First furnace, what a good material to use for the floor?

Discussion in 'Furnaces and their construction' started by Alexander Madsen, Feb 9, 2020.

  1. I am working on my first furnace. What a good material to use for the floor? I have been lurking off the forum for a few weeks and it has been insightful and answered most of my questions.

    -Enclosure= Beer Keg
    -Side Walls and Top = 1" Inswool HP 2400 degree, 1" Inswool HTZ 2700 degree, 1/4 skim coat Satanite 3200 degree.

    -Fuel= Propane to start, but upgrade to an oil burner once I get comfortable with foundry work.
    -Tuyere=2.5" Dia
    -Top Vent=4" Dia

    I plan to start with casting aluminum and brass but hope to graduate to cast iron. I am happy to invest a little extra upfront to have a high-quality furnace with growth capacity.

  2. Hi Alex, floors are considered "consumable" especially if melting iron. The only furnace floors I have direct experience with are cast as one piece together with the plinth out of high temperature 1650 deg C dense castable furnace concrete. The furnace ideally has a removable metal hatch to allow the damaged floor to be knocked out and replaced with a precast floor/plinth that is grouted into place. You could also cut low density alumina furnace bricks to cover the floor and again a removable hatch would assist repairs.
    Last edited: Feb 9, 2020
  3. OMM

    OMM Silver Banner Member

    Maybe there's another way to a sacrificial floor. I'm just thinking outside the box...

    A thin layer of cardboard that is sprayed with graphite spray(which will get burnt off), coated with a mixture of tungsten/carbide, with a binder of high temperature mortar mixed with graphite powder and a touch silica for a glaze.....after fired, it might just vac out.
  4. Jason

    Jason Gold Banner Member

    geez matt... Sounds a little complicated for a beginner.:p

    If ya want a "consumable floor" Why not run standard wool throughout followed by a mizzou hard face then just lay fire bricks on the floor that can be changed out as needed? You mention spending a bit more up front.... That would be a quality hard face like mizzou or Kastolite. Satanite is the rage at the moment, but I doubt it's worth a damn for an iron setup.

    While iron can be the final goal, you'll have plenty to keep you busy with aluminum while you perfect your skills. If there was ever a hobby of walk before run, THIS IS IT!

    One thing the guys around here recommend is buy your crucible first! Start with say a #6 or #10 clay graphite from fleabay. Build to handle the 10. When you use a crucible, it's a good idea to run it 3/4 full to prolong it's life. If you are pouring small parts, you'll appreciate having that smaller 6. Melts will be faster, use less fuel and you won't have to pig out quite so much. (that's making ingots with the unused melt) Beer kegs are great, but they are really BIG even for a #10. You will need to cut it down a lot unless you get one of those smaller kegs. Figure 1.5-2" of wool on the walls and 3/4-1" of mizzou. The floor can be a little thicker, a drain hole is toss up and the exhaust hole 4" minimum. Keep the bottom edge of the tuyere hole an inch off the floor in case you spring a leak and won't flood your burner with molten fury.:eek: Hope you have a welder as it will save you a bunch of time and money. Tools will need to built to handle the crucible. Something to lift it out of the furnace and usually something else to pour. Watch one of my videos and you'll get the idea. Propane is the easiest to get you up and running fast, but an oil burner is not hard to start with. The Kwiky burner will melt alloy, brass and bronze with ease on just cheap diesel with a small blower. And the benefit is you don't need to preheat with propane by doing that. You can always add oil to the kwiky after the furnace is up to temp. Only downside is you need an air compressor. Not much, I run a 60gallon tank and it only runs once every 7-10minutes and then only for a minute or so.
    I'm a cheap bastard so no propane for me. I get free jet fuel so that's all I run now. Oil can make a mess and I haven't made the leap to iron yet.... Someday maybe.
    Mark's castings likes this.
  5. Petee716

