try a concrete "cut" nail. they're quite hard.
     
  16. Apr 14, 2015 #15

    OldEngr63

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    tech99, I would expect the sudden quench you describe to result in hardening if the material is at all harden-able. Instead, I would suggest after heating the material that you simply allow it to air cool, or even better to cool slowly in some sort of insulator (dirt?).

    Soft iron, for the purposes at hand refers to being magnetically soft, not physically soft. Thus the hardness of the material, the sort of thing indicated by a Brinell hardness tester, is really immaterial for magnetic purposes. Further, relative few things are make from iron anymore; more often steel is used for strength.
     
  17. Apr 14, 2015 #16

    jim hardy

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    THAT one hit the nail square on the head.
     
  18. Apr 15, 2015 #17

    sophiecentaur

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    Thank you. We'll let you know
    NEXT!. :wink:
     
  19. May 17, 2015 #18
    'Soft' iron meaning 'magnetically soft' (low coercivity and retentivity) also happens to be physically soft. That is where the term 'soft' originates. This applies only to iron and steel; ferrites can be magnetically 'soft' or 'hard' but are always physically hard.
    Sot iron ( also called magnet steel or 'commercially pure' iron) as used in magnetics is very low carbon-content steel, less than 0.05%. It can be ordered from industrial suppliers but may require minimum quantities and thus be expensive.
    A good substitute is mild steel: with % C ranging from 0.06 (AISI 1006) to 0.3 (1030). Most-commonly encountered are 1010 (0.1% C) and 1020 (0.2%). Machine key stock, the zinc-plated stuff from your local hardware or home center, is generally of those grades. So are SAE Grade 2 bolts (also zinc-plated).
    Structural steel (not concrete rebar, which being made from scrap can have wildly-varying carbon content) of mill (plain) finish, in plate or square bar form, typically used for decorative metalwork, can be obtained from the same sources or from junkyards. It is generally higher-carbon than mild steel, but can be made magnetically (as well as physically) soft by annealing. This is done by uniformly heating to cherry-red (about 1500 F), and allowing it to cool slowly. (Quick cooling--quenching--hardens steels of medium and high carbon content both physically and magnetically, which is good for permanent magnets, but the opposite of what you want.)
    As others have mentioned, transformer and induction-motor cores are made of laminations of magnetically-soft steel of low carbon but high silicon content (the latter to increase resistivity thus reducing eddy-current losses) and are good when AC is involved (but work fine for DC too). These can be obtained cheaply from scrapyards as well.
     
  20. May 17, 2015 #19
    For a supplier, try a blacksmith. Look under horse care if you have trouble finding one in your area.

    I saw a levitating aluminum ring once which used straightened and bundled coat hangers. I can't swear to the metal type though.
     
  21. May 17, 2015 #20
    I hadn't realized that soft iron EI core material was so difficult to come by. Hower McMaster-Carr does sell "gray iron" is all shapes. But what is gray iron?
     
  22. May 31, 2016 #21
    Does anybody know of a material with high permeability in which the hysteresis curve is either big or small doesn't matter.
     
  23. May 31, 2016 #22

    Baluncore

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  24. May 31, 2016 #23

    Merlin3189

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    My physics teacher recommended soft iron binding wire (apparently now called black iron wire.) I haven't seen this around in hardware shops for a long time, but I suspect agricultural hardware shops and maybe even florists would still have it. It is available online at about 5 quid a kilo (>100m of 1.25mm diameter) or 2 quid 100g (plus carriage! So better to find somewhere local to collect.)
    It was straightened by rolling the cut lengths between two sheets of plywood. Then given a coat of lacquer (whatever that is - paint?) for use with AC. I think the stuff we used was about 1mm diameter. I believe, for AC, thinner might be better, but more tedious, or for DC just use the thickest you can get.
     
  25. May 31, 2016 #24

    The Electrician

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    You haven't said what shape core you want, or how big it should be. Do you want a "U" shaped core, or a simple straight piece of iron? Are you going to use with AC or DC?

    You may be able to find a surplus core set such as these: http://www.magneticmetals.com/products/tape-wound-cut-cores

    Where do you live? I may be able to direct you to a source if you're in the U.S.
     
  26. May 31, 2016 #25

    tech99

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    I have used steel bolts and nails for school demonstrations. If you want the magnetism to go when you switch off the current, you can anneal the steel by heating to cherry red and plunging it into water. It is then black and magnetically soft, ie it loses its magnetism. Think in terms of a few hundred turns of wire.
     
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