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Post by pinhead on Jan 7, 2013 7:00:11 GMT -8
Pics???
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Post by pinhead on Jan 7, 2013 6:47:28 GMT -8
Yes; the clay is dry and the cement comes in a "dough." You have to add water to make it pliable and mixable. You have to work pretty quickly, though, because the cement will try to harden. I didn't add enough water to make it runny; just wanted enough to make sure all of the vermiculite can be evenly mixed in. Once it's all mixed together, you have to pack it into the forms, being careful not to leave any voids.
Conversely you could add enough water to make the cement/clay a "slip" and add in the vermiculite in order to "pour" the mixture into your forms. I believe this is how Petersburg does it but I have no experience.
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Post by pinhead on Jan 5, 2013 16:12:37 GMT -8
Build the "core" with fireclay, vermiculite, and stove cement. When the metal burns out, the strong cement core will still remain, giving you a long service life. Don't even worry about the metal burn out; no matter what you do, if you have a good-running rocket the metal will burn out. What type of mixture ratios do you use? vermiculite:fireclay:cement 4:1:1 by volume for the "core" Mine is about an inch thick, between a 6-inch stovepipe and an 8-inch stovepipe. You could probably go heavier on the clay and lighter on the cement, but that's what worked for me. Then insulate around the core with fireclay/vermiculite/perlite/ash, or with whatever homemade mixture that works for you.
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Post by pinhead on Jan 5, 2013 16:03:00 GMT -8
Built correctly, a RMH poses virtually 0 "chimney fire" risk; 99% of the creosote is burned within the burn tunnel and heat riser -- this is one of the big reasons a RMH is so fuel efficient.
The only time I've ever encountered "buildup" within my RMH is after I tried to burn used motor oil (other than some slight ash accumulation).
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Post by pinhead on Jan 5, 2013 15:55:32 GMT -8
I believe it would be at the roof of the burn tunnel, next to the base of the heat riser.
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Post by pinhead on Jan 4, 2013 18:04:09 GMT -8
Build the "core" with fireclay, vermiculite, and stove cement. When the metal burns out, the strong cement core will still remain, giving you a long service life. Don't even worry about the metal burn out; no matter what you do, if you have a good-running rocket the metal will burn out.
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Post by pinhead on Dec 16, 2012 21:56:48 GMT -8
Search the forums for for "Peter channel." Been done. Makes a huge difference if done correctly.
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Post by pinhead on Dec 14, 2012 14:18:47 GMT -8
Permamax, that's how I built mine at first. Worked really well until the inside core burned out and spilled the insulation all over the place.
I replaced the insulation (vermiculite in my case) with a mixture of furnace cement and vermiculite and re-cast the same configuration (6" chimney T inside an 8" chimney T). This didn't insulate quite as well by itself but makes the core extremely robust. I then insulated around that core. This gives the best of both worlds: Extremely good insulation and an extremely strong core. The 6" T has burned out but the furnace cement is still there, holding it's shape. I suspect the 8" T will probably last as long as the furnace cement (which, after 3 years of use is showing NO signs of degradation - no cracks, no missing chunks, etc.
[EDIT]: SORRY!!! I was confused!
The "cores" I am referring to were metal cores such as would be used for the chimney on a propane heating appliance - propane stove or water heater. NOT the clay cores you're using! [/EDIT]
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Post by pinhead on Dec 14, 2012 6:53:07 GMT -8
I've done experiments trying to feed long fuel (2x4's, etc). The only way I've been able to make it work is with a much taller heat riser than normal which allows for a taller feed tube.
My heat riser is about 5 feet tall feeding into two barrels, one on top of the other - with the heat riser stopping at about the middle of the second barrel. I just added a Peter channel which makes the system draw much better, allowing for a tall(er) feed tube.
The tall feed tube has to be shorter than the heat riser and the same size or a bit smaller - you need high air velocity to help cool the fuel and suck all of the smoke and flames down.
The fuel can only stick out of the top of the feed if you're sure the fuel will burn down before the flames get high enough to counter the heat riser's draft. Finding the right height is mostly a trial-and-error proposition.
It won't burn quite as cleanly as a "normal" RMH in this configuration, though, since the large amount of fuel has a tendency to "overload" the rocket - there is a LOT more fuel being burned with the same amount of draft - and some of the heat will be dissipated through the walls of your tall feed tube which CANNOT be insulated.
In my case, I haven't yet finished the mass so I probably need to burn more fuel as-is to stay warm in my extremely drafty shop when compared to a completed RMH. A warm mass should also help support stronger draft.
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Post by pinhead on Dec 13, 2012 10:41:02 GMT -8
I've used two mixes that are surprisingly strong and hard.
Ash, Clay, Sand, 2:1:1 - Clay and sand sourced by hand.
and
Stove cement and vermiculite, unknown ratio -- I mixed by look/feel/consistency and cast it a couple of years ago but I do remember that I used a LOT of vermiculite compared to the cement... I'd guess a 10:1 vermiculite:cement ratio by volume. Doesn't really mean much, though, since the vermiculite is very compressible.
The ash-clay-sand isn't quite as strong as the cement mixture but holds up well to heat and abrasion. Neither mixture shrunk any measurable amount, strangely, and neither have cracked at all. The ash-clay I've only been using for a couple of weeks but I've been using the cement-vermiculite "core" for about 3 years now.
The ash-clay-sand was actually packed into the RMH core and immediately "cooked" without drying. There are no gaps between the ash-clay "plug" and the housing (all the way around), and there are no cracks in it. I was actually really surprised.
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Post by pinhead on Dec 10, 2012 12:59:12 GMT -8
In other words,
For the P-channel to work optimally, the air entering the throat of the burn tunnel through the P-channel needs to be preheated.
Correct?
BTW, is your skp model drawn to scale?
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Post by pinhead on Dec 10, 2012 11:25:50 GMT -8
I modified your Sketchup file to show what I mean... Attachments:
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Post by pinhead on Dec 10, 2012 10:52:01 GMT -8
I've also got a question about the P-channel, specifically with regards to the design in your "ugly" prototype.
How long do you suppose the P-channel would last if it were made of, say, 1/8th inch mild steel?
But would it perform better if it were made out of some type of insulative material?
If it were integrally cast into the burn box it would have to be pretty thick... If it were, say, 2" thick -- in other words, a two-inch-thick overhang -- do you suppose it would perform the same function? I suppose this would have the same effect as moving the P-channel further into the burn tunnel.
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Post by pinhead on Dec 10, 2012 7:49:08 GMT -8
Only one pic per post? And a 1024k limit? I guess I'll upload them elsewhere and link here.
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Post by pinhead on Dec 7, 2012 12:56:20 GMT -8
Updates?
Petersburg: Where can I find a sketch of your latest and greatest design?
And satamax, how's your contraption running?
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