    Petee716 Silver Banner Member

    Welcome Alex,
    You're in luck! As it turns out with a beer keg the size limitation is in the bore diameter not the height. I have a 1" hot face of mizzou backed by about 1.5" fireclay/sand leaving me with around a 10" bore. That allows a #18 clay graphite from Legend
    to just fit allowing for lifting tool. That's 7" diameter X 9" tall. The point being that leaves a lot of extra height. So even if you go to a #20 at 7.5" diameter your still only at 9" tall. If you leave your dome in the bottom, even if you level it off and build up from there, you still have extra height. Standard practice is to have the top of your crucible around 2"" from the lid. My #18 sits on a plinth over 4" high (can't remember exactly) and another 2" gets added when I use my #10. Kind of a pain but I guess it gives the advantage of more combustion space burning waste oil. I don't consider my floor consumable but it does require maintenance from time to time. So, options. More so if you weld. I'll let others discuss the materials, but I will say that the extra 15 minutes it takes my rock to heat up is a drop in the bucket compared to the rest of the time involved in casting.

    Jason likes this.
  6. FishbonzWV

    FishbonzWV Silver Banner Member

    Welcome Alex,
    Both of my furnaces are built with just wool and Satanite on the floor. I do add a couple more layers of Satinite though.
  7. Melterskelter

    Melterskelter Silver

    If you cast iron, drips of slag and iron will melt right through Satanite on wool in a single session. Aluminum and other metals are reputedly more forgiving.

  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hey Denis, weren't you working with Bubble alumina too? How'd that IFB/BA lid turn out?

  9. Tobho Mott

    Tobho Mott Silver Banner Member

    Welcome to the forums, Alex!

    My two furnaces' floors are both IFB, coated with a fairly thick layer of dense castable refractory in one case, and a much thinner layer of much easier to work with Satanite in the other. I figured the IFB would give the floor a little more stability to hold up heavy stuff like plinths loaded up with fully charged crucibles etc. than having just blanket underneath it all would.

    The Satanite furnace is a lot more pleasant to use, and it melts stuff so fast I actually don't even bother setting up much less turning on the oil drip for it - the propane "furnace preheat" mode on my Moya waste oil burner gets it hot enough to melt metal and get it up to pouring temperature almost as fast as it takes just to preheat the other furnace enough to start the oil drip...

  10. Melterskelter

    Melterskelter Silver


    I think the Bubble Alumina is an amazing product. It seems to be extremely resistant to heat and spills.

    I have had no guidance from the manufacturer or other folk's reported prior experience in using it ass a coating. The manufacturer said they had never heard of suing it as a coating as opposed to as a castable---its intended application.

    The lid has held up pretty well despite my fumbling attempts to apply it as a roughly 1/4" thick coating. 1/4 inch is probably about as thin as it can be applied due to the granularity of the bubbles. I think when I initially applied it I mixed it too dry based on prior castable experience. So its adherence was 80 percent with some 3x3 areas flaking off after a half dozen firings. After maybe 30 firings I have had some of the repaired areas fail again a time or two. BUT, since I last applied it with a very wet mix to those areas and pre-wet the brick, it appears to be holding well. So, for someone coming along and wanting to try it, I would suggest a very wet---like a soupy consistency that will pour out of the mix container in blobs--- as a target application for coating IFB. Protected by the BA, the IFB has held up very well.

    I am on the cusp of trying a new method of applying BA the hot face of a new furnace build. But, by paying closer attention to applying Satanite along the lines of the clues supplied by Fishbonz, I am finding the Satanite/Wool side walls of my present furnace to be holding up better. And I have competing casting goals that have preoccupied me and prevented the new furnace build.

  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Is that 2600 IFB?

    That Bonz is a crafty fellow!

  12. Melterskelter

    Melterskelter Silver

    Yup, 2600.Denis
  13. Based on your feedback, I plan will make the floor out of IFB2800 toped with a hard coat of Mizzou and/or Satanist. I will effectively cast a composite brick, then install them.

    I will start with a Satanite hot face of the walls then cast in Mizzou or Bubble Alumina if the Satanite has durability problems. Seems like it would be a straightforward upgrade. I am very intrigued by the Bubble Alumina, a bit pricey but very interesting.

