Tobho's Oil Fired Melting Furnace Build Thread - Highlight Reel

Discussion in 'Furnaces and their construction' started by Tobho Mott, Aug 23, 2017.

  1. Tobho Mott

    Tobho Mott Silver Banner Member

    Original thread with more details and discussion: http://www.alloyavenue.com/vb/showthread.php?11373-Tobho-s-new-furnace-build!!!

    Meet Balerion, the Black Dread, my big waste oil fired melting furnace!

    image4 (2).jpg

    As a frothing mad fan of George R. R. Martin's A Song of Ice and Fire novels, I like to name most of my homemade foundry equipment after characters and artifacts from that series. Here's a little bit of info about the original Black dread in case anyone is interested: http://awoiaf.westeros.org/index.php/Balerion

    This thread will be basically the highlight reel for that original build thread linked above, without all the extra chatter and only the most useful pictures included. It's definitely not the only way to build a well-insulated furnace for melting metal, but it worked well for me. I have sorted out the relevant information and photos into 6 parts, for 6 posts.

    I built Balerion to replace my smaller Gingery charcoal furnace, so that I could 'graduate' from molten aluminum to be able to melt copper alloys (and beyond) without destroying my furnace, and to increase the amount of molten metal (and therefore the size of parts) I can pour. And to get to play around with a burner instead of getting all dirty from handling charcoal...

    Anyhow... let's get into it!


    Part 1: Cart and Shell

    First step was the cart and outer shell. I picked up a 30-gallon (I think - it definitely has an 18" diameter) oil drum to use for the shell. With 2" of ceramic fiber blanket behind a 1" castable refractory hot face, that leaves a 12" bore, ie. some extra room for me to grow into. I built a cart for it, made of a square tubing frame with a sheet metal top made out of an old oven's lower drawer. The sheet metal doesn't support any weight really - I made sure all three of the furnace's legs were supported by the square tubing when I bolted it down and located the pedal activated lever that raises the furnace lid. The cart wheels I eventually settled on came off a "chipper vac" I found in my back shed, which is a scary looking lawn care / yard work machine.

    The pedal only raises the lid just enough to swing to the side so I can access the bore, and I planned on using the drum's "ribs" to lock the refractory in the lid into place in addition to adding some stainless welding wire as 'rebar' to the part of the lid that would be filled with castable refractory. Having never welded anything before, I arranged to visit a good friend's brother in law, who is a millwright and has lots of experience with welding and fabrication. And a welding machine he was willing to teach me how to use and let me have at it for a couple days.

    This pic shows the angle iron legs and hinge brackets already welded on. The brackets were lined up against the seam in the side of the drum so they would be straight and lined up properly. This pic shows how I set it up to weld the hinge pipes to the brackets. If you look close, you can see a smaller piece of angle resting on the buckets and threaded through the inside of the hinge brackets; this is what is holding the entire furnace body up in the air here. The hinge pipe sections are held up by the hinge pin (a slightly thinner piece of pipe) and positioned just in the right place so I could weld the hinge pipes onto the brackets. Also of note, the position of the aforementioned rib in the lid section, which would lock the refractory in pace mechanically... Until the lid cracks one day, I guess, but that has not happened yet.

    003Furnace_shell_005_WeldingHinges.jpg

    Here are a couple of pix of the cart. First the underside, showing the pedal/lever that will push the lid slightly upwards when stepped on. I welded a bolt on the upper side of the far end from the pedal that would slip inside the bottom of the hinge pin pipe, so it would not have to be positioned too precisely, just at least partly on top of the lever. Then a pic of the top of the cart where the hinge pin comes up from below. A flange welded onto the hinge pin is what pushes the lid's hinge bracket upwards when the pedal is depressed. The pipe nipple sitting between the hinge pin and the furnace leg is not attached to anything here, it just happened to be sitting there when I took the pic, so it can safely be ignored.

