Why does carbon steel get magnetized on machining, grinding etc.
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DrPizza
Administrator Elite Member Goat Whisperer
Wow, that's actually a good question.
First, do you understand how magnetism in carbon steel works?
If so, then from that point on, I'd only be speculating.
First, do you understand how magnetism in carbon steel works?
If so, then from that point on, I'd only be speculating.
First of all I think it depends on the type of machining.
But my guess would be a combination of heat (which makes it easier to polarize the material) and induced currents which creates a (weak) magnetic field.
But my guess would be a combination of heat (which makes it easier to polarize the material) and induced currents which creates a (weak) magnetic field.
DrPizza
Administrator Elite Member Goat Whisperer
That was pretty much my guess as well.
But, if you strike a bar magnet, you can often change it's magnetic properties as well. While there is heat energy transferred to the bar, I wouldn't think it'd be enough to make a difference.
I just asked my dad who's a powder metallurgist and he told me that the increase in carbon is directly proportional how easily the steel gets magnetized. Besides for suface grinding, gripping, powerful magnets are used to hold steel, and the steel acquires magnetism from there.
DrPizza
Administrator Elite Member Goat Whisperer
So... it's just steel with a high coercivity being placed in a magnetic field. I figured there was something more complicated going on. (I couldn't figure out where the magnetic field was coming from)
If you have observed, pure iron is pretty difficult to magnetize passively. As the carbon content increases, magnetism also increases. Eg: transformer cores are (pure iron) are weak magnets, and the EMF passing through the windings doesn't exactly magnetize the transformer except when switched on.
but when you consider machining, gripping carbon steel the magnets holding it are sufficient enough to make them permanent magnets because of high carbon content.
Jeff7
Lifer
- Jan 4, 2001
- 41,596
- 19
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The steel is inside Earth's magnetic field. Jarring a piece of metal will allow for a slight realignment of the atoms - with each sharp impact in the same direction, the object becomes slightly more magnetized. Machining something requires applying a lot of little rapid hits to something - this is just what you need to make something magnetic.
I had a book with some science experiments in it - the one thing said that if you hold an iron spike, face north, and hit the end of it with a metal hammer a few times, the spike will become slightly magnetic.
I had a book with some science experiments in it - the one thing said that if you hold an iron spike, face north, and hit the end of it with a metal hammer a few times, the spike will become slightly magnetic.
sao123
Lifer
- May 27, 2002
- 12,653
- 205
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although im off topic, this question raised a question in my mind, so ill ask it here.
Would it be possible to power a sattelite by using its orbit abound the earth inside the earths magnetic field? Im assuming that the magnetic field rotates with the earth, so it would have to be a non-geosynchronous orbit for this to be possible.
Would it be possible to power a sattelite by using its orbit abound the earth inside the earths magnetic field? Im assuming that the magnetic field rotates with the earth, so it would have to be a non-geosynchronous orbit for this to be possible.
(1)There is something called as a domain theory for ferromagnetic substances like iron. A ferromagnetic material like Fe contains small domains(regions) such that the magnetic dipole moments of all the atoms in a domain are aligned in the same direction. A domain has a resultant magnetic dipole moment.
Extreme conditions like heat destroy these domains: The random thermal motion of atomic magnets increase and the coupling between different atomic magnets in each domain become loose. Above a certain temperature (Called the curie temperature) The ferromagnetic substances behave like paramagnetic substances(weak magnets). When the temperature goes below curie temperature, the ferromagnetic substance gets back it's orignal property.
(2)When you beat an iron spike, you are basically re-arranging the domains and thats why it becomes slightly magnetic.
Point#1 re-iterates the fact that HEAT has nothing to do with the magnetism carbon-steel acquires and neither does hitting of carbon steel contribute in any significant way of increasing the magnetic strength of it. I can go more into details, but I presume this info. is sufficient as of now.
Originally posted by: Jeff7
Well, it is the Highly Technical forum. Be as detailed as you can stand to be.
I find it all fascinating; and if my previous information was wrong, well, it's good to be corrected.
You were not wrong rather partially incorrect. And when I say
I will need to refer to those old physics books of mine. I had physics as a subject about 3 years back and now that I am studying computers, I don't have physics as a subject.
DrPizza
Administrator Elite Member Goat Whisperer
If you can go into details on the following, I'd love to know:
(I'm familiar with domains)
If I take a carbon steel bar magnet and smack it with a hammer, it'll result in a much weaker magnet - many of the domains are no longer lined up. HOW do they change?
(I'm familiar with domains)
If I take a carbon steel bar magnet and smack it with a hammer, it'll result in a much weaker magnet - many of the domains are no longer lined up. HOW do they change?
basically mechanical shocks can align the magnetic domains in the metal, and machining is a series of shocks, all in the same direction.
a subsequent shock, or exposure to a strong and random magnetic field will erase this magnetism. also heat-treating the metal will demagnetize.
because the act of "machining" lines up the molecules in the iron. This alignment causes magnatism.
You can also do this by rubbing a steel rod repeatedly from one direction.
Hit it with a hammer to remove the magnatism.
If I'm understanding you correctly, you might be able to get a small amount of power, but it would slow down the satellite (which would eventually cause it to crash into the earth). Solar panels are a much safer bet.
Assuming what I've read is true, yes, you can get power from the earth's magnetic field, especially if you have two sattelites tethered together and rotating. However, when you do the math, this power turns out to come directly from the orbital momentum of the sattelite and will cause it to deorbit and crash. Solar panels are better power sources. Oddly enough, its possible to do this the other way, and expend energy gained from some other source to "push" against the magnetic field and stablize a decaying orbit. Of course, considering the power requirements and the amount of equipment and design considerations, its probably best just to put thrusters on the thing instead of lots of solar panels and a tethered buddy sattelite.
DrPizza
Administrator Elite Member Goat Whisperer
Okay, let me rephrase my question.
What is the mechanism by which the domains align?
Analogy: If I randomly scatter 1000 pennies on the floor, then smack the floor with a sledge hammer, rather than have about a 50/50 mixture of heads and tails facing up, suddenly I end up with a 70/30 mix. How is it that they change?
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