oldnewprobs Posted December 10, 2022 Share Posted December 10, 2022 So I'm planning out my first fuel powered melting furnace in years. Built a simple one 15 years ago with a friend, ceramic wool I'm a steel bucket, shop vac and coal etc. I built an electric kiln a while ago that I melt aluminum in from time to time and it got me hooked again. I have several metal forms to make a furnace from, and I'm thinking I'll build as big as I can do I don't need to do it twice when my ambition grows. It will be waste oil fired as my town stopped collecting it and I've got gallons of the stuff. My question is, if I do a 55galb body, 4" ceramic wool insulation, and then instead of refractory casting (always hard to do well) why can't I just use a steel liner inside? Sure it will corrode over time, but maybe a skim coat of refractory material could slow that down, and then a "cap " of refractory to seal the top of the insulation and the two metal walls. A typical cast reinforced lid and I think I have a simple furnace built in a few days. The only reason I didn't start building already is that I've never seen one like this before. I like innovating, but so many people have built furnaces before me I feel like I might just be missing something here. Any input? Should I just go for it? Quote Link to comment Share on other sites More sharing options...
Frosty Posted December 10, 2022 Share Posted December 10, 2022 Welcome aboard, glad to have you. If you put your general location in the header you'll have a much better chance of meeting up with members living within visiting distance. Don't think small do you? A melter doesn't suffer the kind of abuse a forge typically does so you wouldn't need one of the tougher flame face refractories. Plistex 900 can be brushed on. A steel flame face has a couple issues that come to mind. To prevent it from oxidizing away in a short time you'll need to nail a neutral flame or run it reducing with the CO issues. Then there's steel's extreme thermal expansion from room temp to 1,700f+/- if melting copper alloys. It could warp badly enough to actually trap the crucible. You don't want much clearance between crucible and furnace walls for efficiency's sake. Do you? Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 10, 2022 Author Share Posted December 10, 2022 I didn't consider the expansion issue. Since my fuel is free I'm not super concerned about efficiency, plus my walls will be better insulated than most furnaces I see online so that should help out. My electric kiln is good to 1000-1200C, and gets there pretty quick and with perfect control, but it's a little expensive to run and always a little up small. Inner dimensions are 14x10 8 high, and it's just always a bit too small lol. So I figured I'd be better served just going as big as is practical. I may just do fiber insulation with cut inner bricks, rather than pouring a refractory. It seems like it would be the same price or cheaper, but much easier to do well. Quote Link to comment Share on other sites More sharing options...
JHCC Posted December 10, 2022 Share Posted December 10, 2022 4 hours ago, oldnewprobs said: The only reason I didn't start building already is that I've never seen one like this before. If there's an obvious option that people aren't using, sometimes it's because it has issues that aren't quite as obvious. In this case, Frosty has summed up the main problems with such a setup. 46 minutes ago, oldnewprobs said: I may just do fiber insulation with cut inner bricks That sounds like a much better idea. Quote Link to comment Share on other sites More sharing options...
