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Electromagnet construction for art

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Tobla

New Member
Hi there,
Was going to buy an electromagnet then I thought why not just make one. After hours of reading and YouTube videos I realized that I needed more information specific to the project. Then I found this forum and thought why not ask people who have already done it .

I am creating art using metals in molten glass. I am hoping to create magnetic lines in the glass. The magnet will be exposed to temperatures outside of the kiln at no more than 100C.
There is a 2 inch insulated gap between the magnet and the glass
I have a low carbon steel circular bar 12 inches in length
A 12 volt car battery

My question is what are the options for wire gauge and number of turns to maximize the magnetic field?
 

throbscottle

Well-Known Member
If I remember my school physics correctly, metal at molten glass temperature won't be magnetic (because the atoms can move about too freely?) but of course I may be wrong and it's Good To Experiment.
Were you thinking of just pointing the end of the solenoid straight at the glass? With other shapes of core you could get different patterns of lines (if it will work at all)
I can show you the method here using an example, I can't say if it will be any good to you.
You're going to need quite a powerful magnet. This achieved in commercial solenoids by using thousands of turns of relatively fine wire. I must hold up my hands and say I have no idea how powerful your magnet actually needs to be, but suppose you want to draw 2 amps from your battery, which will run pretty hot. Given that it's in an environment at 100C anyway, you probably need higher temperature rated wire than the standard stuff
So you need the resistance to be around 6 ohms for this theoretical 2A draw. It looks as though you can't use wire thinner than 24AWG (and you may be pushing your luck with that). I got that information from looking at "ampacity" tables for winding wire.
24AWG wire has a resistance of around 2.567 ohms per 100 feet. So by basic maths you would need 234 feet of wire.
You don't give a diameter of your bar, so I'm going to assume a fairly generous average turn circumference of 2 inches, this would assume your bar is something in the order of 1/2 inch dia. So you would need around 1404 turns of wire.
How you distribute that on the bar is another matter, but you should probably cut a section off and use that, rather than the whole thing.
So that is my very estimated "beginning" answer, and I'm sure others here can do much better, who understand the magnetic side of things.
 

shortbus=

Well-Known Member
Most Helpful Member
Throbscottle is right. The melting point of glass is 1400 to 1600C And the curie point of steel(the temp it goes non-magnetic) is 770C. Pretty sure that the glass isn't completely fluid at the melting temp either.
 

throbscottle

Well-Known Member
What about cobalt? (I don't know what other metals might be magnetic apart from iron) Or maybe there are specialist alloys.
 

Tobla

New Member
If the electromagnetic field cannot effect the iron filings in the glass at this temperature then I can lower the melting temperature of the glass. Not what I had in mind but I could use Bismuth which will melt the glass at around 700 C.
I thought it would need that long bar to keep the North and South Poles apart enough to display the magnetic lines?

upload_2016-12-10_15-20-36.jpeg
 

Tobla

New Member
Cobalt is a good idea....I have a small grant to try this experiment, I said I would use iron filings so I am stuck with that to try first.
 

throbscottle

Well-Known Member
Ah, I see - that makes more sense. The trouble with engineers is we think like engineers...
But all you can really do is experiment. And you probably do need a much more powerful solenoid than I described if that's the length of it.
(edit) on the other hand, you have a certain advantage of time, so those particles can move for as long as the glass is sufficiently fluid.
 
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spec

Well-Known Member
Most Helpful Member
I hope I have not missed anything, but why not just use a bar magnet.

Bar the way, the permeability of steel is not to good. Transformer core lamination's would make a much better electromagnet.
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)

Provided you do not saturate the electromagnetic core, the power of an electromagnet is defined by N * A, where N is the number of turns and A is the current flowing through the coil in amps.

For example, you have a thousand turns of wire and the wire resistance is 10 Ohms. If you connected that electromagnet to a 12V battery, a current of 12V/10 Ohms = 1.2A would flow through the coil to generate a magnetizing force of 1,200 Amp/turns.

If, on the other hand, you used thinner wire and the total resistance of the coils were 20 Ohms, the current would be 12V/20 = 0.6A so you would have a magnetizing force of half, at 600 Amp/turns.

spec
 
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throbscottle

Well-Known Member
Informative as ever spec :)
So, are there some magnetic things to compare with which us mere mortals can relate to that can be used to give an idea of how strong a given number of amp-turns is? Lets say on a scale of fridge-magnet to fire-door-holder?
The only in-between thing I can think of is a cash-drawer solenoid - not many people will relate to that though!
 

spec

Well-Known Member
Most Helpful Member
Informative as ever spec :)
So, are there some magnetic things to compare with which us mere mortals can relate to that can be used to give an idea of how strong a given number of amp-turns is? Lets say on a scale of fridge-magnet to fire-door-holder?
The only in-between thing I can think of is a cash-drawer solenoid - not many people will relate to that though!
Thanks TC,

I will see if I can work out a guide to illustrate between the theory and practical of a solenoid.

spec
 

throbscottle

Well-Known Member
That would be a useful thing indeed.
I should have prefaced it with "your challenge, should you choose to accept it, is..."
I'm hoping the OP is going to come back with some photos of results, I'm very curious :D
 

dr pepper

Well-Known Member
Most Helpful Member
You could pull apart a dc relay and use its coil as an electromagnet.
If your wanting something more dramatic you could pull the solenoid from a bendix starter motor.
 

throbscottle

Well-Known Member
So far, really good! Very readable. But I thought MMF was magneto motive force, not magneto magnetic force?
 

throbscottle

Well-Known Member
I'm a fairly good proof reader. Strange, considering I'm dyslexic! Maybe it's because I have to make extra effort.
 
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