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Post by mintcake on Nov 14, 2011 7:58:58 GMT -8
Dear experts...
I'm seriously thinking of making a rocket-bell for our living room. Peterberg, it's all your fault! :-) Not next week, but maybe by next winter... And I won't be at all popular if the thing needs taking apart in less than 10 years, so it's got to last. It'll be supplementary heat in the near future, so it's also got to heat up pretty fast. I'll be replacing a glazed terracotta stove which
needs its door shut at exactly the right time or all the lovely heat goes straight up the chimney.
I'm in central Europe, so local suppliers of non-insulating fire brick for traditional teracotta stoves is no problem. I can also get waterglass and fireclay, if I want to go that way.
I've not found *any* insulating fire brick on sale anywhere in the country, but I have found a producer of "insulating" castable refractory concretes, so presumably some local shop could order some for me, even if the factory won't sell direct. But it all leaves me wondering.
There seem to be 2 categories withing the 10 or so grades of the stuff:
Type A, lets call it, which permanently expand about 0.3% on firing, max working temperatures of around 1000-1150 C and better insulation properties. (0.15-0.3 kCal/m/h/k), densiies about half that of water.
Type B which permanently shrinks about 0.5% if/when it gets to max temperature, have max working temperatures of 1300-1400 C, and loose heat faster (0.4-0.5 kCal/m/h/k). more dense than water.
I don't have access to a kiln to get the thing up to working temperature in a nice even and controlled manner... Should I be thinking of the shrinking or the expanding sort, or try for better insulation with perlite, and hope I don't get above 1000C when it melts according to the local producer (I can probably get hold of perlite, but it looks like vermiculite is not available unless I import it).
What do you all suggest? How long have home made solutions lasted so far?
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Post by Deleted on Nov 14, 2011 8:17:36 GMT -8
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Post by peterberg on Nov 14, 2011 12:18:25 GMT -8
I'm seriously thinking of making a rocket-bell for our living room. Peterberg, it's all your fault! :-) Me? No, honestly, I didn't knock down the walls of Jericho, I was in our home, watching Banana Splits! It'll be supplementary heat in the near future, so it's also got to heat up pretty fast. No fast heating up, it is a masonry heater after all. Warming up could easily take an hour or two. Type A, lets call it, which permanently expand about 0.3% on firing, max working temperatures of around 1000-1150 C and better insulation properties. (0.15-0.3 kCal/m/h/k), densiies about half that of water. Type B which permanently shrinks about 0.5% if/when it gets to max temperature, have max working temperatures of 1300-1400 C, and loose heat faster (0.4-0.5 kCal/m/h/k). more dense than water. Type A is near the limit, but with such a low density it might be the best choice for the syphon. I know, the temperatures inside that could well be above 1000 C. But actual wall temperature is an entirely different story. You could even use normal fire brick and insulate the thing with perlite. Vermiculite is more or less the same, insulation-wise. There's no need for firing the castable, you can use it as it is. Normally it's solid in 8 or 10 hours at room temp. You do need a shaking table of some sort to drive the air out. Wait a minute: do you say in the last sentence the product you are talking about is home made? |
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Post by mintcake on Nov 14, 2011 23:17:37 GMT -8
No fast heating up, it is a masonry heater after all. Warming up could easily take an hour or two. An hour or two is fast enough for the outside- that's about what our current one takes. I was actually thinking about the rocket itself though - It won't be fed all day long, more like a single batch, and if it takes three quarters of a batch of wood burning to get it to temperature then it's not helping much. Wait a minute: do you say in the last sentence the product you are talking about is home made? No sorry, what I was looking at mainly were factory products. I was just thinking of the other threads which are talking about mixing your own, and wondering how well they last. |
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Post by peterberg on Nov 15, 2011 4:33:00 GMT -8
An hour or two is fast enough for the outside- that's about what our current one takes. I was actually thinking about the rocket itself though - It won't be fed all day long, more like a single batch, and if it takes three quarters of a batch of wood burning to get it to temperature then it's not helping much. It would take a quarter of a batch to bring the syphon up to temp, if you ask me. That is to say, starting from cold and provided the kindle fire is made on top of the batch, right at the edge of the syphon. |
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Post by mintcake on Nov 17, 2011 8:02:58 GMT -8
It would take a quarter of a batch to bring the syphon up to temp, if you ask me. That is to say, starting from cold and provided the kindle fire is made on top of the batch, right at the edge of the syphon. I'm new to this, but that seems like quite a lot of not very efficient burning to me. Do you get the impression that main problem area is the fire box or the siphon itself? (i.e. does the firebox need to be hot before the siphon has a chance, or -assuming the fire is lit properly- is it it the siphon that heats up first)? Do you have any idea what the insulation / heat capacity numbers for your siphon or firebox are? It seems to me that getting that time down would be a very good thing. I've seen that you use 1inch thick walls. Would thinner walls just crack? I wonder if some sort of hybrid rock-wool and ceramic skin could work. |
