My Attempt at an IFB Domed Furnace Lid

Discussion in 'Furnaces and their construction' started by Melterskelter, May 6, 2019.

  1. Or perhaps 1.03X.
    Only when the crucible is cold compared to the wall radiating the energy. Once the crucible is hot X goes way down.
    I think with lower mass you have overheated your furnace and have more energy available for melting. A high mass furnace has energy stored and would be able to provide heat in excess of the flame to a cool object inserted.
    Very true!
    Preheat arithmetic is easy. Cast iron takes about one BTU to raise ten pounds one degree F. To melt, it takes about 500 BTU's to melt ten pounds. So if you're melting ten pounds of cast iron from 100F to 2,300F that takes 2,200 BTU's. Then it will take another 500 BTU's to melt, and another 500 BTU's to get it to your 2,800F target. So a total of 3,300 BTU's to melt ten pounds. Maybe another 33,000 BTU's out the stack. If you heat your charge to 1,100F before putting it in the crucible you save 1,000 BTU's, or 1/3 of the melt energy. That would also be something less than 1/3 of the melt time.

    My preheat rack swings out of the way with a gently push of a poker.
     
  2. PatJ

    PatJ Silver

    I think we need to convene in some convenient location (my backyard for instance), and everyone from around the world bring their iron furnaces, and we will measure out identical iron pieces, fire the starter gun, and may the fastest and hottest melt win.
    Extra points if you happen to spill your hot crucible of iron while pouring (without harm to anyone or any wildlife, of course), but we have to capture that on video, or the points do not count.

    And bonus points (like a case, or maybe a keg) if you can explain in layman's terms why your melt was fastest and hottest (none of this political double-speak allowed, such as "we cannot prove that my furnace is hottest, but we cannot disprove it either" crap.

    We would need a good iron-rated pyrometer, and probably copious amounts of ice cold coolant (beer).

    Winner gets to take home everyone else's furnaces and burners for bragging rights/loot.

    But seriously, what about the pulsing fuel pressure.
    I think the pulsing fuel pressure is doing in a thermal-dynamic sense what adding flutes and such to the insides of boiler and chiller tubes does in a mechanical sense.
    The fluted tubes increases the surface area of the tubes.
    The pulsing fuel pressure, as I understand it, does not increase the flame area, but rather increases the areas that are hottest in the flame.

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    Jason and _Jason like this.
  3. Melterskelter

    Melterskelter Gold Banner Member

    So
    I think that a low mass furnace has less thermal momentum than a high mass furnace by definition. Why it would melt added metal faster than a high mass furnace might depend on where each furnace was in relation to its equilibrium hot temperature at the time of metal addition. Presumably the low mass furnace gets close to its high steady-state temperature faster than the heavy one. If that is true, then the heavy furnace is still sucking significantly more heat into the furnace refractory, shell etc than is the low mass one that is already close(r) to steady-state hot temperature. So more heat is available to go into the added metal.

    With all the focus on low mass (I am to blame for that in good measure) I also think that knowing how to run the burner at efficient settings plays a significant role in melt efficiency and believe that low mass alone is not fully the answer.

    High or low mass, I just like to get things done as expeditiously as possible. And I would add to Pat's list above that lone melt times expose the crucible to punishment for significantly longer periods as well. Lower mass means for the same amount of flame generated/exposure more metal gets melted.

    My goal is to perfect the low mass furnace to a degree that allows it to approach the durability of a higher mass furnace. I have some ideas about that that I will be writing up soon and I think may help along the lines of durability while maintaining relatively low mass. I just need a little time to scratch out a couple drawings. Not a big deal, really, just another iteration that takes into account lessons we have learned together.

    Denis

    Denis
     
    oldironfarmer likes this.
  4. PatJ

    PatJ Silver

    I have definitely noticed this effect.
    The iron in my high mass furnace does not start to liquefy for at least 30 minutes, and that is how long it takes to get the refractory up to operating temperature.
    With my new furnace, the metal starts to puddle in about 10 minutes.

    This is most definitely true in my experience.
    A well tuned oil burner will melt iron in just about any furnace, and the flip side is also true, a poorly tuned oil burner may not melt iron at all regardless of low mass.

    I think it can be done, and is somewhat a matter of finding the right combination/rating of ceramic blanket and top coating, or in the case of the lid the right IFB and associated coating.
    I am going to let you debug the concept before I build one.


    Nobody is commenting on the fuel pressure pulsing.
    I see it as sort of like blowing smoke rings, with the overall effect of having more surface area of hotter burning oil droplets.

    Edit:
    Ironsides went with a zircon-coated ceramic blanket design a while back, and I don't think he would ever go back to a cast refractory design.
    I could not locate any zircon for a reasonable price around here, so i did not go with the coated blanket design with my latest furnace.

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    Last edited: May 31, 2019

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