Mondloch on wed 13 nov 02
Hi Heather,
I have a similar kiln and invested in a Fluke double probe pyrometer to help
me figure out what the heck I was doing- put one probe near the floor in
front and the other near the top in back. I can now tell immediately where
the heat is going when I fool with
the damper and burners. Great learning tool.
Sylvia
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
HotArt@silvercreekpottery.com
http://www.silvercreekpottery.com
Heather wrote:
I am having problems evening out the temperature in my kiln also.
about the kiln: It is a gas kiln fueled by propane. The kiln has two forces
air burners (MB500) in the back with a salt port above each burner. It is 54
Cubic Feet. The inside dimensions are 54 x 31.5 x 55. The kiln is hard brick
with soft brick on the outside. I fire in around 16 hrs to cone 10 down
problem: the middle is hot and nicely reduced, top a cone or two cooler and
a little less reduced, the bottom cold and no reduction, and the back cooler
than the front by one and 1/2 cones.
things I have done to date to fix the problem: read everything I can get my
hand on, tried to stack tighter in the middle, opened the bagwall, this load
I lowered the bagwall (we will see how this works tomorrow), I put a brick
in the middle of the flue exit, moved the shelves closer to the back, kept
great firing logs, and tried to change my firing methods with damper
adjustments and air adjustments at the burner
questions:
I have mostly 12 x 24" shelves, but I do have four 13 x 26" shelves also. I
only use the bigger shelves if I have a lot of flat items and need more
shelves, where is the best placement for the larger shelves in the kiln?
Top, Middle, or Bottom?
someone suggested that my problem was I didn't have enough back pressure at
the bottom. During my next firing I found this to be true. How do fix this
problem? I would think by pushing in the damper but this does not seem to
help. What else can be done?
I also have this weird problem on the floor of the kiln of pots looking
burnt and not much reduction on the bottom. How can I fix this? The shelf
post on the bottom seem to melt but the cones do not fall at all and the
glazes are under fired. What's up?
If you made it this far in the post, thank you
any help would be greatly appreciated!
Heather D. Bosworth
Coastal Clay Co
confused but still trying to control this kiln in finally cooler but wet St.
Helena Island, SC
TypicalGirl on mon 21 jun 04
Hello there everyone,=20
Some time back I bought a non-functioning electric kiln, with 4 sets of =
shelves for $100. Its an octagonal kiln, who's inside dimentions are =
about 18" wide and 30" deep.
I bought a gas (propane) conversion kit, that has 2 burners and turned =
it into a reduction, updraft kiln and fired it up last week.
The first problem was that after adding refractory fiber to the kiln =
walls, the shelves fit so snugly that they effectively sealed the heat =
and flame at the bottom of the kiln.
I cut 3 sets of shelves down a bit, and fired some test tiles on the =
middle shelf with some OK results, getting to about 2200 farenheit.
I decided to fire test pieces in a full kiln load and ended up with 3 =
levels of shelves.
The results were *really* uneven, top to bottom and on either side of =
the kiln.
The stuff on the right side of the kiln fired pretty well, though the =
items on the top shelf were a little under-fired.
The items on the left side of the kiln varied dramatically. The bowl on =
the bottom left of the kiln was so hot that the clay body, which has =
lots of iron in it, actually came out with huge blisters in the body =
itself.
The items on the middle left shelf were pretty good, and the item on the =
upper left shelf was very underfired and the glaze had lots of pinholes.
I didn't have a cone pack in the kiln (would you believe a goat ate the =
last of my cones???) but I had my pyrometer at the top of the kiln.
I could not get the top of the kiln above 2100 farenheit, but the lower =
part of the kiln was obviously much hotter.
I tried a variety of flue configurations, but just couldn't seem to get =
the top any hotter.
I am suspecting that my kiln shelves are still not allowing enough air =
circulation around the entire kiln, especially on the left side.
So here's my idea...
Because I have a small kiln and space is precious, I am hesitant to keep =
paring down my shelves.
Would it be a reasonable alternative to drill a seriers of holes in the =
kiln shelves to create more even heat distribution?
Thanks!
Cathi Newlin, Mercer, Mo
mudpuppy@box49.com
http://www.box49.com
Steve Mills on wed 23 jun 04
Dear Cathi,
I have done a fair bit of exploring updraft drum shaped kilns and I
offer these thoughts:
Commercially these kilns are offered with burners that point upwards,
largely I suspect because they are easier to ship in that configuration.
The best set-up I have found is to have the burner(s) coming into the
side of the kiln so that the fire circulates (upwards).
The best shape for a kiln shelf in my experience is square!! if used
with burners in the above configuration, the circulating fire is able to
move easily upwards AND at the same time the shelf corners deflect some
of the heat into the centres eliminating cold spots.
Finally I have a slot in the lid rather than a round hole. With the
latter the (still) circulating fire arriving at the top forms a cone
shape and exits too easily leaving a very cool area at the top. With a
slot, the fire has to change direction substantially so the slot becomes
a passive baffle retaining much of the heat that would otherwise be
lost. Also with a slot it is possible and easier to control the
atmosphere and the speed of the firing, which helps to conserve fuel.
With a Kiln set up as above, I have regularly fired in reduction to cone
9 at the top and effectively 9 and a half at the bottom. In a Kiln just
over three cubic feet in capacity I got three and a half nine hour
reduction firings out of a thirteen Kg bottle of high pressure propane.
There is a leaflet on this sort of kiln on the Bath Potters website
Steve
Bath
UK
In message , TypicalGirl writes
>Hello there everyone,=3D20
>Some time back I bought a non-functioning electric kiln, with 4 sets of =3D
>shelves for $100. Its an octagonal kiln, who's inside dimentions are =3D
>about 18" wide and 30" deep.
>
>I bought a gas (propane) conversion kit, that has 2 burners and turned =3D
>it into a reduction, updraft kiln and fired it up last week.
>The first problem was that after adding refractory fiber to the kiln =3D
>walls, the shelves fit so snugly that they effectively sealed the heat =3D
>and flame at the bottom of the kiln.
>I cut 3 sets of shelves down a bit, and fired some test tiles on the =3D
>middle shelf with some OK results, getting to about 2200 farenheit.
>
>I decided to fire test pieces in a full kiln load and ended up with 3 =3D
>levels of shelves.
>The results were *really* uneven, top to bottom and on either side of =3D
>the kiln.
>The stuff on the right side of the kiln fired pretty well, though the =3D
>items on the top shelf were a little under-fired.
>The items on the left side of the kiln varied dramatically. The bowl on =3D
>the bottom left of the kiln was so hot that the clay body, which has =3D
>lots of iron in it, actually came out with huge blisters in the body =3D
>itself.
>The items on the middle left shelf were pretty good, and the item on the =
>=3D
>upper left shelf was very underfired and the glaze had lots of pinholes.
>
>I didn't have a cone pack in the kiln (would you believe a goat ate the =3D
>last of my cones???) but I had my pyrometer at the top of the kiln.
>I could not get the top of the kiln above 2100 farenheit, but the lower =3D
>part of the kiln was obviously much hotter.
>I tried a variety of flue configurations, but just couldn't seem to get =3D
>the top any hotter.
>
>I am suspecting that my kiln shelves are still not allowing enough air =3D
>circulation around the entire kiln, especially on the left side.
>
>So here's my idea...
>Because I have a small kiln and space is precious, I am hesitant to keep =
>=3D
>paring down my shelves.
>Would it be a reasonable alternative to drill a seriers of holes in the =3D
>kiln shelves to create more even heat distribution?
>
>Thanks!
>
>Cathi Newlin, Mercer, Mo
>mudpuppy@box49.com
>http://www.box49.com
--
Steve Mills
Bath
UK
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