Help! Furance Design Plan review

Discussion in 'Furnaces and their construction' started by The Desert Yeti, Oct 7, 2020.

  1. Hey Gents,

    I have been spending some time drafting up my furnace plans. Have made a ½ scale model and uploaded it here as well as a schematic drawing.

    The general description is a three piece furnace consisting of a lid, body and base. The lid and body are both movable on a set of rollers on a track that allow each piece to be moved upward. If you are familiar with Kelly’s ( Al2O3) furnace imagine a cheaper less shmick version.

    The idea is to have 3” of Kaowool insultation after being well persuaded by oldironfarmer and his point on thermal gradient. I am choosing fiberglass insulation because it is lightweight, cheap, and more easily replaced. (I like simple and your boy is ball ‘n on a budget). It will be 3, 1” layers with the inmost being a sacrificial layer. Inmost facing on the insulation will be a coating of satanite. The base floor and plinth will be 2300F soft brick with a satanite coating as well and will have a 2 inch drain hole with drainage veins. The lid will have of radial wedges of wool with satanite coating as well ( it will be 3-inches thick).

    I have been surfing the forum for a while now and each of these design questions are their own thread(s) but given a hollistic view of the furnace I am just curious what your opinion is on the design and I am looking for mistakes, critiques etc. before I start builiding some fundamental parts.


    Some design questions.

    Tuyere height: It is about ¼ inch above the floor and a ¼ inch below the plinth height. It that a reasonable clearence? Too low? Too High? ( It will be a drip waste oil burner so I understand that it takes some time for the burn to complete so the hot spot is a little higher)


    Ceiling Height: I have 80mm (3- 1/8”) clearence from A16- lid and about 130mm ( 5- 1/8”) of clearence for the A8 crucible to lid. Is this too much? The thought is that that space will allow heat to stay longer before venting, increasing internal temperature. Have you noticed an effect on spacing or have a recommendation?


    Vent Diameter: I have a 4-inch diameter vent right now. Considering my dimensions does that seem ok? What do you run? Why? What does vent diameter effect? (noise? Heat retention? etc.)


    Any other things you notice? Please let me know.


    Yes its in metric partially, because building materials are US customary but I am partial to metric when I can, it’s better.


    white board schematic.jpg

    Draft

    Cross Section with diamensions
    cross sectional view draft 4.jpg

    Thanks in advance!
    -Yeti
     

    Attached Files:

  2. That all looks pretty good to me, extra crucible clearance is good as the hot gases can cause molten aluminium to swirl around and splatter, not to mention stirring in contaminants and dross. A removable hatch cover on the bottom is useful in case a crucible fail causing a major leak as you can knock the plinth and floor out and replace with a newly cast floor and plinth.
     
  3. FishbonzWV

    FishbonzWV Silver Banner Member

    Here's my two wool/Satanite furnaces.

    IMG_3857.JPG IMG_3856.JPG

    The A6
    1ea. x 2" x 8 lb wool. You can leave your hand on the shell.
    Space between crucible and lid, 1 1/2", space to walls 1 1/2".
    3" vent, 7/8" drain hole. The only time used was as a scrapper, no crucible.


    The A10
    4ea. x 1/2" x 6 lb wool. Cannot leave hand on shell.
    Space to lid 2 1/2", space to walls 1 1/2".
    3" vent, no drain.

    Both have 1" tuyere, same burner used for each 3/4" propane. (Oil is overkill for these furnaces)
    Tuyere is almost at floor level.
    Both have domed lids.

    Vents: The most efficient furnace would have no vent. Most of the time mine is choked off with ingots preheating.
     
    Last edited: Oct 7, 2020
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Don't use fiberglass insulation! With just about any burner you will reduce it to a melted blob of glass in no time. You can't cheap out here. Buy ceramic wool.

    I know about all furnace designs include drain holes, and mine have them too, but I think they are probably an unneeded complication. Not sure what kind of burner you are planning but if it's one you will extract before pouring, I'd suggest you consider just making the base flat disc and have the Tuyere in the furnace body. If it's small and light propane it could lift with body. If it's an oil burner you'll pull it anyway. I'd suggest you make the top layer of the floor hard fire brick and don't glue it in place. That way it can be easily replaced. Just use a plinth to position the crucible height. Now there are several instances wear folks here have had a crucible failure and had the hole plug and ended up with the base full of metal any way. IF you build it as I suggest, you'll just want to make sure in the unlikely even you have a spill, you can accommodate some molten metal running out around your furnace base, meaning elevate your burner fuel lines.

    Among other benefits, Satanite coated wool furnaces are very light weight and this is especially helpful for a lift off furnace. I'd suggest you keep the furnace body very light too.....like maybe a small metal garbage can. Cut a hole in the base of the can the size of your furnace bore and do your wool and Satanite build up. This would probably only be <25lbs so you could probably easily lift this by hand with no lifting mechanism, but I think the simplest thing to do is just install two large eye bolts on the furnace body, and drive a post into the ground to guide it, and just set the base in place beneath it. If you wanted to, you could but a pulley on top the pole, run a cable up and over to a can filled with cement or ballast and the body would become zero weight to lift. You could add a post and single eye bolt to the other side to keep the furnace body aligned.

    You'd have an inexpensive efficient bronze duty lift off furnace when you're done, and as a bonus, you could dispense with building tongs and use an open ring shank to snatch and pour in one motion.

    For the lid, I'd be tempted to just buy some rigid ceramic fiber board (may glue two 1-inch layers together with and coat inside surface with satanite) and call it a day.

    -My 2 cents.

    Best,
    Kelly
     
    HT1 likes this.
  5. FishbonzWV

    FishbonzWV Silver Banner Member

    Lift off body violates the KISS principle!!!!!! :)
    Oil burner violates the KISS principle!!!!!!!!! :)
    :p
     
  6. HT1

    HT1 Gold Banner Member

    Listen to Kelly His Ducks are in a row , if you want a drain and I recommend it consider draining out the rear of the furnace rather then the bottom , you place a channel in the floor of the furnace leading out the rear of the furnace through a 1.5 inch hole , My furnace being cast refractory it was easy to build into the floor , this is how the guys building aluminum breaking furnaces do it , i would show pics , but Photobucket has them locked down

    V/r HT1
     
  7. Hey Kelly,
    I didn't make that clear in the post, I am using 2600F rated ceramic wool.

    That's the idea! Not sure if you had much struggle getting the counter weights balanced or not. My rollers came off an old fume hood with a counter wieght closure. I didn't get into details about that here since I'm just focusing on the furance itself but I might message you some questions.
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Sounds good Yeti. Have fun with the build. Happy to help if I can.

    Best,
    Kelly
     
    The Desert Yeti likes this.
  9. Thanks Fishbon this is helpful to see your set up and diamensions
     
    FishbonzWV likes this.

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