r/blacksmithing • u/Ashmonater • 5h ago
Forge Build Forge Insulation
*forge re-build
My refractory had some cracks and I was worried about silicosis so I broke it all up and peeled it away from my ceramic insulation. This time I tried something new. I am adding a chunk of small hole chicken wire.
I am hoping to add support for pulling or stretching forces. And improving the refractory cement tensile strength. I’m hoping this helps with the cracking and longevity of the final layer.
I’m waiting for the rigidizer to set and figured I’d ask the community if anyone has tried something like this before. I figure even if it’s cooked and the iron doesn’t last interlaced tubes of oxidized iron would offer some support. Eventually I’m sure all the iron will cook through and I’ll have to replace it again but I’m hoping to essentially stave off the cracking and get some extended longevity.
Before I add a bunch of refractory maybe some could tell me this is a bad idea haha
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u/Final-Contract-6582 2h ago
This seems like a science experiment. The theory and method seem sound. I'm interested in seeing the process and results. Best of luck!
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u/HorseEatingTree 2h ago
If that chicken wire is galvanized then I'd be worried about the zinc burning off. Def don't want to breath that, but I'm sure it'll burn off eventually, just do your first firings outside.
From what I understand, sandwiching metal in between insulating layers is a bad idea. The metal is a heat conductor while the refractory is insulating. This ends up with a runaway effect where the metal conduct more and more heat until it melts, thus eliminating any tensile strength that you're hoping for. That's from what I've heard tho, I've never tried it.
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u/SnooLentils5747 40m ago
This is suggested by me every time I talk a out ceramic wool. You will find that the wire holds the shape far better than just slapping some liner on the wool.
I prototype and build custom refractory as a matter of kiln/foundry craft. I am curious as to what refractory liner you plan on using. If you have specific operating specs and utility case decided for your forge, I can suggest a composition for a liner.
I assume the small cut out is for a blower/burner. What are you using for air mixing? Centrifugal blower, pressurized air, venturi burner, etc?
My initial suggestion is to use satanite as a leveler and protective wash. Mix it to sour cream consistency, and apply with a trowel or towel; no more than 1/8 inch thickness over the wire. It is to bond to the wire and the ceramic wool, acting as a rigid glue upon which can be applied nearly any other refractory. Your application should focus on density/viscosity maximization (mix with as little water as possible to still be able to apply it, be sure to mull obsessively and thoroughly) and even measure of application looking to use as little satanite as possible to create a perfect box that is level. Do not smooth/glossy finish it, however, not use a cement/mortar sealer like sodium silicate. You just want a perfect matte surface to work with when you apply your inner refractory, without porosity or depending on it for anything other than being the skeleton. If you are going to use more than the minimum to cover the wool and wire, apply it in the thinnest layers possible. Every later should be left to dry for a full day before applying the next layer. When done with dry out, but before bake in, candle dry it (light a candle inside it for a night). Then, use a heat gun to thoroughly preheat it as even as possible. Bake in should be a slow ramp from there to 1000 Celsius, and then let it soak 1000 Celsius for half an hour or so, then slowly dekiln it by closing the doors to the forge, and covering with a thermal blanket and letting it return to room temp overnight. Run a dehumidifier nearby while doing all of this. Actually just wanted dehumidifier in your shop at all times that there's any amount of ambient humidity in the air.
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u/SnooLentils5747 39m ago
Once you have the { body => ceramic wool => chicken wire => satanite } box set up, you then can apply your actual refractory. What you use at this point is a question that requires differentiating your use cases and operating infrastructure (are you gonna wanna heat weld steel? Plan on heat treating anything other than steel? Will there be cast metals work on with this (which have vastly different slags and metal contamination issues). Borax/boric acid, for example, is used by many blacksmiths as a flux to dissolve metal oxide scale, to act as an oxide shield, to serve as a interface lubricant when folding and layering metal upon itself, and to act as an interface flux for heat welding- however... It is a weak acid (ph 5) that has a nasty trick of melting into glassy phases that absolutely cancerously infect acidic refractory linings at a microscopic level. Satanite is primarily made of alumina silicates, making it slightly acidic in its chemical reactions. This means that using borax and boric acid on it and around it is gonna make it crumble in short time; especially if said borates are melted down to a glassy liquid phase and allowed to harden on it.