Frosty Posted December 10, 2022 Share Posted December 10, 2022 If you use Plistex 900 or the ITC combination being currently discussed in the, "Rebuilding Forge" thread, you'll be golden. None of those products is castable, they are all spread (Like plaster) or brush applications so it shouldn't be a chore. Is there a reason your melter is so deep? Even if you have 4" top and bottom it's more than 24" deep. The casters I know try to keep everything as close to the crucible as reasonably possible. You're introducing the burner flame at the plinth in a strong swirl. Yes? Don't you want the lid and exhaust hole as close to the top of the crucible as possible? It prolongs flame hang time on the crucible and doesn't allow so much room for debris to end up in the melt. Lastly letting you monitor the melt through the exhaust hole and not lift the lid to check. It's like baking, opening the oven door frequently to check tends to ruin cakes and make the TV dinners dry for being in the oven so long. Were it my project I'd cut the drum's height down. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 10, 2022 Author Share Posted December 10, 2022 Oh sorry those dimensions are of my electric kiln, it's a commercial frame that I built heaters for so I was working with the dimensions I had. For my new melting furnace (what's the right word for that btw?) I plan on picking the height based on the dimensions of the fiber I use to build it. Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted December 10, 2022 Share Posted December 10, 2022 Melting furnace works for me. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 12, 2022 Author Share Posted December 12, 2022 So maybe I should start a build thread for this thing... The design goals are waste oil burning, not too loud, useable with no crucible, ie drain hole in the bottom so I can melt down large awkward scra without cutting it up too much and just put a mold under the thing. Also it will be well insulated because it bugs me when things like this aren't. Final requirements it lives outside in the elements year round, so water ingress control will take front row seat in design. Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted December 12, 2022 Share Posted December 12, 2022 I would use this thread for the build, no reason to start another. BTW: Welcome from the Ozark mountains. If you put your general location in your profile, you may be surprised how many members are close to you. Also a lot of questions are location dependent for an accurate answer. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted December 12, 2022 Share Posted December 12, 2022 Foundry? Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted December 12, 2022 Share Posted December 12, 2022 Good to see you logged on Thomas and responding. Yep foundry, but do you think I could pull that term out of my memory? Heck half the time I can't remember what I had for breakfast. Quote Link to comment Share on other sites More sharing options...
Frosty Posted December 12, 2022 Share Posted December 12, 2022 Boy Randy, now I have your name and "lost and Foundry" as a brain worm! Oldnews, what you're building is called a "Cupola melter" and should be lined with a Kastolite covered hard fire brick flame face, backed by IFB for insulation. It WILL take a lot of banging around as you drop scrap in. If the firebrick is backed with something soft like refractory blanket, even rigidized, the brick WILL get knocked out of place and molten scrap will leak into the liner. One of the guys here melts iron in a cupola but uses pet coke and breaks everything up into pretty small pieces. Has his students do it if they want to learn to cast iron. Cast iron has a lower melting temp than steel and I've watched Pat trying to beat a fist sized piece of cast iron out of the tap hole that didn't get broken small enough. Lots of swearing going on, I could hear it from where I was demoing about 100' away over my propane burner forge. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted December 12, 2022 Share Posted December 12, 2022 You want to argue with me about Brain Issues right now? Just had Gamma ray knife treatment on my Brain Tumor! Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 13, 2022 Author Share Posted December 13, 2022 Haha my plan is to do 90% of my melts in a crucible, melting directly in the furnace is a last ditch I'm feeling lazy approach. So I'm not going to design around that too much but I like having the option. And honestly if I ever get a bandsaw hopefully all my melts will be in crucibles. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 23, 2022 Author Share Posted December 23, 2022 Well I couldn't figure out how to change the title of my thread so I'm starting a fresh one now. The plan is to build a quite large melting forge (possibly melting cupola) for doing all kinds of metal casting. I've done tons of metal work before and I'm very handy, but I only ever melted metal in my electric furnace (separate thread later!) And a few times in highschool in a very unsafe charcoal metal drum furnace with uncoated ceramic insulation. So I found two large metal pressure vessels I was going to use as forms, which set in my mind I want a large furnace. I also don't want to do the whole "hmm I should build a larger one now" I have some left over 55 gallon drums from my grill and tandoor builds, so I'm going to use my failed charcoal oven to make this burner. The plan is above average insulation compared to most builds I've seen, as I think that will make everything easier in use, as well as managing water ingress so I can leave it outdoors while not in use. A 55 gallon drums has about a 22" diameter, so I settled on 2 wraps of 2 inch insulation. I was in on the fence between castable lining vs fire brick. I think cutting fire brick is something I'm better at than working with cement (my driveway will back me up on that) so I've decided to line it. I hope that that also means it will be easier to fix if damage happens down the road . At the last second I went to 1" insulation, so I can either do 3 or 4" of insulation, since fire bricks are hard to predict what I can find locally. Attached are my sketch ideas, I'll put up some annotated ones later when I figure out how to do that more easily. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 23, 2022 Author Share Posted December 23, 2022 so thats a sketch i made at work because I work way faster in real cad, but now I'm home and need to re-do it in much worse free software. It's very not clear there what the floor looks like, but its a few insulating bricks on edge, cut into small pieces, with ceramic wool filling up the rest of the space, with a 1-2 inch latyer of castable refractory on top of it. it is sloped towards the center with a drain mostly for "in case my crucible shatters when i drop it like a dummy" and possibly so i can use it as a cupola in case i want to make ingots out of akward scrap without needing it to break it down before hand, as all my crucibles are actually quite small currently. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 23, 2022 Author Share Posted December 23, 2022 also ignore the dimensions in that photo, they are close but wrong, I was trying to figure out the geometry of an 8 sided shape where 1 side was a different size than all the rest, I figured it out later but forgot to re-print apparently. anyways the materials will be 8# ceramic HTZ 3200 firebrick for the liner versaflow 70 plus castable refractory I think it will be about $500 for the materials. I think all the steel i have lying around in form of misc junk in the basement and yard. the refractory is to seal the fiber at the top, as well as make the lid and floor. in the lid it will be backed with even more ceramic wool insulation. big question for the viewers, should i stick with my 4" of insulation, 1.5 inch of firebrick, or should i go bigger and just use 3" of insulation? it seems most folks only use 1-3" of insualtion/castable, but the castable is not much of an insulator, so i think i'll surpass that easily. either way the gap between the walls and the crucible will be larger than is a great idea, but the fuel will be waste oil so i'm not too worried about cost, but it needs to work. I hope the extra insulation makes up for the bad optimization. Quote Link to comment Share on other sites More sharing options...
Latticino Posted December 23, 2022 Share Posted December 23, 2022 That's a very large melter, and going to need a powerful burner. I made a Glory hole for glassblowing out of a 55 gallon drum with pleated refractory blanket insulation around 3" thick. Used a multiport burner head rated at around 250 MBH and at full bore it never got to steel melting temperatures. Won't go into all the safety issues about casting steel, since presumably you already know about those, but please get the right PPE and be extremely careful. Not sure exactly what you plan on accomplishing here. Just recycling steel? Making sculpture? Attempting to batch out some kind of interesting blister steel or wootz? I think it gets kind of tricky maintaining the right carbon content to be successful. Might be tough to maintain the correct atmosphere with an oil burner. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 23, 2022 Author Share Posted December 23, 2022 did I say steel? I meant cast iron. I plan on melting aluminum and copper right now (I have a collection of ingots I've made on my electric furnace) but at some point in the future I want to have the option of cast iron without building a new furnace. I also know cast iron is very hard on crucibles, and I'm not looking forward to replacing them regularly, so right now I'm only worried about the easier metals, mostly aluminum becasue of all my scrap VW parts that need a new life. honestly I have no need for any of this, it's just something I've always wanted to do haha. I'm bad at impulse control. but your input says my gut feel that more insulation is gonna be more better will be used as guidance. a 12" internal diameter is nice, but would need some thin insulation, so I think 10.25" is more reasonable target. that lets me have 3" of firebrick, and 8.75" of insulation Quote Link to comment Share on other sites More sharing options...
Latticino Posted December 23, 2022 Share Posted December 23, 2022 Based on the proposed size of your operation I don't see a lot of practical reasons behind casting iron other than for small sculptures. Even if your goal is short runs of replacement cast parts for manufacture, the energy burden and clean up requirements may make it more reasonable to just fabricate out of steel. From all accounts it is an order of magnitude more difficult to cast iron safely and effectively than making simple ingots of aluminum or copper. I strongly urge you to take a casting class with an experienced iron caster to get a handle on this prior to trying it on your own. We are talking maiming or life threatening levels of safety concerns. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 23, 2022 Author Share Posted December 23, 2022 overkill it until it's dead, right? regardless, I suspect I will only be casting aluminum and copper alloys for the first year or two, I just want to know the thing will be ready for iron when i am. I don't want to re-line it or anything dumb like that. Quote Link to comment Share on other sites More sharing options...
oldnewprobs Posted December 25, 2022 Author Share Posted December 25, 2022 Thank you whoever fixed my thread! I also got a new app on my phone for looking at and edit dxf, so I'm trying to figure it out, but here's a dimensional sketch Quote Link to comment Share on other sites More sharing options...
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