A thin hotface medium/low mass beer keg (drum size) furnace for melting Iron

Discussion in 'Furnaces and their construction' started by PatJ, Aug 24, 2017.

  1. PatJ

    PatJ Silver

    That is some nice mold work.
    Did you CNC that?
     
  2. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Nahh. Old school. Belt sander, hand guided table router work, and wiped in wax fillets. Anxious to see your castable work come together but cant say enough to encourage you to build a vibe table. Concrete figurines, brick makers all use them. You'd be amazed, once good vibe hits that castable it will settle so densely you'll barely be able to stick a 3/8" dowel rod into it. Just mount four stout springs on the corners of a piece of plywood and excite it with a fractional horse motor with an eccentric mounted on the shaft, or maybe a long john body sander or something like that. It has to have a little giddy up cuz you'll probably have 50-100lbs of refractory. Test it with a dummy weight. Also helps to fashion a makeshift funnel of sorts to direct the castable into the thinner annular gap as you shovel it in. Sounds like a lot of work but not really and you wont regret it.

    A close second is using a vibrating wand but you will find it challenging to manage that in the gap while your moving all the castable into the mold.

    Best,
    K
     
    Last edited: Sep 1, 2017
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    PatJ, I did manage to restore the picture content in the refractory section of my furnace build thread. If you click the link in the earlier post in this thread it is now active and updated with pictures.

    Best,
    Kelly
     
  4. PatJ

    PatJ Silver

    Thanks Kelly, I appreciate your efforts and time.
    I will take a look at your build thread.

    Edit:
    I was able to see the photos you restored.
    Cool stuff. Quite a build I must say.
    It will take me a while to study all that.

    Oddly enough, I don't recall seeing all those photos, so either alzheimer's is setting in, or I just was not paying attention.

    Thanks again.
     
    Last edited: Sep 2, 2017
  5. PatJ

    PatJ Silver

    It was relatively warm here yesterday (almost 50 F), so I decided to go for it and ram my new low-mass furnace.
    Things went pretty well.
    I used my big Hobart mixer to mix the Mizzou, and had to mix it in approximately 30 lb batches since the mix was relatively dry.
    The mixer really struggled when I mixed in the stainless needles, but I got those mixed in as well.

    The ramming seemed to go ok.
    Originally I was going to ram one section at a time, and stack the sections as I went, but that did not turn out to be practical, so I decided to tape all the forms together and ram from the top using a 1/2" wood dowel rod, and that worked out.
    I added the refractory in about 1.5" layers, ramming as I went with the dowel rod.

    I put the whole shell in a plastic bag to keep it from drying out, and then made a small tent affair and added a heater to bring the mass up to about 90F.
    It took about six hours for the refractory to start its exothermic reaction and set, but I could tell it happened because the temperature in the tent went up to 100 F, and the shell got hot.

    I used about 80 lbs of Mizzou for the entire shell, which is a tiny fraction of the refractory I used in my first furnace.
    I will keep the shell in a plastic bag for about 2 weeks in order to get a full cure, and will keep a little heat on it to prevent freezing.

    I did not get any photos while I was mixing and ramming the refractory.

    The sides and bottom of the shell are 1" thick, and I rammed the furnace upside down, and that seemed to work well.
    I will use two 1" thick layers of ceramic blanket around the shell.

    I still have to ram the lid, and I am still working on that exact design.

    The inner and outer forms are waterproofed with foil tape, and both are hot glued to a wood base to prevent form floating (like my first furnace nightmare).
    The inner form has several circular wood forms within it to maintain its shape.

    The burner tube form is 2.5" diameter muffler pipe.

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    Last edited: Dec 18, 2017
    Tobho Mott likes this.
  6. PatJ

    PatJ Silver

    I stripped the forms from the furnace today and was very pleased with how uniform the wall thickness was. Its nice when things go right for a change.
    I was concerned that the forms would shift and I would not be able to maintain the 1" thickness.
    There are some small air bubbles, but nothing I am going to worry about.
    I wanted a monolithic shell with the bottom and sides all in one piece, which is why I rammed the furnace upside down.

    And I poured a couple of plinths, for small and large crucbiles.

    I was able to salvage all but one of the interior round wood spacers, so I can reuse those if I ever need to ram another shell.

    The stainless needles are not visible, but they are inside the refractory, and according to scavenger, they work well to hold the refractory together, for the same reason I guess that they use rebar in concrete.

    Now I need to make the forms for the lid, which will be domed.
    The lid will have a lip which will protrude down past the top edge of the furnace, to hopefully prevent those annoying horizontal furnace/lid junction leaks.

    I really like the weight of this furnace shell, which is about 70 lbs.
    It makes it so much easier to move around and handle, and should greatly improve iron melting times.
    I am starting to get excited about melting iron again.

