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Thread: Planning stages for a new furnace

  1. #1
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    Planning stages for a new furnace

    Hi all, I have been reading in this site nearly every day for 8 weeks now! I have learned a tremendous amount and am essentially on information overload. All that being said, I am planning a furnace build. I always thought that I never did anything small ... until I read MarCaap's build thread! Well my furnace will not be that big or elaborate, 30gal drum more on the lines of Mjonkman's and Tobho Mott's.

    I really want/need to pour iron (I know, I know, at some point) and want to build a furnace to take me there. At max I can see a B10 or B12 crucible, not sure if I will get there ... but want the ability to go that large. I have a lathe, milling machine, etc, so I could end up like myford boy (I wish!) and I also repair old farm windmills, thus the want/need to pour iron.

    Anyway, enough babbling. Here are my current thoughts on dimensions etc:
    • 11.25"d x 14.25"h interior with 1.25" hot face.
    • Hot face probably from Sparcast LC 32 AL (rated for 3200*F, but still waiting for info from another supplier).
    • Hot face wrapped with 2" of ceramic wool.
    • 3" high plinth.
    • 3" top clearance on a B12.
    • Lid similar to the sides ... HF and wool.

    Now for my questions:
    • What should I back/support the bottom hot face with? I was thinking IFB, then saw some comments that talked about not enough support. So what about dense firebrick? Any other suggestions? My thought was to pour the bottom in place like Tobho Mott did.
    • SS needles or not in the hot face, lid, bottom? I have read yes, no, maybe on different aged threads ... what are current thoughts.
    • How much will a 2" layer of ceramic wool "fluff up"? Rough measurements, I will have .5" of diameter unaccounted for (to the barrel diam). Will a 2" layer of wool expand an extra .25" all the way around?


    Let me know your thoughts and opinions. This will not be a fast build, but I will be sure to post pics (I see you guys like them). :-)

    Thank - Ed
    Last edited by Mister ED; 02-28-2017 at 03:08 AM.

  2. #2
    Senior Member cactusdreams's Avatar
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    Welcome Ed. Looks like it should work fine. I supported the bottom by casting feet of refractory with one in the center. http://www.alloyavenue.com/vb/album....chmentid=11576 On the wool, I was told by the guy who sells it at IFSCO where I bought it, which I did with great success and I know will get some dissension on here, is pack it down don't fluff it up. Like they do in pizza ovens. I put 2 x 1" layers into 1.25". Plinth seems a little high but that's me. Also remember the crucible number is lbs. of Al so with Cu alloys or iron will be around 3x as much. Plus the weight of the crucible itself and tongs you need to maneuver. You didn't mention your fuel but the oil folks seem to leave more room around the crucible while propane only needs as little space as your tongs need to get in there.
    People who say it cannot be done should not interrupt those who are doing it.

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    Thank you Cactus. I do plan on WMO for the burner (I should have said that originally), thus the side clearance that I have planned. If I do grow into a B12, I should have 2 1/8" clearance at the bulge. And if I am running a B6, I should have just shy of 3" bulge clearance. So I think that is good? Thinking about this, I may cut the height down two inches. 2" plinth and a B12 would give me 1 7/8 top clearance. And the B6 on the same plinth would have 3 5/8" clearance (maybe a little much, but maybe I could use a touch taller plinth?).

    I do like your support structure underneath (especially since it looks like you have a domed bottom). Maybe I will change my mind and cast the bottom outside of the barrel. I think if I do that, I will use a foam doughnut and cast solid under the plinth and outer edge. With the foam I could also segment it into 4 pieces and basically cast reinforcement from the plinth to the outer edge (I think I saw a build like that).

    Oh, and looking at your other pics ... I love that you finally found a practical use for one of those wooden/woven salad bowls!!

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    I think the crucible number represents kg of Cu. I think the IFB would give you enough support in the bottom. I just cast mine solid. As long as you're not dropping stuff in there. Your minimum plinth height will be determined by the tuyere height. Mine comes in an inch above the bottom and is 2.5" in diameter so my plinth is about 4". I actually stacked another piece on top so my crucible sits high enough for my pouring shank to get a good grip as I've recently built a new furnace and my shank was built for my old furnaces shallower depth. Placing a steel rod into the hot furnace for a minute or so through the exhaust hole shows that the hottest height area in the furnace is right about where the center of the crucible sits. It cools nearer the top and bottom of the furnace. It makes sense that the bottom is cooler because of the blower, but partially covering the exhaust brings the upper part of the column to a higher temp. I have about 3" of clearance to the vent which is 4"diameter.
    I have some experience wth wool but not much knowledge as to whether it should be compressed or not. I think trying to fluff it would be a wasted effort. I have a few feet of 1/4"x24" from an old project that I could sell you for cost plus postage if that's what you decided to do, but I wouldn't deviate from the manufacturers recommendations too much as far as how to install it goes.
    Scavenger makes pretty good use of IFB here
    http://www.alloyavenue.com/vb/showth...ight=Scavenger

    Pete

  5. #5
    Senior Member Tobho Mott's Avatar
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    The floor of my furnace that you mentioned is sort of both of the options you are considering - castable refractory poured over IFB's, in the hopes that the castable is strong enough to protect the IFB's from getting crushed by the weight of crucible and plinth. So far it has held up great, not that it has exactly seen hundreds of hours of use yet or anything. It also had some gaps in the IFB at the outer edges and around the drain in the center (both thanks to the quarter-circle corners I sawed off the bricks at the center to make a cast refractory lining for the drain - see the attached pic), so the castable has some little "feet" to help support it and take some of the weight off the fragile bricks.