    004Furnace_cart_001_pedal.jpg

    005Furnace_cart_002_hinge.jpg

    And here is the completed shell sitting on the completed cart, note the aforementioned flange on the hinge pin, for lifting the lid. It is welded to the hinge pin but not the hinge pipe, if that makes any sense. The welding wire rebar is also visible here. I bent it in a zig-zag pattern to (poorly) mimic the texture on actual rebar and on the 'refractory needles' some have used in hopes of holding (eventually) cracked refractory in place:

    006Furnace_shell_007_complete.jpg

    Jeff
     
    Last edited: Nov 14, 2018
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  2. Tobho Mott

    Tobho Mott Silver Banner Member

    Part 2: The Floor

    I wanted a drain hole in the floor. In case of crucible failure or possible attempts to melt large scrap directly. I can't fit whole car wheels in there or anything, and that is what I like to use for aluminum casting, but it is nice to have the option to melt other things that might be too big to fit into a crucible... Anyhow, I cut an overized drain hole in the bottom of the drum and cut six 2300F-rated insulating firebricks to fit around it as a sort of sub-floor. The rest of the furnace uses ceramic fiber blanket for insulation as mentioned above, but even as fragile as these IFB's are (and thet are almost as light and soft as styrofoam) they are more capable of suporting the weight of a castable refractory floor than fiber blanket. I left room around the oversized hole so the drain could have its own "hot face" of castable refractory.

    furnace_floor_001_bricks.jpg

    I made a form out of a brass tube (a sink part, I think) to cast the drain hole into the floor. I gave it some wooden "fingers" that slope down towards the hole so that molten metal can pass underneath a plinth so the hole would not be blocked in case of a crucible failure. I used to use steel crucibles, so this was a real possibility.

    furnace_floor_002_DrainForm.jpg

    Then I cast the floor using a 3200F rated dense castable called Unicast-70. The refractory came from Smelko Foundry Products, Inc., in Milton, Ontario. that is a 5-hour drive from where I live, but wow is that place amazing, so worth the trip. I was heading to nearby Guelph anyhow that weekend, with a little improvised road-trip sized charcoal furnace, to help a friend with a casting project for a club he is in, I guess it's the kind of club where you get really fun homework? molding, melting, and pouring metal in the densely populated suburban townhouse backyard of one of the guys in my friend's club while he was not even home was a little nerve-wracking, but the neighbours didn't bat an eye, much less call the cops and the fire department on us... Anyhow, the refractory was tricky to mix as dry as you're supposed to do it. I learned from pouring the floor that it works better to mix up a little at a time in a 5-gallon bucket than in a wider, lower container. I copied myfordboy's refractory vibration tool (a pole attached to a sander) but it did not work as well for me as it did for myfordboy, whose oil furnace build can be found on his most excellent youtube channel. After the floor was poured, I later came up with a similar idea that worked better for me, I'll show that in the next post. Well, the floor is probably the worst built part of my furnace due to the extra water I used, but it is also probably in the mildest area of the furnace, so I am not overly worried as even if it cracks, who cares? It can't fall out, the drum and to some extent the bricks will support the cracked pieces if/when that happens. I was able to remove the "fingers" but the brass tube was not going to budge no matter what I tried; it would remain in the drain hole until the refractory was fired, at which point it finally just melted out.

    furnace_floor_004_PouredForms.jpg

    Jeff
     
    Last edited: Nov 14, 2018
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  3. Tobho Mott

    Tobho Mott Silver Banner Member

    Part 3: The Lid

    I used an old toboggan/sled thing known as a Krazy Karpet as a non-stick smooth surface to mold the bottom of the lid's layer of castable refractory. A piece of an old cardboard carpet roll tube made a fine form for the exhaust vent and crucible-feeding/viewing port. That was centered just by eyeballing it, I may have measured it somewhat, but the lid shell is not 100% perfectly circular... In cases like this, if it looks centered, it is centered! :)

    lid_refract_001_ventForm.jpg

    The plan was to have the bottom of the lid poured in dense castable, with 2 walls of castable going up to the top of the lid - one around the vent hole, and one around the outer edge where it would lock into the barrel rib. I wanted a 2" deep recess between the two walls, so I cut a form out of some 2" thick styrofoam I had left over from some lost foam patterns I had been making.

    lid_refract_002_insulForm.jpg

    Here's where I needed to make a better vibration tool. My sander had shaken itself to bits when I built it myfordboy-style, so I used a cheap reciprocating saw instead, Just had to cut and file one end of a piece of thin steel bar to match the back end of a saw blade, and it easily chucked up in the normal way as if it was a blade. This worked REALLY well! I was able to mix the refractory super dry, which is desirable and results in a stronger casting. Castable refractory is amazing stuff, it is mixed so dry, but when you apply vibration, it compacts down and the water rises to the surface. By the time I was done vibe-ing it, as dry as I had mixed it, there was standing water on the surface splashing everywhere!

