I have been researching for some time and feel I have a good grasp of the concepts and methods, sufficient to take some "next steps" in the basic engineering of these stoves. I can see some of the inherent issues associated with thermal gradients and stresses in the commonly used materials and being a Toolmaker, I have fairly good skills in troubleshooting designs of all sorts.
It appears that the primary area of premature stove failure is in the materials used for the extreme heat areas of the stove, specifically the lower portion of the riser tube. After some consideration and noodling about this issue, I have an idea that I would like to pass on to the group for feedback and possible testing.
It is clear that a refractory material is necessary to line the riser in order for it to last for the maximum time. Common materials used in the research I have seen are fire brick and pearlite/clay mixes, both with inherent issues. The brick option takes up a lot of space and is difficult to insulate and the pearlite/clay mix requires a form to maintain integrity of structure and that form, typically steel tube, will go away after a few seasons.
So, I have thought of a potential solution.
I have found castable refractory materials that, although a bit pricey, will handle the 3000 degrees and survive the heating/cooling expansion/contraction cycles quite well. My method to use these is this.
Roll out a thin slab of this castable material like rolling out a pie crust, with wire mesh embedded in it for stability (I suppose one could use any adjunct commonly in use if one has trouble with wire mesh), wrap this "crust" around a disposable form or even the commonly used stovepipe, then wrap that in rockwool with a split stovepipe covering to hold it all together. This should provide a riser life that far exceeds the common steel riser, far greater insulation and performance than firebrick and with careful packaging, should be able to be shipped or moved easily without damage.
The choice of castable refractory material will need to have some variability in its mixing to create a fairly thick consistency, like pie dough, but I don't see this as a significant issue.
If one were to roll out the "dough" on a fireproof cloth type material, the rolling around the form will be rather easy... If in doubt, ask Gramma how she keeps the pie dough from sticking to the breadboard... She will have some great ideas that can be adapted.
Curing of the "dough" may require it be open to the air for a time, but I don't see this as a significant issue provided the stability adjunct (wire mesh, hair, straw, whatever) and the cloth you roll on can support the weight without distorting or allowing the "dough" to flow or move.
I would like to test this myself but personal issues prevent me from experimentation at this time.
So I put this to the community for perusal, disassembly and debate in the hopes that one of you intrepid pioneers have or can obtain the materials necessary to further the research.
Thank you for your time.
There will be an innovators meeting in days and I encourage you to Repost most of your comments directly to ->
rocket workshops / innovators gathering / September 2014 (wheaton laboratories forum at permies)
I will be watching this space knowing that it Should draw useful comments. Thank You! For the Good of the Crafts Big AL !
Late note : While waiting on your initial responses , perhaps you might want to look at the use of Ceramic felt with a stiffener perhaps Sodium or potassium (?)
Silicate, I THINK having said that, there is much to consider in your proposal ! A.L.
One of the things that really drives me nuts is folks that seem to be stuck thinking in boxes... Compartmentalization has destroyed innovative thinking for so long that it is almost normal now. I'm doing what I can to reacquaint folks with the idea that there are NO boxes... There are no areas anywhere that can be viewed truthfully without taking into account how they relate and are associated with everything else... I mean, who else would have thought that making a rocket stove could be associated with baking a pie? LOL
John C Anderson wrote:Roll out a thin slab of this castable material like rolling out a pie crust, with wire mesh embedded in it for stability (I suppose one could use any adjunct commonly in use if one has trouble with wire mesh), wrap this "crust" around a disposable form or even the commonly used stovepipe, then wrap that in rockwool with a split stovepipe covering to hold it all together. This should provide a riser life that far exceeds the common steel riser, far greater insulation and performance than firebrick and with careful packaging, should be able to be shipped or moved easily without damage.
You don't specify the kind of castable refractory material. I've been working with those materials off and on for the last 30 years, but I am not familiar with a kind which let you roll it like a pie crust. Are you able to name a brand or specification?
I'd think it isn't advisable to use wire mesh in a vey hot part like the riser. The reason being that the metal will expand much quicker as compared to the refractory, making it falling apart.
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