Eager to build my first furnace and need a good direction to go

Discussion in 'Furnaces and their construction' started by Ray Swicz, May 27, 2024.

  1. Ray Swicz

    Ray Swicz Lead

    So I cleaned as much as I could from YouTube and realized I know nothing when it comes to designing a foundery furnace.
    I have came to the same conclusion about most content creators on that platform too.

    So I have been collecting a lot of materials to build my first furnace.
    What I realize is I've been fortunate that what I've acquired so far has been very inexpensive and I will get one chance to do this right without costing much.

    We had in the shop a part of a lime kiln from a quarry for repairs. And after the "Brickies" we're done I asked them if I could have a few of the bricks. They left me 5 boxes of HWI 23 soft bricks, 9 x 4 1/2 x 3.
    I got quite a few feet(15?) of 2" kaowool from a boiler repair job.
    And one of the electrical contractors we hire now and then is a glass blower and he donated a 50# bag of kastolite 30.
    So I think I have most everything I might need to build the furnace.
    I am finishing up the burner. My plan is to use diesel after seeing Mark Preslings build, I thought I could do a similar build .
    My take on it relies more on automotive parts. 5 gal fuel cell. 140psi fuel pump, injector pressure regulator, fuel filters and a 3.5gph oil burner nozzle B type 60deg solid cone.
    I currently have a clay graphite a 12? Crucible and will in the next few weeks buy an A20 and A30.

    So my plan for the furnace so far is to use a 55 gal drum cut down to 20 inches in height

    Put 2 inches of kaowool in the bottom, rigidize it with sodium silicate and coat with kastolite.

    Cut 13 bricks into trapezoids and mortar them together on end giving me a 15 inch furnace bore .
    Cover that with kastolite also.
    Stuff kaowool between the bricks and wall of the barrel.
    Cut 7 more bricks into trapezoids and halve them to add another 4 1/2 to the bore height.
    Cap the kaowool from the wall to bore with 3inches of brick and cover that in kastolite too
    In my mind this seems the way it should be assembled.

    Am I way off base here?
    I have no idea if I am going about this corrctly
  2. Hi Ray, what size crucible do you plan to use?, that will define furnace chamber size to a certain extent. Also oil fuelled furnaces tend to need a larger chamber size than faster burning fuels like gas so the slower burning oil stays in the chamber long enough to fully combust and release the heat. So you want at least a 2"-3" air gap all around the largest crucible you plan to use, based on my furnace that has a 1" air gap around the crucible mouth and struggles to reach 1350 C/2400 deg F with an A25 crucible yet gets easily hot enough with an A8 to cast iron. The smaller crucible allowed more volume for combustion in the furnace.
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's a good list of materials and with a diesel burner, likely some high energy available. What metal will you most often melt and what size castings are you wanting to tackle?

  4. Ray Swicz

    Ray Swicz Lead

    I have an A30 clay graphite crucible in a cart ready to purchase in the next 2 weeks.
  5. Ray Swicz

    Ray Swicz Lead

    I would love to do huge cast iron castings. But the reality is A60 crucibles are costly. Old bronze litters our shop, like there can be random 100 lbs pile anywhere you look. The main stay of my place of employment is Lake Freighter repairs. And we just had 2 welders pass their bronze prop certs. Any one of those prop blades weigh in at 10 tons each. I think the one out front they said weighs 35000 lbs.
    I see in my future making LOTS of yellow hammer heads any where from 5 to 20lbs.

  6. In that case, forum member Melterskelter has a well sorted iron melting furnace sized to suit an A25 crucible and plenty of detail on lifters etc. in his other posts. His furnace is using fibre refractory with a refractory lining but the dimensions should be a good starting point

    Last edited: May 28, 2024
  7. HT1

    HT1 Gold Banner Member

    sounds familiar

    go read this start to end
    now do it again

    How do you intend to handle an A30 of cast Fe or brass? that is a two man lift. I run an A-20 and it tis all that I can handle, And I'm A large fella

    if you make the floor of your furnace out of kaowool, even rigidized, the Plith and crucible will sink into it, probably flip over,(Very Bad Day)
    the floor needs to be solid i would highly recommend MIZZOU the floor does not need to be insulated all that heat is going up, but it does need to be very strong and durable MIZZOU is one of the best
    BLU-RAMĀ® HS PLASTIC Monolithic Refractory is another great product

