Kim Lindaberry on tue 30 nov 04
Hi All,
Here's a problem I'm not sure how to approach. Hopefully someone will
have a great answer.
At school we have a large oval Olympic kiln with a Bartlet Controller.
WE had a problem with it not reaching temp and discovered that the
connection between the middle zone and lower zone was burned out and
needed to be replaced. In the process of finding this problem we
decided that we would go ahead and replace the thermocouple because it
had been bent down from careless loading of the kiln over a 2 year
period of time. It just seemed as long as we had things opened up it
would just be easier to do now rather than later. Everything got
replaced by the school's electrician.
I started the kiln to refire the ^6 glaze (buff clay) load already in
it. I left the same witness cone in place that was in there figuring it
would be an approximate indication of what temp we reached. The kiln
fired and finally reached a temp high enough to flux the glazes, BUT
the cone did NOT bend even slightly. I hit the "Review" program button
and it indicated it had indeed been programed to fire to ^6 and it read
it had reached the correct temp. Since the glazes fluxed I was happy.
Next we did a ^08 bisque and everything appeared fine. The other
teacher that loaded it did not put any witness cones in the bisque but
it looked good so again I was happy.
Yesterday I loaded a ^04 glaze firing in and I put a witness cone in.
Today when I opened the kiln it was way over-fired. The witness cone
was a lump on the shelf. The terra cotta clay body was burnt and in a
few cases even slumped some. The glaze on a few pieces ran off and
puddled. I hit the "Review" program button and it indicated it had
indeed been programed to fire to ^04 and it read it had reached the
correct temp. Despite what the controller says this load was definitely
over-fired.
So I have a ^6 load that seems to be under-fired and a ^04 that is
positively over-fired. I know that the Bartlet Controller can be
adjusted (temp offset) to fired higher or lower than what it is
reading. If I offset to prevent the ^04 from over-firing won't it also
lower the firing range of the ^6 setting and make it even cooler?
Is the solution to just program to fire to ^05 when I want to do a ^04
glaze? Or is there a great solution to the problem? I am probably
missing something really simple but I just can't see it yet.
cheers,
Kim
Arnold Howard on wed 1 dec 04
Kim, the inconsistent firings may be due to a grounded thermocouple. The
thermocouple should not touch the kiln case.
Make sure the thermocouple lead wire ends are separated where the insulation
has been stripped.
Even though you installed a new thermocouple, it may be defective. Reach
inside the kiln and wiggle the thermocouple tip. If the temperature display
becomes erratic, the thermocouple is defective.
The thermocouple lead wires should also be kept away from the other wires
inside the kiln's switch box.
During your next firings, you should position the witness cones so that you
can see them through a peephole. If the kiln keeps firing after the cone
bends to 6 o'clock, turn off the kiln. If it turns off before the cone
bends, turn the kiln back on.
I would not adjust Thermocouple Offset until the kiln begins to give
consistent results.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
arnoldhoward@att.net / www.paragonweb.com
----- Original Message -----
From: "Kim Lindaberry"
> At school we have a large oval Olympic kiln with a Bartlet Controller.
> WE had a problem with it not reaching temp and discovered that the
> connection between the middle zone and lower zone was burned out and
> needed to be replaced. In the process of finding this problem we
> decided that we would go ahead and replace the thermocouple because it
> had been bent down from careless loading of the kiln over a 2 year
> period of time. It just seemed as long as we had things opened up it
> would just be easier to do now rather than later. Everything got
> replaced by the school's electrician.
>
> I started the kiln to refire the ^6 glaze (buff clay) load already in
> it. I left the same witness cone in place that was in there figuring it
> would be an approximate indication of what temp we reached. The kiln
> fired and finally reached a temp high enough to flux the glazes, BUT
> the cone did NOT bend even slightly. I hit the "Review" program button
> and it indicated it had indeed been programed to fire to ^6 and it read
> it had reached the correct temp. Since the glazes fluxed I was happy.
>
> Next we did a ^08 bisque and everything appeared fine. The other
> teacher that loaded it did not put any witness cones in the bisque but
> it looked good so again I was happy.
>
> Yesterday I loaded a ^04 glaze firing in and I put a witness cone in.
> Today when I opened the kiln it was way over-fired. The witness cone
> was a lump on the shelf. The terra cotta clay body was burnt and in a
> few cases even slumped some. The glaze on a few pieces ran off and
> puddled. I hit the "Review" program button and it indicated it had
> indeed been programed to fire to ^04 and it read it had reached the
> correct temp. Despite what the controller says this load was definitely
> over-fired.
>
> So I have a ^6 load that seems to be under-fired and a ^04 that is
> positively over-fired. I know that the Bartlet Controller can be
> adjusted (temp offset) to fired higher or lower than what it is
> reading. If I offset to prevent the ^04 from over-firing won't it also
> lower the firing range of the ^6 setting and make it even cooler?
>
> Is the solution to just program to fire to ^05 when I want to do a ^04
> glaze? Or is there a great solution to the problem? I am probably
> missing something really simple but I just can't see it yet.
>
> cheers,
>
> Kim
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