J Lutz on tue 22 feb 05
I recently purchased a new Skutt 1027 kiln with an envirovent.
I had the impression that an envirovent would help create an even firing
atmosphere in the kiln. I also thought that by having a computer controller
with a thermocouple that I would more accurately reach the proper
temperature/time for the cone programmed.
I realize that I have a lot of issues here and would appreciate any
suggestions anyone would care to offer.
I'm in contact with Skutt but they have had change in personnel so I'm not
at the top of the priority list.The local distributor isn't much help.
I just want to know if these issues/problems are normal or not. It just
seems that for $2000 I should have a better kiln and firing experience that
I did with my old manual kiln.
This is the what has happened so far.
The first test firing was done per Skutt's recommendation. ^04 at medium
speed. The kiln was empty except for kiln shelves and witness cones. Per
Skutt the firing should have taken 71/2 hours. It took 8 hrs. 49
minutes. None of the 04 cones bent past 4 o'clock and that was only on the
second shelf. All the rest were only slightly bent. The bottom of the kiln
was the coldest.
The next firing - also empty except for kiln shelves and cones was fired to
^06 on medium speed. It took 8 hrs 28 min. The cones in the top and
bottom of the kiln were just about right on at 6 o'clock. However, the
cones on the 2 middle shelves were completely slumped.
Another firing at ^5 on slow with a load of glazed ware took about 12 hrs
34. min.
The cones at the top and bottom of the kiln were unchanged. The cones on
the 2 middle shelves were at 2 & 3 o'clock.
Conclusion is that the kiln is firing hotter in the middle but still not
going to temp. with ware in the kiln.
The lid (Lid Lifter) holds the lid open 1/4 inch. Even when I place a
cinder block on it during firing the left half of the lid still does not
come into contact with the kiln top.
The kiln rocks on the stand. Is it possible that the bottom of the kiln is
warped or that the kiln stand is not level? I'm not comfortable using a
wooden shim as was suggested. For that much money why should I have to
jerry rig it?
My specific questions are:
Can I expect the kiln to fire more evenly?
Can I expect the thermocouple to control the firing to match the cone?
Can the lid be adjusted to fit or does it need to be replaced?
I didn't expect to encounter problems of this type or I would have done
more research prior to purchase.
Needless to say I'm not a happy camper.
Jean Lutz
Prescott, AZ
Arnold Howard on wed 23 feb 05
----- Original Message -----
From: "J Lutz"
> I just want to know if these issues/problems are normal or not. It just
> seems that for $2000 I should have a better kiln and firing experience
> that
> I did with my old manual kiln.
>
>
> This is the what has happened so far.
>
> The first test firing was done per Skutt's recommendation. ^04 at medium
> speed. The kiln was empty except for kiln shelves and witness cones. Per
> Skutt the firing should have taken 71/2 hours. It took 8 hrs. 49
> minutes. None of the 04 cones bent past 4 o'clock and that was only on
> the
> second shelf. All the rest were only slightly bent. The bottom of the kiln
> was the coldest.
>
> The next firing - also empty except for kiln shelves and cones was fired
> to
> ^06 on medium speed. It took 8 hrs 28 min. The cones in the top and
> bottom of the kiln were just about right on at 6 o'clock. However, the
> cones on the 2 middle shelves were completely slumped.
>
> Another firing at ^5 on slow with a load of glazed ware took about 12 hrs
> 34. min.
> The cones at the top and bottom of the kiln were unchanged. The cones on
> the 2 middle shelves were at 2 & 3 o'clock.
>
> Conclusion is that the kiln is firing hotter in the middle but still not
> going to temp. with ware in the kiln.
>
> The lid (Lid Lifter) holds the lid open 1/4 inch. Even when I place a
> cinder block on it during firing the left half of the lid still does not
> come into contact with the kiln top.
>
> The kiln rocks on the stand. Is it possible that the bottom of the kiln is
> warped or that the kiln stand is not level? I'm not comfortable using a
> wooden shim as was suggested. For that much money why should I have to
> jerry rig it?
>
> My specific questions are:
> Can I expect the kiln to fire more evenly?
> Can I expect the thermocouple to control the firing to match the cone?
> Can the lid be adjusted to fit or does it need to be replaced?
Jean, since you are keeping firing records, you know how the controller
fires at each cone, so it should not be difficult to correct the firings.
This is how I would fire your kiln:
1) The center section fires hotter than the top and bottom. I would load
less ware in the top and bottom and more ware in the center. The greater the
load density, the more heat required. Glass artists use a similar technique.
They position cordierite scraps on sections of the kiln shelf that get too
hot. The pieces of cordierite absorb heat.
2) If the kiln is firing slightly too cool, add 10-15 minutes of hold time.
If it is firing too hot, recalibrate the thermocouple a few degrees.
