Another lightweight fiber blanket furnace

Discussion in 'Furnaces and their construction' started by Tobho Mott, Apr 29, 2019.

  1. Tobho Mott

    Tobho Mott Silver Banner Member

    I picked up some more fiber blanket. It's the 2300F stuff. Now the outer layer around the bore is that stuff, and the inner layer is still 2600F blanket. I used the 2600F blanket that used to be the outer layer to line the lid. No pix of the lid yet, I'll get to that soon.

    I also got the foot that is an inch made. 20190504_023935-1040x780.jpg
    I welded a nut on the other side of this washer and this washer onto the end of this piece of pipe...
    And this is what screws into it. So I can adjust the height of the foot to level the furnace.

    Also got the push handle made. It's just bent rebar. 20190504_023920-1040x780(1).jpg

    The ends slot into these two pieces of pipe that are bolted to the bracket on the back of the tank. The bolts take up enough of the inside of the pipe that the rebar can't go in any farther. 20190504_023952-1040x780.jpg

    Tuyere is cut, but still kinda sloppy. 20190504_024002-1040x780.jpg

    Somehow even after putting the ceramic fiber in and taking it out so many times, the top of the wall is surprisingly level! That's a 1/4" donut of compressed ceramic fiber blanket sitting on top. I've had a sheet of it that I got at Smelko's for a couple years but could never think of any good use for it except maybe a gasket for a furnace lid... 20190504_024129-1040x780.jpg

    That's all for now.

    oldironfarmer and joe yard like this.
  2. oldironfarmer

    oldironfarmer Silver Banner Member

    Going to be a nice light furnace!
  3. Tobho Mott

    Tobho Mott Silver Banner Member

    Yeah, can't wait to see how my melt times are affected now that I've done what we've all been telling people for years and designed the furnace to fit the crucible, not to mention the super low mass design.

    So far it's coming together faster, easier, and only a little more expensive than I expected.

  4. oldironfarmer

    oldironfarmer Silver Banner Member

    Sometimes you just got to spend your nickles.:D
    Tobho Mott likes this.
  5. FishbonzWV

    FishbonzWV Copper Banner Member

    I think once you get the Satanite on there, you won't have enough combustion room to run nothing but propane.
    But don't worry, the efficiency of this style furnace can't be beat.
    I think the Black Dread will just be a home for spiders after you get use to the Red Devil. :D
  6. Tobho Mott

    Tobho Mott Silver Banner Member

    Maybe you're right about the size, we'll see I guess. If I ever get a bigger crucible I'll be using the old furnace again for sure. I can always unblock its drain and use it to break down half-wheels and other large scrap as needed too.




    Between the friction fit and the 3" drywall screws, the blanket in the lid isn't going anywhere. I shook the bejeezus out of it and everything stayed in place. The screws point sideways to pin 2-3 strips of blanket to each other, not inwards toward the heat. I just turned them in by hand. Was gonna weld the screw heads in place but it's all fitting so snug I don't think it's necessary unless I notice the rumble of the burner is shaking them out or something.

  7. oldironfarmer

    oldironfarmer Silver Banner Member

    Are you going to be able to get the bejeezus back in, or is the blanket too tight?

    I'm afraid your lid is screwed. Nice idea. I would weld them.
  8. PatJ

    PatJ Silver Banner Member

    The fire time should be really quick with such a low mass.

  9. oldironfarmer

    oldironfarmer Silver Banner Member

    Would you put on more than 1/8" Satanite?
  10. FishbonzWV

    FishbonzWV Copper Banner Member

    Two layers on the lid max.
    The walls, I shoot for three layers. But to get a fairly smooth bore, first layer I put on vertical just for the ease of application. Second layer goes on horizontal, around and around to start the smoothing process. Then I coat the depressions vertically as many times as it takes to fill them, third layer is horizontal again.
    My firing sequence, first layer fired until it turns black and then it turns grey (you're driving the water out but not curing it). Apply second coat and bring furnace to cherry red. Then I start filling the voids (optional), if it takes multiple coats to fill them, fire to grey between them. Last coat on and put the crucible in and fire until crucible is red.
    Last edited: May 5, 2019
    Tobho Mott likes this.
  11. Tobho Mott

