Ceramic PreMade Stove Cores

Take a look at what I found at German EBAY ? We could use to get some ideas perhaps

It would appear to me these ceramic flue liners are optimized for the expense of the materials.
Somehow I'd thin kthat the thin inner core is the expensive hi performance stuff that takes the
extremely hi heat or..... Maybe its performance lies in the area of toughness instead of heat tolerance.

I wonder what its insulation value is and if it will really handle the heat. Terracotta chimney liners sure dont.

I have read that metal oxidizes at these stove temps and that steel pipes will crumble quickly? Has Ceramic coated steel pipe (or stainless pipe) been done before? Ceramic Coatings are used on race car exhaust systems to keep the heat in the pipe and get it out of the engine compartment. It's not at all a cheap easy or earthy solution but just wondering if it's has been done, or if people are just trying to use more masonry type solutions. That ceramic chimney on the ebay ad looks promising. Hoping to have time to experiment with my first rocket stove this afternoon.

I have not used ceramic lined pipe but we have used SS for the riser and it didn't work out very well. the SS will melt and eventually it to burns out. this happens as we get better and better insulation's. this is the cast able we are talking about so keeping the weight down is also an important consideration.

Has anyone tried casting the whole insulation interior out of refractory cement and perlite? Would this be durable enough, too heavy, or is there a need for a liner? I read that a two part perlite and one part cement would make a good brick, but have no experience with it.

What about simply buying a bag of cone 13 clay (refractory body), and forming your own riser liner? could be pressed, coil-pot style, between two pieces of pipe that have a 2" difference (6"dia and 8"dia, or 8"dia and 10"dia) such that you are left with a clay pipe with a 1" thickness. Firing the liner before installation would be ideal, but kilns of that size are problematic in location and use... still, they do exist. As an alternative, you could keep the liner in the two-pipes form, install it in a system, and have an initial "burn-out" phase wherein you intentionally burn out the first liner, thereby crudely firing the clay liner in place. Seemingly simple, this possibility has issues as well since the temperatures would vary greatly between the top and bottom-- a sustained, long-term burn would fire the bottom to 'reduction' temps, but the top just won't get that hot, almost ensuring heat-shock and cracking.

I like the idea of forming a liner out of refractory powder and perlite, but I would imagine this to be better at a 2 to 3 inch thickness. but you still run into the issue of heat-shock and crumbling of the upper end over the long term...

*DING* {light bulb} : How about dipping ceramic wool in refractory clay slip and wrapping it around a 6" pipe that you intend to burn out-- like high temp paper mache`? Ooooo... I like that idea-- super-insulative, strong, virtually impossible to fracture, would be comparable in cost to a kiln brick riser... I think that would definitely be worth testing out.

Hmmm... think I might be spending my xmas bucks at OxArc

I was thinking of forming the whole center from the riser pipe to the outside of the inner barrel. Not using a pipe or a barrel at all... only the perlite and refractory mix. With an 8" riser and leaving 1 - 1.5 inches around the edges for exhaust that would be about 6" thick if i am thinking correctly. I thought of using a sauna tube and a cardboard barrel of the right size as a mold for the mixture and let it burn out when the first fire was lit. If the mix wouldnt be smooth enough then i figured 1/8" stainless steel might have longevity to hold the mix. But then I wouldnt really need the refractory cement would I? Maybe to form the cap?

It looks like something i am familiar with.
In our country we have chimney systems similar to this. Usually this kinds of products are rated for solid fuel heating (which means they have to be pretty heat resistant).And since most of such heating systems are prone to sooth build up some makers specifically market their product as chimney fire tolerant. Chimney fire is a pretty damn hot, i guess those products could be used without much worry as heat risers.
But i don't know anything about this particular brand.

For nearly $800 and $200 shipping it should be amazing. I think I will buy something else.

