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Hi all-
We used the great fornobravo plans to build a 40 inch oven with firebrick. Our stonemason, who has done such wonderful work for so many years for us, said that he'd use the plans and had a lot of experience to create a masterpiece - especially because back in his village when younger and since, he said he'd built a whole bunch of hornos.
We referred to the plans and he got going. I was around a lot; building is not my skill set, so I acted as his laborer with cement and such. I checked in with him periodically, twice asking if it was really ok that his dome was significantly vertically steeper and higher (like a high beehive) than the plans showed in the pictures. I mean, he made it peaked inside at 30 inches high inside the dome. Forward of that we didn't just do a door; he built a tunnel 15 inches high, 20 inches wide, and about 20 inches long from oven floor to door, and a hinged fabricated steel door 1/4 inch thick that swings outward, hinge attached directly to the front face. For the distance from the dome floor to the door through the tunnel, there's an arch that is 18 inches high and at it's peak is an 8 inch hole that goes up to the chimney. Addition: later in the process for some reason I do not know, he did not attach the door hinges directly to the face but instead had me go back to the fabricator to weld a rod through them such that it would swing on a small friction point at the base, down inside a pipe to be included in the outside door cooling shelf area. I do not know why, but when it came time that he installed the door, he then had to build a brick structure on the top end into which to put the pipe that protruded upward from the door instead of attaching it to the wall as planned. It is a bit crooked in brick-laying, sticks out on one side of the oven front, and we have since had to hire a metal fabricator to come out and face it and it's opposite side in symmetry to disappear that.
Bottom line is that it seems to take 4 hours and 1/5 cord of split oak (by my IR gun) to read 500 at the dome peak (not white, yellow, red or any other color but slightly soot black up there) while the floor pushes 250 to 300 max. I was able to get 500 on the floor once, but that was 5 hours firing and a TON of wood. *Help*!! Can someone help about this??
Ok, 3 things to look at which have so far been suggested by people we've had look at it:
1. Lower the dome inside say, 8 inches? Options we've thought of include bolting a round or octagonal ceramics kiln refractory shelf up there, stuff some hi-temp kiln insulation blanket material (or pump some castable refractory) up behind it. Not a good idea, as with heat and flexion we would be breathing exiting fibers. Another was castible refractory material to fill the void behind it. Similar concerns; we do not know what might escape to be breathed while tending the oven. Still looking or material ideas there. That (would) reflect heat down mostly, not absorb too much. It's surface would be flat, not domed, but then that's not really that much interruption of the dome up there. Heat (would) come up to it for reflection from the heat absorbing walls, so that might work? Other ideas on that?
2. Curing:
I had not yet found this forum, so I didn't know to do slow firings gradually. He advised us to wait 2 weeks, then light up a big curing fire... Good news is that I did, and there was only a little cracking on the top of the dome; not worried about that. But man was there ever moisture blowing out of that brick in the front face while that thing was going. Steaming, even weeping water. Uh-oh I thought, this oven could blow or crack, but it was fine. *Then* I found these forums, and now 2 weeks later, learned to slow fire. Just to be sure, I have done the successive firings as I have found suggested reading in other areas. But again, it takes quite the fire even to get 200 floor when it's 500 above. FYI, at current proportions, the base of the smoke layer over incoming air through the door is about 12 inches high off the floor, which over a reasonable fire of say 3 pieces of split wood, the smoke layer sits about 5 inches above it.
*If* we close the door (it has 1/4 inch air leakage all four edges when closed) but leave the chimney open, there may be slightly more heat, but only 30 degrees or so. If we put a piece of sheet metal on top of the chimney to completely close it and let the door do *all* air/exhaust exchange, the smoke stays at same levels but looks richer of course coming out the top of the door, but again it still doesn't seem to affect the temp really.
So. (I) - not an engineer's mind - think that we've just got a lot of heat rising too far up, and bouncing around the high dome peak, and then exiting with smoke where it should have instead have heat-saturated a lower dome that would then be blasting it's head straight down into the floor.
Can someone please help on engineering insight here?
Thanks so much!
We used the great fornobravo plans to build a 40 inch oven with firebrick. Our stonemason, who has done such wonderful work for so many years for us, said that he'd use the plans and had a lot of experience to create a masterpiece - especially because back in his village when younger and since, he said he'd built a whole bunch of hornos.
We referred to the plans and he got going. I was around a lot; building is not my skill set, so I acted as his laborer with cement and such. I checked in with him periodically, twice asking if it was really ok that his dome was significantly vertically steeper and higher (like a high beehive) than the plans showed in the pictures. I mean, he made it peaked inside at 30 inches high inside the dome. Forward of that we didn't just do a door; he built a tunnel 15 inches high, 20 inches wide, and about 20 inches long from oven floor to door, and a hinged fabricated steel door 1/4 inch thick that swings outward, hinge attached directly to the front face. For the distance from the dome floor to the door through the tunnel, there's an arch that is 18 inches high and at it's peak is an 8 inch hole that goes up to the chimney. Addition: later in the process for some reason I do not know, he did not attach the door hinges directly to the face but instead had me go back to the fabricator to weld a rod through them such that it would swing on a small friction point at the base, down inside a pipe to be included in the outside door cooling shelf area. I do not know why, but when it came time that he installed the door, he then had to build a brick structure on the top end into which to put the pipe that protruded upward from the door instead of attaching it to the wall as planned. It is a bit crooked in brick-laying, sticks out on one side of the oven front, and we have since had to hire a metal fabricator to come out and face it and it's opposite side in symmetry to disappear that.
Bottom line is that it seems to take 4 hours and 1/5 cord of split oak (by my IR gun) to read 500 at the dome peak (not white, yellow, red or any other color but slightly soot black up there) while the floor pushes 250 to 300 max. I was able to get 500 on the floor once, but that was 5 hours firing and a TON of wood. *Help*!! Can someone help about this??
Ok, 3 things to look at which have so far been suggested by people we've had look at it:
1. Lower the dome inside say, 8 inches? Options we've thought of include bolting a round or octagonal ceramics kiln refractory shelf up there, stuff some hi-temp kiln insulation blanket material (or pump some castable refractory) up behind it. Not a good idea, as with heat and flexion we would be breathing exiting fibers. Another was castible refractory material to fill the void behind it. Similar concerns; we do not know what might escape to be breathed while tending the oven. Still looking or material ideas there. That (would) reflect heat down mostly, not absorb too much. It's surface would be flat, not domed, but then that's not really that much interruption of the dome up there. Heat (would) come up to it for reflection from the heat absorbing walls, so that might work? Other ideas on that?
2. Curing:
I had not yet found this forum, so I didn't know to do slow firings gradually. He advised us to wait 2 weeks, then light up a big curing fire... Good news is that I did, and there was only a little cracking on the top of the dome; not worried about that. But man was there ever moisture blowing out of that brick in the front face while that thing was going. Steaming, even weeping water. Uh-oh I thought, this oven could blow or crack, but it was fine. *Then* I found these forums, and now 2 weeks later, learned to slow fire. Just to be sure, I have done the successive firings as I have found suggested reading in other areas. But again, it takes quite the fire even to get 200 floor when it's 500 above. FYI, at current proportions, the base of the smoke layer over incoming air through the door is about 12 inches high off the floor, which over a reasonable fire of say 3 pieces of split wood, the smoke layer sits about 5 inches above it.
*If* we close the door (it has 1/4 inch air leakage all four edges when closed) but leave the chimney open, there may be slightly more heat, but only 30 degrees or so. If we put a piece of sheet metal on top of the chimney to completely close it and let the door do *all* air/exhaust exchange, the smoke stays at same levels but looks richer of course coming out the top of the door, but again it still doesn't seem to affect the temp really.
So. (I) - not an engineer's mind - think that we've just got a lot of heat rising too far up, and bouncing around the high dome peak, and then exiting with smoke where it should have instead have heat-saturated a lower dome that would then be blasting it's head straight down into the floor.
Can someone please help on engineering insight here?
Thanks so much!
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