Received a Visit From The Kiln Fairy.

Discussion in 'Furnaces and their construction' started by Nick Lazenby, May 27, 2023.

  1. Nick Lazenby

    Nick Lazenby Copper

    I’m in the midsts of converting a kiln into my new furnace and wanted to share some progress.

    I was actually gifted these two bad boys from a local artist I met at a dog park who happened to overhear my buddy and I talking about metal casting and what not. He’s a ceramicist so naturally I asked him where he sourced materials and if he knew anyone selling firebricks or refractory materials for the new build. He said he had some bricks back at his studio and that I’d be more than welcome to have them. Apparently he was pretty jazzed that I did this in my backyard and wanted to support where he could. Well anyways I show up to his place with my metal cart and he looks at me kinda confused and says “ that’s not gonna work we’ll need the forklift” now I’m confused and that quickly turns into bewilderment when these bad boys get loaded into my truck.

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    I immediately called my buddy who works at a local foundry supply company and told him about my score and he said they had a big unused crucible get returned (I guess they ordered the wrong one) and they couldn’t resell it because most places balked at anything “used” and it would likely get sent back to the manufacturer. He said I could have it for 25% off and fellas let me tell you this thing is a monster. Total price was 400$.

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    I’m about halfway through fabbing up the wheeled frame the furnace will sit on and when I’m done I’ll post some pics. I’ll also be adding an additional 2in 3000f refractory + 3in layer of blanket to the kiln, bringing my sidewall distance closer to 8in. I figured I’d want extra room for the hoist tongs and I’ll be running oil on my new burner.

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    (I know I’ll want a better valve for the oil but I just used what I had on hand and figure I’ll upgrade eventually.)

    Any advice or suggestions on the edge distances? Or whatever
     

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    Last edited: May 27, 2023
    BattyZ likes this.
  2. Jason

    Jason Gold

    And you plan on melting metal in those pottery kilns????
     
  3. Nick Lazenby

    Nick Lazenby Copper

    For some reason my post omitted a paragraph but I edited it back in.

    “I’m about halfway through fabbing up the wheeled frame the furnace will sit on and when I’m done I’ll post some pics. I’ll also be adding an additional 2in 3000f refractory + 3in layer of blanket to the kiln, bringing my sidewall distance closer to 8in. I figured I’d want extra room for the hoist tongs and I’ll be running oil on my new burner.”
     
  4. Jason

    Jason Gold

    Do those kilns work?
     
  5. Nick Lazenby

    Nick Lazenby Copper

    nah they had all the controllers stripped off
     
  6. Jason

    Jason Gold

    meh... Controllers don't mean shit to me. I thought you were going lost wax ceramic shell? If that is the case, don't turn them into furnaces for melting metal in them. They would be better suited to preheating ceramic shells up to 1700. If you look around here, you won't find people turning old pottery kilns into furnaces. They are too big and can be put to better uses.
     
  7. Nick Lazenby

    Nick Lazenby Copper

    I’ll probably add the missing components to the smaller one but it’s going to save me a ton of time and $ turning the other into a furnace. It’s not like a paid anything for them ha. Idk man I needed a furnace body and these are going to make for some good bones plus I pretty much exclusively run lost foam but maybe I’ll branch out to CS if I can land a deal on the slurry.
     
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Free kilns can be a good source of IFB, but depending on size (those look pretty big), can vary on how easily they adapt to foundry furnaces. What metals will be melted?

    So are you just going to disassemble the IFB from the kiln to create that 8" thick cascading refractory layer using the outer kiln metal skin for the furnace? Hard to tell for sure from the pictures on therir size, but what will be the ID of the furnace and gap between the inner wall and most often used crucible?

    In any case, IMO, 2" of refractory hard face is a bit excessive. It will be such high mass even with a monster burner it will take a long time and a lot of fuel to heat the furnace. 1" would be plenty especialy if backed by several inches of IFB. If you're typical session is a single pour, you'll regret it. If a typicall session is many melts, maybe not.

    Kiln lids always need a lot of work to convert to a high temp furnace. Usually they are just flat IFBs mortared together bound in a lid ring. If you try to cast additional refractory onto the bottom, it'll weigh a ton and usually they end up falling into the furnace. What's your plan there?

    Best,
    Kelly
     
  9. BattyZ

    BattyZ Silver Banner Member

    Eek...don't mean to be a thorn in your side but I have 2 old kilns that have served me very well as melt furnaces. Not the most popular on the forum for sure, but my converted, lift-off has been the ticket for me! Of course I would love to do a custom low-mass too.

    I guess I should also say I have converted them to run off a single temp controller and they also both heat treat as well for me.
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    This is a big plus if you are casting 35x series aluminum for mechanical parts, especially if they will be machined. Big difference machining a gummy t0 versus a t5 temper. Good for tool steels too. Just need a little stainless foil pouch or a little inert gas purge. With Nick being an art caster, he may not care, unless he wants to polish aluminum to a high luster.

    Best,
    Kelly
     
  11. Petee716

    Petee716 Gold Banner Member

    I scrolled down the OP and my eyes got wide when I saw your burner test. I think I uttered the f word. That thing is a beast.
    I'd give Kelly's suggestions some thought. Big-ass looks like a good idea at first but if it's hard to heat, hard to maintain, and hard to operate, the luster can wear off pretty quickly. I know you made a significant investment in that crucible but it'll keep. I'd consider scavenging IFBs from one of the kilns and putting them in a 55 gal drum with an inch of 3000F refractory. You can still end up with a 16" bore. The bricks are easy to cut (the mortar/adhesive will smooth the teeth off a bandsaw blade pretty soon though.)
    Just my 2 cents.