    Edit:
    If I had to do over again, I would have cast the tuyere extension at the same time and made it an integral part of the furnace hot face.


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    Last edited: Nov 29, 2018
    OCD, Jason and Tobho Mott like this.
  7. Tobho Mott

    Tobho Mott Gold Banner Member

    Looks like a winner, good job!

    Jeff
     
  8. PatJ

    PatJ Silver

    Thanks, I am excited about this furnace.
    I am trying to get the lid figured out today.
     
  9. Jason

    Jason Gold

    That's the best looking shell I've seen! Take 50bucks for it?
     
  10. PatJ

    PatJ Silver

    Thanks, I got lucky on this one.
    And a thin shell uses a lot less refractory, so much less expensive than a thick one.
    Its a little less than a bag and a half (55 lb bags).
     
  11. Petee716

    Petee716 Gold Banner Member

    Not much luck involved there! Thorough planning and execution won the day. Anchoring and reinforcing that inner form seems to be a spot where folks run into trouble. Our forums have many examples of off center bores and floated forms. Nice work.

    Pete
     
  12. Tobho Mott

    Tobho Mott Gold Banner Member

    Their buckets floated & sono tubes buckled so that ours didn't have to! :D

    Jeff
     
  13. PatJ

    PatJ Silver

    Thanks all for the encouragement.
    I had enough trouble with the first furnace to last a lifetime, so I am trying to get this one right.

    I worked on the lid last night.
    The idea is to have a lid with a lip on it that will hopefully stop and flame leaking out of the furnace/lid junction.

    I made a trip to the hardware store, and the only dome I found that seemed about the right size was a clay pot.
    I probably should have gone to the kitchen store and found some nested pots, but I will try to make this work.

    There is not much in the way of guidance online about a lid like this.
    I did review scavenger's lid, and it is similar.

    I am sort of stumbling through the form making for this lid.
    I hope to cut some shapes from foam to go around the exterior, and I guess ram the lower part first, then put some refractory on the curved part, glue on the forms to sort of retain it in a curved shape, then top off the top lip.

    I made the lid opening large (8" I think), with the intent that I can always make a refractory insert to make it smaller, and the insert would act as a mini lid-within-a-lid arrangement.
    I would like the lid opening large enough to perhaps allow some skimming without opening the entire lid.

    Its a pretty large dome; perhaps taller than I want/need, but I have it formed up now, so I will forge ahead.
    I don't think a tall lid will affect the furnace performance, and it may allow one or maybe two sizes larger crucibles than I originally designed.

    The top lip will only protrude up perhaps 1", although the top (blue) form is 2" tall.

    I was originally going to use the top of the beer keg as a form, but the diameter was not right.

    I am not sure exactly what the sheet metal around this lid will look like.
    I have considered using it without a metal jacket, but I really need something to cover the two layers of 1" ceramic blanket.

    This lid has turned out more complex than I intended, so I am not positive I will stick with this design, and I only have 38 lbs of refractory remaining and would prefer to not purchase any more.

    In retrospect, I should probably just cut off the bowl, and ram it flat, which will work with refractory needles for support (I think), make skimming a lot easier with the lid closed, make ramming the refractory a lot easier, and lower the mass of the lid.

    Edit:
    This domed lid design was not a good one, and I did not use it.
    I cam up with a better domed lid design later in this thread.


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    Last edited: Nov 29, 2018
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Pat, if you figure out how to construct the outer form for lid such that it has a uniform wall, you might find that one a little more difficult to ram. If so might be a good time to consider vibe. I did reconstruct my furnace build thread photos so the links earlier in the thread should have pictures now.

    Best,
    Kelly
     
  15. PatJ

    PatJ Silver

    Kelly-

    I reviewed your furnace build thread.
    Thanks for restoring all those photos; great stuff.
    You are definitely operating on a much higher level than the stuff I do; I can only dream of building things like you do.

    I did a mock-up of the lid without the flower pot, and it comes up 35 lbs.
    I have about 38 lbs of refractory remaining, so I will go with the flat lid design.
    I will use a hard fire brick to choke off the lid opening a bit.

    Edit:
    I don't want to vibrate the refractory because it has needles in it and some coarse grain, and I don't want either of those to settle out.
     
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Pat, You're very kind but I think you do very well for yourself. I noted you mentioning several times the concern about settling out aggregate/grog/filler but I really haven't found that to be the case unless you apply vibe for excessive amounts of time. As near as I can tell nearly all the manufacturers recommend vibe placement. The first time I used the Greenlite 45L insulating castable I over-vibrated it. That stuff has really fine granular, light, insulating filler. Consequently it is very buoyant. It also makes the refractory flow very well because that filler is like marbles. I would just load up the mold with a funneling shoot and hit the vibe for just a minute or two with that stuff and it would lay down quickly, so much so in a fraction of a minute you could barely stick a wooden pencil into it. You can tell when you start to overdo it because water starts to comes to the surface. With the dense castables this was much less the case.