    Furnace_002_refractoryVibratorcloseup.jpg

    Furnace_001_refractoryVibrator.jpg

    I had to get creative weighing down the styrofoam donut that formed the blanket-hole!

    lid_refract_003_pouredWeights.jpg

    Here is the cured lid refractory with forms removed, and a shot of its underside - that krazy karpet worked great, look how smooth it came out!

    lid_refract_005_formsRemoved.jpg

    lid_refract_006_VentCloseup.jpg

    lid_refract_007_UndersideCloseup.jpg

    Here's the lid with support turnbuckles and the first of two layers of 1" thick cermic fiber donuts installed:

    furnace_insulation_005_donut1placed.jpg

    And again, here's an out-of-sequence pic showing the lid with both layers of cermic fiber and a steel cap disc to keep the fibers in. The steel disc is really just sitting there, supported by the two walls of refractory. It only gets used outdoors and I saw no advantage in trying to weld it on or anything.

    furnace_lid_cap.jpg

    Jeff
     
    Last edited: Nov 14, 2018
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  4. Tobho Mott

    Tobho Mott Silver Banner Member

    Part 4: The Hot-Face

    For the forms: I had a 12" sono tube for the inside of the bore (an actual 12" tube, not just nominal - each nominal size arrives at (ie.) Home Depot nested like Russian dolls, so bring a tape measure when your're picking one out if you're copying this build and have a specific measurement in mind).

    My initial plan for the outer form was to use a piece of the same 14" duct tubing I had used for the outer shell on my Gingery furnace This proved inconvenient, as I had no idea how I was going to remove it once the wall was cast. I still had not been able to pull out the brass tube I used to form the furnace floor drain after all! even if this one could slide out, I was worried the spiral seam would get caught up, and my hands are too big to fit into the 2" gap to cut the form off with a dremel or something. I ended up buying some aluminum flashing and duct-taped a piece of it into a 14" tube. It wanted to stay teardrop shaped because of the tape seam, but you'll see how I got around that problem in a bit.

    One of the guys from the other forum (goes by Razortoe but spells it with a bunch of numbers in place of half the letters) made me up some printable templates based on my measurements. I was able to tape these onto my forms so I'd know exactly where to cut them so my tuyere form would fit in place properly. This shows the wrong outer form as explained above, but I still had the template intact after peeling it off this one, so it was easy to redo it.

    Furnace_HotFace_001_forms.jpg

    I used strips of that same 2" styrofoam to center the outer form and force it to stay circular despite its tendency to go teardrop-shaped. This worked amazingly well! The inner form was centered on the edges of the drainage channel "fingers" in the floor. Once the tuere form was in place, I filled the inner form with sand to keep it from moving and protect it from buckling when the refractory was poured and vibrated into place - those sono tubes are only waxed on the inside and are designed to keep concrete IN, not OUT! My tuyere form was a piece of auto exhaust tubing with flared ends, so that 2 pieces the same size can nest together to make one longer tube. I wanted to keep this form to use to line the actual tuyere of the finished furnace, so that I could take advantage of that flared end when placing by burner in it to melt stuff. More on that later...

    Furnace_HotFace_004_formsNewOuterFormWspacers.jpg

    I poured (actually scooped-in) the refractory and my sawzall-vibe worked its magic once again. that thing could vibrate the entire height of my hot face, the vibrating bar would just sink all the way to the bottom between the forms with hardly any resistance (I discovered this once it was done - I installed and vibrated it in just a couple inches at a time when I was actually doing the install, just to be safe), so awesome! See how wet it looks on top? Again, this was a SUPER dry mixture when I scooped it all in, I know many will say you can just ram the stuff in with a stick but I highly recommend using vibration. My hot face has hardly any bubbles or anything as a result, and so far the only cracking has been a hairline it picked up when I first fired it. Nothing I am worried about at all. Note, I gave the exhaust tubing tuyere form a quarter twist a couple of times after pouring but before the refractory cured. This kept it from being permanently stuck in there like my drain form was.

