Teach
Junior Member
Posts: 89
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Post by Teach on Feb 8, 2009 8:36:01 GMT -8
You are absolutely right! Simpler is better I usually find and I did not even consider that half way down the pipe that it would not be hot enough to burn off the paper. Good point. Ur thinkin hehehe
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Post by johnjmw on Feb 9, 2009 4:17:38 GMT -8
For building a test/demo system the sand would be so much easier and more reusable just poured into the cob trough. This would also be a lot less work.
There is a video on youtube of a person that uses a light sheet metal form around the feed tube, burn tunnel and heat riser. He then fills the space with vermiculite and cobs over that. I thought that was a great way to insulate the stove. I just have not found vermiculite in the larger bags yet. Probably a Cleveland thing. That and I have not started to check out the supply stores just the retail outlet hardware stores.
John
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ekw
New Member
Posts: 14 
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Post by ekw on Feb 9, 2009 19:01:43 GMT -8
You talking about the pipes inside the thermal mass? lining with paper to burn off?
I don't think it would get hot enough to burn off.
If you don't want metal in your stove, you could do the whole thing like a masonry stove - look for mortar that is suitable for flue gas. Lime mortars seemed to work OK for the romans - I heard about a hypocaust masonry heater that was built 1500 years ago and is currently in use. (Ernie says it's cheating because it wasn't used for 500 years in the middle.)
I'm glad to hear that sand is working OK for you as a thermal mass. There was some speculation at this year's Pyromania workshop that sand was too insulative for the purpose. Our masonry stove expert from Montana loves soapstone (almost as dense as water) as thermal mass, and had some cool ideas for insulative shielding too. Mostly expensive. Oh, well.
My question is, has anyone found a really good material (or method for combining materials) for that first brick in the roof of the burn tunnel?
I can recommend against decorative facing brick (tile); ours is cracked through already and the stove's not 6 months old.
Ianto recommended old brick (the ruddy soft red kind that tolerates expansion and contraction) but I've seen it fairly scuffed up by wood. Firebrick also seems too soft for this purpose.
I'm going to ask the masonry heater guy again when I talk to him.
Any other materials people have tried and liked?
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Post by Donkey on Feb 10, 2009 8:05:18 GMT -8
Hello ekw.. Welcome to the board! Yeah.. That first brick always gets it no matter what it's made of. I haven't tried a whole lot of things that I've thought of.. Like making that guy out of refractory or something. What I have tried is using a steel plate across the length of the burn tunnel and placing bricks on top of that. The first brick still gets heat shocked and cracks up, but there's no way it can fall in or cause trouble.. At that point the bricks are pretty much just for looks and Ernie will probably call me a cheater for it.. But what the heck, it works.  |
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Teach
Junior Member
Posts: 89
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Post by Teach on Feb 10, 2009 8:52:28 GMT -8
Donkey, coming from my artist blacksmithing background in building propane fired forges. We would use high temp insulating fire bricks..........the 2300 degree stuff that tends to crumble easily when hit accidently. We would coat the bricks with a IR reflector that is painted on by hand much the same way you would paint on a glaze on pottery. The coating would reflect heat back into the forge and keep it away from the bricks. The result was that we had more heat in the forge with less fuel and the bricks lasted far far longer.
I wonder if this coating could be used for the burn tunnel? Or at least the first brick? The product was called ITC-100.
Teach.....
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Post by Donkey on Feb 10, 2009 11:43:30 GMT -8
Why not??
It might be good coating the heat riser too.
Is it inexpensive, is it non-toxic, is it easy to get?
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Teach
Junior Member
Posts: 89
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Post by Teach on Feb 10, 2009 12:36:49 GMT -8
Sure you could coat any surface within the combustion chamber to good success I would think. I know in propane fired forges it is difficult to get enough heat within the forge to do a proper forge weld. With the ITC100 coating it was much much easier and with less fuel. The stuff is not cheap. It runs somewhere between 40-50 USA dollars a pint. One pint should cover approx. 10-15 square feet? I'm guessing with that but it should be close. Toxic? = it is ceramic in nature so I don't think so. Easy to get yes. Just google it, you will get lots of hits on it. It is offered in several formulations based on heat levels. Choose the appropriate one. Hope that helps.
Also; only the surfaces that are directly exposed to the heat need be coated so usually only one side of the six sides of a brick will need to be coated. As you can see, a pint could go a long way considering it is first diluted with water before being applied. Also, high temperature fire brick is far more porrus than the regular fire brick we use in the combustion chambers of rockets heaters so It will go farther yet. I suspect two people could go half on a pint and get enough to do two rocket heaters.........fingers x'd.
Say you split a pint with some one and it prevented that first brick from cracking and the duration of the stove life between rebuilds doubles.........wouldn't that be worth the 20-25 bucks you forked out for the ITC100? I think it would be even just to try it to find out would be worth 25 bucks. I took a gamble with in on my forges (three of them) and I am a believer in the stuff. It makes a big felt difference.............how much can be measured I don't know because I don't have the measuring equipment. I could not do proper forge welds before I used it. After I used it I could.......that says enough for me. I went from getting 7 hours of good working temp from a 20lb bottle of propane before coating the forge with ITC100 to 12 hours of good working temp from the same size bottle. I was impressed. I will be using it in my rocket. Good luck.
Teach......
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Post by broadturn on Feb 16, 2009 6:04:14 GMT -8
Has anyone used rock powder or dust, such that comes from a quarry? Very small particles of stone... Clay is flat like plates on a microscopic level, which works best in terms of its contact with the heat source. Sand is very different -- spherical in structure. Using both clay and sand together -- sand being a better mass to hold the heat, and clay to make the connection between it and the heat source (i.e. cob), is the best. But is there a potential use for powders? Just curious, because it is very easy to use, and free.
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ernie
New Member
Posts: 32
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Post by ernie on Feb 17, 2009 11:24:49 GMT -8
Broadturn I would think that in either sand or dust alone would have to much air in it to be very good for thermal mass. there are two presentations of clay one is called plate clay we commonly use it for pottery and the other is called ball clay we commonly use it for bricks. ball clays have you guessed it a ball shaped partical structure. ball clay is actually better for building thermal mass (a very fine distinction).
by all means use rock dust or masonry rather than beach sand. beach sand is not recommended for cob as the bond to the rounded grains is not as good. masonry sand is either sifted from a rock crusher or from high in the mountains. beach sand is found lower down the river. as the sand moves down the river it gets polished. the best sand for building is sharp edged and still rough on the faces.
a magnifying glass will allow you to see the diffrence. then mix in a bit of clay slip and see what has the better adhesion. then make a couple test bricks and bake them the texture will not only be different but one will dust off more than the other.
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