Small Kiln Auxillary Melting Furnace.

Discussion in 'Furnaces and their construction' started by Melterskelter, Jan 30, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    MS,

    I haven't tried working Kanthal wire hot or welding it so you're out in front there. I'm in danger of telling you more than I know, but though you may be shielded when you TIG FeCrAl, it oxidizes in air and becomes some kind of oxide at the surface but I don't know how deep that oxide layer goes. How much that contributes to embrittlement I'm unsure but embrittlement with heating cycles in air definitely occurs but may be natural progression of the alloy too.

    Oddly enough, I was told that when pottery folks (and I think by ESC here on THF) suffer element failure, as a temporary fix they just mechanically force an overlapping 1"-2" section of coils together and carry on.

    When I splashed aluminum on the coils in my first furnace and they failed, I did this and it worked amazingly well, and then when I rebuilt the furnace I used the old coils the same way on a fire brick I carved in 10 minutes with a rasp when I made a make-shift high power heating source to cure refractory......and I still have and use that brick!

    25 Improvised Heating.JPG

    Best,
    Kelly
     
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  2. Melterskelter

    Melterskelter Gold Banner Member

    I have no idea why I did not ask here. Duh! I did do a Google search a couple times on Kanthal repair and came up with practically nothing. At that point I just figured I'd have to give it a go. TIG was not really a help. I am hopeful that the twisted-together repair will hold. Seems like it should as it is just like a pigtrail only in the course of the wire/coil. Tiem will tell. Not a tragedy if it does not as winding a new coil is pretty easy.

    Thanks for the info. Intertwining two short segements of col would be oh so easy.

    Denis
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It will hold for a while, maybe quite a long while. With a hot joint, over time oxidation will probably degrade the joint. A failure during a melt can be a little more problematic than a heat treating cycle.

    Best,
    K
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    Sounds like it is time to order some more 12ga wire and wind a new coil. Having a mid-melt failure hanging over me is no good.

    Denis
     
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It adds a little complexity but in part why I designed for two coils in my furnace. If one coil fails I still have 4kw cookin to finish the job, but it's only happened twice in 5 years. One was caused by the splash of metal onto the element and the other was the cold joint connecting the conductor alloying. Doubling/tripling the resistive wire lead fixed the latter.

    I had the luxury of starting with a clean slate for furnace shelf/grove and element design. You had to get 2x-3x more power/coil surface area into an existing groove, but you may appreciate the benefits of only having to replace one of multiple coils instead of the entire thing, even though it requires some additional connections. Good idea to have enough Kanthal on hand to twist a replacement coil if/when needed.

    Best,
    Kelly
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    I found some on Amazon at a good price. Comin tomorrow.

    Denis
     
  7. dennis

    dennis Silver

    KanthAL has *aluminum* in it - probably wants AC...
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    All Kanthal has aluminum. There are four commercial Kanthal alloys (A-1 is most common) but they are all FeCrAl. Kanthal is just a trade name. It's also the (Swedish) company's name. All Kanthal alloys are 22% Cr, and 4.8-5.8% Al, with the balance Fe. They call their NiCr alloy Nikrothal, also just a trade name for what is more commonly referred to as Ni-Chrome, the most common resistance wire being 80/20. NiCr alloys came into existence around 1900 and FeCrAl in the 1930s.....according to the Kanthal handbook :)

    For resistance wire, AC or DC doesn't matter. AC is just a more practical power source.

    Best,
    Kelly
     
  9. Peedee

    Peedee Silver

    I think Dennis was reffering to the welding set up maybe?
     
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  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Ah, didn't pick up on that.....but it's a small component, and probably not a helpful one when it come to welding of any kind.

    Best,
    Kelly
     
  11. dennis

    dennis Silver

    Supposedly, Tig-brazing with Aluminum-Bronze wishes A.C.. (as per J. Collier, unless I remember wrongly) Usually, aluminum in such brazing alloys is ~ 5-10 percent.
     
  12. dennis

    dennis Silver

    Yes. If there is more than a trace of alumin(i)um in an alloy, it's likely to want A.C. to weld properly.

    Note that I'm assuming one is using TIG. Spot-welding might well manage with DC.
     
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hey MS,

    Had some questions from another member and remembered this thread. What were the melt times like after you increased the power of the resistive heating elements?

    Best,
    Kelly
     
  14. Melterskelter

    Melterskelter Gold Banner Member

    1 hour almost exactly for an A20 with about 15 pounds of aluminum in it.

    Denis
     

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