    Furnace_HotFace_005_poured.jpg

    Here's a peek at the inside and outside of the hot face after the refractory had cured and the forms were removed, note the very few (IMO) bubbles that are visible:

    Furnace_HotFace_008_formsremoved.jpg

    Furnace_HotFace_006_outerformremoved.jpg

    I had mixed up some extra refractory, so to save my bucket I poured it into an old margarine container and hit it with the vibe wand, thinking maybe I'd get lucky and it would magically turn out to be just the right height and width to use as a plinth. Guess what? That actually came true! The top of the plinth is about even with the center of the tuyere, and both my old steel crucible and my newer #12 Silicon Carbide crucible both fit on it just about perferctly...

    Furnace_HotFace_007_plinth.jpg

    Jeff
     
    Last edited: Nov 14, 2018
  5. Tobho Mott

    Tobho Mott Silver Banner Member

    Part 5 - Insulation

    I cut two 12" wide strips of 2600F-rated ceramic fiber insulation, the same stuff I put in the lid, long enough to wrap the hot face.

    furnace_insulation_001_fiberstrips.jpg

    It was not easy to slide it in between the outer shell and the cast hot face! They say this blanket is 1" thick, but I'm telling you right now, 2 layers of it is thicker than 2". but I can only assume that compressing it a small amount so that it actually is he thickness it is advertised to be does not impair its effectiveness. Have I mentioned that it was not easy to slide into place? I totally understand why some people wrap their insulated hot face with sheet metal instead of building in a drum like I did. But it did work. You can see in this pic through the tuyere from inside the furnace, that the blanket successfully slid down this far at least. I am pretty sure it slid all the way down to the bottom all the way around.

    furnace_insulation_002_stuffedtuyerecutout.jpg

    I had intentionally built my shell and hot face a little taller than the 1" tall wall of ceramic fiber blanket, so that I could add some more castable on top of the blanket to seal in the fibers, which pose a serious respiratory hazard otherwise. When I was buying my refractory and green sand at Smelko's (described in an earlier post), I also picked up a sheet of compressed ceramic fiber blanket. I cut some strips off of it to make a layer on top of the existing ceramic fiber layer that would be a little more waterproof than the uncompressed blanket. I should mention that Tim Smelko (owner) has recommended I line my drum with this stuff and pour a 3" thick dense castable wall to use as my furnace. All the builds I had seen from other hobbyists were based on a thin hot face and good insulation behind it, so I ignored that suggestion. Since then, I have learnd that some people have build really good furnaces with a thin dense castable hot face but with a sand and clay mixture that sounds more dense than insulating behind it, which by all reports work great with an oil burner and may tend to crack less. Maybe one day I'll add a hot face to my gingery charcoal furnace and convert it to run on oil instead to have a smaller furnace I can play around with, but that is not a priority right now. But perhaps worth considering for new guys reading here and trying to settle on a design for their furnace builds... Anyhow, a pic:

    furnace_insulation_003_stuffedgasket.jpg

    Then I mixed up some more castable and stuffed the top of the outer gap to seal in the ceramic fibers. I filled it to the top of the oil drum, bulging out just a bit higher than the tops of the drum and hot face (which are about the same height), vibrated it a bit, then I set down that krazy karpet sled (nonstick flat smooth surface) on top of the bulge and then put the heavy lid down on top of that. This squashed the bulge of refractory flat, so that the lid would form a good seal against it once it had cured. This worked great, I still have enough of that compressed blanket to make a gasket the lid can seal down onto if I need one, but so far I haven't, it still seals pretty well. I get fire coming out the drain hole, but not from under the lid when the furnace is running full blast...

    furnace_insulation_007_sealsquish.jpg

    furnace_insulation_008_sealdrying.jpg

    Jeff
     
    Last edited: Nov 14, 2018
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  6. Tobho Mott