Yeah it looks pretty expensive, i did not comment on that since i don't know what is meant by 1 unit on e bay. 1 what? piece? meter? crate? 6 meter high complete system?
When i last did a drawing, a 9 m complete system from a similar looking product had a material cost of 1200 - 1500 $. (equivalent in our currency)
But sometimes one can find left over pieces on sale for reasonable amounts online. (this region at least)

The core is called in Germany: Schamotterohr
Its heat resitant up to 1250°C (= 2282°F)
See for example this ebay article:
http://www.ebay.de/itm/Schamotterohr-160-mm-fur-Ofenrohr-150mm-/321035999081
It's possible to get in several sizes.

I just read about a special glue/cement to get these Schamotterohr together. This glue is resistend to water, acid and fire.
see here: http://www.auka.de/saeurekitt.htm

Konstantin

I just found that there are High-Tech-Keramik-Tubes developed. They are thin and more strong against heat etc.
And its possible to get them in 100cm length, so the combustion room would be made out of one piece.

Thats the german list of properties found at this page: http://www.auka.de/schamotte.htm
UNOTHERM High-Tech-Keramik-Rohre • Dünnwandig • Temperatur- und Temperaturwechselbeständig • Montagefreundlich • Feuchtigkeitsunempfindlich • Säurebeständig • Korrosionsbeständig • Langlebig • Montagefreundlich • Abriebfest • haben eine hohe, innere Oberflächenglätte • bieten hohe Sicherheit bei statischen Belastungen • werden aus zukunftssicheren, heimischen Rohstoffen hergestellt • haben keinen Schwermetallabtrag

automatic translation:
Thin-walled • temperature and temperature change resistant • installation friendly • moisture resistant • acid resistant • corrosion resistant • durable • mounting-friendly • abrasion • have a high, inner surface smoothness • offer high safety under static loads • manufactured from future-proof, local raw materials • have no heavy metal removal

And maybe the best I found is a 3 in one tube: This high tec ceramic-tube combined with insulation and steel at the outside. I can't find prices, but I will ask. It's called "Keranox" from the manufacturer Auka
You can read about this here: http://www.auka.de/auka_keranox.htm

What about simply buying a bag of cone 13 clay (refractory body), and forming your own riser liner? could be pressed, coil-pot style, between two pieces of pipe that have a 2" difference (6"dia and 8"dia, or 8"dia and 10"dia) such that you are left with a clay pipe with a 1" thickness. Firing the liner before installation would be ideal, but kilns of that size are problematic in location and use... still, they do exist. As an alternative, you could keep the liner in the two-pipes form, install it in a system, and have an initial "burn-out" phase wherein you intentionally burn out the first liner, thereby crudely firing the clay liner in place. Seemingly simple, this possibility has issues as well since the temperatures would vary greatly between the top and bottom

I like the way you are thinking. I am thinking we could use a 1/4 wall pipe for the inner pipe, and do a forced air burn chamber in a temp outside unit. The thicker wall pipe would transfer more heat up the length of the burn chamber, and the forced air input would get the temps up much higher than normal use. I might have to use an open top barrel and an oversized 1/2" plate on top to keep the barrel from melting down. Fire that for a few days and see what happens.

Also the clay could be mixed with E glass or basalt fibers. Both have high temp ranges and might just keep the clay together. I was consulting on a basalt fiber project a few years ago, the temp range was in the 2200F range (from memory, I could be off on this one), with good tensile and elastic modulus characteristics. We were getting a chopped fiber that was meant for concrete additive, perfect for mixing with clay and working into a form. If I remember right, the basalt fiber has no coatings on it, because unlike fiber glass, it does not react to concrete over time, so it can be used un-coated. I think the fiber we were getting was just the raw fibers chopped, and ran about 12 bucks for a bag that was meant to reinforce a yard of concrete. I didn't source the material, so I don't have a link right now. I will look for one.

