Starting build with 30 gallon barrel

Discussion in 'Furnaces and their construction' started by Bentation Funkiloglio, May 23, 2020.

  1. Making my second furnace. It'll have oil burner. Would appreciate help in deciding on dimensions and/or identifying problems before I begin construction. After reading about iron melting furnaces on forum, I decided that my original plan was flawed. Original plans were informed only by my propane burner experiences.

    Required temps:
    Main goal is to smelt iron from magnetite but would like to try my hand at melting/casting also. Smelting requires temps around 3000 F, maybe a bit less, depending on flux used.

    Crucible sizes:
    I typically use two different crucible sizes. Small one has approximately 4.5 inch diameter at top and height is about 5.25 inches. Larger crucible is about 6.25 inches in diameter at top and about 8 inches tall.

    Barrel size:
    I have a 30 gallon steal barrel with in inner diameter of 18 inches.

    Refractory:
    I have a 55 lb bag of castable refractory on hand but will be making run to refractory provider next week, so I can get just about any type (plastic, castable, etc.) that I want. Cheapest is plastic refractory, which is rated for 3200 F. Costs about $130.00 to buy enough for a 12 inch high furnace with 12 inch o.d. and 8 inch i.d. (refractory only). I don't mind spending a couple hundred bucks on refractory.

    Original plans:
    Original plan called for another 8 inch i.d. refractory shell and some combination of plastic refractory and kao-wool. I only had experience working with propane, which allows for minimal space around crucible. Hence, the small inner bore.

    I've read that oil powered furnaces are different. They should allow for at least 2 inches between inner furnace wall and crucible.

    New plans:
    This is a tough decision for me given my lack of experience working with oil powered burners.

    Primary constraint seems to be minimal required distance between furnace inner wall and crucible. Questions:

    1. Since crucibles are tapered, would a 10 inch inner bore be adequate. In other words, could I round down max crucible diameter down from 6.25 to 6 inches?

    2. So, assuming a 10 inch inner bore, I'll have 4 inches to work with between furnace inner wall and barrel wall. Is 4 inches enough space for hot face and insulation? If so, what is a good use of that space? Would 1 inch of refractory and 3 inches of insulation such as kaowool work. The wool that my refractory guy has lists it's max temp as 2700 F.
     
  2. The usual deal is to size your furnace bore to suit the largest crucible you plan to use, I have an 11" bore for an AT30 crucible and I would have been happier with 11.5" to 12" to let the crucible gripper clear the walls better. I'm burning oil to melt iron with dense castable backed by mineral wool insulation. There are some issues with burning oil fast enough.

    Dense castable is difficult to work into place using the recommended water without some form of vibration so a rammable refractory would be preferable in that respect.

    ...After a lot of thought, I now think the main trick is to arrange for the fuel spray to hit some incandescent hot refractory so as to break the oil down into flammable gases as quick as possible. Nobox7 on YouTube has a series of oil burners that are very short at under 6" long where his fuel spray hits hot stainless or hot silicon carbide to give a hot blue flame like a propane burn in appearance. Also some of the forum members here have the oil spray hit the hot furnace wall to vapourize and burn well.

     
    Last edited: May 23, 2020
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  3. How thick is your refractory? Do you use kaowool?
     
  4. Petee716

    Petee716 Gold Banner Member

    If I were going to build another crucible furnace it would be a 1" hotface mizzou and 2" kaowool. That would leave you with a 12" bore. You won't regret having 12". Mizzou is a castable. Some means of vibration is helpful but not totally necessary in my experience. I mixed it in a washtub with a military entrenchment tool (shovel) with the recommended amount of clean water and rammed it up as I went with a 1" dowel. It worked out fine with no major cracking issues.
    I used a similar ramming method when I made a forge with Blu-ram HS (plastic) and it was a pain. You have to ram it really hard. The forms for the forge were all 2x4 lumber and 1/2" plywood so they withstood the beating. But I don't think typical sheet metal forms like we generally see used in a foundry furnace build would tolerate it. If you were to use plastic you may want to ram it in a flat form to the desired thickness and roll it around a cylinder.

    Pete
     
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  5. @Petee716, 1 inch of hot face and 2 inches of wool would be pretty sweet. Would be really light.

    Only concern would be heat loss. Will 2 inches of kaowool be adequate given that this furnace will need to get and stay hot enough to melt iron?
     
  6. It's 2.5" of dense castable and 3" of kaowool: I started with dense castable only and added kaowool later on.
     
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  7. OMM

    OMM Silver

    Will you be using this indoors or outdoor? Do you have a welder? For oil, are you using compressed air? Or oil drip? And what kind of blower are you planning on using?

    During my my first big melt (my stainless steel crucible) failed on the second charge melt. It failed from the inside out. I was using 304. It happened in less than 40 minutes.

    I am using 2.5 inches of IFB backed with 2 inches of ceramic wool. The fact that the 304 stainless steel melted, the fact that my bricks became slightly loose, and the fact that I experienced aluminum stainless steel alloy mixture pool at the bottom of my furnace, and I kept that first ring of shame as a learning experience. I learned a few things. My furnace can get hot fast, but tragedy can happen fast too.

    I start my furnace up with diesel and a blower for five minutes-ish. Then I switch over to WVO. I preheat the WVO using add 200W magnetic heater. (This has brought the viscosity of the oil into check for the needle valve.) I use compressed air to move the oil and diesel. The IFB brings the flashpoint.

    My furnace I have left 1.5 inches of space, on the outer skin to add Rockwool to, with another skin... Totalling 6 inch walls. But… I have a bad feeling that my lid might fail well before.

    I have listened to the guys here and on YouTube closely. My lid is 4 1/2 inches thick. 2.5 inches of IFB surrounded by 2 inches of insulating wool.... I did make some minor changes to the exhaust chimney after showing and receiving input from the guys here.