    Tobho Mott Silver Banner Member

    Part 6 - Finishing Touches and Firing the Refractory

    Remember that exhaust tube with the flared end, used to form the refractory tuyere? I kept that to use as a tuyere liner that would have a built-in stop for the burner, to make it easy to get the burner positioned correctly. to do this I cut it short at the flared end. the cut was made on an angle so that the end would all be resting on the hot face, keeping the cermic fiber away from the direct heat and keeping the fibers from easily floating out to be inhaled.

    furnace_tuyere_001_cuttofit.jpg

    Then I just slid that into the tuyere, a prefect fit! Because of the angle I had cut it on and the fact it enters the furnace at a tangent to the inner wall, giving it a slight twist once it was in place served to lock it in place fairly tightly. I still have seen no need to weld it in place. In fact, I prefer not to, in case it ever needs replacing.

    furnace_tuyere_002_inplace_twist.jpg

    I used a piece of the other end of the exhaust tube to make a sleeve for my burner that was sized to nest into the flared end on the outside of the furnace. I tapped some holes in it so I could add bolts to act a bit like set screws, so I could adjust how far the burner protrudes into the tuyere.

    furnace_tuyere_003_sleeve.jpg

    furnace_tuyere_004_burner_testfit.jpg

    It normally goes a little deeper into the furnace than in that last pic, now that I've had a couple summers to play around with it at different depths and see what works. The first time I used this burner (it's like a Hot Shot or a Moya burner, ie. forced air propane preheat and oil drip injection once the furnace is hot enough to ignite the oil) I was suprised when flames shot back out between the 1" black pipe burner tube and the sleeve, but I should not have been. The solution: stuff that gap with leftover scraps of ceramic fiber blanket. Presto, no more flames blasting back at my propane line!

    Anyhow, this isn't the burner subforum, but fitting the burner to the tuyere seemed like part of the furnace build, so that is why I included all that here.

    Next, once the refractory had had a few weeks to sit and dry out with a lamp shining into it for warmth and a garbage bag over the top so it would hopefully dry somewhat evenly, it was time to fire it! They say you should build up the heat very slowly and gradually, and I did what I could to accomplish that. But this was not 100% successful. I had read somewhere that forced air propane burners only need a low pressure regulator like from a gas BBQ to work, so that is what I used. but my burner's 1" tube is not your typical design for a forced air burner. I guess on a larger Brute burner, it might have worked. For me, that skinny 1" pipe built up too much pressure from the blower to even allow the gas to enter the burner! It kept blowing out when I used a blower giving more air than my old hair dryer turned way down low. So I ended up turning up the gas more than I'd have liked earlier than I'd have liked to do so, and ended up switching to waste oil and my intended blower, a 5-gallon shop vac, earlier than intended as well, just to keep things moving. It seems to me that castable rerfactory, at least the brand I used, is a lot more forgiving than people realize. The slow firing schedule some refractories are meant to be fired with did not happen here, and yet it seemed to come out just about perfect, just that one hairline crack I mentioned, which has not gotten any worse since then. you have to keep in mind, thise firing schedules are meant for indutrial use, not for some dude in his backyard. Maybe if I had cast a 3" thick wall like Tim Smelko had suggested, it would have mattered more. Once it was running on pure oil, I was able to resume ramping things up more gradually. I kept this up for a couple hours until it was just about white hot inside, then I shut it down and sealed up the vent hole and tuyere with a couple of old ordinary red clay bricks to try and keep the heat in so it would cool gradually inside my shed overnight.

    furnace_firing_001.jpg

    furnace_firing_002.jpg

    furnace_firing_003.jpg

    furnace_firing_004.jpg

    That is my old steel crucible in there to give the flames something to swirl around. It looks so tiny in there, but it was max. capacity in my old furnace

    And here is the furnace right after I shut off the burner. This is all just actually glowing that bright from high temperatures, no flames present at all inside the furnace at this point:

    furnace_firing_006b_aftermath_real.jpg

    And the next day. See how it turned white inside instead of grey like it was before? That means it's properly cooked! :)

    furnace_firing_008_nextDay.jpg

    That's basically it, other than adding a lost foam aluminum "Balerion" name plaque I installed on the side of it.