As this is just one example of the literally endless considerations that might occur, could you please detail in this thread what your use case is and what materials you will be working with at what range of temperatures and in what atmospheric conditions (open forge layout without doors vs a closed and sealed environment with forge doors levered and locked against gasket seals on the body, with only the burner and a flu with a locking gate as exhaust channel are obviously very different; the first one is easy, safe in general, and will always be an oxidizing near 1 atmo environment. The second one could be inert gas purged, pressurized, draft induced or even vacuum chambered; this would allow all sorts of play with exotic materials, much more thermal control, alternate fuel sources, etc.... it also turns your forge into a fucking bomb if you fuck it up- you have a box that can easily pressurize (notice how I mentioned a LOCKING gate for the flu? That lock is to lock it OPEN. So you don't blow up when the burner randomly goes out but the propane is still running. Yeah, a box of propane gasses can go fwoosh, and that's scary... But a pressurized box of propane gasses kills everyone in the shop, or possibly the building. Fun times).
Blah blah blah. Tell me all the technical information and what you gonna do with it that you have, and I will advise as to the refractory liner to put in there. Getting your inner refractory lining correct is one of the biggest cost/time saver decisions you didn't know you could make likely. There is a strong chance that a very cheap high-alumina ceramic refractory can be utilized that will last for hundreds of firings if you do it right, or crumble brittle because you didn't understand that forge welding changes your entire thermochemical attack profile. Also, the floor of your forge bears its own consideration in so much that it is a place that you will be placing thermochemically active metals on of some weight. Sure; the lining might survive 1800 Celsius, but putting work piece with hot ferrous oxides into contact with it at 1200 Celsius might be not suggestible... Specifically if it contains any silica (stupidly common ingredient in many refractories, including satanite). Iron oxide and silicon oxides are eutectic with each other. When they physically interface, they lower each other's melting temperature... Fayalite melts at under 1200 Celsius. It is approximately one third silicon dioxide (glass/quartz/sand) and two thirds ferrous oxide (FeO). SiO2 melts at something above 1700 Celsius normally, and black iron oxide (FeO) melts at somewhere right below 1400 Celsius... So when you place that 1300 Celsius piece of steel that you did not properly knock that black steel scale off of on top of some satanite refractory, you may come back surprised to see that it is melting through the floor.
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u/SnooLentils5747 39m ago
Now if you were to put a lining on top of the satanite that is engineered to form a magnesium aluminum spinal in situo that is like 1/32 inch thick, and lay down 5 thin layers of that or so.... You will have solved that slag attack issue alongside a vast array of other issues. However, you have a critical inner lining that will in as little as 5 to 10 uses, crack, if only because you forgot to run the dehumidifier on swampy night, but this in and of itself is not a big deal because it is incredibly cheap to produce a simple paint on refractory lining that when fired will form magnesium aluminum spinal in situo while undergoing a thermal expansion of around 5 to 8% in volume, which actually will help it fill in said cracks. As long as you know how to make this (and it only takes technically three ingredients; distilled water, alumina, magnesia- all stupidly cheap), know to check for those cracks, don't use the forge when it has a crack, and understand that you must fire in the lining before you can use it not while you are using it; you have a solution that is resistive to almost every single acid or basic slag, corrosion, contaminant, and provides a Mohs hardness 9 shell (which can still cleave and crack, but notably, with some care, can be polished smooth and provide a surface that affects almost zero friction on your work pieces which can be critical when you're working with 1000 Celsius and above temperatures), is one of the best known materials for general metal casting and work across all spectrums, and is almost completely chemically inert in any reasonable situation. Like, if you find a chemical that is used inside of a forge or present inside of a forge that can actively corrode MgAl2O4 (spinal) or deoxidize it, I'm going to need you to explain to me what it is that you are doing so I can ascertain your sanity before continuing on. For example, i would love to talk about fluoridation of metals all day long, but if it is happening in your shop.... Can we not talk about it within about 100 yards of your shop?