    My Keg is a full-size keg (1/2 barrel). I got a good deal on craigslist. My Satanite and Inswool arrived today. Last night a found a local supplier source for structural insulation and refractory, Rubix Composites Inc, so the materials are about to get a lot less expensive with no shipping charges.

    Jason, Why buy the crucible early? It is for sizing hot faces and other furnace internal features.

    Petee716 likes this.
  14. Jason

    Jason Gold Banner Member

    That is right. Plus when you have the mizzou mixed up, you'll need to pour your plinths. A cool whip container worked perfect for me. You want to size it so when the crucible sits on it, the flame is NOT directly hitting the crucible. All of this will relate to floor height and tuyere height. Plus, you'll need it for making your tools.
    I've used this seller a couple of times and his crucibles are good to go. Others here have had good luck with him also.
  15. FishbonzWV

    FishbonzWV Silver Banner Member

    He'll need to go bigger than an A6. Kegs have a 16" diameter, with 2" wool and 1/4" Satanite, that's an 11 1/2" bore.
  16. Petee716

    Petee716 Silver Banner Member

    Sounds like a solid plan.
  17. Jason

    Jason Gold Banner Member

    A #10 isnt that much bigger really. This is one of the reasons I think kegs make lousy candidates for furnaces. Too wide and too tall for the average joe.
  18. Denis.

    FYI High Temp Tools has the following guidance on BA as a skim coat for fiber blanket. Alumina

    "How do I mix/apply the Bubble Alumina?
    Mix the Bubble alumina to a troweling consistency and trowel it in place onto dampened Inswool ceramic fiber blanket Let it dry for a few hours and then slowly fire up your forge to fully cure it. This is one of the most flux resistant coatings we have found, I'm sure you will be very pleased with it!

    What thickness coating do you recommend for the Bubble Alumina and how do I figure out how much to order?
    I generally recommend a coating of at least 3/8" on the floor of a horizontal or vertical forge...."
  19. OMM

    OMM Silver Banner Member

    I actually think it’s the perfect size. The half barrel you would lose 2 inches off the bottom and probably 4 inches off the top for your inside height. So you’re inside dimensions would be about 17”T x 16”dia. If you reduced these two sizes by 5”(wool + hot face). 12” inside height with a 2 inch plinth and 11” diameter. You could pretty much safely use a A12 having 2” Air gap between any of the faces and the crucible.

    All my outers (walls, top and bottom) have 4 1/2”, So this didn’t work for me. My goal was to try to get a inside 14”T x 12”dia. I designed a little backwards. I wanted something that could fit in a 24 in.³ space. In the end it didn’t work out as the total height reached just over 29” (with the casters and opening mechanism).

    Last edited: Feb 10, 2020
  20. Jason

    Jason Gold Banner Member

    Let's take the half barrel keg. That's 16.5" diameter. Now look at a #10 for example. A 10 crucible is only 6.3" across.
    Let's allow 2" on each side of the crucible for lifting tool. That's 10" total. So you are left with 6" to eat up with wool and hotface. Most people
    are too cheap to use a full 2inches of wool and 1 inch of castable refractory. (1 full inch of mizzou means it will probably take at least 5bags of mud!:eek:)
    Given the size of a half barrel, ya better cut that bastard in HALF or it's going to be one expensive and heavy can to cover the inside at these specs.
    It's 2 inches too wide and over a foot too tall for my taste. Add in the stainless steel pain in the ass factor and it's tall order for the average FNG.
    I used a 14" steel air compressor tank and it's still huge for my #10. My only regret was not cutting off another 6" off the length.:oops:

    The idea of building just one furnace for all your needs from the start is a pipe dream. It sounds good in theory, but we all make mistakes in the beginning.:(
    A guy spends a grand in materials to build the ultimate furnace and then just melts beer cans to dump in some ant hill.:rolleyes: Once the novelty of making silver
    muffins wears off and they realize the melting part of this stuff is just 10% of casting, they lose interest pretty damn quick. The real key lies in the ability, skill
    and imagination to create patterns. That's what metal casting is all about to me.;)

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