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Post by stephenson1 on Apr 11, 2016 17:37:51 GMT -8
I had to replace my experimental fireplace style heater core because it had begun to burn dirty, the lime plaster had cracked, and it wasn't very efficient any more. I dismantled the core and barrel. When I lifted the barrel I found sheets of rusted steel lying all around the riser and obviously blocking gas flow. I used the specs from the MHA interview with Peter Van den berg to build a batch box core out of hard fire brick. I dry fitted all the parts I'd made, added a robex glass window, and used my old ceramic fiber riser. I haven't gotten to the angled bricks in the fire box yet, but I'll do that before gluing it all together with furnace cement. This first burn is really impressive to me particularly given all the leaks. I can only hope it burns as well when the new barrel goes on! I'll make my new barrel out of diy refractory mix (3 parts sand, 1 part portland cement, 1 part hydrated lime, 1 part, dry fireclay) and probably use a 1/4" steel plate to cap it off with some fiber blanket material as a gasket. I'll also try fitting another robex window near the top so I can see the fabled toroid flame around the top of the riser. This link will get you to a video that was taken at both five and twenty minutes into the first burn. Thank you so much Peter! www.youtube.com/watch?v=elTKYFkSADE&feature=youtu.be
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Post by Deleted on Apr 12, 2016 4:06:58 GMT -8
Without some additional pozzolan the hydrated lime jn your mixture makes not much sense. You could powderize some perlite to use it as a pozzolan. About 40% of the portland cement would be sufficient. If you want to use additional hydrated lime you need powderized perlite two times the weight of the lime. Waterglass could serve as a pozzolan too. Waterglass may cause a very short potlife.
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Post by stephenson1 on Apr 13, 2016 3:19:19 GMT -8
Hi Karl.
I got the recipe from the Forno Bravo website and was trusting that they understand the chemistry. They recommend this as a mix that can be used for high heat applications though not in direct contact with flame, or "hot face" applications as they call it.
I've been working with this mix as I've been building my outdoor oven and I can say that it is wonderful to work with. It is stiff, which makes it highly sculptable. It remains somewhat plastic for hours after mixing, but doesn't tend to slump. However, if it's unstable over the long haul, I'm wasting a lot of time and energy.
I spent quite a while looking for DIY refractory mixes online and there doesn't seem to be any definitive source of information. The recipes I saw that claimed very high heat resistance included relatively exotic materials such as calcium aluminate. These are very expensive particularly when shipping costs are added.
Could you possibly share a mix with specific proportions by volume, and using readily available materials? And could you explain why specific materials don't work, or do?
Thanks, Mark
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Post by Deleted on Apr 13, 2016 5:26:49 GMT -8
Lime needs pozzolan and water to form thermally stable compounds below sintering temperatures. In absence of pozzolan lime can only react with carbon dioxide from air to form calcium carbonate, which will at high temperatures be reduced to quicklime and thus starting the cycle again. Portland cement contains lime in excess. If the excess lime is bound by pozzolan the resulting concrete becomes much more chemically and thermally stable. Premixes of lime and pozzolan are sold as hydraulic lime. Premixes of portland cement and pozzolan are sold as pozzolana portland cement (PPC). Pozzolan en.wikipedia.org/wiki/PozzolanPozzolana en.wikipedia.org/wiki/PozzolanaHydraulic lime en.wikipedia.org/wiki/Hydraulic_limeBehavior of blended cement pastes at elevated temperature www.doiserbia.nb.rs/img/doi/1451-9372/2006/1451-93720602133K.pdf
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Post by stephenson1 on Apr 13, 2016 13:14:12 GMT -8
Thanks for that Karl.
Pardon my ignorance and confusion.
From what I read in the wiki link about hydraulic lime, that term refers to hydrated lime which has been slaked. That's the material I've been using the past couple of years to protect my various cob projects (all of which have blown apart with frost here in New England). Do you mean that if I properly slake hydrated lime and then add it to the refractory mix, it is helpful, but that if I just add dry hydrated lime out of the bag it is not helpful?
Looking for Pozzolana Portland cement online I find only books about it. Assuming I can obtain Pozzolana Portland cement somehow, what would your idea of a refractory recipe be?
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Post by Deleted on Apr 14, 2016 4:17:40 GMT -8
Hydraulic lime is a lime pozzolan mixture, which can harden under water, because it does not need carbon dioxide from the air. Quicklime and slaked lime cannot harden submerged in water. While quicklime undergoes a hydraulic reaction with water to become hydrated lime it does not become hard by the hydration as it cannot form crosslinked three-dimensional structures without finely divided silica or alumina respectively reactive aluminum silicates. You should be able to get perlite, vermiculite, diatomaceous earth or fine grog. Perlite or vermiculite can be easily powderized by shaking in a container with hard balls or stones. Mix 6 parts of portland cement with 4 parts powder of perlite, vermiculite, diatomaceous earth or grog. Or 1 part lime with 2 parts powder of perlite, vermiculite, diatomaceous earth or grog. Then mix the lime or cement mixture with fireclay and sand. From the the lime mixture you will need a bit more than from the cement mixture. My personal preference would be a geopolymer. donkey32.proboards.com/thread/1701/geopolymer-low-tech-tinkererBTW Wood ashes have pozzolanic properties too, usually more than natural pozzolans but less than Class C coal fly ash. Engineering Behavior and Characteristics of Wood Ash and Sugarcane Bagasse Ash. www.mdpi.com/1996-1944/8/10/5353/pdfGreener concrete using recycled materials ejournal.narotama.ac.id/files/Greener%20concrete%20using%20recycled%20materials.pdfEvaluation of wood ash as a partial replacement to cement ijsetr.org/wp-content/uploads/2013/10/IJSETR-VOL-2-ISSUE-10-2009-2013.pdf
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Post by exwatermark on Apr 14, 2016 9:58:21 GMT -8
I had to replace my experimental fireplace style heater core because it had begun to burn dirty, the lime plaster had cracked, and it wasn't very efficient any more. I dismantled the core and barrel. When I lifted the barrel I found sheets of rusted steel lying all around the riser and obviously blocking gas flow.
