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  1. #1
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    Induction furnace

    Hello!

    Im thinking of building a induction furnace of about 2,5 kW! The electronics seem to be very simple to build! With a vacuum pump and a good chamber it should be possible to cheaply and cleanly melt just about every kind of metal or to make perfectly homogenuos alloys

    http://www.richieburnett.co.uk/indheat.html

    How would you solve the pouring in the closed chamber? I was thinking of using a solenoid to "pull the plug" in the bottom of the crucible. It would take much space to tilt the crucible and harder to get the pour in the right place

    What kind of refractory should i use to be able to melt higher temperature metals? How high vacuum would i need? Will i need flux? What material should i use for crucible?

    /Jay

  2. #2
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    I'm sure there is a reason why commercial furnaces don't use "pull the plug" on their crucibles....could be differences in thermal expansion.

  3. #3
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    I was thinking about a cone as the plug with a spring who push it down in the hole with the same draft angle.. Something like this! The spring should keep it tight

    /Jay
    Attached Thumbnails Attached Thumbnails cruicible.jpg  

  4. #4
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    Just out of curiosity, what would you make the 'plug and rod' out of to keep it from melting?

    EDIT: Nevermind, read better and answered my own question. :idea:
    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
    Check Out My Build-Log: http://www.cnczone.com/forums/showthread.php?t=6452

  5. #5
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    Well the same material as the crucible i guess... Perhaps graphite or some kind of ceramic I dont want it to react with the metal! Would graphite change the properties?

    /Jay

  6. #6
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    Quote Originally Posted by JBV
    Well the same material as the crucible i guess... Perhaps graphite or some kind of ceramic I dont want it to react with the metal! Would graphite change the properties?

    /Jay
    So you would be planning on having someone custom make the crucible?

    I looked at the cost of graphite crucibles once, they ain't cheap!

    I guess I don't see why the hold/plug custom crucible would even be needed? Judging from the page you linked - it would seem that you would just make your coil large enough to put the crucible inside and use hooks/tongs to get the crucible out of the center off the coil (after you shut it off, I would assume).

    Now that I think about it, you should be able to embed the coil in the wall of a self-made furnace... :idea:

    I don't know, I just like to keep things ASAP - As Simple As Possible.
    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
    Check Out My Build-Log: http://www.cnczone.com/forums/showthread.php?t=6452

  7. #7
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    I'm planning on doing all melting and casting under vacuum in a closed chamber to avoid oxidation, so i have to be able to do the casting by "remote"

    A ceramic crucible (and plug) should be very easy to make... Just build a form for it and then burn it in a kiln.

    Simple solutions is working... But takes away the fun in building and designing And is often not optimal This is what i'm thinking of... I guess it could be a problem with sealing. :P I guess it would be nice to be able to measure temperature! Can you use a IR thermometer trough glass?
    Attached Thumbnails Attached Thumbnails furnace1.jpg  

  8. #8
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    There are lots of simple ways to protect the melt from oxidization other than a vacuum. As far as bottom tapping goes many have tried different methods of plugging and sealing without much success. Even the smallest leak that can't be stopped can ruin you furnace. Depending on what you are melting home made crucibles are fraught with danger, a bit like juggling eggs.
    If you want to see a very successful home made induction furnace check out –http://home.iprimus.com.au/cmckeown/...on_furnace.htm
    This furnace primarily melts cast iron. The results are an extremely high grade of metal.

  9. #9
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    Yep i have seen that one Very cool! Well if i build the electronics its easy to try different coils and configurations... I guess i would start with something simpler like that! Just to get started anyway

  10. #10
    I've been aprofessional metalcaster for close to 25 years witha degree in metallurgy. Oxidation is least of your concerns when processing steel. Depending upon the composition, nitrogen is the biggest culprit.
    You also use different molding materials for steel. Petrobond won't do. Kiln dried ceramic makes great mold and casting, all of that with it's own process restraints and problems.
    You don't want to use graphite crucibles with steel, the molten metal dissolves the graphite in the crucible and you end up with a stainer.
    You have to have steel in the 3050 degree F range to pour it and it looses heat really fast!!!! All the prep work and you end up with a mis run casting.
    Commercial vacuum induction furnaces, especially with aerospace castigns and alloys, have the preheated ceramic mold on top of the induction furnace, at the proper time teh whole unit is inverted and the mold filled.

  11. #11
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    Were there any schematics posted somewhere for the one shown in the link?
    It's OK I did'nt look hard enough (chair)
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  12. #12
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    Have there been any development in this field lateley??
    I am in the process of gathering information on a furnace that could be used for melting Al and possibly for making some Al/Mg alloys.
    Ideally, I want to use electricity as the energy source, and have already made a ill-conceived attempt at making a resistive heater, but I can't find a suitable castable refractory, so I resorted to fireplace-brics and leca, loosely fitted in a large steel bowl, and using nicrothal wires coiled up as springs, and fitted in slots carved in the bricks.
    The result was a big spike in the electric bill, and alot of red-hot leca and fire bricks...
    The Al I managed to melt, ate it's way through the capped steel pipe crucible, and generally made a big mess..

