...while I'm out of the country at Smeltfest.
Monday, March 28, 2011
Friday, March 25, 2011
Heat under AFRICA
This is the third of my short overviews of the activites at Smeltfest with other members of the North American Iron Undergound. Note to readers : I’m reporting on events several days in the past at this point.
Work on Tuesday started with preparing the large African prototype furnace for firing.
This is the interior of the furnace, showing the set of the individual tuyeres, with four set in each of the four arch quadrants. The slag pit below the furnace has been filled with short lengths of green branches, each about 15 inched long.
This is the same shot, with the bed of the furnace established. A thin mat of broken straw covers over the stick ends, topped with a thin layer (about 1 cm) of charcoal fines. Its fully expected that the ignited charcoal will establish its own working level. The layers seen function to keep smaller pieces of burning charcoal from falling straight down between the sticks into the pit.*At this point the first layer of clay tuyeres have been installed into the open arch. The initial spit wood fire has been started. Next the remaining gap will be filled with a loose high sand and rough clay mix to seal the base of the furnace completely.
At that point, the furnace was charged with small pieces of dry wood. About enoung to fill a standard garbage pail had been pre-split into roughly 1 x 1 x 10 - 15 cm long splits. On top of that material was added larger flat pieces mostly the same length.perhaps twice again as much material.
The heat created operated the furnace like a big charcoal retort at this phase, resulting in considerable smoke from the stack. This certainly indicated that the tuyeres were in fact drawing enough air to produce a significant natural draft. Jeff figured it was more than time enough to ignited the exhaust gasses, touching these off with burning paper at the lower charge door. The effect was quite dramatic...(The handle for this can be seen in the bottom of the pipe in the image above.)
Once that wood fuel was obviously fully ignited, rough charcoal was added to fill the lower chamber. Of course some of the wood had burned away by that point. It took about two 40 lb sacks of charcoal to fill to the ‘neck’ where the shaft starts. Jake Keen, the smelt master for this experiment, is seen adding charcoal via the charge door in the image above
The charging cycle of 5 lbs of charcoal and 5 lbs of roasted and crushed Lexington rock ore was started almost imediately after.
The furnace would settle down to a fairly uniform consumption rate of 5 ore plus 5 charcoal roughly every 10 - 15 minutes. Of course there would be variations on this! Twice the furnace almost stalled out, with internal temperatures obviously dropping and consumption greatly increasing. With a total of 200 lbs of prepared ore on hand, many long hours of furnace tending were expected. The initial fire had started about 2 pm on Tuesday, it was fully expected to take 24 - 36 hours to run the complete smelting cycle.
One effect that came to be relied on is seen above. As each individual charge was fully ignited inside the furnace, the stainless steel stack pipe would start to glow a dull orange to red along its whole length. (The image above is hand held at about a half second exposure.)
I personally ran out of juice by about midnight Tuesday. I set my alarm for 4 AM and grabbed some sleep. Various others retired at other points. When I got back to the site. Jesus Hernandez, Dick Sargent, Lee Sauder and of course Jake Keen where the only ones still functioning.
The last charge was made about 5:30 AM, so roughly 14 1/2 hours after starting. It was agreed that many hours would be still be required until the ore already involved would burn down to tuyere level. We all went back (or to!) bed....
(next entry : opening the furnace)
Work on Tuesday started with preparing the large African prototype furnace for firing.
This is the interior of the furnace, showing the set of the individual tuyeres, with four set in each of the four arch quadrants. The slag pit below the furnace has been filled with short lengths of green branches, each about 15 inched long.
This is the same shot, with the bed of the furnace established. A thin mat of broken straw covers over the stick ends, topped with a thin layer (about 1 cm) of charcoal fines. Its fully expected that the ignited charcoal will establish its own working level. The layers seen function to keep smaller pieces of burning charcoal from falling straight down between the sticks into the pit.*At this point the first layer of clay tuyeres have been installed into the open arch. The initial spit wood fire has been started. Next the remaining gap will be filled with a loose high sand and rough clay mix to seal the base of the furnace completely.At that point, the furnace was charged with small pieces of dry wood. About enoung to fill a standard garbage pail had been pre-split into roughly 1 x 1 x 10 - 15 cm long splits. On top of that material was added larger flat pieces mostly the same length.perhaps twice again as much material.
The heat created operated the furnace like a big charcoal retort at this phase, resulting in considerable smoke from the stack. This certainly indicated that the tuyeres were in fact drawing enough air to produce a significant natural draft. Jeff figured it was more than time enough to ignited the exhaust gasses, touching these off with burning paper at the lower charge door. The effect was quite dramatic...(The handle for this can be seen in the bottom of the pipe in the image above.)
