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IrC
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Reading woelens thread (first link) got me into building ZVS circuits. After many different variations I have to wonder if anyone has considered this
for an arc source. I have not read all posts in this thread but if it has not been mentioned some studying of that thread may be useful. Properly
designed for the application I think it would work well. I found three threads that discuss the ZVS circuit.
http://www.sciencemadness.org/talk/viewthread.php?tid=31147
http://www.sciencemadness.org/talk/viewthread.php?tid=3626#p...
http://www.sciencemadness.org/talk/viewthread.php?tid=33577#...
"Science is the belief in the ignorance of the experts" Richard Feynman
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macckone
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An arc furnace uses large current at low voltage.
Any number of power supplies will work.
Welders are ideal as this is basically what they do.
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macckone
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Ps. Most welders can be turned down to a point of continuous operation. Ie a 40% duty cycle machine will probably operate fine at 60% output with
100% duty cycle.
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metalresearcher
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Well, the issue with EAF is not the obtaining an arc hot enough, but the material one uses where the reaction takes place. The arc vaporizes ....
Everything including magnesia. Any firebrick will melt to a sticky mass and lots of fumes consisting of condensed MgO / CaO / Al2O3 vapors appear.
Commercial EAFs (e.g. steel factories) let the carbon rods hover above the metal bath to minimize refractory wear.
Since recently I am experimenting with a 200A (140A continuously) DC inverter. The positive electrode gets a lot hotter than the negative one. Maybe
immersing the (+) in the molten metal bath and hovering the (-) above it, will be my next experiment.
Here an test of Aluminum metal boiling (between the molten cell concrete) :
http://www.metallab.net/jwplayer/video.php?v=L2NsaXBzL0JvaWx...
[Edited on 2015-10-26 by metalresearcher]
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IrC
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While arc welders are the good old way they are big, bulky, heavy, and expensive. With the very high power fets at low cost today I think the ZVS
approach should be tried. A cheap lightweight supply should be easy. Winding a special transformer on a large ferrite core would seem the only real
cost of time and money. If I had the need for an arc furnace and the materials I think I would be working on the idea. Maybe in the future if I come
up with a need for one.
Never bothered to look at the idea before but a quick search yields some videos:
https://www.youtube.com/watch?v=Sh1GwpoSO9g
https://www.youtube.com/watch?v=LSDRn21Y0Tk
https://www.youtube.com/watch?v=K-bvOoOwOPI
https://www.youtube.com/watch?v=GbphsBo3kek
"Science is the belief in the ignorance of the experts" Richard Feynman
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IrC
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Quote: Originally posted by metalresearcher  | | Since recently I am experimenting with a 200A (140A continuously) DC inverter. The positive electrode gets a lot hotter than the negative one. Maybe
immersing the (+) in the molten metal bath and hovering the (-) above it, will be my next experiment. |
Have you studied the inverter circuit? I am wondering why not just remove the rectifiers and filter capacitors, using the raw AC output from the
ferrite transformers instead of DC. If anything it will eliminate the loss from the drop in the output rectifiers. The AC may be in the kilohertz
range but I do not see why that would be a problem. Just thinking out loud but I have to wonder if this would not equalize the electrode temperatures.
Assuming you feel like hacking the inverter circuit. Should be very simple at least. Thinking the internal circuitry monitors the DC output as part of
the control, this could be compensated for by tracing the circuit, adding diodes (small 1 amp types) to recreate the needed DC voltage for feedback.
Not forgetting to cut any foil traces as needed. Simpler still is if there is room to just connect to the transformer(s) AC output and running that to
the electrodes. At least this would avoid any worries about control circuit paths and no other mods would be required.
"Science is the belief in the ignorance of the experts" Richard Feynman
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3DTOPO
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I am using an inexpensive solid state arc-welder (~$200), and it runs so smooth you wouldn't even know its on at 50 amps other than the (literally)
blinding white light that is!
It runs on a MOSFET and it can run continuous when plugged into 120v at 50amp (roughly 1000 watts) and 80 amps continuous when plugged into 240
(roughly 2000 watts) (see pic running at 1000w).
I even mounted the electrodes on linear bearings, but as others have noted here, it eats refractory like pancakes.
To that end, I am currently designing a small (8.5" cubed useable area) vacuum furnace. I am thinking of going with graphite insulation board,
graphite heater elements in a water-cooled tank. Based on my research 29" of Mg is plenty of vacuum (alternatively 2psi of Argon).
Once you make the plunge to go vacuum, it seems all kinds of problems go away such as heat transfer through convection while at the same time all
kinds of heater elements become possible (operate at 3000C with ordinary tungsten or molybdenum). The nightmare of oxidization all but vanishes.
Having a water-cooled pressure vessel allows the use of inexpensive silicone seals.
When I have more to share on it I will.
[Edited on 16-2-2016 by 3DTOPO]
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Texium
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Thread Moved
22-11-2023 at 20:06 |
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