    HWI 23 soft bricks : you have to make sure these do not come in direct contact with your burner flame they are rated for 2300F your furnace will be hotter then this and the direct flame from the burner will kill them first heat if you cast a half inch of Kastolite over them, and patch them regularly it will be ok.

    think long and hard about your lid design I will never do a Side swing again its in the way! a cantover deesign is much better and simpler,
    additionally sealing that lid! I Fouled that up so bad , my next build with an cantalever design lid will interlock to seal as solid as humanly possible https://www.backyardmetalcasting.com/catalog.html

    your brick design sounds like you are doing a lot of extra cutting so just think 2 inch floor two 9 inch bricks stacked you have 20 inches, thats what I did, but you still have to figure out that burner hole, it can be very tricky

    V/r HT1

  8. Ray Swicz

    Ray Swicz Lead

    On my second go though on that linked thread. Thank you for that.
    It seems to be what I am imagining for my build.

    I haven't even begun deciding on the lid. I'm not there yet...mentally.
    I am very curious about this cantilever mechanism you mention.

    Your advise on the 1/2in layer over the kastolite will be used. That is exactly the sort of details I know I needed to know.

    Making a twier bore won't be too difficult for me. I just need to determine the height. I intended to put it on a horizontal boring mill and mount a 2inch core drill in the spindle and pop it in

    As for handling the mass of the crucible I figured I would make some sort of lift and maneuver assistance.

    I hope you take this as intended. But I aim to copy as much of your build as I can. Your furnace as I said before is near the outcome of what I have in my minds eye. I've always felt the view is best when standing on the shoulders of giants.

    Thank you.
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    If you are really going to do iron melts, it's just a fact of life that the refractory is consumable. Melterskelter was probably doing on the order of 60+ melts/year. You can read his learning curve but in the end he settled on using phos-bonded plastics (like BlueRam) in segments for hot face and good sealing was important to longevity. If this is the case, you may want to design with the ability to rebuild/replace the refractory.

    But....many new to the hobby build their furnace for largest melt and most challenging scenario......but often never use it for such. If so, you'll pay the price of longer melt times and higher fuel cost than necessary.

    Lids have a tough life.

    Might even go up to 1", and at either thickness, seal/pre-coat the K23 brick with some thinned Kastolite and let it dry before you do the casting or the K23 IFB will suck the water out of your casting layer and wreak havoc with the cast.

    Don't expose any good machine to K23 dust. It's aluminum oxide and abrasive as all heck. K23 is so soft you can cut it with a woodworking hole saw and cordless drill.......mortared joints are a different story.

    I built a gantry with an electric hoist lift for my A60. Check out my signature and videos for its use in my one-man foundry.

    HT1 likes this.
  10. HT1

    HT1 Gold Banner Member

    remember I based mine on the Mifco B301 , do the google search

    IMG_1243.jpeg IMG_1242.jpeg IMG_1327.jpeg IMG_1326.jpeg

    here is pictures of my previous furnace with the much better lid design, and for all clarity this is an enlarged version of the Lionel Oliver II Hobby Melter which was my first furnace, extremely good simple design, but not big enough for me.

    the reason i got a way from the cantilever lid, is I kept running into the handle end and it was right at eye level, definitely should have just hung a red rag on it.
    now why is this better then the side swing , the open lid is very high up from the grounds and out of the way, and because it lifts the lid straight up you can cast an interlock on the lid and the top of the furnace so it will seal perfectly

    also this furnace as you can see has a rear emergency drain, which can also be used to break large pieces of aluminum and drain out the rear, this required a complicated floor design, but if I make another furnace this is definitely the route I will go

    V/r HT1
  11. HT1

    HT1 Gold Banner Member

    ooops made a boo boo

    V/r HT1
  12. Ray Swicz

    Ray Swicz Lead

    I believe I get the jist of how that lid works.
    I ran in to the electrician again today. He says he has another bag of kastolite for me
    Is kastolite sufficient to use as the floor? Or a better question might be, what characteristics does
    Mizzou have the makes it the superior choice for a floor?

    Thank you again for your time and expertise.

  13. Tops

    Tops Silver Banner Member

    Hi Ray,

    Welcome to the forum, it is great place. Sounds like you have a bevy of gifted materials to start with, nice!