Once that wood fuel was obviously fully ignited, rough charcoal was added to fill the lower chamber. Of course some of the wood had burned away by that point. It took about two 40 lb sacks of charcoal to fill to the ‘neck’ where the shaft starts. Jake Keen, the smelt master for this experiment, is seen adding charcoal via the charge door in the image aboveThe charging cycle of 5 lbs of charcoal and 5 lbs of roasted and crushed Lexington rock ore was started almost imediately after.
The furnace would settle down to a fairly uniform consumption rate of 5 ore plus 5 charcoal roughly every 10 - 15 minutes. Of course there would be variations on this! Twice the furnace almost stalled out, with internal temperatures obviously dropping and consumption greatly increasing. With a total of 200 lbs of prepared ore on hand, many long hours of furnace tending were expected. The initial fire had started about 2 pm on Tuesday, it was fully expected to take 24 - 36 hours to run the complete smelting cycle.One effect that came to be relied on is seen above. As each individual charge was fully ignited inside the furnace, the stainless steel stack pipe would start to glow a dull orange to red along its whole length. (The image above is hand held at about a half second exposure.)
I personally ran out of juice by about midnight Tuesday. I set my alarm for 4 AM and grabbed some sleep. Various others retired at other points. When I got back to the site. Jesus Hernandez, Dick Sargent, Lee Sauder and of course Jake Keen where the only ones still functioning.
The last charge was made about 5:30 AM, so roughly 14 1/2 hours after starting. It was agreed that many hours would be still be required until the ore already involved would burn down to tuyere level. We all went back (or to!) bed....
(next entry : opening the furnace)
Tuesday, March 22, 2011
SMELTFEST 11 - African part 2
This is the second report on doings at the annual SMELTFEST intensive at Lee Sauder's shop in Lexington Virginia.
Work has been progressing on the African prototype passive draw smelting furnace:
This is the furnace, part way through Jake Keen 'tarting it up'. The core structure here is seen as the gray colour clay. This is straw cobb, about 5 - 4 inches thick laid over a withy framework (see the last post). Next a cushion of straw, roughly 2 inches thick was applied. On top of that is a second clay layer, this dug straight out of the back behind Lee's workshop. Jake plans to extend this covering over the entire structural surface. The extraction slot I laboriously dug into the (mainly rock!) soil has been back filled with loose soil and small gravel (where Jake is kneeling).
Jake is seen here checking one of the clay tuyeres he has been making for rough fit. The plan is to have 16 of these, four for each of the quadrant arches. At this point the exact fit for these has not been established. Likely these will have a pronounced down angle, the tips placed close to the centre of the furnace.
As of last night the construction of the furnace is finished, and an increasingly large wood fire had been built in the interior. Later in the evening, the furnace was packed with stove wood pieces, metal plates put over the arches, and left to burn out over night.
Plan for today is to prepare the furnace for the full smelt series, hopefully to start about noon. The big unknown (for me) is if the interior will be cool enough to permit this work. (The interior chamber is just over 24 inches in diameter.) The lower pit is to be filled with vertically standing green sticks, cut to roughly 15 inches long. These will support the initial combustion, then the developing slag bowl. As more and increasingly fluid slag is produced, it will run down into the gaps between the sticks. Eventually the building mass of slag will slowly burn out the tops of the sticks allowing the block to sag into the pit. If all goes as its supposed to (??) this keeps the developing bloom at the ideal placement inside the furnace.
Wish us luck!
Work has been progressing on the African prototype passive draw smelting furnace:
This is the furnace, part way through Jake Keen 'tarting it up'. The core structure here is seen as the gray colour clay. This is straw cobb, about 5 - 4 inches thick laid over a withy framework (see the last post). Next a cushion of straw, roughly 2 inches thick was applied. On top of that is a second clay layer, this dug straight out of the back behind Lee's workshop. Jake plans to extend this covering over the entire structural surface. The extraction slot I laboriously dug into the (mainly rock!) soil has been back filled with loose soil and small gravel (where Jake is kneeling).
Jake is seen here checking one of the clay tuyeres he has been making for rough fit. The plan is to have 16 of these, four for each of the quadrant arches. At this point the exact fit for these has not been established. Likely these will have a pronounced down angle, the tips placed close to the centre of the furnace.
As of last night the construction of the furnace is finished, and an increasingly large wood fire had been built in the interior. Later in the evening, the furnace was packed with stove wood pieces, metal plates put over the arches, and left to burn out over night.
