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Post by sayvetz on Dec 4, 2014 16:08:09 GMT -8
Hello all!
Wondering if there are good/bad experiences to be shared with cast iron combustion chambers?
Or if there are desired experiments that have yet to be tested with them?
I have the great opportunity of helping with two cast iron pours a year, and am seriously considering making molds/castings for a combustion chamber. Particularly inspiring is the design of the cast refractory dragon stoves, which offer many interesting design ideas.
Next pour isn't until April or so, but I'll need to design/make patterns in the meantime and am accepting all suggestions.
Leif
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Post by DCish on Dec 4, 2014 21:11:10 GMT -8
Welcome!
As I understand it, cast iron likes to suck up and to a degree store heat. In typical rocket construction the combustion area is targeted to be as insulated as possible to achieve and sustain high temperatures (and thus efficient combustion) as quickly as possible. And then there is Satamax and his favorite comment on the role of metal in rocket stove combustion areas...
There could be some fun uses for cast iron in the heat harvest portion of things, though, I would think.
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Post by satamax on Dec 4, 2014 21:30:51 GMT -8
Ok, first, metal is doomed!  But cast iron, poured thick enough, could survive may be 2 heating seasons! Make it in several parts, not two halves i'd say, so it can expand and contract. And insulate the hell out of it. So it doesn't ditch all the heat it gathers. What would be intresting is to see when the whole burn tunnel and heat riser are red, or even orange, if they help in the gases reburn more than an usual heat riser! |
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Post by sayvetz on Dec 5, 2014 7:27:52 GMT -8
Fully agree on the thermal properties issue. Cast iron has a (relatively) very high conductivity, though lower than wrought iron or steel, which is why it was used for radiators for so long. This makes the most difference early in the burn and lengthens the time approaching max efficiency. However, it would hold the heat for later firings just due to its mass.
The goal I was hoping to achieve was durability. I understand steels have very limited life-span in these environments, but I believe cast-iron is much more stable as its metalurgic properties are more glass like and its melting point is something like 1000F degrees higher than most steels.
I appreciate the idea of multi-part. I've run into that issue before definitely.
I also have the ability to make cast refractory at the foundry, but I feel it would have to be replaced often considering its (usually) fragile nature. Do the dragon chambers have fibers (fiberglass or other) or other strengthening additives?
The cupola we melt iron with has a pyrolysis zone of something around 3500F and we have to resurface or replace much of the refractory parts every time we use it. That's the only reason I didn't jump at the idea of a refractory chamber.
The hybrid idea would be to have an oversized casting with a refractory liner, but that may bring the worst of both worlds rather than the best.
Thanks for helping me think through this
L
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Post by matthewwalker on Dec 5, 2014 9:16:38 GMT -8
I don't know if Sandy(Dragon Heaters) uses tensile reinforcement in her castings, but stainless needles is what is typically used in that application. They work well, although as you know, refractory will not hold up indefinitely in these wide cycles. My preference is refractory in the burn zones, with a sealing surround so the inevitable cracks don't matter. I don't think the CI is going to add much to the overall build, although you could do a beautiful "container" for the whole works. Inside, it could work but it's not ideal and will eventually suffer the same fate as the refractory parts, with (probably) lower performance on the way there. Just some thoughts, it's fun to think about. That's a material most of us don't have access to, so it will be cool to see what you come up with regardless.
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Post by peterberg on Dec 5, 2014 9:17:01 GMT -8
I also have the ability to make cast refractory at the foundry, but I feel it would have to be replaced often considering its (usually) fragile nature. Do the dragon chambers have fibers (fiberglass or other) or other strengthening additives? Not as far as I know of. There're using a commercial available refractory castable with a relatively high working temperature. The 3500 F you mention for the pyrolysis zone is insanely high for a rocket heater. Normally those could have working temperatures from 1000 to 1200 C, 1830 to 2190 F. A refractory with specs of up to 2300 F is just fine for this application and will last for many years. The hybrid idea would be to have an oversized casting with a refractory liner, but that may bring the worst of both worlds rather than the best. Actually, I think that would be a very nice idea. The outside of the casting need to be insulated though. |
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Post by sayvetz on Dec 5, 2014 12:35:23 GMT -8
Going back over the numbers, I was off base about the melting points, don't know how I got that fouled up. So my high-fallutin' ideas about heat durability compared to steels are likely all wrong since some equations describing heat damage can be roughly based on functions of the ratio of temperature and melting point.
Maybe I'll just leave cast iron to doors...
or perhaps a custom lid for the heat exchanger?
ports for pots/pans like the old wood-ranges,
or convexity/concavity to influence the air flow?
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Post by DCish on Dec 5, 2014 14:43:56 GMT -8
Once you get to the heat exchange metal has a good track record... The burn is over by then, and lots of folks have cook tops, steel barrels, etc as radiators that have good long lives.