Hi Mark, where did all the rusty metal in the riser come from?
Regards Mark
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Post by stephenson1 on Apr 16, 2016 3:31:47 GMT -8
Thank you for the extensive information Karl. When I have the time I'll try to learn a little chemistry so I can understand the geopolymer information. It almost looks like I could use soaked wood ash for the lye component in those recipes, but I'll do some more reading.
To reiterate your suggested recipes: Powdered forms of perlite, vermiculite, diatomaceous earth, or grog (which I take to mean finely ground clay that has been fired to sintering temps. This could be old bricks or other ceramic material) are all interchangeable as ingredients.
So your two recipes would be (measures by by volume): 1. 4 parts any of the above 6 parts portland cement 1 part fireclay 1 part sand
2. 2 parts of any of the above 1 part hydrated lime 1 part fireclay 1 part sand Do you have an estimate as to the practical temperature ranges the resulting mix would be useful for?
To answer Exwatermark's question, the rusty metal came from the steel barrel. The moist hot air of these devices peels the metal away day by day.
The two solutions I see to this inevitable occurrence are to either build in a way that allows simple removal and replacement of the barrel periodically, or fashioning a barrel out of a ceramic material. Since the steel barrel also needs to be covered with a heat moderating layer (like cob) in order to make it less dangerous to spend time around, I favor he ceramic idea if I can figure out how to make a reliable mix. This is why I'm so grateful to Karl for helping with this information.
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Post by Deleted on Apr 16, 2016 4:40:17 GMT -8
The mixtures of cement/lime with pozzolan will make just 1 part in the final mixture. The excess lime in portland cement makes it possible to replace a parts of it with pozzolan. A mixture of lime and pozzolan is known as roman cement.
Yes, one could powderize old bricks or other ceramic material.
Grog and wood ash are more reactive than natural pozzolans, thus a smaller amount can bind all the excess lime in portland cement.
The lye in wood ash is to weak for geopolymers, but it is possible to concentrate it. Look up soap making to find out how.
One should always mix by weight not volume.
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Post by stephenson1 on Apr 28, 2016 3:13:47 GMT -8
Hi again Karl.
I'm finally getting back to all this. I want to make sure I'm not missing something regarding wood ash. You mention that it also has pozzolanic properties. Can it then be used as grog in the cement type and geopolymer recipes? If so, it would be a very cheap source of materials, and globally available. I would expect that it's structure is rather weak when compared to ground brick, but perhaps that's not relevant.
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Post by Deleted on Apr 28, 2016 5:19:51 GMT -8
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Post by Deleted on Apr 28, 2016 6:43:50 GMT -8
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Post by stephenson1 on Apr 28, 2016 13:04:06 GMT -8
Man you have a lot of information Karl! What's your trade?
I take it then that the wood ash is a fair substitute for grog, perlite, vermiculite, or diatomaceous earth.
So a recipe for a high temperature refractory castable mix could be (By weight): 1 part- A 1 1/2 to 1 ratio mix of Portland cement to either grog, powdered perlite, powdered vermiculite, diatomaceous earth, or wood ash 1 part- Fireclay 1 part- Sand
Does that work?
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Post by Deleted on Apr 29, 2016 4:47:32 GMT -8
Two professional degrees in woodworking, each equivalent with a bachelor. The focus of one degree was interior design, which also requires profound knowledge of common building materials, heat and sound insulation and moisture protection. A third degree of a private school in mechanical engineering without state acknowledgment. Retired for almost 30 years due to a fatal disease.
I was always very inquisitive, pretty good in research for things of interest, and love experimenting. Often successful despite experts claimed it is impossible.
I have used similar mixtures with succes, but would opt for more fire clay. Waterglass with lye will make the mixture harder and more durable.
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Post by stephenson1 on Apr 30, 2016 4:14:29 GMT -8
Broad experience and natural curiosity about physical properties. It makes sense that your knowledge is extensive. I'm very sorry to hear about the illness though.
How much more clay would you add? And how much of what ratio of waterglasss to lye? I do have the better part of a gallon of liquid sodium silicate on hand. I expect I could get powdered lye in the form of drain cleaner locally.
My ultimate goal would be pourable/castable refractory so I could make some simple forms to cast a 3' tall cylinder with 2" walls and a diameter of about 30". Once cast, I'd put some ceramic fiber on top of the cylinder wall and top with a sheet of 1/4" steel cut to shape so I'd have a ceramic barrel with removable steel top.
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