Did a search, but didn't find much so this thread is born to fork off the subject from another thread. I'd not heard of the method of vacuum forming ceramic fiber shapes before they were brought to my attention by Al3O2. The process looks like one that might be adaptable to the DIY methods. Found a couple of YouTube that show the process. Looks a lot like making paper the old fashion way - or things like paper egg cartons.
Not sure how many more participants we'll get in the thread. It was 2 1/2 years ago for me and did see those same videos plus a few others, and read a number of the commercial companies offering such. They weren't very informative about the process or materials. But the core of the process was a porous mold form to which vacuum is applied while the mold form is submerged in a slurry. So my mind went to how to practically replicate the molding apparatus and slurry. The slurry was comprised of chopped ceramic fiber which is readily available and suspended in what was just generally referred to as organic and inorganic binders. I never found mention of what that was but I suspect colloidal silica for the inorganic stuff. This can be bought and is commonly referred to as rigidizer but is expensive for what it is. You can make a close approximation by mixing fumed silica (which is inexpensive and available on eBay) and water. For the organic binders, your guess is as good as mine. These were just to give the unfired molded part better green strength and decomposed after being fired the first time. The same is true of commercial ceramic fiber board, and moldable material. The organics will initially turn the surface black when fired and then completely go away at higher temps leaving a pristine white surface. For the mold, you could just machine it from some suitable porous material, or use very fine beads and sodium silicate or organic glue to approximate something like a sintered structure. You need to be able to pull vacuum from the interior of the mold. How much vacuum was never mentioned but based on the large diameter hose I'd say 3-7"Hg which would probably be had from a multistage vacuum motor like you see folks use for thermal forming plastic sheet. Supposedly, this deposits the fiber on the mandrel/mold form and when lifted out, sucks out a portion of the water from the clinging fiber. The ceramic fiber still retains a huge amount of water and needs to be dried with heat. Not sure how you keep it from slumping or if release agent is required. At this point, I had all but lost interest in it for molding my furnace insulation. It was a hollow 16"D x 18"T cylinder with a with a 10" bore and would have required a lot of slurry to submerge a mold that size and I'd probably only consume 5% of it. I'd already made a cardboard and foam plug for the bore mold but making a porous plug would have taken a lot of effort. So I decided for a one off, just troweling on the pumpable version of the ceramic fiber, and air drying was what made sense. http://forums.thehomefoundry.org/in...w-mass-electric-furnace.607/page-2#post-12702 If I wanted to make a lot of small shapes like the reusable offset pouring basins I use, all of the above might be more feasible, but for just a couple, painting material on a foam plug makes more sense. You might be able to make a very dilute sodium silicate coating for chopped fiber and mold that. You have to use catalyst to cure the SS. May not work with high water content. Fumed silica and water is probably a better but think you'd almost certain need heat to get dry it and get any green strength. The fiber will be heavy and soaking wet. I think maybe for what you're looking to do, something like your SS bound Perlite beads may make more sense. I think you just need to look for a more suitable bead material than perlite, like Alumina spheres. The issue there will be getting low density spheres, otherwise you're just replicating castable refractory. There are porous alumina ball media like activated alumina and zeolite sorbents. Another thought, make a fairly dilute low viscosity ceramic slip coating and mix in with Polystyrene beads. Mold it, dry it, and fire out the foam. Here the issue will be getting it dry enough to achieve green strength before firing. You wont be able to use much heat because of the foam beads, maybe vacuum to evaporate the water would help. Or the slip needs to be a cement that hardens in the presence of water. This is what it's like to be a thought in my head! Good luck! Best, Kelly
That is pretty much what I found as well. Need to look up some patents for more details. The organic binder could be anything from PVA to sodium polyacralate - the later also being useful for gelling water in the toilet bowl when you need to move one. For small scale projects like those most of us might attempt it looks like there could be a lot of waste. If there were a practical way to spray or drip the slurry on the forms - as seen in the one video where the worker patches the hole made with a wire to gauge thickness - then the amount of slurry needed might be minimized. I've used hollow micro-spheres made of glass and phenolic but had never heard of ones made of alumina. More learning to do............ That path looks very interesting, depending on cost. Regarding the use of foam beads: This is one other path I'm considering. Some of the old patents for IFB used little more than sawdust in the mix that gets burned away during firing. The beads I ordered to experiment with may or may not expand when heated. Un-expanded beads in an already dry brick might cause some problems during firing. Expandable beads might be used in the wet slurry with the intent to expand when brought to boiling temperature thus filling the mold with low density refractory. Thoughts in my head would probably find yours to live a calm and structured life.