    38lb to net 35lb would be cutting it pretty close. Instead of dome, you might also consider a shallow cone....easier to fab and you get most of the same benefits but nothing wrong with a disc with a short vent stack.

    Best,
    Kelly
     
  17. _Jason

    _Jason Silver

    Pat,

    For a "flattish" form, I wonder if you look at something like a Rubbermaid garbage can lid for a form? It will have a shallow bowl shape and you could trim it to diameter as needed and add ring around the outside as a damn to hold the refractory. They're available all over the place and cheap.

    Just trying to help thing outside the box.


    -Jason
     
  18. Jason

    Jason Gold

    A lid inside a lid. Clever! My form a few years ago crept on me too. :-( As luck would have it, it was directly across from the tuyere. 2 big handfuls of mizzou worked to build that area back up. Not pretty, but melts bronze
     
  19. J.Vibert

    J.Vibert Silver

    Awesome efforts thus far Pat...

    I never considered my furnace to be low mass, (knowing how heavy it is) but seeing as we're sharing the same dimensions on the refractory end of things I guess I'm apart of the club...lol.

    I've been eager to make another furnace as well for ~indoor~ use, but on the lighter scale for better efficiency. I guess it will be in the "flyweight" class.. ;)
     
  20. PatJ

    PatJ Silver

    Thanks all, I appreciate the comments.

    The garbage can lid idea is a good one; wish I had thought of that, but I have this lid formed up already in a flat shape, so I will go with it.

    I did remove the bowl today from the forms in order to make a flat lid, and changed the lip depth from 2" to 1".
    I wish I had another 55 lb bag of refractory, but it is just as well that I am running short on refractory because the whole idea behind this furnace was to keep it low mass, and it would not make any sense to have a low-mass furnace with a high-mass lid.

    Some have speculated recently that a shell this thin will need reinforcing from the back, such as insulating fire bricks like scavenger used.
    I am not convinced of that since I am using stainless refractory needles, but I guess if that becomes an issue, I can lift out the liner and add insulating fire bricks behind it.
    I am pretty sure the hot face will work without insulating brick reinforcing, but I guess if I did as much iron work as scavenger, then the insulating fire brick would be cheap insurance.

    I am going to try to ram the lid tonight, and will post more photos.
    I considered making a stainless cover for the lid, but I don't want the stainless acting like a large heat sink, and I think it would since it would contact the refractory around the perimeter of the lid, so I will omit a metal cover.
    I think what I will do with the lid is add two layers of 1" ceramic blanket on top of it, and spray the outside of the blanket with watered down furnace cement to rigidize it and keep the fibers from becoming airborne.
    I am going to try the lid without a lid lifter, and what I will do is imbed two handles made from 1/8" stainless steel wire in the outer edges of the lid, just above the outer lip.
    With a lid-within-a-lid design, I hope to only have to open the lid once (when I pour).

    I guess the ultimate low-mass furnace is the one ironsides is using, which uses ceramic blanket with a sprayed-on or brushed-on zircon rigidizer.
    Ironsides seems to have the fastest iron-melting times, and the lowest fuel usage of any I have seen published online.
    I am not sure how the zircon-coated ceramic blanket holds up over time. Perhaps ironsides can weigh in on that.

    I have toyed with the idea of an indoor furnace, but the risks are rather high.
    The main risk is what the wife would do to me if I burned the house down, not the actual damage to the house.
    But there are several guys in the UK who have indoor furnaces, apparently in their shed/shop behind their house, and they use a tall metal pipe as a sort of chimney to vent the fumes up high in the air.
    There is a guy here in the US (I think member here) who also has an indoor furnace with some sheet metal surrounding it, and a sand pit in front of it; I forget who that is.
    I would not be worried about spills and fires so much, but rather the fume and monoxide issues. A fire extinguisher will take care of just about any fire, but if you can't breathe, you don't stand a chance.

    Since furnace lids seem to leak a lot, I would be concerned with an indoor furnace from a fume and carbon monoxide standpoint.
    If I did melt metal indoors, I would use propane, and I would not attempt to melt iron indoors.
    If I had a very large shed/shop, I suppose I could run the furnace indoors with the right ventilation, but my shop is small and full of stuff.
    I would definitely use a carbon monoxide detector for a fuel-fired indoor furnace, and ventilation would still be required to get rid of any metal fumes.

    I run a pressurized fuel system (about 5 psi on the diesel tank), and should that fuel line rupture, as has been seen by at least one member on one of these forums, then you can get a rather large pool of flaming fuel going around your furnace in just seconds.
    Not a big deal if you are outside on concrete, but that would be a disaster if it happened indoors.

    More photos tonight.
     

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