I like the idea of forming it on the ceramic paper as well. What if you laid the paper down with a temp wooden frame around it, poured a ceramic slip mixed with basalt fibers onto the paper. Let that set up to the bendable stage, then carefully rolled it into the pipe shape and glued the edge with more slip, or let it overlap the edge and press the clay into the back of the ceramic paper. Stand this on edge, and let it dry all the way out to form a ready to fire pipe. Maybe do these in 6 to 8 inch tall sections for firing in the temp outdoor setup. Then you would have stackable sections that have been past the heat needs of your stove.

Now that I think about it, ceramic rings could be molded with a stepped lip. Fired and stacked, that would make a nice inner wall for the combustion tube. Everyone has a local potter with a kiln large enough to do the pipe as sections.

I made a video for those of you who want to cast your own. I do my risers with the same material, sometimes just with temporary wood molds, sometimes with flue pipe inner and grease drum outer. There's lots of ways to do it, here's one...

Great video Matt!

You inspired me to draft up a cast combustion chamber, and cast pipe sections. I have a CNC, so making the molds would be easy for me. I would make the parts out of wood and just let them burn out. I tilted the burn tube for clearance at the feed tube opening. There is a metal grate for the wood to rest on while it burns, the ash falls through to a clean-out area, the barrel has an integrated stand with an adjustable clamp to raise or lower the barrel.

I designed this as a 6in system, with an 8in thermal mass heater.

How did you come by the mix ratio? How much fiberglass do you use in your mix?

Thanks Shane. I used about 2 sq. ft. of around 20oz matte fiberglass total in this one. The mix, well, I've just been experimenting, and this one works well for me for this design.

I'm sorry to say I doubt it's tough enough to handle what you have drawn there, unfortunately. It's still very clay rich, which means it doesn't go anywhere with the heat, but it powders fairly easily upon abrasion. Your sharp corners and metal grate area and all that just would eventually turn to powder with this mix. To build yours, I think you'll need to look to the premixed refractory blends or something along those lines. You could do something similar to my mix but with a lot more furnace cement, but at that point it would probably be more economical to just buy the good stuff.

What I've shared in the video is an improved mix over what I've been burning in my home for a year now. It's great for a basic J tube, the feed area cooks hard enough to handle the abuse, and if it wears it can be patched with a handful of more of the same. I don't think it will be appropriate for your complex design though. I could certainly be wrong though, I'm pretty good at that!

Your design is neat, I hope you experiment with it and find a way to do it that works for you.

Matt Walker wrote:I'm sorry to say I doubt it's tough enough to handle what you have drawn there, unfortunately. It's still very clay rich, which means it doesn't go anywhere with the heat, but it powders fairly easily upon abrasion. Your sharp corners and metal grate area and all that just would eventually turn to powder with this mix. To build yours, I think you'll need to look to the premixed refractory blends or something along those lines. You could do something similar to my mix but with a lot more furnace cement, but at that point it would probably be more economical to just buy the good stuff.

What I've shared in the video is an improved mix over what I've been burning in my home for a year now. It's great for a basic J tube, the feed area cooks hard enough to handle the abuse, and if it wears it can be patched with a handful of more of the same. I don't think it will be appropriate for your complex design though. I could certainly be wrong though, I'm pretty good at that!

In your experience, will your mix work for the castable/stackable pipe? I designed for using a removable lid barrel, and being able to get in and inspect/replace the sections. If I got rid of the ash clean-out, then it would be a simple J tube. Perhaps a redesign with a sheet metal liner for the feed area to avoid any abrasion in the first place.

Thanks again for posting your video, I would like to explore this method further.

I don't think it would hold those small detail tabs you show in the drawing for the sections Shane. It also most likely would be fragile for handling. I use it for the riser, but cast in place as a single piece. It works excellently for that, since once the riser is in place there should be no abrasion or handling stress. Your design calls for something a bit more robust since you intend to handle the components.

