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Thread: Pete's new furnace

  1. #1
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    Pete's new furnace

    I've been talking about building a new furnace since last year. I finally got moving on it. I've had the half keg for a couple of years and got the stinking SOB cut open a few weeks ago. I reviewed a few other builds, read Colin Peck's book again, and the had at it. The first thing after cutting it open and removing the lid' dome was to make the lifting mechanism.

    https://m.youtube.com/watch?v=7ZCE42RknN0

    Of course I can't do anything simple. I did get to use my lathe and mill on this part of the job, so that was cool. I learned a lot while doing it.

    The keg makes a great shell. I've never done anything with stainless before. It's "interesting" to drill through. I also had to do a bit of Mig welding on it as well for the burner holder. I made the burner holder by bending some 18 ga steel around a 2-1/2" shaft (aluminum copier fuser roller). I clamped it good and heated it with one of those propane weed burners up to red hot to get the spring out of it. It worked great.

    I originally planned on 2 1/2" solid Kastolite30 but the brickie who gives me the stuff couldn't get it anytime soon, so I got mizzou. I also didn't want a solid mizzou furnace so I decided to do 1-1/2" of sand/fireclay as a backer with a 1" mizzou hotface. The lid is 2" mizzou and will have an inch of ceramic fiber.
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    After finishing the lid lifter I mixed and poured the lid and leveled the floor with mizzou. As part of the form for the lid I cut a piece of 1/2" plywood with a vinyl mask on it so the refractory wouldn't stick. I burned it out later.

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    I made two sets of forms for refractory. One at 12" diameter and one at 10". I used the bandsaw to cut disks for each. I used 30ga HVAC duct for the forms. I used two 6" ducts to make a 12" form.

    I made a rolling base for it using plastic wheels and a leveling foot. I'll cut to the end and tell you that the plastic wheels will not get hot enough to fail.

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    Then I mixed the sand/fireclay (2:1) and and about a liter of water. Total weight was about 60lbs. I used my muller to do the mixing because, um, why wouldn't I? I mixed in the water until it had the squeeze properties of greensand.

    image.jpg

    More tomorrow.


    Pete

  2. #2
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    I've never done anything with stainless before. It's "interesting" to drill through.
    "Interesting" is a bit of an understatement. The thing about stainless is that it work-hardens almost instantly. You have to drill fast. If you let the bit turn without much pressure, the stainless work hardens and will dull your bit in a New York instant.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  3. #3
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    Nice idea with using the muller to dial in the water content of the refractory. Hadn't seen that before...

    Noticed you also went for the drain. Crazy how that tiny aspect gets so debated.
    FLAME ON...!!!!

  4. #4
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    Because of the amount of service the drain in my charcoal furnace has seen, I've always been an advocate of it. I mentioned Colin Peck's build book. His design has a spout incorporated for direct melts and a dropout bottom. The spout can be seen on Nudge's furnace. The dropout bottom was a no-go for me and the spout would have been too much of a hassle to form because of the concave keg bottom. I thought about cutting the bottom out but after cutting the top off the keg I decided against it. That stainless almost instantly murdered every blade I tried to use on it so I ended up using the recip saw very slow and worked the blade back and forth to keep from smoking it. I cut the dome out the same way. 4 blades in the trash. I used an angle grinder to level the top of the keg off because it was pretty hacked up by the time I was done. I flipped the ring and put it on the radial arm saw with an abrasive wheel on it. After about 50 pulls on the radial arm it was nice and level.
    I felt like the time, labor, aggravation, and spent tools wasn't worth the minimal utility of the dropout bottom. So I just put the drain hole in the bottom and called it a day. I already have a reverb furnace for direct melting. How's that for a short response?lol

    I had to put a 1-1/2 hole and a 2-1/2 hole through the keg for the drain and tuyere. I used hole saws from a newer Milwaukie set I have. I was surprised at how well they cut through the stainless. I used my 1/2" drill motor so the sped was pretty slow and I used plenty of cutting oil from a spray bottle. I used the angle grinder to finish opening the tuyere to accommodate the pipe angle.

    Pete

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    Attachment 21061

    After sitting in buckets for a day I rammed it in hard. Pics out of order.
    image.jpg
    Attachment 21062

    The form gave in a little where I overdid it but I was able to scrape the excess off after I stripped the form out. I also thinned the area where the target wall will be so the hotface will be a little thicker there.

    image.jpg

    I decided it would be a good idea to fire the backer before installing the hotface so it wouldn't get damaged and could be treated as a separate project.
    I took it outside and stripped the form out yesterday. It was about 35F out and no wind. As good as it gets these days! I started a small fire in one of those charcoal starters and maintained it for about 4 hours. I also started a charcoal fire on top of the lid to burn the plywood form off. It turned out to be a waste of time and a hindrance. After the drying period I put the oil burner in fueled with siphoned diesel set pretty low (relatively). After a 30 minute warmup I switched to pressurized waste oil and pretty much let it rip for about 2 hours. The furnace interior was almost blinding hot for the last hour or so.