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gjh42
Junior Member
Posts: 61 
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Post by gjh42 on Dec 6, 2014 20:58:40 GMT -8
You could make some really pretty cast iron parts to substitute for the barrel. It is a common complaint that the exposed barrel is ugly. A mold to make parts in four or five sections, maybe doubled vertically, with nice decoration would be popular. Even if you couldn't reasonably make them for sale, you could have a strikingly unique heater for yourself.
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Post by PNW Dave on Dec 7, 2014 3:04:00 GMT -8
...perhaps a custom lid for the heat exchanger? ports for pots/pans like the old wood-ranges, or convexity/concavity to influence the air flow? I think this is a great idea, a custom cast iron barrel-topper. I'll take one for a 55 gal barrel, with an 8" port in the middle and these attachments please! 1) Flat port cover 2) 2" deep port "plug" 3a) 5" port sleeve 3b) 2" port sleeve (not pictured) #4) hot plate Shown in the pic below is my concept for my RMH in progress. Shown in green are the attachments and a second barrel placed over the regular heat exchanger barrel. 1) a startup bypass allowing exhaust to exit between the two barrels straight to the chimney 2) blocks the bypass for normal bench heating operation 3a) blocks both the barrels, essentially a heat riser extension through the barrels (for use with a custom pizza oven with its own chimney) 3b) blocks the bypass path but allows bench heating access (see #4). 4) basically a cast iron skillet set upside down, it sits over #3b so the underside is in direct contact with hot gasses before they go to the bench. Can cook directly on the hot plate or use pots/pans on it.  Of course this is still just a concept and I'll have to test to see if it actually works as intended. I plan to make the parts "quick and dirty" out of metal for testing, then if it works I'd make the parts out of fireclay and fire them in my kiln, but cast iron would be awesome! I'm sure it would be a pretty expensive thing to have custom made though. Just wanted to throw the idea out there for other minds to play with. |
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Post by Daryl on Dec 7, 2014 4:22:02 GMT -8
Welcome! As I understand it, cast iron likes to suck up and to a degree store heat. Which in some ways isn't a bad thing, especially with stand alone mini stoves. |
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Post by Daryl on Dec 7, 2014 4:24:21 GMT -8
Next pour isn't until April or so, but I'll need to design/make patterns in the meantime and am accepting all suggestions. Good luck to you. I look forward to seeing your creations. |
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Post by sayvetz on Dec 7, 2014 14:51:08 GMT -8
Of course this is still just a concept and I'll have to test to see if it actually works as intended. I plan to make the parts "quick and dirty" out of metal for testing, then if it works I'd make the parts out of fireclay and fire them in my kiln, but cast iron would be awesome! I'm sure it would be a pretty expensive thing to have custom made though. Just wanted to throw the idea out there for other minds to play with. Well I've never been commissioned before for cast iron, would have no idea what would be fair pricing. I'm doing everything from breaking recycled iron into quarter-sized pieces with a sledge-hammer to pouring. Shipping prices would be awful. Half inch thickness would be a 50lb casting on a cuff calculation. An issue is that my molds are secondary to student work, so I can't make indeterminate amounts of castings, and my prep time in the studio is compressed into an Ohio trip where I'm also helping art students who aren't terribly knowledgeable about shop work (how to use a power drill, even). Those caveats aside, I'm open to the idea. www.youtube.com/watch?v=E2MMQK7IGcIThis is our fall 2013 pour. Don't know who chose the music. One thing I'm really interested in is experimenting with rocket ovens to melt metal. Wouldn't be a big deal with cooler metals, but cast iron would be a real challenge. Don't know what size chimney it would take to have enough forced air, or a hybrid design with a tuyere perhaps.(A professor at Bowling Green has melted iron with used cooking oil!) Then I would be able to process at home and more reasonably be commissioned for outside work. Pipe dreams... I'm mulling on your double barrel design, I'll wait until the rocks settle in my head (there are plenty of those!) before I comment... My first impression is intrigue. Do report if you follow through. As to another suggestion on cast iron heat exchanger, I wouldn't for myself. I enjoy the aesthetic of the barrels being a huge fan of upcycling. On a farm we're always making ad-hoc solutions out of what's available. I suggested cast iron caps largely for better cooking properties or if different geometries than a flat-top could offer design extensibility. |
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Post by sayvetz on Dec 7, 2014 16:42:29 GMT -8
Short answer to my own question. No. One can not melt iron usably with wood. Guess it's worth the pilgrimage to the devil-invoking coke fired cupola. Maybe I'll look into a forge using a rocket, that seems more reasonable.
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Post by satamax on Dec 7, 2014 23:37:38 GMT -8
Short answer to my own question. No. One can not melt iron usably with wood. Guess it's worth the pilgrimage to the devil-invoking coke fired cupola. Maybe I'll look into a forge using a rocket, that seems more reasonable. Theoreticaly it could be possible with forced air. donkey32.proboards.com/thread/998/squeezing-last-degrees |
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