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Author Topic: iron cores; how important is iron vs other magnetic ore  (Read 8985 times)

mcorrade

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iron cores; how important is iron vs other magnetic ore
« on: March 18, 2008, 10:38:32 PM »
I can't seem to find iron anywhere for my coil cores. How important is iron vs steel or some other magnetic ore?

triffid

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #1 on: March 24, 2008, 07:46:12 PM »
Try coat hangers for a cheap source of iron.

poopypantallons

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #2 on: April 16, 2008, 07:20:52 PM »
Thats is a great question!

Let me piggyback on it....

More importantly, what is the best metal/alloy to use that works great as an elctromagnet in a coil but does not retain its magnetism when powered off?

I recall someone indicating that a concrete anchor bushing of some sort had great properties. However, no material make or metal type was identified, that I recall. It hink it was hoptoad who said it. Wish I could find some here in California.

Thanks

solinear

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #3 on: June 23, 2009, 06:20:50 AM »
What you want to do is think of magnetism as a circuit, just like electricity.... but one that *IS* going to close the circle, no matter what you do.  Think of permeability as conductance.  Air/space has a permeability rating of 1 (very bad).  Steel has a permeability rating of 700... in other words, it conducts magnetism around 700 times better than air does.  To put this in better terms, the impact upon 1cm of air will be the same as having around 200 cm of steel to run that magnetic field through.  As long as you can get something well over 100 permeability rating, it won't much matter what material you use.  Thinking of a 1cm electromagnet with 1cm of air gap between the poles with steel as a core, the steel core would contribute approximately 1/800th of the coercivity (inconsequential).  Going from that steel to some of the insane levels of permeability materials (alloys with up to 1,000,000 permeability rating), you would go from 100.12 coercivity rating to a 100.0001 total coercivity rating.  Basically no difference at all, but you just spent a crapload of money getting the 'perfect' core material.  Shortening the air gap would have a much larger effect than changing your core once you get something over a 100 permeability rating.

As for finding something that won't retain it's magnetic properties, it's based upon the material and how strong of a field that you're putting on it.  2000 gauss is quite a bit.  Wikipedia can give you a bit of good information about permeability (how much magnetism likes a material), paramagnetism (materials that won't keep a magnetic field) and so forth.

The Observer

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #4 on: June 23, 2009, 07:15:10 PM »
MC...

You may be interested in knowing how and why magnets/ electromagnets work.

Something, I am afraid to say... most here do not see as I see.

      Sol says permeability has to do with how well magnetism is conducted.

     This makes no sense since the ferromagnetic materials become magnetic by way of already existing dipoles turning from contrasting positions to similar positions in terms of direction.

A piece of iron has 'tons'  of magnetism in it before any other magnetic field comes close to it.

When a magnetic field does come close to it...the dipoles in the iron turn (line up direction) and ADD...

     yes I said ADD...

             to the external magnetic field !

the formula for a coil solenoid is this...

B = (μ0 * μr * N * i) / l

Explanation of this and more is contained in an explorative posting I made last summer entitled.

      Magnetic Permeability.. I can't find anyone talking about this !!!!!

         http://www.overunity.com/index.php?topic=4831.0;wap2

Here you will find more information about how magnets work than anywhere else on this site.

( I say this because you have to be talking about magnetic permeability if you are talking about how magnets work. And quite frankly, I am about the only one !)

If anyone else is more interested at this point... Let's explore this !

Good Tidings to All,
                                The Observer




solinear

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #5 on: June 24, 2009, 03:50:09 AM »
Most people here aren't looking for an explanation of magnetic realms and how the electron shells work into this, it's useless for their purposes.  They want to find a good magnet core and basically once you get to a certain point, it doesn't really make a difference.

I gave them a basic understanding of how the core affects an electromagnet.  If you follow the logic (reduction and impact upon the magnetic field strength by the air gap), you will easily understand why most industrial magnets for lifting have the poles on the same face (which is done by wrapping a ferrous material from one side to the other - so the magnetism can travel through it) - because it reduces air gap and increases the strength of the magnet by reducing total coercivity (which you somehow don't mention at all) and why those magnets far exceed twice the strength of magnets with their poles on opposite sides.  I also never stated that it conducts magnetism, I said to *think* of it as conductance then continued to explain in terms that are easily understood by someone who basically understands an electrical circuit but doesn't understand the physics of magnetism.

What I stated was relatively accurate, while you gave very little detail (in your other article) as to the shape of your electromagnet, leading one to come to the conclusion that it was a straight rod.  Which means that, even with the cobalt-based alloy 2714A (1,000,000 permeability at high frequency), a 2cm magnet (or any magnet, regardless of length) would not be 5000 times as strong as one with an air core.  Because of the way magnetism travels through mediums and the low permeability of air, you would have to basically wrap the poles around to where they were 1/5000th of the distance (actually less, because of the permeability of the material you're using as a core).  No.... if you had a magnet that was 5000cm long and wrapped the 2714A back around from one pole to the other and made it so that the poles (ends of the core) were less than 1cm apart, then you could make a magnet that was 5000 times as strong as it would be with an air core.

But just think about it for a second... 1 amp turn (1 coil of wire with 1 amp going through it), figuring for a reluctance of 1 (permeability of 1000) and 1cm core surface area, will generate 1 gauss (pulling this off the top of my head).  Now throw enough turns to fill up 1cm - what, 15-20 of 26 gauge wire (just an offhand guess)?  So now we're up to 15 gauss.  Drop it down to .2 amps and when you multiply that by 5,000 and all of a sudden we would all be running around making 15k gauss magnets in 10 minutes, no more of these electromagnets with thousands of windings.  Of course, you still have to deal with the saturation point of the material, so we couldn't really make many 15k gauss magnets anyway.

