blazingICE Posted March 7, 2022 Report Share Posted March 7, 2022 Good Day! Im not sure if im in the right place here. if im not please remove/move the post to the correct section, Im planning to to build my own tiny electric lab kiln, but im abit stuck as its very difficult to get firebricks where i am,. so i was looking into casting a chamber with refractory cement, i can get high contant calcium aluminum cement, but as this is a dense cement it hes very poor isolation properties. does anyone know what i could use to get some proper insulation in place, i have a few thoughts about casing in 2 layers, a) dense cement inner lining, and cement mixed with perlite as outer insulation layer, b) dense cement inner lining, and perlite and sodium silicate composite as outer lining the kiln parameters are : a cylinder of 16cm diameter / 20cm height im setting it up to use about 1500watts and would have need to have a max temp of about 1200c I know perlite nor sodium silicate will hold up with temperatures of upto 1200c but maybe it would work as a secondary insulation layer, im not sure about this, so it would be nice to see if ppl here have some experience in this. kind regards! Link to comment Share on other sites More sharing options...
neilestrick Posted March 7, 2022 Report Share Posted March 7, 2022 If you're referring to the refractory cement we use for mortaring bricks together, I don't think you can cast that. I would expect it to crack since it shrinks a bit as it dries. If you're referring to castable refractory cement, that probably wouldn't be great for the kiln, either. It's very dense, and the mass of the cement would absorb a large percentage of the heat output of the elements, even if you back it up with some other insulation. Plus both types of refractory cement have some soluble materials in them that might be a problem for the elements to be in direct contact with. And I'm not sure how you'd mount the elements, unless you cast a groove directly into the form. And I would expect the cement to crack. How do you plan to mount the element(s)? All that said, at 1500 watts in a kiln that small you can may be able to overcome the issue of the mass of the cement. I'm also thinking you could mix in something like sawdust to lighten up the cement and improve its insulating properties, and it would probably reduce cracking, too. Another option is to make your own insulating brick, or some sort of blend of refractory cement and fireclay and sawdust. It would take some testing, but it would be fun for a project that small. Do you have access to another kiln that you could use to burn out the sawdust? Link to comment Share on other sites More sharing options...
blazingICE Posted March 7, 2022 Author Report Share Posted March 7, 2022 Good day, these are all very good points indeed, i hoped it might just work with some extra power. but still it would be nice not to loose all that energy, so making fire bricks would be a option i suppose. not sure on what to use though as usually firebricks are fired , and i do not have a kiln or forge nor the space to do that, so cant burn out the sawdust either. do you know a a good mix for firebricks that does not need to be fired and can take the heat of about 1200c..? for the elements i wanted to cast a spiral directly inside of it so that the elements would be inside grooves.. but i imagined this is going to be quite some work removing it from its mold , if not impossible without breaking. but as i do need the kiln i was willing to try it out. but as you were saying it also sinks allot of heat . so it might just have to go back to the drawing board, kind regards Link to comment Share on other sites More sharing options...
neilestrick Posted March 8, 2022 Report Share Posted March 8, 2022 3 hours ago, blazingICE said: do you know a a good mix for firebricks that does not need to be fired and can take the heat of about 1200c..? I don't have a specific recipe, but fireclay can handle that temp, so you'll just need to make sure your cement can, too. You'll need to figure out a blend that is durable enough without being fired. Link to comment Share on other sites More sharing options...
Russ Posted March 8, 2022 Report Share Posted March 8, 2022 A high alumina cement can handle quite high temps. Mixed with sawdust or other burnable material should give it insulating properties. i used a castable refractory for my kiln door and mixed in Styrofoam beads so theyd burn out and make the door more insulated. Other than the horrible smell of melting Styrofoam (wear a respirator and do this outside) it far exceded my expectations on insulative value. Its 6inches thick and at cone 10 inside its about 150f outside. Link to comment Share on other sites More sharing options...
blazingICE Posted March 8, 2022 Author Report Share Posted March 8, 2022 good day! I See.. would you think a fireclay, alumina cement with expanded clay spheres used in gardening (2-5mm).. would work.. i see that these expanded clay spheres form at around 1200c, so i would think that these could handle the temperature they have allot of air pockets duo to its expansion. so it should work to give it some insulation as well, kind regards Link to comment Share on other sites More sharing options...
Russ Posted March 8, 2022 Report Share Posted March 8, 2022 Expanded clay spheres? Please elaborate on the composition of these. Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted March 8, 2022 Report Share Posted March 8, 2022 I don’t know about using hydroponic medium, or hydroton. From what I can sus out, it looks like some kind of earthenware that’s rolled with a bunch of organic material and fired in a rotary kiln. Top end, about 2000*F. The word “expanded” kept coming up. That says to me the organics are burning out to make it porous, and the clay may be fluxing in the range the OP is talking about working at. If you’re really limited in material availability and you happen to have it to hand, you could try it. But if you have to order it from somewhere, it wouldn’t be on my list of chosen materials. Link to comment Share on other sites More sharing options...
Russ Posted March 8, 2022 Report Share Posted March 8, 2022 Right. Something that burns out completely ie; sawdust, coffee grounds etc would be the preferred material in this case. Not something that would be melting at high temps more toward the inside hot face and probably not on the exterior. anything that is small and granular that melts or burns at low temperature would suffice. Link to comment Share on other sites More sharing options...
blazingICE Posted March 8, 2022 Author Report Share Posted March 8, 2022 @Russ this is from wiki Quote Lightweight expanded clay aggregate (LECA) or expanded clay (exclay) is a lightweight aggregate made by heating clay to around 1,200 °C (2,190 °F) in a rotary kiln. The yielding gases expand the clay by thousands of small bubbles forming during heating producing a honeycomb structure. LECA has an approximately round or potato shape due to circular movement in the kiln and is available in different sizes and densities. LECA is used to make lightweight concrete products and other uses. so i suspect that its some composition of silica, alumina or magnesia, the unfired version pops like popcorn at around 1100-1300c, its used in cement as well apparently, and as i live in a flat, and even when i would BBQ, i will have the police at the door, its not a good idea to burn materials out even though that would be a good solution sadly, so i was kind of searching for something that i could add to it like airy ceramics, to make it lighter and more insulative. i thought these materials would be quite easy to find but sadly i was wrong, edit: apparently the LECA composition is something in the range of this @Callie Beller Diesel Top end for popping it is 1300c so that about 2372f, then sinisters into a ceramic so it should be able to take match more heat then perlite or vermiculite, i can get this locally for 10e for 40L bag so its quite easy to get. I just found a place i could get burned chamotte granules, or i think better known as grog, it melts at 1780c and hes a K value of 1W/m.K at 1000c, i suspect this would be a better material to add ? maybe mixed with alumina cement as a binder it would make a descent firebrick..? or would you think fireclay would be a better binder for it.. kind regards Link to comment Share on other sites More sharing options...
neilestrick Posted March 8, 2022 Report Share Posted March 8, 2022 4 minutes ago, blazingICE said: or i think better known as grog, Grog would reduce shrinkage and cracking of the mix, but it would not increase insulating value. You need something that can burn out in order to reduce mass and increase insulation. Any chance you could put it into a fireplace or outdoor fire for the burnout? It would need to heat very slowly, like gradually moving it into the fire over long period, then getting it to red heat all the way through for complete burnout. Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 8, 2022 Report Share Posted March 8, 2022 1 hour ago, blazingICE said: I just found a place i could get burned chamotte granules, or i think better known as grog, it melts at 1780c and hes a K value of 1W/m.K at 1000c, i suspect this would be a better material to add Its fairly small, you might prefer to make it from a castable Link to comment Share on other sites More sharing options...
blazingICE Posted March 9, 2022 Author Report Share Posted March 9, 2022 On 3/8/2022 at 9:19 PM, neilestrick said: Grog would reduce shrinkage and cracking of the mix, but it would not increase insulating value. You need something that can burn out in order to reduce mass and increase insulation. Any chance you could put it into a fireplace or outdoor fire for the burnout? It would need to heat very slowly, like gradually moving it into the fire over long period, then getting it to red heat all the way through for complete burnout. mm thats sad, i get what you mean though it needs pockets for insulation.. @Bill Kielb the prob is its hard to get in my country so i need to ship it from over seas, so if i need to ship it from far anyways, im going for the ideal stuff. Im doing a inquiry now on some bubble alumina, this is used in high temp castables as well,.. using those with high alumina cement as a binder should be able to make a good enough insulating firebrick that last me up to 1500-1600c. one other option would be to use ceramic wool rigidized with colloidal silica. if i cant get this stuff, i will prob just redesign the thing and go with a lower temperature so some more materials are available to me. its far from ideal but will have to do.. kind regards Link to comment Share on other sites More sharing options...
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