Has anyone tried casting riser bricks using refractory?
Standard off-the-shelf rectangular bricks seem to make OK, but not great, risers. The preference seems to be to sculpt a whole riser in place, which makes a very good end product, but is much more difficult to make. I was thinking that by using a standardized mold to make bricks, one could create a very good riser that isn't very difficult to build.
Below are three variations on this. The measurements are all for an 8" system and have about a 50 in^2 CSA but could easily be scaled down for a 6" system. I imagine that one could take fiberglass fabric and wrap the outsides of the risers and then coat with final layer of refractory mud to create a unified riser that has both compressive and tensile strength.
Tom Ohern : A very interesting 'Thought Problem', a good place to start researching this topic would be in Erica Wisner's Thread Extension/response of Dec 20th to my
Dec 14th 2013 attempt (Fake Fire Brick) to describe the 3 most common types of Fire/Kiln Brick and assign a preferred value to them! Some errors and mistakes
occurred in my original Post which Erica Cleared up rather well ! I Will re-write the whole post eventually but right now it helps humble me a little !
If you all-ready had access to a medium sized kiln, preferably a gas kiln that could be adapted to run on Gasification products eventually, then it would be possible that
the rest of the needed materials would be 'close to hand' ! The Heavier/Denser Fire brick contains a High percentage of "Burnt Clay Grog" which increases its density,
and resistance to 'Heat Stress'. If you had an unlimited source for high Temp Unglazed Porcelain Grade broken or Miss fired Pieces you could make a superior Fire/Kiln
Brick, (any of your mis fires could be endlessly recycled! ) It would be iterating to talk to a 'Real potter/ceramist about glazed pottery as grog, and it probably would be
interesting to experiment with Sintering Re-cycled Glass Cullet !
You may have been thinking about making a lite-weight fire/kiln brick for the Heat Riser and I find her Answers about Dense fire/kiln brick over Lite brick to be very
compelling, I Think that if I was making a Rocket Mass Heater for a Third person I Would feel compelled to use the Denser Fire/Kiln Brick ! -This is in spite of
success (so far ) with poured Perlite and Clay-slip Heat Risers !
While I have anecdotal evidence of Potters/Ceramists helping on Rocket Mass Heater Builds, I have yet to see a report from ANY potter/ceramist that they have made
a rocket mass heater RMH, This is where I would have looked to see the 1st success with this type of project, but if you have access to the materials Free or cheap,
and are going to play with this please keep us informed !
You may also be interested in the Design/build plans of Fellow Member Alistair Warburton '' New to this … New Heater? " in the Rocket stoves Forums, I bumped
it up to make it easier to find ! For the good of the Craft ! Big AL
Success has a Thousand Fathers , Failure is an Orphan
My idea was inspired by posts like yours and others who were attempting to use off the shelf materials to do what we really need a customized product for. Much of what Erica was saying applied to the burn chambers but the main point she made about about the risers was "It's particularly critical that the heat riser have reliable insulation and no leaks before the top."
"The materials that have been shown by experience to give adequate insulation around the heat riser include ... Cast-refractory heat risers using perlite aggregate, or other methods to create insulation value, various thickness (1" to 2" have been successful in short-term prototypes but long-term data not available)."
My idea is to create a custom solution for that last suggestion. The problems that people have with firebrick risers, as Erica pointed out, is that they are "leaky" and not insulative. Cast-refractory/perlite can solve this, especially if the bricks are designed to fit together in the right shape for a heat riser.
I do not think a kiln would be necessary since most heat risers are build wet, and dried in place. This brick version wouldn't be much different except that much of the drying can be done before the assembly, in a slower fashion, which should reduce cracking and damage.
Simpler, yes. Good and quick. Which reminds me of that old sign that says "Good, fast, cheap, choose any two" I downloaded their catalog but couldn't find any prices, which tells me something. Yes, you only need a couple of feet for the riser so it can't be all that much. But, this takes us to the problems discussed in the shippable core thread. In the burn tube, the elbow, and the riser we need specific shapes that have to hold up under extreme conditions and still be insulative. To get good quality, with "off the shelf" speed, it's going to be expensive. Isn't this whole forum is about the slower, cheaper, do it yourself approach.
One big question I have is "just how good does it have to be?". I'm a blacksmith and I've made several forges of the "dragons breath" variety. You just line a container with rock wool and poke a propane torch into it. But, under those conditions rock wool breaks down and emits asbestos sized particles. Not something you want to breath. I've tried lining the forge with ITC-100, and that works fine... till you start working at the forge. The ITC is brittle and if you give it the slightest bump with your iron it flakes off. In the real world you're constantly moving your irons around in the fire and you're going to bump the sides of the forge.
The inside of your core and riser doesn't get bumped, why not (again, other than price) coat it with ITC? ITC used to have an ad where they showed spraying the inside of a cardboard box with ITC-100 then firing pottery in it to 2000 degrees. ITC makes a formula just for coating metal. Why not just form up your J-tube core and riser out of stove pipe and spray the inside with ITC? I think I've seem a thread about that but I haven't read it yet, because I'm remembering ITC prices being in the first born child range.
I suggested to Pyro Man Dan that he search "paper kiln" on U-tube. I think I'd use fiberglass cloth instead of paper but the technique looks like a way to make a more durable inside liner for your riser. Wrap a PVC pipe in newspaper (as a mold release), lay on your slip coated fabric, put a larger metal tube over it and pack the space between with clay-slip/perlite mix for insulation(or use Dan's technique to use straight perlite), then slide the PVC pipe out and let it dry. Seems like it should work. If someone gets around to trying it before I do let me know.
BTW, a friend who is more knowledgeable than I says that firebrick grog has to be made from high fire clay... but it doesn't have to be high fired. Having it fired reduces shrinkage in the bricks you make from it, but there's a point of diminishing returns on shrinkage that occurs in the low fire range. He says to mix your clay slip with sawdust and form bricks, then fire them till the sawdust burns out. He says the firebox in my Kentucky wood gobbler should get plenty hot enough. Once the sawdust is burnt out the bricks are easy to crush down into grog. I haven't tried it yet, but it's on my list.
Click on the blue links next to the crosses if the pics don't show.
Yes clay flue liners crack, only once usualy. But even then, they stay together. And they can whistand the heat better than steel. I'm dubious that the clay perlite mix with a metal tube which burns off, will last longer than clay flue elements surounded by an insulator.
Well, i'm trying to advocate this method. I couldn't find any tubes for the us posters before. There's a few who have tried this in europe. For me, it's cheap, i cross the border into italy, go to the suplier just on the other side, and buy three or four pieces of tube, and it rarely costs me more than 30 euros. I like their 18cmx18cm rounded corner square tubes. Perfect for J tubes.