Plan for today is to prepare the furnace for the full smelt series, hopefully to start about noon. The big unknown (for me) is if the interior will be cool enough to permit this work. (The interior chamber is just over 24 inches in diameter.) The lower pit is to be filled with vertically standing green sticks, cut to roughly 15 inches long. These will support the initial combustion, then the developing slag bowl. As more and increasingly fluid slag is produced, it will run down into the gaps between the sticks. Eventually the building mass of slag will slowly burn out the tops of the sticks allowing the block to sag into the pit. If all goes as its supposed to (??) this keeps the developing bloom at the ideal placement inside the furnace.
Wish us luck!
Sunday, March 20, 2011
SMELTFEST 11 - initial doings
As some of my closer readers know, I'm away right now at Lee Sauder's shop in Lexington Virginia for the annual gathering of the North American Early Iron Underground. Here's a fast report...
One of several projects and investigations under way is the construction of an African styled passive draw furnace under the direction of Jake Keen*. (Jake seen in the image above.) It is a slag pit furnace, with a long trench off one quadrant, intended to drag out the eventual slag block. The core of the furnace is framed with saplings, we are using sections cut from an old water heater to frame the openings where the clay tuyeres will be inserted. Believe it or not, there are even MORE rocks in the 'soil' here at Geminal Ironworks than the ground in Wareham.
The construction of the furnace is clay cobb, mixed with chopped local plants (a wild variant of broom straw). Jake is inserting a layer of straw between the frame and the applied clay mix. This is to allow the clay to shrink without cracking (we hope) as it dries. My job at this point was applying a further 4 inch layer of clay like soil, another line of straw, then revetting with stone and back filling with earth. This is to support and keep the bottom 18 inches or slow from slumping.
This is the construction of the furnace as it was completed. You can see the dome of the furnace proper extending to the shaft. To speed construction, we have constructed a stainless steel pipe as chimney. A natural draft furnace needs a certain minimum height to create the air flow dynamic. (Our combined brains are a bit fuzzy on the details here, best guess is at least 6 feet of height is required.) Not seen in this image is a sliding hatch cut in that allows for feeding ore and charcoal at the bottom edge of the pipe. In Africa, likely some kind of scaffold would be used (??) to add new material.
This is a type of furnace that Jake, Lee and Mike McCarthy had seen as ruins in their recent trip to Africa. As partially buried furnaces, the lower construction is a matter of some guess work here. Of course the upper shafts were all erroded off, so the exact working height is unknown as well. Our stainless pipe extends at least 10 feet up, working on the theory that taller is better here.
Today Jake will start a gentle fire in the lower pit, attempting to slowly heat and dry the massive clay walls with out excessive cracking. Also for today will be making all the clay tuyeres. The plan is to start with four tubes for each of the four arches framed by the metal pipe.
* This is the famous ' Are you ... JAKE KEEN?! '
More to come...
One of several projects and investigations under way is the construction of an African styled passive draw furnace under the direction of Jake Keen*. (Jake seen in the image above.) It is a slag pit furnace, with a long trench off one quadrant, intended to drag out the eventual slag block. The core of the furnace is framed with saplings, we are using sections cut from an old water heater to frame the openings where the clay tuyeres will be inserted. Believe it or not, there are even MORE rocks in the 'soil' here at Geminal Ironworks than the ground in Wareham.
The construction of the furnace is clay cobb, mixed with chopped local plants (a wild variant of broom straw). Jake is inserting a layer of straw between the frame and the applied clay mix. This is to allow the clay to shrink without cracking (we hope) as it dries. My job at this point was applying a further 4 inch layer of clay like soil, another line of straw, then revetting with stone and back filling with earth. This is to support and keep the bottom 18 inches or slow from slumping.
This is the construction of the furnace as it was completed. You can see the dome of the furnace proper extending to the shaft. To speed construction, we have constructed a stainless steel pipe as chimney. A natural draft furnace needs a certain minimum height to create the air flow dynamic. (Our combined brains are a bit fuzzy on the details here, best guess is at least 6 feet of height is required.) Not seen in this image is a sliding hatch cut in that allows for feeding ore and charcoal at the bottom edge of the pipe. In Africa, likely some kind of scaffold would be used (??) to add new material.
This is a type of furnace that Jake, Lee and Mike McCarthy had seen as ruins in their recent trip to Africa. As partially buried furnaces, the lower construction is a matter of some guess work here. Of course the upper shafts were all erroded off, so the exact working height is unknown as well. Our stainless pipe extends at least 10 feet up, working on the theory that taller is better here.
Today Jake will start a gentle fire in the lower pit, attempting to slowly heat and dry the massive clay walls with out excessive cracking. Also for today will be making all the clay tuyeres. The plan is to start with four tubes for each of the four arches framed by the metal pipe.
* This is the famous ' Are you ... JAKE KEEN?! '
More to come...
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