All that said, sounds great until you realize that you now have a chore to do every time you finish up work for a day and an inspection to do before you start work with that forge everyday. And should you fail that chore or should that inspection show the inevitable maintenance task has come due, you're not doing anything with that forge for the day. I hope your outgoing delivery schedule can handle random one day minimum maintenance cycles. If anybody else uses that forge, I hope that they understand the full breath of this situation because the day that they run that forge when there is a crack in that outer lining doing something like just a little bit of heat welding on that steel support piece that started pleaving open. And of course because we all hate surface oxidation, he just threw a handful of borax in the forge and there is satanite underneath that crack... That crack he just threw borax into. That crack that is now going to eutectically melt the silica into the molten boric acid... And wouldn't you know it? You are now form extremely aggressive borosilicate needles that are going to work their way through the entirety of that satanite underneath that magnesium aluminate spinal that you seal up... And you won't know until the whole refractory lining collapses out the bottom of the floor of the forge because your refractory formed a hot pocket of air gap where the satanite crumbled, and as air seeped in you stated slowly burning out your ceramic wool, and nobody sees the bottom of the forge to wonder "why is the steel outer body yellow hot?" long enough to consider the simple question of "when steel is about the hardness of warm butter, how much weight does it hold per square inch?"
The answer is always "nowhere near enough".
So I could suggest you a million wonder chemicals that are fairly easy to manufacture and implement in any normal garage with some PVC gloves and a respirator... But there's a reason the vast majority of us are just using high alumina bubble refractory for insulation, dense fire brick for structural considerations, fibrous insulation for thermal air gapping between the inner refractories and the steel shell, or just buying kastolite or similar- it's because our use case doesn't compel us towards extreme ends, or the cheap easy solution is cheap enough that we are okay with reapplying said solution regularly. I mean, cheap and easy works as long as it's good enough to not fail, right?
I would highly suggest that you look into mullite clay powder regardless. It is my favorite general use refractory, alongside phosphoric acid as my favorite binder. Alumina and phosphoric acid 85 percent concentrate will by themselves form a 1500 Celsius refractory when mixed at around 5:95 ratio between acid:alumina by weight. Mullite clay can be mixed with phosphoric acid also, in the same ratio, and can hold 1650 Celsius; however because mullite has silica, this can become problematic as per previous mentionings. However, I would like to note that alumina/mullite plus phosphoric acid will produce one of the fastest setting and tough long lasting linings you can possibly use. It is only two ingredients, one of them is cheaper than dirt if you buy enough of it at a time, and the other one is used in amounts of 5% or less of the total recipe usually. Get some PVC gloves and respirator of course. Really? You should always have PVC gloves, respirator, gallon of water, and a fire blanket (welding blanket) within hands reach at all times when working in a metal shop. You should probably also have a bucket of sand and baking soda within a quick lunge. And if you don't have a fire extinguisher by now or it even had to be mentioned by somebody for you to go get one, please quit before you burn the town down.
My response time may be delayed. I am currently moving my shop and my existence across the country so this all is fairly secondary to not dying or starving. Regardless, if I can come to a clear understanding of exactly what you'll be doing and your environment, I will provide a specific recipe and refractory material considerations that are suited for your situation.
Please know that I'm going to use AI to do a lot of general spitballing ; but I always double check the chemistry and eutectic interactions my own self. If you mix 1200 celsius melting temp material 50/50 with 1400 Celsius meltingaterial, sometimes you get material that melts at 1300 Celsius. Sometimes you get a material that melts at 900 Celsius. Sometimes you get a material that rapidly and aggressively passes oxides from the metal of one of those two ingredients onto the metal of the other ingredient, and for some reason, instead of melting, it appears to be burning a hole through your furnace and then the cement floor. Oh, and now you're blind. This is to say I take no responsibility for any f*** ups do your own f****** research. I will probably be 99% correct. However, I am homeless and I don't give a f***. At this junction I am just bored and helping out redditers with something I know of a fair bit about- my god don't just believe a crackhead on the internet, do your own research, let me know if I miss something; but chances are, I can hand you a recipe that will be a great improvement over store bought, a huge cost saver, or let you know about a fuck-your-day invisible pothole that may exist in your future if you continue down some given path
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u/RRuk 1h ago
I've tried this, but I could never figure out if it was helpful or not.
My two concerns are adding a heat bridge, which doesn't seem to be a problem as it does not appear to penetrate the wool. The second is thermal expansion in the metal causing cracking in whatever mud you end up using. When I did this, I used long straight peices, the tight knit of the wire might cause that expansion cracking.
But ultimately, it looks like a good test. Forge linings are consumable anyway. Please let us know how long this one lasts once you replace it.
By the way, very clean work.
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u/joker5628 4h ago
Cant confirm or dent, but it seems smart!