    Attachment 15595

    If I had to do it again, I might line the oil drum with IFB's instead of ceramic fiber blanket; that way, the bricks themselves could act as the outer form for the castable hot face and there would be no craziness trying to slide two 1" layers of blanket into the 2" gap between the hot face and the oil drum - 1" thick ceramic blanket apparently is (sometimes?) actually thicker than 1", so I had a heck of a time with that... Or else I'd wrap the hot face in ceramic blanket, then wrap the whole deal in sheet metal, much like myfordboy did in his furnace build videos. The oil drum bottom did make the floor easy to make though, and I'd cast my lid in a ribbed section of an oil drum again in a heartbeat - that barrel rib filled with castable holds my whole lid together so it can't fall out of the steel shell. Well, that and the stainless steel wire I used as rebar, which may or may not prevent more trouble than it causes...

    If you are going to use cardboard sono tubing for your forms when you cast the hot face, make sure you bring a tape measure when you go to buy them - a given size of sono tube might have a (for example) 12" diameter as advertised, or it might have less; they arrive at the store by truck grouped by size and nested inside each other, so the measurement printed on them should be considered nominal, not actual. Also, make sure you backfill the bore with something like sand so the cardboard tube will not collapse when you pour the hot face and it gets soggy due to being waxed only on the inside (have you seen Keith Rucker's furnace build videos on youtube?). That will work well. Those tubes are meant to hold concrete IN, not OUT! Otherwise they work great, you can just peel (or burn) them out afterwards, easy as you could ever want.

    Hope that is helpful, and good luck with your build!

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

    How I built my oil furnace | My Photo Album | My Videos

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    Gentlemen - Thank you for the replies so far. They have helped me decide a couple more things and reminded me of a couple things that I had already read, but lost in the vastness of void between my ears.

    I think I have decided to cast the bottom outside the drum. Cast it upside down and use some foam to make some void areas in the bottom (to be filled with wool). I think I have seen similar around here someplace. I guess if I am going to cast the bottom outside the form, I will do the sides that way as well. Use the set up bottom as part of the form and pour right on it. I suppose they will stick together. For the tube forms I have several 3'x5' 19ga sheets laying, they should suffice.

    Height, I guess I will think through that some more to try and give the most flexibility up to a size 12 crucible.

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    I used HVAC duct for my forms. I also cut 4 disks from 1/2" plywood for each form. I used them so my forms wouldn't cave in while ramming. They might also prove helpful to you in forming your metal too unless you happen to have a roller. I didn't feel like driving out to my plumbing supplier for the 12" duct so I bought 2 pieces of 6" at Lowes and joined them to make 12. The disks were a tight fit but they came out pretty easily and the sheetmetal peeled out easily too.
    This is my newest furnace
    http://www.alloyavenue.com/vb/showth...-s-new-furnace

    Pete

  8. #8
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    I actually have a Pexto Slip Roll, so no issue making the tubes. I just watched Myfordboy's video again (I think for the third time) on his pour, and I think that is the direction I will go. I had forgotten he had cast his floor separate. I think however I will pour the rim, after the wool and balance of the hot face is in the drum (like Tobho Mott did). That might make it a bit easier to get it all in the drum and to make sure the wool is correctly in place.

    Temp depending I may start mocking up the forms this weekend and maybe make a run to the scrap yard to scrounge for some appropriate base steel. Hopefully I will have the opportunity to get the refractory in a week or two.

  9. #9
    Senior Member HT1's Avatar
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    be very careful with crucible sizing, the system is not standard anymore A used to be Lbs of AL, B Lbs of Brass, now often B = Bilge(shape) and the number after that can mean anything. Pick a supplier I recommend http://www.lmine.com/graphite-crucibles-c-1_2_142/

    Check their literature Pick a crucible, Buy it and work around that.
    I had no trouble with their budget crucibles. Bought a whole case

    V/r HT1


    P.S. here is my actual Order from Legends I wish they still had that case of three deal I've been using those crucibles for 7 years and need more

    17368-3 # 16 Budget Graphite Crucible - Case of 3 $116.00

    17358 # 10 Silicon Carbide (SiC) Crucible $118.80

  10. #10
    Senior Member r4z0r7o3's Avatar
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    +1 on the Salamander Super. You can get some sizes on Amazon, they come well packaged, and their fit/finish is top-notch.

    Can't add much to what else has been said above. So my only build-advice is: consider simpler designs/forms, building the burner first, and be sure to get enough extra refractory that you can re-do any component.

    It's going to take 3x longer and cost 10x more than you think, don't do like me and spend half a year building the forms. Hindsight being 20:20, I would have gone with Tobho's pour-in-place design which it seems you're leaning toward. The fewer forms you need to build, the better.

    I suggest building the burner first because you need it to cure the refractory, and it allows you to guarantee the tuyere fit/placement up-front. You can special-order large (3+ inch) black-iron pipe (heavy/robust but hard to work) from Lowe's or use exhaust-pipe (cheap, easy to work but thin) from an auto-parts store.

    Both refractory and insulating blanket are really odd materials in use and feel. They don't behave quite like you'd expect from looking at pictures. Have extra on hand to get use-to and make mistakes with.

    Oh, and welcome, from a relocated-Michigander
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

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