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I am trying to make an electromagnet, i would like to know what kind of core would work best, from what i have read a soft iron core would work best BUT i know some metals are known by number and i would like a number just to be more specific (if possible). i also need to keep the core from rusting and i was thinking of copper plating the core, would the magnet still work after doing so why or why not? (i know what wire i need to use i only need to know these last few things i asked)

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  • \$\begingroup\$ Some electromagnets work better without low permeability cores - what is your application, how many turns and what current are you feeding it? \$\endgroup\$ – Andy aka Jan 3 '14 at 21:19
  • \$\begingroup\$ Epoxy paint/coating will prevent rust and will be less expensive than copper plating. \$\endgroup\$ – HL-SDK Jan 3 '14 at 21:19
  • \$\begingroup\$ Oh right, i need an electromagnet that will easily demagnetize which is why i believe i need the high permeability core (soft iron). And as far as preventing rust, i know about painting it or coating it, i was just wondering if i copper plated a soft iron core would still work, would it work better or maybe make the electromagnet weaker? thanks for quick replies i appreciate it. \$\endgroup\$ – user35054 Jan 3 '14 at 21:37
  • \$\begingroup\$ I think copper plate would be fine. Be aware that electroplated will have pinholes and voids that eventually get rust under them and pop the copper layer loose. It is a big enough problem that in high vacuum systems plumbing is "electroless copper" so it doesn't outgas. Are you trying to prevent rust in air? Or is it going to be exposed to liquids? \$\endgroup\$ – C. Towne Springer Jan 3 '14 at 21:53
  • \$\begingroup\$ Cu plate OK for DC. If AC used then solid conductive layer will cause eddy current losses. \$\endgroup\$ – Russell McMahon Jan 3 '14 at 22:33
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You are talking about a DC electromagnet right? So wrought iron is the best but it is almost impossible to find this days. Maybe in a flea market selling very old door's accessories etc. But you can search for Armco iron. Bellow is the relevant magnetic behaviour enter image description here

Next choice is Steel 1010 with maximum permeability of 1800 and saturates at 1.6T. Don't use ferrite for this applications. Magnetic Irons is already coated in bronze-like coating (galvanised?). See a core of a loudspeaker. Painting does not degrade core characteristics, unless this coat insert a significant gap between coil and core. You can shape the tip of core to maximize the strength, like focus! And don't forget: Core cross section plays major role on electromagnet's pulling/holding strength. Finally keep in mind that core also plays a role in the electromagnet thermodynamics, so mass of core is also critical (ok...not only because of this).

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  • \$\begingroup\$ Yes i thought of ferrite but i knew it wouldn't work because the core will be impacted by another piece of metal. but thanks for this answer it is very help full, only thing i need to clarify, so if i was to have a 1010 steel (or any iron) core powder coated to prevent rust it wouldn't affect its functionality? \$\endgroup\$ – user35054 Jan 3 '14 at 23:32
  • \$\begingroup\$ I wonder if the flat sheet metal layers that power transformers are made with would be good? You can find an old high current E core transformer and cut the coil free with a hacksaw. The layers come apart and you can cut the long side to the "E" shapes to get strips. I have never tried it for a core but it could be a worth while experiment. Powder coat won't hurt anything. Note on wrought iron: Most things that say they are, are not. And you wouldn't need rust protection. \$\endgroup\$ – C. Towne Springer Jan 4 '14 at 0:54
  • \$\begingroup\$ Laminated core is sweetable for AC electromagnets. If using in DC, magnetic flux is lower than solid at the same current, and responds to a higher current. In addition you don't need the air between lamination! Solid core low carbon alloys is the answer to DC electromagnet with low residual magnetism. \$\endgroup\$ – GR Tech Jan 4 '14 at 6:36
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The classic core is iron wire (or very mild steel) in a bundle. Much better than a solid core. They were dipped in varnish then wrapped in paper. Nothing wrong with doing that now. I don't have a number for you but as a ready source, I buy iron wire in big rolls at garden or hardware stores. It seems to weigh a couple pounds. I recall it in tool/cement working sections. (If you want to go faster, use the wire used by construction people to assemble rebar. It is thicker and a lot harder to bend. it won't work as well.) Stretch out a long piece like 10 or 20 feet and tie it to something solid. Pull on the other end until you feel it yield. There is a point where you feel no stretch and with a little more force, it "gives". If you pull much more it will break. It "yields" when you exceed the elastic limit. The wire takes on the new shape and will stay very straight. You can cut it into equal lengths as needed. If I need a bunch, I store lengths in a cardboard shipping tube. You may need some leverage (or a car) to pull hard enough, and do it with the wire supported by a table or on a flat floor. (This works with copper wire too and it gets a little smaller in the process and will slip out of the insulation if you want it bare. I do this to get nice wire for bread boards and stripping the ends is very easy. Worth experimenting with.)

I have used the plastic spool from anything like wire or fishing line and made a core to fit. You can get enameled wire for windings easily enough. The current and number of turns determine the magnetic field strength. There is nothing in the equations about keeping it perfectly aligned while winding. I like to keep it neat, but not gaudy.

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