Ya-know, after I wrote that ramble I searched YouTube for how to make insulating fire bricks or DIY IFB. What a mistake. Total bunch of garbage. There were similar Perlite mixes that claimed use up to 2100F.....not sure how much faith I would put in the claims though. So I just took a quick look at the typical IFB composition. Those are simple relatively easy to be had base materials. You can buy the Al2O3 and SiO2, but most high alumina mortars are very close to this composition (but you could add a little silica flour) and already contain the other elements. You sound like you have a better grasp on the chemical composition than I do but the rest looks like cement and may phase change after firing. So if you made a thinned slip to coat polystyrene bead, experiment with the slip viscosity to get the desired coating thickness, could you just very the bead diameter to control the IFB density (smaller beads produce a denser brick). I don't know if that mix would produce any green strength without heat or some additional binder, but if you could mold it in a cheap foam and cardboard (like concrete casting Sonatube) it could take gentle heat with a light bulb inside say up to 200-250F, and then just fire the whole shebang. You wouldn't even have to demold, just burn it away. -You might have something. If you think about that foam plug I made in the "Muses Thread", just put another tube around the outside, then vibe pack the whole thing, dry and fire it, might work. You could also potentially do it in two diameters with more dense/higher refractory mix on the inner layer, and maybe for good measure paint on a dense mortar onto the plug surface for a hard durable hot face. I'm nominating you to give it a try Best, Kelly
Story of my life - never get nominated for anything I really want to, or have time to. do. My beads should be here the first of the week. Then I can play in the mud some more. I don't have access to a large enough 'cooker' for a one piece kiln shell. I'm limited to shoe box sized pieces for that. I also need to sieve the sand out of the refractory mix I have and try again with some viscosity reducing agent. The last try had very little spread between just enough water and too much. Too much water and it lost it's 'fluff. Too little and my blender doesn't have the Hp to mix it. Takes forever to dry as well with too much water.
I've done a bit of testing with sodium silicate and it expands on heating into a white foam which then becomes hydroscopic, soaks up atmospheric water and turns to liquid sodium silicate again. It seems to be used as part of expanding fire stop material to prevent fires spreading between floors of multi story buildings and is a "single use" product. Perlite on the other hand is a form of volcanic glass and can be made to melt at lower temperatures with a flux like lime and I expect alkaline sodium silicate will have the same fluxing effect too. Youtube has a plethora of videos where people make so called "refractory" but you never see the result of any prolonged high temperature use afterwards. Heated sodium silicate which later reverts to liquid again: Hot fluxed perlite Refractory Aggregate service temps and refractory mixes
Interesting about the silicate foaming. When used as a sand binder for cores in iron casting, if it is not weakened with sugar, it forms a rock-hard sand-silicate aggregate that I found impossible to remove. I tried chipping it out, exposing it to acids and alkalis, long exposure to water, acid and alkalis. Nothing worked. I ended up scrapping the part. I also did not forget to add the sugar subsequently! When weakened with sugar, the core is very soft and crumbly after casting. Denis
I've used perlite as the insulator in my hotface. Never doing it again!! that green glass fluxes everything. I will look around I think I have some photo's of the destruction before I patched it . I have also used sand and sodium silicate to patch the flux eaten hotface. I've also used sand sodium silcate mix to create whole molds. Stuff turns to a kind of rock that doesn't break down without impact or weight (like used it to fill potholes in my driveway!) I will admit that I was closer to 10-20% sodium silicate to sand on some of it (the patch stuff was more like fiber glassing with sand than greensand... mold was 8-10% maybe...really didn't measure... just added it till the dampness matched green sand).
That photo above is from a bit of liquid un-cured material hit a with blowtorch for a few seconds: it dried out and went hard probably from burnt gas CO2 before foaming up like the photo. Days later I noticed the sample was liquid again, this is in a warm humid environment. The same batch of sodium silicate has been used to make moulds and I still have a sand cylindrical core made with it containing sugar that is still holding up fine. What ever the foaming phenomenon is, it's reliable enough to make tubes lined with sodium silicate to block cable conduits during a fire. I'm guessing silicate sand holds up fine when exposed to molten metals but the longer prolonged heat exposure of a furnace refractory will see material failure.
Another thread motivated me to start down the second path to light weight IFB. Ordered some aluminum powder today - from of all places Walmart. Also have some other potential ingredients on the way for testing/experimenting. If I get anywhere near something usable I'll start a thread dedicated to lightweight IFB.