    Tobho Mott Silver Banner Member

    Got a piece of 2-1/4" exhaust pipe extension tacked in to act as a tuyere. I used a piece of the same type of tubing on my other furnace. The flared end accepts the sleeve I have bolted onto the 1" black pipe burner tube on my Hot Shot, so I positioned the new furnace's tuyere so the burner will also slide in here to end up at the proper depth (pulled back just a bit from inside the actual furnace bore).

    Looking forward to the arrival of the Satanite, so I can finish off this build and start having some fun with it!


    Melterskelter likes this.
  12. oldironfarmer

    oldironfarmer Silver Banner Member

    You may need to change vendors on that Satanite. Those guys don't seem to know how to ship.:eek:
    Tobho Mott likes this.
  13. Tobho Mott

    Tobho Mott Silver Banner Member

    Nah, these guys were such a good deal, to me it's well worth the wait. I'm in no rush.

    Not saying I don't check the mail first thing when I get home every day mind you, but that's just eagerness - no looming deadlines here.

    oldironfarmer likes this.
  14. Tobho Mott

    Tobho Mott Silver Banner Member

    Well actually a time factor did come into play, my seal coal guy Josh Van Noy from Van's Blacksmithing contacted me to see if I could help him out. He doesn't do very much casting, but he needed to pour 10kg of copper around a stainless steel coil to make an condenser to make liquid argon for a local university's physics department's dark matter experiments. :eek: Apparently they looked and looked and there's nobody else in this area they could find who could produce something like this, so that is how an old school coal forge blacksmith ends up working on a dark matter physics experiment with a computer programmer with a weird hobby. o_O He had burned out one of his forges trying to to actually melt enough copper to do it. So he was in a bit of a pinch and asked if I could help him melt the copper, then he'd pour it into a mold that he would make.

    This portable furnace was so close to complete I went ahead and did it. That awful thing. I got the 2700F chimney mortar stuff in the little plastic tub from Canadian Tire that everyone knows won't work. I figured if I could get one melt out of it before it all fell off, I could help Josh out and hopefully not have to replace too much ceramic fiber, then fix it back up once my satanite arrives.

    I started out applying it like in Fishbonz' satanite video, this stuff comes already mixed but I took some and watered it down for the first coat so it could wick into the ceramic fiber a little ways. Coated the whole inside that way as carefully as I could, then gave it a bit of propane with the hot shot. This seemed to work well, it was glowing hot in no time, the stuff hardened nicely and I stopped before I had it glowing hot for too long.

    I actually did 2 coats with it thinned like that, fired it after each, then two coats straight out of the tub, smeared on quite thin, like 1/16 - 1/8" or so. The second coat cracked and curled a bit when I fired it, but most of it stayed put, and in the cracks where it curled up the surface of the wool that had soaked up the mortar seemed fine.

    Worst case scenario, I have enough fiber blanket to replace any that might melt if it all went wrong... So I slapped a hinge on the lid, tossed all my stuff in the back of the minivan and headed over to Josh's smithy today.

    His mold wasn't set up the way I would have done it... He had it set up for an open pour in a sand mold with a plaster of Paris and sand core in the middle and the stainless coil in the space between the round sand mold cavity and the core, with the bottom end of the coil rammed up buried in the sand at the bottom of the mold and the top end of the coil sticking up above the top. His flask was also a few inches taller than the top of the mold, so he had to pour a fairly long way down just to get to the top of the mold much less the bottom of the cavity. It really bubbled a lot, and the stainless coil started uncoiling as it began heating up, so it touched the side of the mold in a few places. (He figured they had coiled it using a cold process where using a hot process might have avoided that problem). His crucible also wasn't big enough to fill the whole cavity as it turned out, so we did a second melt and he poured it in on top of the first.

