Sandi Nelson on tue 18 sep 07
I have a small electric kiln=852.5 cf and have been firing for a year, =
so
still consider myself new at the process. My last few glaze firings to =
^6
appeared to be =93perfect=94 in that my witness cones were just touching =
the
shelf on two shelves and slightly above the shelf on the third shelf. =
Then
I did a bisque firing=85my target cone was 04. On the top and bottom =
shelf
the witness cone was only at 11:00=85on the middle shelf, the cone fell =
to 9
o=92clock=85yet the final temp on the control panel indicated what it =
should
have (1945) and the time of the firing was =93usual.=94 I have 36 =
firings on
the kiln. When I talked to the company rep, he indicated the =
thermocoupler
was beginning to drift and said I should increase the final temp on the =
next
firing. My first question is=85at what point do I replace the =
thermocoupler
and/or elements? My second question is, should I refire the bisque =
firing
or glaze the pieces for a glaze firing? =20
No virus found in this outgoing message.
Checked by AVG Free Edition.=20
Version: 7.5.487 / Virus Database: 269.13.22/1015 - Release Date: =
9/18/2007
11:53 AM
=20
Arnold Howard on wed 19 sep 07
From: "Sandi Nelson"
Then
I did a bisque firing=85my target cone was 04. On the top and=20
bottom shelf
the witness cone was only at 11:00=85on the middle shelf, the=20
cone fell to 9
o=92clock=85yet the final temp on the control panel indicated=20
what it should
have (1945) and the time of the firing was =93usual.=94 . . .=20
at what point do I replace the thermocoupler
and/or elements?
-----------------
Are you using self-supporting cones or regular cones? At=20
maturity, the tip of the self-supporting cone is even with=20
the top of the sloped cone base. The tip should not touch=20
the shelf. On the other hand, the tip of the regular cone=20
should just barely touch the shelf.
The bend of a self-supporting cone at maturity could be=20
interpreted as a 9 o'clock bend, though it's called a 6=20
o'clock bend.
Either style cone with an 11 o'clock bend is underfired by=20
about 25 degrees F. To correct for the next firing, I would=20
add maybe 17 minutes of hold time in Cone-Fire or raise the=20
target temperature by around 18 degrees in Ramp-Hold.
Or you could correct the next firing with Cone Offset, which=20
makes the controller change the thermocouple's temperature=20
reading.
I don't think your thermocouple is worn out yet. It would be=20
a good idea to keep a spare on hand.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
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