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Can AC Induction be Harmful?

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jmedlen27
#1
Jun1-10, 10:13 AM
P: 1
I am currently looking into using a master magnet to seperate aluminum from food products by AC induction. First, does anyone know if this would be at all possible? I know that recycling companies use Edy machines which sound like the same process of seperating cans from other materials. I am also wondering if this process would be hamrful to use with food because I have only found incidences of this with waste and recycling products. Please let me know what you think.
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LostConjugate
#2
Jun1-10, 12:30 PM
P: 842
Aluminum will not feel a force due to AC induction.

You will need a way to charge the aluminum and attract it away.
Nik_2213
#3
Jun1-10, 12:44 PM
P: 217
Sorry, LC, but Alumin(i)um is repelled by an alternating field. That is the basis of the eddy-current separators mentioned.
See...
http://college.usc.edu/labs/physicsd.../eddy.cfm#em53

How cost-effective it will be at clearing scraps and slivers of metal from eg animal feed, I have no idea. Sieving or screening may be a better option. Sadly, the best option may be to tackle the source of the debris...

LostConjugate
#4
Jun1-10, 01:03 PM
P: 842
Can AC Induction be Harmful?

Its non ferrous, so it shouldn't have any loop currents? It shouldn't feel any force. Also if there were currents wouldn't they follow the currents of the inductor and it would attract?
Naty1
#5
Jun1-10, 01:25 PM
P: 5,632
Well if microwave energy doesn't have any proven harmful effects with food, it's hard to imagine ac inducion would. On the other hand, if the power density is sufficient, you might slightly cook (heat) the food depending on frequencies involved....there was a thread about microwave cooking here in the last few months if you are interested...seems most of the effect is related to dipole moments in water molecules...
cjameshuff
#6
Jun1-10, 05:35 PM
P: 210
Quote Quote by LostConjugate View Post
Its non ferrous, so it shouldn't have any loop currents? It shouldn't feel any force. Also if there were currents wouldn't they follow the currents of the inductor and it would attract?
A material doesn't have to be ferrous to experience eddy currents, it only needs to conduct electricity, and the induced field opposes the applied one.

Take a thick aluminum plate and wave a rare earth magnet across it...when you approach the plate closely, you'll feel the drag produced by the eddy currents induced in the aluminum. Works with coins, too...put a US quarter on a piece of cardboard and slide a large rare earth magnet around beneath it. The coin will "catch on" the moving magnetic field and move along with the magnet. With an AC powered electromagnet, you can easily achieve repulsive forces in highly conductive non-ferrous materials while still having net attractive forces on ferrous materials. Aside from recyclable metal sorting, it's used for electromagnetic brakes and repairing dents in aluminum aircraft skins (electromagnetic "dent pullers").
cjameshuff
#7
Jun1-10, 05:39 PM
P: 210
And to answer the actual question...it shouldn't harm the food directly. Depending on the construction, you may heat parts of the container excessively or possibly induce currents that could cause electrochemical reactions between the container and the food. The latter seems unlikely, but is something to watch out for.
cragar
#8
Jun2-10, 05:22 AM
P: 2,469
Quote Quote by cjameshuff View Post



Take a thick aluminum plate and wave a rare earth magnet across it
It still amazes me every time I drop a magnet down a copper or aluminum pipe.
LostConjugate
#9
Jun2-10, 10:26 AM
P: 842
Quote Quote by cjameshuff View Post
A material doesn't have to be ferrous to experience eddy currents, it only needs to conduct electricity, and the induced field opposes the applied one.

Take a thick aluminum plate and wave a rare earth magnet across it...when you approach the plate closely, you'll feel the drag produced by the eddy currents induced in the aluminum. Works with coins, too...put a US quarter on a piece of cardboard and slide a large rare earth magnet around beneath it. The coin will "catch on" the moving magnetic field and move along with the magnet. With an AC powered electromagnet, you can easily achieve repulsive forces in highly conductive non-ferrous materials while still having net attractive forces on ferrous materials. Aside from recyclable metal sorting, it's used for electromagnetic brakes and repairing dents in aluminum aircraft skins (electromagnetic "dent pullers").
I guess I just find it amazing that the currents refuse to follow the current from the electro magnet but are willing to curl in the opposite way.
cjameshuff
#10
Jun2-10, 07:23 PM
P: 210
Quote Quote by LostConjugate View Post
I guess I just find it amazing that the currents refuse to follow the current from the electro magnet but are willing to curl in the opposite way.
For it to do otherwise would be...surprising. A growing field penetrating a conductor would make itself grow faster. A magnet pushed into a copper tube would accelerate, with acceleration proportional to its velocity. (actually, I'm not sure you could say that much...since the Lorentz force would have to flip direction to allow it, and if it did so randomly, there should be no overall induced current)

http://en.wikipedia.org/wiki/Lenz%27s_law


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