    Here's a video I got of the first pour I made using the new furnace. - More lost foam stuff. I am more focused on green sand casting these days, and I am not using my steel crucible anymore.



    Anyhow, that's it, how I built my furnace. Feedback, comments, questions are welcomed!

    Jeff
     
    Last edited: Nov 14, 2018
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  7. Jason

    Jason Gold

    Pictures pictures pictures... LOVE it! We live in the world of monkey see, monkey do. This will make it easy to replicate for our own purposes.
    Great job Jeff! I see the return of some really kick ass threads!
     
    Tobho Mott likes this.
  8. Tobho Mott

    Tobho Mott Silver Banner Member

    Well the first time it took me 38 pages to post it all, so I'm thinking you are right, this would be easier to follow along with if anyone does want to try copying it. And if it's too still much for a few of those monkeys of yours, there's always the king. We all gotta start somewhere... :)

    I have no regrets about this build, but if I were to rebuild I might replace the ceramic fiber insulation in the walls with a rammable sand plus fireclay mix and simply trust in the power of waste oil. Like my Gingery charcoal furnace, but with a tangential tuyere and an added thin cast hot face. Rasper and Petee both seem to like theirs...

    Jeff
     
  9. Tobho Mott

    Tobho Mott Silver Banner Member

    Edited to replace thumbnail pics with full sized images upon another member's request. I hope this has made the thread easier to read.

    Additional note: the lid support turnbuckles appear to have had their turny bits made of Zamak or something; both of them melted off during a bronze melt this summer when I had the burner running a little rich and the flames raging out of the vent were a little too close to the turnbuckles. The lid seems to hold up its own weight just fine since then, so I haven't replaced the supports. Yet...

    Jeff
     
  10. smithdoor

    smithdoor Copper

    Looks great good size for home uses

    Dave
     
  11. PatJ

    PatJ Silver

    A great improvement in the post (full sized photos), and a cool furnace build.
    Thanks for the update.

    With the Unicast 70 dense castable refractory (rated 3200F) you used for your hot face shell, I see iron melts in your future.
    This furnace has "iron" written all over it.
     
    Last edited: Nov 14, 2018
  12. Petee716

    Petee716 Silver Banner Member

    The king. Huh.
    This thread has enough of your blood sweat and tears behind it, the king doesn't deserved to be mentioned here. You learned a bunch of great stuff on that project and we got to watch you do it. Doesn't get any better than that.
    Great write-up Jeff. As good a tutorial as I've seen.
    Cheers.

    Pete
     
  13. DavidF

    DavidF Administrator Staff Member Banner Member

    Looks like your ready to cast that bronze sword now ;)
     
  14. Tobho Mott

    Tobho Mott Silver Banner Member

    Haven't tried for cast iron yet, but I built it with the goal of not ruling anything out...
    Other than the melted turnbuckles, the only reason for bumping this thread was to make it more readable by making the pictures full sized rather than thumbnails, which was requested. So, nothing has really changed significantly since I finished the build back in 2015.

    Jeff
     
  15. PatJ

    PatJ Silver

    This is a great build thread, and somehow I have previously missed seeing it in all one piece, so I am glad I discovered it.
    I was a bit shocked to see that I made an almost carbon-copy of Jeff's furnace, since I don't really recall seeing more than a few early bits and pieces of this thread back in 2015.
    The only thing I remember vividly is scavenger using a leaf blower on his stick welder to bump up the rating.

    Perhaps I subconsciously used it, but I swear on a stack of bibles that I don't recall seeing the 1" thick hot face shell before I built my furnace.

    .
     
  16. Tobho Mott

    Tobho Mott Silver Banner Member

    I "borrowed" a lot of ideas from Indiscriminate Scavenger, Myfordboy, and too many others to list or remember. The thin hot-faced, highly insulating design was certainly one of those ideas, it was an approach I saw again and again when I was researching old build threads on AA. I saw a bunch of old threads where people were DIYing clay-based insulating builds using ground up foam etc. too, and a few builds with just a thick wall of insulating castable as well. (Could be mistaken but I seem to remember Dallen's 'blue pig' was an all Cast-o-lite build, at least at some point in its life, which has included many iron melts...)