BTW, I'm not sure why, but you seem to have not seen the nearly dozen times I used the word permeability.

My biggest issue here is that so few people talk about watts and joules.  I can't count the number of times I've seen quotes like: "I'm putting 12 volts in and getting 36 volts out!!!" without any mention of the watts in or out.

Paul-R

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #6 on: June 24, 2009, 04:28:21 PM »
Try coat hangers for a cheap source of iron.
I'm not sure this is so. I think they are steel. Check out this:
http://www.publicbookshelf.com/public_html/The_Household_Cyclopedia_of_General_Information/steeliron_cej.html

The Observer

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #7 on: June 24, 2009, 05:13:20 PM »
Hey Sol,

A very interesting response.

An industrial lifting magnet that has both poles on the same end. A U if you will.

    The reason is two poles are twice as powerful as one because iron will attract to
    both north and south poles.

You mention what I assume is Magnetic Coercivity.
   
    Magnetic Coercivity can be likened to the "Stickyness" of the dipoles with respect to
    spinning freely about it's center.

      - Ferromagnetic Materials which have low coercivity like iron and super malloy
        have dipoles that are very susceptible to turning in the presense
        of external magnetic fields. "Not very Sticky"

       -Ferromagnitic Materials that have high coercivity are magnets like neodynium and
         its dipoles are not susceptible to turning in the presense of an external magnetic
         field. "Very Sticky"

So you might see that I am a little confused when you say "reduce the coercivity'.
This can only be done by changing the atomic makeup of said material.

Yes the formula mentioned above is for a straight rod wrapped with wire.

It is important to realize that Magnetic Permeability is represented by the μr in the
aforementioned formula.

B = (μ0 * μr * N * i) / l

If you were to stick a material that has a Magnetic Permeability of 1 Million into a coil.
the resultant magnetic field would (1 Million) x (the magnetic field of an empty coil).

I've said it quite a few times without many people seeming to understand.

It is so important to realize that whether magnet or magnetic material, the magnetism
comes from dipoles.
 
     When a magnet that has 1 Million dipoles comes near a piece of iron that has
     1 Million dipoles... the total number of dipoles now pointed in a single direction is
     2 Million. !

Sol. I'm sure you know this, but I would really like others here to realize what is going on.

If go down this road, you will come to a strange form of energy not mentioned by many.

                Anisotropic Energy.

I claim we are already reaping the benifits of this energy with out acknowledging it.
I think we will reap huge benefits from this energy once understood.

(if you are wondering what we already use.. a simple example is a speaker)
If you tried to make a speaker work without a Magnet or a Ferromagnetic Coil Core,
it would take 100's perhaps 1000's times the energy to make it work.

Well, thanks for your response Sol, I am looking for anyone who wants to have a dialog
about this.

Walk Lightly and Carry a Big Stick,
                                                        The Observer

solinear

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #8 on: June 25, 2009, 12:39:19 AM »
I think that this is a futile argument.  You're using calculations based upon closed circuit magnets (no air gap) and likely don't realize it.

My recommendation: Go get a bunch of magnet wire, a nice variety of cores and a gaussmeter.  Until you actually do it yourself, you're going to hold onto your current understanding of how electromagnets work in relation to their cores.

Here is a good article on how to calculate magnetic strength of an electromagnet: http://sci-toys.com/scitoys/scitoys/magnets/calculating/calculating.html

The Observer

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #9 on: June 25, 2009, 02:51:02 AM »
Hey Sol,

As far as the formula goes...it was garnered from Wiki as well as numerous college Physics text books.

As far as me needing to build my own coils.
                                                                      You are right.

However, could you be the one person who says they understand that a piece of iron
turns into a magnet in the presence of a magnetic field or another magnet's magnetic field?

I will be clear.
    2 items are placed next to each other

                                      - 1 magnet with 1 million dipoles  =  -->
                                      - 1 piece of iron with 1 million dipoles =  -> <-
   
                                                          (-->) + (-> <-) = (---->)

Translation... 1 million organized dipoles + 1 million disorganized dipoles = 2 million organized dipoles.
(ALL POINTED IN THE SAME DIRECTION)

Anyone else that's with me, I would really like to hear from you.

Be Grand,
                The Observer
 

pinestone

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    • bending light with magnetism...
Re: iron cores; how important is iron vs other magnetic ore
« Reply #10 on: September 22, 2009, 03:56:13 PM »
I can't seem to find iron anywhere for my coil cores. How important is iron vs steel or some other magnetic ore?

I've used welding rod for many of my cores. Easy to obtain (any welding supply store) and very inexpensive. You can coat each rod with lacquer paint before you cut it into the required length so they are insulated from one another.
If you want to make a high rpm motor, keep the core size small so the hysteresis is low.
If you want a lot of torque at slower speeds, make the cores larger.

see: http://en.wikipedia.org/wiki/Hysteresis

good luck !


onthecuttingedge2005

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Re: iron cores; how important is iron vs other magnetic ore
« Reply #11 on: September 22, 2009, 06:25:48 PM »
Winding resistance

Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses.
 
Hysteresis losses

Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected.

Eddy currents

Ferromagnetic materials are also good conductors, and a solid core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.

Magnetostriction

Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers, and in turn causes losses due to frictional heating in susceptible cores.

Mechanical losses

In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power.

Stray losses

Leakage inductance is by itself lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat.