eddy heater

[shipto]

No nothing to do with applying a lighter to your friend Edward 

I was sat thinking today about induction heaters, from what I have read about them the heat in the metal comes from eddy currents which effects all metals and other materials to a certain degree. Unless I have misread this effect will heat as low as 200hz.
So if you were to take a 2 pole motor which i believe runs at 2800rpm or there about just spinning a few strong magnets around a crucible would give you around 46hz obviously not enough to heat much if anything at all.
so if you spun a sun gear at that speed then had many planetry gears with a ratio of 1:10 ( or is it the other way around?) then the magnets would be spinning at 28000rpm. So unless I am way off (which I probably am  ) you will have a frequency of 466hz.

forgive me for rambling but this sounds good in my head and it has always been a problem for me to write it down the same way as it is in there.

So feel free to correct me and tell me it will never work  even have a good laugh at my foolishness if you like 

[PTsideshow]

Check out induction heaters, induction forges or induction metal melters. No point reinventing the wheel with a lot of moving parts.
Photo's of an induction melter used by dental labs and jewelers from the 50's and 60's it was combined with the centrifugal casting machine. it was imported to the Us for the dental trade.
The new versions have become more efficient

mini cast unit made in Italy

Looking at the innards

Looking thru the current carrying straps and cooling tubes at the coils

High freq generating tube and other parts

Heating and crucible unit, along with the water cooling tubing. as the unit was made to rest and make multiple casts as fast as possible.

A device on the back of the unit some type of breaker

Closer look at the induction coil

a video

And just for fun a smoking red hot ice cube

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There are a ton of home made units on U tube also

Google induction forges and you will get all the info you will want or need.
The final work they are expensive to buy. I have a friend that owns a off center induction unit and when she bought it it was over 5 grand.

[shipto]

I agree I very much doubt it would be worth building such a contraption as I described. I just wondered if it woud work is all.
might be fun to experiment with.

[John Hill]

I believe your theory of moving magnets is fine but it is easier to use the magnetic field associated with an electric current to do the same job.

On the other hand, we now have super strong magnets available to us and like a lot of ideas this one might be worth revisiting.  However, we can never get more out of the machine than what we put in so if we want 3kw of heating we would need at leat a 3kw motor driving the magnets and considering the likely inefficiencies we might be needing someting like, maybe, a 10hp motor. 

[shipto]

Yes that would probably be the whole down side to this idea the inefficiency. the power to run the motor would almost definatly be better served running a coil rather than spinning magnets.
I know the eddy currents put a strain on a moving magnet which is proved if you get a small round neo (I have the ones with the countersunk hole) and put it into the top of a copper pipe. it takes ages to fall out of the bottom. Quite cool actually i stumped some of the guy's at work with this trick (between you and me though thats not saying very much  )

[AdeV]

A device on the back of the unit some type of breaker

Aha, I think I've just spotted what makes it work... 

[PTsideshow]

my feelings exactly when I was give it originally! 

[Baldrocker]

this sounds good in my head and it has always been a problem for me to write it down the same way as it is in there.

At last, at last! Someone else with my complaint

br

[picclock]

Just my 2 cents :-)

The heating is caused by the resistance of the metal in which the induced current is produced, so good electrical conductors heat less for a given current.

The frequency of operation and the gap distance (air gap between magnet and metal) control the coupling of the components, and the amount of energy transferred (current induced). At low frequency's (100's of Hz) the gap must be very small, thousands of an inch. At high frequency's (1Mhz upward) the gap is still important but it can be much larger. Also at high frequency's the current travels mainly in the skin of the metal, making the resistance higher and improving the surface heating.

Even to heat a small piece of steel this way requires very large currents to flow.

Good luck with your experiments - I'd be interested in seeing any results you get.

Best Regards

picclock