    I've only cast aluminum and bronze, so Rasper and Petee's furnaces that have the thin castable wall backed up by a more dense (than ceramic fiber) rammable sand/clay mix seems like it would have also been a good choice that might be more durable. I don't expect The Black Dread to fall apart any time soon though, and although Rasper has shown that his Lio-style drip oil burners make insulation irrelevant when melting bronze, I wonder if that is still true if you are trying to get cast iron up to pouring temperature.

    I think mine probably got up there when I first fired the refractory, but I don't think I've had it glowing that bright since then. Here it is that day again (rerun pic), this is after I had shut the burner down...

    View attachment 117

    Jeff
     
  17. Melterskelter

    Melterskelter Gold Banner Member

    So, for me the question is: “what is the thinnest cast hot face that can be practically used?”

    I am impressed with the strength of fired castable thinking it is something like that of stoneware. If that is true, perhaps face thicknesses of 1/2” are practical. In the interest of making the lowest mass possible furnace, I would (and might) skip the cast face altogether and just use rigidized ceramic blanket if I didn’t think I would be bumping and thus damaging a blanket-only furnace lining. My hoist technique has improved with practice. But I still often bump the walls as I hoist out the crucible. A thin face might be just durable enough to withstand these bumps and bruises.

    Would troweled satanite be tough enough to minimize scrapes from incidental hoist contact?

    Denis
     
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The dense castable refractory in my big furnace (14" ID) is 5/8" wall and is freestanding. It has insulating castable flanges. I'm not melting iron though so even though the refractory can be cast that thin, not say it would do well in iron service.

    4 Main Body and Bore.jpg

    I believe Ironside's furnace is high temp wool with Satanite and seems to do just fine with iron. If you bump it, not much work to fix it.

    Best,
    Kelly
     
  19. PatJ

    PatJ Silver

    I have noticed that I can totally ignore insulation and refractory thickness when melting aluminum, since an oil burner and even a propane burner can just power through any heat loss with ease, and the refractory does not have to reach a high temperature in order for the aluminum to melt, so I assume the metal is melting mostly by the convection process and conduction thru the wall of the crucible.

    I have not tried to melt iron without insulation, but I suspect it could be done as long as the refractory reached a very hot temperature, but it would be really hot standing next to the furnace and would probably use more fuel.
    I think the furnace insulation is as much for operator comfort as it is for retaining heat in the furnace.
    And it seems like there is not much melting action of iron until the refractory has reached a very high temperature, probably due to the radiation from the walls of the furnace that is needed to transfer enough heat into the crucible to be able to melt iron.

    I have been reading he Audel's book on Oil burners, including Chapter 3 "Heat" including topics such as radiation, conduction and convection of heat, and also Chapter 4 "Combustion", and these chapters shed a lot of light on what is happening with a furnace/crucible/metal when it is heated by an oil burner.

    My hot face refractory seems to come up to temperature faster with insulation containing the heat coming off the outside of the hot face.
    The 1st and subsequent melts seems to get sped up (more efficient too) when a good exterior insulation of some type is used (insulating fire brick, ceramic blanket, sand/clay, or some insulating material), and I would guess the higher the insulation rating, the faster and more efficient the melt.
     
  20. PatJ

    PatJ Silver

    When I have tried to trowel hot face material (ITC100) onto any surface, it just cracks/peels off.
    Rigidizer only seems to stay on if thinned with water and sprayed on.

    Refractory does crack, and sometimes spald, and the thickness is more a matter of allowing for the minor cracking/spalding to be repaired with ITC200 or equivalent material, while still maintaining something rigid behind the patching compound.

    Scavenger tried a thin coat of hot face material on top of a rigid board and/or ceramic blanket, and as I recall that did not last long.
    He ended up with perhaps a 1" thick hotface of rammed refractory.
    Scavenger mentions having support behind a thin hot face, and mine has a 1" layer of ceramic blanket followed by a layer of insulating fire bricks, and that does not give much support to the hot face, but so far I have not had problems.

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