3) I would also watch witness cones through a peephole until you are
satisfied with consistency of firing results. If the kiln shuts off but a
cone needs to bend a little farther, reprogram the kiln with added hold
time. Then turn the kiln back on. You should achieve greater accuracy with
each firing,
Since you are concerned about accuracy, you might also consider using an
S-type thermocouple instead of the K-type. A digital kiln is only as
accurate as its thermocouple. The platinum S-type thermocouple is more
expensive, but it lasts many times longer than the K-type. Tim Frederick,
who used to work at Orton, once told me that his S-type was 12 years old and
still going. Unlike the K-type, the S-type has virtually no temperature
drift.
The S-type is encased in a ceramic protection tube and very fragile,
however. You have to be careful not to bump it with a shelf.
When you set up your kiln, did you check your stand with a level? The kiln
must not rock. That could stress the firebricks.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
arnoldhoward@att.net / www.paragonweb.com
Mike Gordon on wed 23 feb 05
Jean,
Put a level on the lid in 2 - 3 different directions north south -
east / west & in between. Level it with shim shingles your floor may
not be level, I know mine isn't. There is nothing wrong with the stand,
they are made level, it is your floor. This may solve the lid not
sitting flat on the kiln. The lid lifter should not be holding the lid
up at all during firing. Period. Mike Gordon
On Feb 22, 2005, at 2:12 PM, J Lutz wrote:
> I recently purchased a new Skutt 1027 kiln with an envirovent.
>
> The lid (Lid Lifter) holds the lid open 1/4 inch. Even when I place a
> cinder block on it during firing the left half of the lid still does
> not
> come into contact with the kiln top.
>
> The kiln rocks on the stand. Is it possible that the bottom of the
> kiln is
> warped or that the kiln stand is not level? I'm not comfortable using
> a
> wooden shim as was suggested. For that much money why should I have to
> jerry rig it?
>
> Jean Lutz
> Prescott, AZ
>
> _______________________________________________________________________
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>
Susan Stannard on wed 23 feb 05
I also just recently purhased a new Skutt 1027-3 with an envirovent. It's
the first kiln I've ever owned, so I didn't know what to expect.
> The lid (Lid Lifter) holds the lid open 1/4 inch. Even when I place a
> cinder block on it during firing the left half of the lid still does not
> come into contact with the kiln top.
I have the identical problem, including the lid not quite down all the way,
even when weighted.
> Can I expect the kiln to fire more evenly?
In my first bisque firing, I fired on slow speed to cone 06 with a 20-minute
hold. It took slightly more than 12 hours. The cones in the lower half of
the kiln were at 5 and 6 o'clock (with the middle of the kiln the hottest),
but the cone on the top shelf was barely deformed.
For the glaze firing, I put another shelf at the very top of the kiln under
the holes in the lid. I fired to cone 5 with a 15-minute hold. It also took
a little over 12 hours. All the cones were at or near 6 o'clock. Although
the upper and lower areas of the kiln were still a bit cooler than the
middle shelves, the overall differential wasn't bad -- less than half a
cone.
The "capping" shelf definitely helped to even out the temperature in my
kiln.
william schran on thu 24 feb 05
Jean wrote:>Skutt the firing should have taken 71/2 hours. It took 8 hrs. 49
minutes. None of the 04 cones bent past 4 o'clock and that was only on the
second shelf..... The next firing - The cones in the top and
bottom of the kiln were just about right on at 6 o'clock. However, the
cones on the 2 middle shelves were completely slumped.<
Given the many variables involved, it would be difficult to determine
exactly what would cause uneven firing in a kiln. Position of the
kiln furniture could even be part of the cause. Are there 1, 2 or 3
thermocouples in this kiln? One in the middle would only read what's
going on in that zone.
Preprogrammed firing schedules - slow bisque, fast glaze, whatever -
who the heck knows what you'll get. You'll need to program your own
schedule to get what results you want. We have an L&L programmable
kiln at school we use for crystalline glaze firing. For the speed we
fire, we determined ^6 goes down at 2132=B0F - so we programmed that
with a 5 minute soak that evens out the firing top to bottom.
>The lid (Lid Lifter) holds the lid open 1/4 inch. Even when I place a
cinder block on it during firing the left half of the lid still does not
come into contact with the kiln top.<
I'm sure there's an adjustment on the lid lifter device. DON'T use
the cinder block!
>The kiln rocks on the stand. Is it possible that the bottom of the kiln is
warped or that the kiln stand is not level? I'm not comfortable using a
wooden shim as was suggested.<
Is your floor level? Was the stand level before you installed the
kiln on it? Think you need to go back and check this first. If
they're ok, then shim with metal.
Bill
Valice Raffi on thu 24 feb 05
Hi Jean,
I've just been experiencing the exact same problem, except I bought a 1227.
Like you, this is my first new kiln, first Envirovent, first computer
controller, and much bigger than my last kiln which was a funky, ancient
Duncan Studio kiln that fired great, and I worried that I had made a huge,
expensive mistake.
My first fire (like yours) was to ^04, medium speed with shelves and posts.