    Pete
     
  12. Jason

    Jason Gold

    This is not one of those times where you say good big or go home. It's one of those walk before you run times.
    All depends what the end goal is. If you have big pours, you need a lot of melted metal.
    Just BE CAREFUL! Even on a small scale, this stuff can be life changing.
     
  13. Nick Lazenby

    Nick Lazenby Copper

    Good feedback and I'll happily omit the additional hard-faced and just use the fiber blanket. The firebrick is about 3" thick

    I removed one of the rings on the 1st kiln bringing the inner height to 18"
    The Inner diameter is 23.5"
    C=73.78"

    I'm planning on using an A20 Salamander and that currently sites around 8" from the sidewalls . I'll start with 3" CFB added leaving 5" gap and go from there.

    I've welded a frame the furnace body sits on that should provide adequate support for the floor. The frame will also serve to anchor the burner and lid. I'm almost done just need to add some cross support to the frame and eventually an armature for the burner/lid. 95% of melts are Copper/brass/Bronze

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    Last edited: Jun 1, 2023
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I didn't mean no hot face......just that you didn't need 2" of it. You didn't say what duty/metals you'll be melting, but regardles, I wouldn't use bare IFB in a fuel fired furnace. Most kiln IFB is K23 or K26. It's good insulator, but not very high refractory and will likely be exceeded by flame temps. IFB also is not not very durable, is easily damaged by tool contact, is aggressively attacked by molten metals, and also corrosive combustion gases. On the latter, there was a member here that had an IFB only furnace that reported no deterioration (Oldironfarmer), but most would agree with my comment and for sure higher temp melting. If it's just aluminum duty, a thin coat of mortar like Satanite would do.

    Just to confirm, you are adding that blanket to the outside of the IFB.....correct? It's still a large furnace. Are you planning to accomodate larger than A20? And what's the plan for the lid?

    Best,
    Kelly
     
  15. Nick Lazenby

    Nick Lazenby Copper

    Defenanlty
    I snuck this in at the end but definitely worth repeating
    95% of melts are Copper/brass/Bronze

    I was planning on doing most of the "reinforcement" on the inside (see below)

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    hard to tell from the picture and wish I had grabbed one but the top of the crucible is about 10" from the lid

    For the lid I was leaning towards pivoting it on a pipe with a side to side open vs the overhead hinge that's going on now. The pipe/rod is welded to the main body and I'll have that anchored or at least heavy enough to prevent overturning.

    I have a much larger crucible (mentioned above) but don't really need that to fit at the moment. I have a special use case I'll retrofit this when the time comes
     
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The usual order of things is using the hardest most durable refractory on the inside of the furnace (which are typically lesser insulators) and then more fragile but higher insulating refractory toward the outside. So the material cascade from inside to outside would be a high temp castable or plastic hotface, IFB, then CFB. Will it work the other way around? -Sure. Will it work for long? Doubtful. The CFB will be rapidly reduced by the oil burner by both the flame temp and the corrosive combustion gases.

    Granted, the kilns were given to you, and after the wool becomes reduced after a melt or two, the kiln wall IFB can probably still be salvaged. You may not be as lucky with the IFB in the lid and the base. It's a fast way to make furnace but really just a matter of how much time and money you want to spend maintaining your furnace verus using it to melt metal. I'm more of a cry once kind of guy. If it were me, I'd salvage the IFB and make a purpose built furnace around your crucible.

    Dont know how big your large crucible is but at a little under 11"OD, my A60 lives well inside my larger 15" bore furnace based upon a 55gal drum. Your A20 still seems to get lost inside the CFB diameter, and I'd suggest you make a 4"-6" tall plinth for it to get it above your Tuyere an initial entry of burner flame.

    Best,
    Kelly
     
  17. Nick Lazenby

    Nick Lazenby Copper

    I've done a similar method with two other furnaces over the years but seeing as I'll have a surplus IFB it would likely behoove me to build from the ground up and take your advice.

    This is an outline of the last layer to the blanket:

    I'll apply some rigidizer to each layer of ceramic fiber with the final layer receiving a generous coating of relatively:

    75% KAST TECH™ F80
    10% Grog
    10% molochite
    5% rigidizer

    I add water per the KAST TECH 8-10% , staying on the lighter side so as to yield more of a paste. That gets uniformly spread around and worked into the final layer.

    I ended up getting 50+ sessions on my older furnace using a similar mixture (however much more crude and lacking a proprietary castable like KAST TECH. ) before replacing that outer layer.

    I hear you with the edge distances but I was hoping to squeak my larger crucible in.
     
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I guess I just cant read your posts properly. You seem to have a plan and some experierence with the materials and method but I'll be darned if I could have figured that out before your last post. There are lot's of examples of mortar/brush coated hot face on fiber furnaces here.

    -Good luck with your build.

    Best,
    Kelly
     
  19. Nick Lazenby

    Nick Lazenby Copper

    No
    ha I appreciate the patience - I was multitasking with some work nonsense and got a little lazy with the outline - I appreciate the advice and plan on trying the re-build approach (disassemble kiln for IFB and flip the refractory syntax ) once the blanket fails on me.
     

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