The sheet metal will work for a short time, then it will burn away. I use the hardibacker because it holds up to the heat long enough that by the time it's gone the clay is hard enough to handle the abuse. The metal may do the same, but I'd fear it's expansion and contraction might work against you. There are solutions that would work for your design for sure Shane. Places like HighTempInc. on ebay and Western Industrial Ceramics in CA and OR are a couple starting points for some truly high tech materials for your application. My home brew probably will frustrate you if you are set on complex shapes. If you keep it pretty simple it will work well, but again, it's pretty fragile. If you've ever handled a Light Fire Brick, the kind used to insulate kilns, it about that strong. You can easily break one with your hands.

I'm not trying to discourage you Shane, just sort of a disclaimer of sorts. By all means play with casting a few shapes with this mix and throw them in a fire. Once cooked and cooled, you should be able to get a good idea of what's possible. Good luck on the build man!

Thanks Matt.

We are going to be doing several outdoor greenhouse heaters, so I think I will save the experimentation for those this summer, and use refractory brick for the three we are building in the basement. You certainly have me thinking about how to cast a unit. If some high temp materials were laid out against a form, then use your mix to cast around them to get one monolithic block burn tube, one could create any shape desired. I like the idea of being able to put the burn tube on a 30deg tilt. It keeps the burn tube short, and yet has clearance for the feed tube. It might give the hot gasses a better draw right from the start. I suspect, a little more rocket effect would be achieved, but that is just my seat of the pants engineering talking. I do a lot of that.

Does anyone have any experience with the Insboard product sold on the bottom of this page: http://www.hightemptools.com/inswool.html ?

A quick search led me to this page: http://www.hwr.com/EEC/Incineration/Products.asp?Product=CERAMIC%20FIBER which lists Insboard 3000 which I assume is rated to 3000 deg F but I don't think that it's heavy duty like the 2300HD or 2600HD and I can't get the actual product spec sheets (I have to admit I haven't tried that hard yet).

A quick read of the FAQ page at High Temp Tools says that the Insboard can be cut easily with a tablesaw or other standard cutting devices which would make building a lot easier. It would be very easy to set up a CNC machine for mass production of standard parts. Mortar the pieces together inside a prebuilt enclosure, coat the insides with a layer of ITC100 and fill the airspace between the enclosure and the core with insulating material of your choice.

I have a couple of sketch-ups I've made for chip-burning rocket stoves but they're not specifically mass heaters but a modular power-plant/core that can be hooked up to various systems, from a water heater to a steam boiler (don't worry, ex Navy Nuc, know all about boom-squish!) to a charcoal retort (personally not for biochar but for playing with my forge).

I'd post some pictures of the sketch-ups but they'll need a little more polish before they can stand up to Shane's nice ones there.

I have fabricated with the ceramic blanket, paper, and board. Not this brand. It is good stuff, but not meant for anything but insulation. It will tear, chip, and chunk-out if impacted, or rubbed against. Usually, it is protected by some other material. I don't think it would work well as the inside of the burn tube, however, that said, I think it might be a good substrate to cast onto and hold the shape until the clay is heat set. Like I mentioned in an earlier post, it would be interesting to pour a ceramic slip onto/into the paper or blanket. Let it set up, then use it. You can get the blanket in thicknesses up to 6", but I think a 1/2" thick blanket might work well. It cuts with scissors, or razor knife and straight edge. I have a friend that I get mine from, he usually has some left over from industrial clients. I will give it a try, and post my results this summer.

Another idea, would be to hot glue the blanket onto a hollow wooden combustion chamber form. Then saturate the blanket with the clay slip, pressing and forcing it in and painting it on in layers. This would form a ceramic fiber clay matrix that might be pretty tough once heat set. After it cures, put it in a molding box like Matt did, and use his mix for the overall body. Burn it outdoors, nice and hot, alternating the chimney over both the output and in-feed holes. That way you get the clay heat set on both ends of the J channel. This is simple enough for anyone to duplicate.

Thanks for the compliment to my designs, but don't hide your light under a bushel. I engineer for a living, and I am also an artist, so my stuff has a little polish on it (good tools). Back in the day, I did plenty of drawings scratched out on the shop floor, and we built stuff from them that worked just fine.