    I told him that if this part can't be used, I definitely have some ideas about how to approach this casting differently. From what he told me I guess the physicists are so happy they found someone who'd even take this job around here that they don't really care about how good the casting is as long as enough of the coil is coated in copper for it to work. He also thinks he might know a guy who can braze over the exposed coil sections enough to fix it, but whatever, if he has to redo it I have a feeling I'll be getting a call earlier on in the process next time.

    The good news is, the furnace held up great considering the stuff I lined it with, and wow did it heat up fast! Basically I lit the propane, closed the lid, put on my gloves, started the oil drip, turned up the blower, turned off the propane, and that was it for the whole startup routine, this takes a good 10 minutes if not 15 in my other furnace but it was less than two here and could have been faster if I had my gloves on already. At one point during the melt it was glowing so bright in there, I couldn't see into the crucible without sunglasses on. The copper melted quick and easy.

    As for the lining, I didn't have high hopes for the innermost layer of ceramic fiber blanket, but other than that unthinned layer or two of chimney mortar curling up everywhere it had cracked a bit more, and a hole about the size of a two dollar coin melted into the blanket right at the inside of the lid vent, it's nothing I can't snap the curled up edges off of and smear over with Satanite one of these days. I think I can stuff a bit more ceramic fiber in that one hole and it'll be about good as new. :D

    He let me keep the crucible, it's too big for his setup anyway. And he offered me a free spot in one of his one day blacksmithing courses at some point, so that should be fun too.



    Dark matter experiments astronomy and stuff, who'd have thunk it? Sounds like science fiction to me - forget about a red devil, this furnace is the Red Dwarf!

    More pictures and some video to come later.

    oldironfarmer likes this.
  15. oldironfarmer

    oldironfarmer Silver Banner Member

    Pretty cool. Just when you don't think you know much, you run across a competent person who really knows a lot less. From all you've said I have a lot of respect for your blacksmith friend. I laughed out loud at that flask. However I would have likely missed that the coil was going to unroll. Good lesson for the future, embedded stuff needs to be securely anchored. And anchoring it at each end where it is exposed might not do the job, it could still bow like an unrestrained spring.

    You probably got stuff too hot. Time to turn down the burner and not try to melt in 0.4 sec.

    Wonderful, physicists need help from a blacksmith who calls on a computer programming axe maker to save the day! Right after GoT on your local channel.
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Poured pure copper? Tell us a little about the melt management. Did you use some sort of cover flux? Any pictures of the part after the pour? That's a party foul Jeff!

  17. oldironfarmer

    oldironfarmer Silver Banner Member

    What am I missing? I've been making copper ingots for cleaning up scrap. Nothing special other than brass flux.
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Again, just curiosity but that's why I ask. I have no foreseeable need to cast anything from pure copper. Some report as you do, others say it rapidly oxidizes.

  19. Tobho Mott

    Tobho Mott Silver Banner Member

    He had his crucible preloaded, I think there was some sort of flux already in it which floated on the melt in a thin layer and left a glassy residue on my skimmer. That goo was really all there was to skim, which I did as soon as I couldn't feel any more lumps in the melt with a steel rod probe. He poured it right after that with a two in one crucible tool which you can see part of in the pic above.

    I'll get a pic or two of the casting up today at some point but he was still chipping out the core when I left. At that point it looked like a big black sand crusted blob, the first thing I said when he shook out the mold was, "That's a big ugly chunk of copper!"


    You can sort of see where a bit of the coil is exposed where it hit the side of the mold here:


  20. Tobho Mott

    Tobho Mott Silver Banner Member

    Here's a better look at some exposed coil.


    The casting itself looks a bit like... Er, dark matter. Hard to imagine what's inside it after the copper got drizzled in from a foot and a half above the bottom of the mold and after how much the plaster core had the mold bubbling. Maybe it'll still work as an argon condenser?


    Here's Josh chipping away at that core.



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