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Post by peterberg on Nov 17, 2011 13:30:55 GMT -8
Do you get the impression that main problem area is the fire box or the siphon itself? (i.e. does the firebox need to be hot before the siphon has a chance, or -assuming the fire is lit properly- is it it the siphon that heats up first)? Preferably, the syphon has to heat up first before anything else. That's why it has thin walls. But... the thing is a mass heater, you wouldn't start a cold stove during winter, only the first fire in autumn. So, heating up in say, December, would take 10 minutes tops. I've seen that you use 1inch thick walls. Would thinner walls just crack? I wonder if some sort of hybrid rock-wool and ceramic skin could work. Didn't try thinner walls, it's quite tricky to get it right as it is. What you could do: use 1000C-graded vermiculite-plate to construct the riser. Low mass and insulating walls. Normal rockwool is held together by a resin which is disintegrating at 500C+, so it is falling apart fairly easy. |
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Post by mintcake on Nov 30, 2011 7:16:29 GMT -8
Didn't try thinner walls, it's quite tricky to get it right as it is. When you say "get it right", do you mean get the cement into the whole mould, or getting the mould to be the right shape, or ...? |
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Post by peterberg on Nov 30, 2011 9:10:31 GMT -8
When you say "get it right", do you mean get the cement into the whole mould, or getting the mould to be the right shape, or ...? The refractory castable won't consist of aluminum cement only. Of course, there's aggregate in there, usually fine gravel size. The aggregate itself has been made of ground porcelain or fire brick. To obtain a good end result you'll have to use as little water as possible, so the mixed concrete is rather damp than wet. The thin walls of one inch will make it difficult to fill the crevices completely, even with the use of a vibrating table. When you fill it up to the top and switch on the table, there's a stiff chance not all the air will come out. So you have to do it in stages, fill it for a part, vibrate say one minute, top it up and vibrate again, etc. I've done it in three or four stages. |
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Post by swoprofessor on Mar 18, 2012 1:18:26 GMT -8
traditionaloven.com has some info about self made heat resistant refractory concrete. What is fire clay and where to get it www.traditionaloven.com/articles/101/what-is-fire-clay-and-where-to-get-itok the one link says 'fire clay' is light color but all i see in the pictures online are more terra cotta - so clearly we are talking apples and oranges. While the info on fire clay is useful - I was refereing to the the clay used to make the bench. Seems not to be fire clay. Feel free to correct me if i am wrong. Jim |
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Post by Deleted on Mar 18, 2012 2:24:16 GMT -8
swoprofessorThe color can only give a hint. Alumina and silica are white. A high content of lumina and silica gives a light color and high heat resistance. The simplest way is to get the stuff at Ebay. You will not get another answer from me anymore.
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Post by Donkey on Mar 18, 2012 9:58:22 GMT -8
No.. The bench is NOT made of fireclay, not unless you find it in your soils anyway.
The only place you might need fireclay is inside the firebox itself, in contact with the hottest conditions.
Red clays that set in very wet conditions for a long time will loose their red coloring.. Normally, the clay will turn grey or black, sometimes it will go white. The red (usually more orange) comes from iron oxides (rust) in the clay. Under water, the oxide will be driven out (by some chemical process) leaving behind just the iron which is black. Over time, the iron can be leeched out, leaving behind white. So, just because your clay is white, it doesn't make it fireclay. It's a likely candidate, just not proof positive by color.
The only way to know is to put the stuff in a fire and see what happens. The clays here at my place are NOT fireclay, more like brick makers clay. It does just fine inside a standard rocket stove. In my foundry however, after a while it turns into a slushy, liquid and when it cools it looks like glass. Clear indication that it isn't fireclay.
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Post by eodtek32 on Jul 10, 2012 19:46:22 GMT -8
@donkey
So what you are saying, not necessarily recommending, is that standard fired brick should suffice for a standard RMH.
As an aside, I am considering using the caliche soil on my property as a cob ingredient
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Post by Donkey on Jul 11, 2012 13:33:14 GMT -8
@donkey So what you are saying, not necessarily recommending, is that standard fired brick should suffice for a standard RMH. I have seen them work to good effect, yes. I've heard the word "caliche" used for SO many different things.. The term has been used so loosely that for me, it's lost any real meaning. If you mean "clay rich soil" then yes.Try it.. Don't forget to test EXHAUSTIVELY before you commit. |
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