If you want to see some of my work, here is a showcase video; http://animoto.com/play/VDBnTdYkQziDndNhpXsm4g

Shane McKenna wrote:... Not this brand. It is good stuff, but not meant for anything but insulation. It will tear, chip, and chunk-out if impacted, or rubbed against. Usually, it is protected by some other material. I don't think it would work well as the inside of the burn tube, however, that said, I think it might be a good substrate to cast onto and hold the shape until the clay is heat set.

I'd like to get my hands on some of the High Density Board. From the HTT website: "Insboard HD is a hich density vacuum formed ceramic fiber board with excellent insulating characteristics and an increased mechanical strength. This high density board is very robust!" They talk about using it for sliding doors on small furnaces, which I think would see more abuse than the inside of a rocket stove. Build with expansion joints and I think that you would have a pretty long-lasting core. I'd also like to see how long a steel burn grate coated with ITC-213 would last under prolonged use vs. ceramics exposed to the physical abrasions/shocks from the burn material. Seems to me that a well designed core would end up with the burn grate being a part designed to be replaced because steel will pit/oxidize/melt away and ceramic is so brittle it won't hold up to the physical abuse for very long.

There's so many great materials out there that would lend themselves to optimizing a rocket stove, but it's hard enough justifying to the wife buying the occasional scrap for my "hobbies", let alone shelling out good money for materials that I just want to experiment with...

I just got off the phone with my friend who manufactures with the paper and blanket, he is going to save some off cuts for me. I will play with it and see how it works. As far as the board, I have done some projects with one of our local refractory supply companies, so I think I can get some samples pretty cheap or free. I will get a sample of the board and give it a try as well. I really think a matrix of refractory cement, and the ceramic blanket could make a good cast product. It will cost less than a 100 bucks to find out. I would like to have the time to do it right now, but I have other irons in the fire until spring/summer. When I do, I will document, film and post the results.

http://www.youtube.com/watch?v=dM-GbmlVGXo

Here's some shots of a rocket stove core that I've been mocking up. I tend to have lots of woodchips, so the burn grate is designed for those, but it wouldn't be hard to change the grate to handle sticks or pellets either. The Horizontal Burn chamber and Heat Riser would be made from castable, 3" kaowool blanket around the heat riser, the rest made from appropriate metals. I'd coat the burn grate with ITC-213 to help the steel handle the temps better, but I still think that it would be considered consumable.

There is a similar design. But the owner had to modify the system so that the air supply cools the feed tube. Otherwise the fuel cooked in the tube. (complete with smoke and creosote in the pipe)
link for his page

Balint Bartuszek wrote:There is a similar design. But the owner had to modify the system so that the air supply cools the feed tube. Otherwise the fuel cooked in the tube. (complete with smoke and creosote in the pipe)
link for his page

This has been mentioned as problem on donkey's board as well, yet I haven't experienced that as a problem with any of the trial systems I've made so far. I think that part of the reason for tha is the fact that I'm burning wood chips which seem to be self-insulating.

That sounds logical. Still better be safe than sorry.
You mentioned, that you may want to burn sticks or pellets in it. I came across a pellet system that had this problem as well. The guy had to modify his system several times. But luckily he put it on youtube. web4deb/rmh
He also looking into the grate erosion problem as well. Maybe you could ask him how the stainless grates are holding up?

I found another company who produces ceramic pipes for stoves: http://www.tona-schornsteine.de/de/Produkte/SanReMo/star.html
On this page there is a video where they make a test with more than 1000°C: http://www.tona-schornsteine.de/de/Unternehmen/Ueber-uns/Unternehmensfilme.html
The price for a pipe 100cm (3 foot) long and diametre 13 cm is 120 Euro + Tax. The size 15 cm is at 130 Euro. This includes the insulation and the outer stainless steel tube.
The price for only the ceramic is about 50%. This price is quit high. Some RMHs hase been build completly with less money.

The wall thickness of the ceramic is only 4mm!!