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    Afterwards I covered the furnace under its new house. My small bucket furnace lives under the smaller drum in the background. I'll bring it back into the barn today to inspect the results.

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    If you can zoom in, you'll notice there is still snow under the furnace wheel. I think the wheels will be okay.

    Pete

  6. #6
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    The mizzou in the lid fired fine. The plywood form on top of the lid was reduced to ash from the heat that permeated the refractory. The turnbuckles are evidently not steel like I thought they were. The damage occurred after I put the barrel over the furnace when I shut it down.

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    I'll be filling the lid with kaowool. My friend had some from an abandoned maple syrup project a few years ago and he was happy to find a home for it. It's 1/4" I think, but he gave me about 20ft of it. I'm not sure how I'll cover it. I'll probably tack weld sheet metal over it.
    The interior fired as expected. I doesn't exactly ring, but has a pretty telling sound when you thump it. It did not fire effectively under the tuyere form. Either it was too cold there or it wasn't compacted enough. Where I had hand-pressed sand around the top edge didn't fire either. Probably for the above reasons. That ended up coming out as well.

    image.jpg

    A small amount of sand got blown off the surface by the compressed air, blower, and rumble of cumbustion and was loosely attached to the bottom in a thin layer. I had to tap it pretty good to break it out.
    The mizzou went into the furnace ok. Hopefully it went in solid around the tuyere and the little bit of loose sand that sloughed off the sides won't cause any problems. I'm sure glad I fired it yesterday. That sand/fireclay would have never held up. I didn't put a vapor barrier in between the two layers. I have my fingers crossed!

    image.jpg

    So the plastic is on till tomorrow with a lightbulb down inside the bore and the 55gallon drum over the top. At this point the bulb is only for heat so it doesn't freeze. After a couple more days I'll strip the form out and let it dry for another week or so.

    Pete

  7. #7
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    The mizzou turned out ok. I had to pack some under and around the tuyere after I took the form out, but it looks pretty good.

    image.jpg

    I started working on a sheetmetal cover to cap in the kaowool in the lid. I butt welded two 8x16" pieces of 16ga hot rolled sheet together and will cut it to fit the lid. I'm still a novice welder so the steel warped resembling a seagull.lol. Some reheating and hammering shaped it up pretty good.

    Pete

  8. #8
    Senior Member Tobho Mott's Avatar
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    Wow, my last furnace took months to get this far along! Looks great.

    An yeah, another +1 for using your muller to mix the sand and fireclay backing. Gingery's instructions for preparing his similar recipe in The Charcoal Foundry basically boils down to: "Mull it like greensand, maybe with just a little bit more moisture".

    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

  9. #9
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    Make no mistake, I've been working on this for a number of weeks. Going on a couple of months now. Many hours went into the lid lifter, cutting and drilling the body, welding, and making forms. Every aspect has been a project in itself!
    A couple of guys (you I think) mentioned perspective recently. I've seen things on the forum or on YouTube and think "yeah, I'm going to do that. Looks pretty straightforward." 3 months later I realize it must have taken the presenter weeks or months to do. You're not slow, it really takes that long! Lol

    Pete

  10. #10
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    I decided to recut the steel lid cover out of one piece instead of the scraps that I'd unsuccessfully tried to weld together. I'm glad I did. I rough cut it with a jigsaw and brought it into round with the rotary table on the mill. I couldn't figure how to cut the center hole on the mill without hazard to myself, the job, and the mill, so I just cut it out with the jigsaw as close as I could and filed the burr. I'm sure that after a few firings that inside diameter will find its own shape anyway, so it's good enough.
    The rolled top rim of the keg already had 4 conveniently spaced holes drilled in it around 3/16" diameter so I was able to just open them up with a #7 drill bit and tap 1/4-20 threads. The steel on the rim is about 1/8" thick so I was able to get a good couple of threads in there which is all I needed. I still broke a tap in the process.
    So I cut my insulation, installed it and put the cover on. I needed 1-3/8 thickness and happened to have some 1-1/2" from a previous project, so in it went!

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    I was planning on firing it today but it's 19F outside with a stiff breeze. If it weren't for the breeze I would do it. I'll just keep it warm with the lightbulb for now.

    Pete

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