    I'm pondering a new design, using a red clay crusible and furnace liner/heat wire holder and using mineral whool for insulation.

    While browsing the net, I found out about induction heating, and started to seriously consider this as an alternative route.

    Al is a very conductive material and also it's not magnetic, and I would guess that it would be pretty hard to develop enough heat to melt it.

    How would clay stand up to the thermal fluctuations that one could expect from a furnace like this?
    Just hours ago, I exploded a small square of hardened glass by ignoring the stresses caused by uneven heating.
    I made a small coil from my heating wire, and placed it on the glass, and placed a piece of Al inside...
    The al melted, and solidified into a blob on the glass...
    I removed the glob, and put the glass aside to cool down.
    After maybe 5 minutes, it exploded, and sprayed small glass cubes all over the place...
    Would clay behave in a similar manner, or is it more flexible?

  13. #13
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    Hello All,

    I am new to posting to this forum. However, I have been a scientific lampworker for nearly ten years now. If you wish to make an electric furnace for the purpose of melting metals then you should contact these companies (they are both owned by Amaco): Amaco and the Brickyard.
    This link is for the electric elements. The ones you all probably will want to use are the metal enameling replacement elements. I have one of these kilns, produced in 1948, and it reaches temperatures in excess of 2500 degrees C on 120VAC! The kiln has two elements of 500 watts each, connected in series for the high temp setting and in parallel for low (or the other way round, I cannot remember). A pyrometer and thermocouple show absolute temperature.
    http://www.amaco.com/jsps/grouphome1...0Amaco%20Kilns
    The elements can simply be stapled to kiln brick, which is fairly cheep when not precut, in a zig-zag or cyclic fashion.

    For kiln brick for any style of refractory, contact the Brickyard http://www.brickyardceramics.com/

    For the making of high temperature crucibles as described to me by a dear friend:

    1. Choose a suitable clay (some experimentation may be necessary for your exact application, e.g., type of metal).
    2. Form some of the clay into thin pieces (about 4mm thick), dry, and bisk fire in a kiln, or your furnace, to a cone of less than that of the final firing, see later steps. Large underground kilns have been used for centuries for this purpose, heated by wood or charcoal.
    3. Break the bisk into small particles, fine grind with a hammer, or some other means.
    4. Combine up to about 50% bisk back into the original clay, this should be as homogeneous as possible.
    5. Form into a crucible shape, either with a wheel, or core-formed. I would not recommend hand-built techniques, as it should be a single piece of material, not joined parts.
    6. Dry, and fire the second time at a higher temperature.

    Notes: After the firing process is heated to the desired temperature, always cool the stoneware inside whatever it was fired in, and as slowly as possible till completely cool. The addition of bisk clays provides for more strength and higher temperature capabilities compared to that without.

    The crucibles can be made into any size and thickness. As small comercially available crucibles are relatively cheap, however, the larger ones are a bit expensive.

    Hope this helps...

  14. #14
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    Just throwing out an idea here.....

    An Argon 'flood' would probably be alot easier than vacuum. Argon is heavier than air, and tends to pool in low places (this is a serious safety concern in welding, use extreme caution when TIG welding in a confined space :drowning: ).

    All equipment and refills are readily available at welding supply places. You could rig a system to keep a slow steady stream flowing into the furnace and simply displace everything but the inert Argon. Figuring out a way to pour might be tricky, but the flipping method mention earlier sounds like a winner. :cheers:

  15. #15
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    Um, since AL is non-ferrous, I don't think you can use inductive heating on it, since inductive heating relies on eddy currents from the magnetic field..since AL is not magnetic, it won't work - only for iron and steel...

    -niko

  16. #16
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    Well steel and iron loose the magnetic properties after the curie temperature.. about 800 if i remember correctly... You can heat all conductive materials with induction!

  17. #17
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    Yes you are right, I was thinking about that too - when iron and steel get beyond a certain heat they lose their magnetic properties..so thanks you have answered it..

  18. #18
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    It works partially on eddy currents... but also on skin effect!

  19. #19
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    I have done some more research! I belive you could just bypass the output rectifier on a welding inverter and use it for induction heating! I don't know if the switching frequency is optimal for melting metal! But it should work!?

  20. #20
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    Actually it works on any conductive material. The steel and other magnetic materials heat *faster* initially due to being constantly remagnatised, but loose that effect over ~750C. somewhere around there.

    Your basically relying on a huge field of electron charge, concentrated in the center of the coil, and running down the inside (or up)..> It sort of looks like a stretched out donut, with electrons running down the middle and around, up the outside.

    Thats all I can remember from physics

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