I programmed in a 15 min. hold at the end. The fire took 9 hrs., 16 min.
the cones were perfect on the top & bottom, the middle was a bit too hot.
I called Skutt. Good thing because while the electrician installed #6
copper wire for the new breaker, he neglected to account for the distance,
which I wouldn't have known without this firing problem.
So the electrician comes back, digs up my yard again, and installs #2 wire.
I tested the kiln again (same program w/out the hold) and this time it
took 8 hrs., 54 min. The cones read too cool. Called Skutt. This time I
talked to Michael, who asked what load I had in there (both times were 8
half-shelves, posts, and three tiles with witness cones on them. Because I
had not programmed a 15 min. hold time, the firing time was almost exactly
the same as the first, but the heat work was insufficient to properly melt
the cones.
Michael said that with the load (shelves, etc.) of about 200 lbs., the
firing time was fine. What I don't understand is why the manual says to
load the kiln with empty shelves and it will take 7.5 hrs., but when you
do, the firing is "normal" at a longer time. I forgot to ask him that as I
was asking about so many things; whether altitude would affect the firing
time, plus making sure my numbers for amperage, voltage, wiring and
breakers were correct.
He did say that it was normal for the middle to fire hotter, and to load
the ware heavier there. My last kiln required turning the switches off and
on and gradually lowering the lid to control the heat rise. I would
normally do that for somewhere between 4.5 to 6.5 hours (depending on
thickness and dryness of the ware) before "letting 'er rip". The fire
usually took 6.5 hours after that before shutting off, so i suppose that
the firing time of the new kiln is not really abnormal. I think I only
thought so because the manual told me how many hours it was supposed to
take.
Programming a hold at the end should help your cones melt properly.
I would dismantle the kiln and level the stand and the envirovent, then
check the level of each section if you're concerned about a problem with
the kiln itself, but most likely, your floor is not level and shiming from
the bottom is perfectly ok, and the easiest way to fix the problem.
On the lid raising, there was a recent thread on this and you can check the
archives, but the gist of it is that it's normal.
in commiseration,
Valice
in Las Cruces
Laurie on thu 24 feb 05
On Feb 24, 2005, at 8:18 AM, Valice Raffi wrote:
>
> My first fire (like yours) was to ^04, medium speed with shelves and
> posts.
> I programmed in a 15 min. hold at the end.
Hi Valice,
That's very interesting to read. I have a Skutt 1027 and mine fired a
bit on the cool side, too, so I programmed in a 10 minute hold at the
end for 04 firings and it's fine now. The "fires hotter in the middle"
thing is interesting to know, too. It explains some things I was
noticing (I know, I know - witness cones all through the kiln! Would
have figured it out sooner).
Laurie
Sacramento, CA
http://rockyraku.com
Potters Council, charter member
Sacramento Potters Group, member
p.s. - How's Las Cruces? You missed the two small tornadoes that
touched down in Sacto on Monday in Natomas & West Sacto. I'm out near
Freeport and it was sunny all during that time period. Talk about
localized weather problems!
Arnold Howard on thu 24 feb 05
----- Original Message -----
From: "Valice Raffi"
> He did say that it was normal for the middle to fire hotter, and to load
> the ware heavier there. My last kiln required turning the switches off
> and
> on and gradually lowering the lid to control the heat rise. I would
> normally do that for somewhere between 4.5 to 6.5 hours (depending on
> thickness and dryness of the ware) before "letting 'er rip". The fire
> usually took 6.5 hours after that before shutting off, so i suppose that
> the firing time of the new kiln is not really abnormal. I think I only
> thought so because the manual told me how many hours it was supposed to
> take.
Here are other ideas on improving temperature uniformity:
1) Load more ware in hot sections of the firing chamber and less ware in
cool sections. The greater the density of ware, the more heat required in
that section of the firing chamber. By changing the load balance inside the
kiln, you can alter the heat distribution by about half a pyrometric cone.
For instance, to reduce the heat in a hot section of the kiln, load short
pieces of ware that require extra shelves. Load fewer shelves in the cooler
sections of the kiln. The shelves are heavy and require extra heat energy.
2) On digital kilns, program a hold of around 15 minutes at the end of the
firing. This will help even out the temperature. Firing slower also helps.
3) A down-draft kiln vent that is operating properly helps even out the heat
distribution by as much as 1/4 - 1/2 cone. While the kiln is empty and
unplugged, turn on the down-draft vent. Hold a lighted match inside the kiln
just above a vent hole in the bottom. The flame of the match should be
pulled toward the hole.
Turn off the vent and load the kiln. Insert the peephole plugs and close the
lid. Then turn on the vent and hold a lighted match above and level with a
lid vent hole. The flame should be sucked toward the hole.
If the lid rises during firing, the down-draft vent will lose efficiency,
because it must create negative pressure inside the kiln. Opening the lid or
removing peephole plugs reduces the negative pressure.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
arnoldhoward@att.net / www.paragonweb.com
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