    Mizzou is considered a 'dense' castable, Kast-o-lite is considered 'insulating' so less dense as installed.
    If you are using K30 the temp range is about the same, the Mizzou would be preferred for abrasion resistance. I am currently using K30 in one build as a 3/4" (19mm) hot face covering Kaowool and soft brick. My small furnace that is running has Mizzou as a thin hot face, sort of the wrong material for the job but was available in small quantities from a local pottery supply and is holding up great. I have since discovered that area of town also had a firebrick supply and an industrial abrasives (sand) vendor AND they are all near my fiberglass vendor (boats are my main hobby) so I can take an afternoon and get stocked up on supplies for all fronts.

    I started down the road of a 55-gallon shell and realized that it would be way too big for most of my work and then spent an inordinate amount of time cutting a barrel down and re-welding it. My current, half-finished furnace is a Kaowool and K30 lid (completed), Kaowool and K30 sides (not done), and firebrick with a K30 tuyere/plinth as a hot face (bricks are laid and mortared). I am hung up on casting a K30 tuyere assembly and the hot face cylinder for the sides.

    I also messed with two burners, one is done for propane and drip diesel and the other is a pile of parts for a pressurized oil...neither has been fired although I managed to spray water through the pressure nozzle once.

    Your desired outcome sounds a lot like a Melterskelter-esque rig: cast iron temps with a crucible lift. I would look at his threads and videos when linked, you will be inspired.
  14. HT1

    HT1 Gold Banner Member

    abrasion resistance, understand this one simple truth you are going to get molten metal on the floor of your furnace, you need to get it out , this will be easier on a dense castable then on a insulating refractory

    V/r HT1
    Tops likes this.
  15. Ray Swicz

    Ray Swicz Lead

    Ok. So now I am trying to figure out how much Mizzou to order.

    Is there a formula for dry weight to say cubic inches?

    Or anyone care to say how many pounds I would need to cast a disc 2" thick by 22.5" diameter?

  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It's about 140lb/ft3. See attached.


    Attached Files:

    Tops likes this.
  17. Tops

    Tops Silver Banner Member

    Here is some spitballing. Keep in mind I am not a real engineer, I just play one at work :)
    Ray Swicz and HT1 like this.
  18. HT1

    HT1 Gold Banner Member

    buy extra, it will be your go to patch material, after you work with both Kastolite and Mizzou you will understand, Mizzou is easier to fill into cracks and to add thin layers
    Ray Swicz likes this.
  19. Petee716

    Petee716 Gold Banner Member

    Hi Ray, welcome.
    I found myself in a similar-but-opposite situation on my last build. I used a fireclay/sand backing layer for my bore and wanted to use kastolite for the hotface but the guy GIVING me the refractory only had Mizzou so that's what I used. I made the bottom solid mizzou. So what I ended up with is a tough as nails bore with a less-than-optimal insulative ability. I run an oil burner and of course have no trouble with aluminum or bronze (although it take awhile on the first heat). I've melted iron on several occasions but it can be a bit of a challenge. Part of that challenge may involve air/fuel ratio and volume, but that's another subject. But the efficiency of the furnace (insulation) is definitely part of it. If you use kaowool behind your hotface, you should be golden regardless of which exact product you use.
    I have a 4" high plinth made of mizzou which is semi-permenantly stuck to the floor so any debris or incidental metal that falls on the floor that can't be removed when cool just lives down there. If I were melting brass (zinc) or something else that gets smokey I would probably be more meticulous about it.

    Ray Swicz, Tobho Mott and Tops like this.
  20. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    For the oil furnace I built (link in my sig) I used a 1" hot face of dense castable refractory (similar to Mizzou far as I can tell) backed up by 2" of ceramic fiber blanket. Floor is insulating firebrick under a layer of more of the dense castable. The lid is dense castable backed by kaowool too. It works well but like Petee was saying that first melt of the day takes a while as the furnace has to heat up. Nobody warned me not to use the dense castable back in 2015, so I've never seen it as an issue, it's just a furnace that is optimized for doing back to back melts. I also have a smaller and much lower mass furnace that's almost all insulation which I usually use for doing one-and-done melts, that's the propane furnace in my links. It gets lit up a lot more often since I rarely have enough molds made up to need more than one melt to fill.

    Tops likes this.

Share This Page