    Sometimes it's good to have a non-solicited, socialism forum ideas... I do like tried and tested.
     
    Last edited: May 23, 2020
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  8. OMM

    OMM Silver

    As for box7 youTuber, he sent me a personal message once and said "quit wrecking his channel and discouraging his customers with my facts" "he's just trying to run a business and YouTube is part of it".........this guy is a scammer....This is just my opinion, freedom of speech.
     
    Last edited: May 23, 2020
  9. Whatever his failings, that is a pretty good combustion flame in a compact package for a non forced air burner: simply by getting the fuel spray to hit a hot surface.
     
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  10. @OMM, furnace will be outdoors. I do have a small welder, not 220. Probably not adequate for welding heavy piece of steel. I'll be using compressed air and a delavan .85 GPH siphon nozzle. Shop vac will be blower. I have a ball valve inline that I use to regulate amount of air shop vac delivers to furnace. Same set up as my propane furnace.

    Appreciate info about your setup. Biggest struggle right now is deciding on trade off between bore hole size and amount of refractory/wool. Absolute smallest bore hole size I can go with is 10 inches. This gives me 4 inches of room for dense refractory and wool. Steel drum has 18 inch interior diameter.

    I was thinking about 2 inches of dense refractory and 2 inches of wool. This would almost certainly be adequate insulation. However, I suspect that I'll end up wishing that I had at least an 11 inch bore hole diameter.

    I'm trying to understand the thermal conductivity numbers for my refractory. The rating at 2000F is 11.5 btu in/hr ft^2 °F. Unfortunately, manufacturer doesn't provide conductivity numbers for temps higher than 2000 F. Max refractory temp is 3200 °F.

    it's super tough but looks like conductivity of my plastic refractory is a lot higher than either mizzou or kast-o-lite. Hrmmm. Might need to rethink this.

    Still haven't decided on lid design.
     
    Last edited: May 24, 2020
  11. You'll be fine with 1.5" of dense castable and 2" of kaowool insulation, heck you could have 3" of dense castable and the Kaowool on the outside of the steel drum. I can point you to info on a furnace with 2.5" dense castable only: the outside of it gets to 360 deg C but it works perfectly fine and has even been used to cast monel alloys.
     
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  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I think 1" of dense refractory is fine. It's plenty of structure and easy enough to cast at thickness . Beyond that you're just adding more mass to heat, increasing the time needed to achieve melt temp, and spending more money. 2" of wool is also adequate. If it wasn't a hobby furnace that will spend most of it's life being heated for only one or two melts at a time more refractory might make sense......but otherwise I'd say not necessary or desirable.

    Best,
    Kelly
     
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  13. Tobho Mott

    Tobho Mott Gold Banner Member

    My 18" drum based oil furnace (build thread link in sig) has 2" of 2600F ceramic fiber blanket behind 1" of 3200F dense castable. At 12" ID, it is bigger than I need for just about everything I do, so it doesn't get lit up very often anymore. But I am happy with that design. If there is anything I could change, I might try to cast the hot face thinner.

    Jeff
     
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  14. I really like the idea of having only 1 inch of dense refractory and rest insulating wool. I don't think that the plastic refractory that I've used in the past would be up to the job. It's thermal conductivity is way higher than some of the popular castables like mizzou and kast-o-lite.

    So, I'll switch over to a castable with better thermal properties. Should be able to pick this up along with some wool this week (assuming that I'm still on covid holiday).

    Ok. Think that I have what I need for furnace body. I've seen several good videos/discussions about lids, so probably good with this as well.

    Burner should be assembled this week assuming final parts come in mail in next day or two.

    Excellent. Appreciate all the advice!
     
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  15. One more question.

    What do you all use for forms when casting 1 inch thick refractory? I have a 12 inch concrete form but next size up (in my area) is 16 inches. Plan is to use 12 inch form (filled with sand) for inner form. However, not sure what to use for outer form, which would require a 14 inch diameter.
     
  16. Jason

    Jason Gold

    :rolleyes: not surprised and was never subbed anyways.
     
  17. I use PVC pipe and add or remove strips to get the desired diameter. You need to have removable strips with a slight wedge or lengthwise taper on the inside tube to allow it to collapse and come out. Duct tape will keep the strips in place and a few circles of chipboard/MDF help keep it all in position. The prep work you do before the casting will pay off with ease of disassembly afterwards.
     
    Last edited: May 28, 2020
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  18. Whatever his personality, he's melting iron with sump oil using a small naturally aspirated burner, so I think he has something to contribute to the art.
     
    Last edited: May 28, 2020
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Just buy the concrete tube closest to your desired size, cut a section out of it to produce the diameter you want, and use filament tape on the seem on both sides. I used my table saw to cut the tube but razor knife and straight edge works too. I also covered the OD of the inner tube with packing tape to water proof it because only the ID of the concrete tube is waxed/water proofed.

    6 Casting Form.JPG

    Best,
    Kelly
     
    Last edited: May 28, 2020
  20. Petee716

    Petee716 Gold Banner Member

    I used HVAC duct. I got the heavier gauge stuff at an HVAC supply place. Lowes only had the thin stuff. Plus they only had 60" lengths available and it was expensive. The stuff from the supply place was 36". You could also roll out of galvanized HVAC sheeting. The heavier gauge.
    I cut plywood disks to support my inside diameters for ramming. 3 was enough. Sand should be ok in your sonotube but you may want to wrap the outside of the tube in food wrap so it doesn't get soaked and weakened.
    Those concrete forms are often various sizes and even though they are spec'ed at a particular size you might find one thats large enough (or small enough).

    Pete
     
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