mel jacobson on wed 26 jul 06
when my gas kiln pyrometer reads:
2550F and the kiln has been on for 8 hours...
i know that cone 10 will be going over soon.
the kiln is not at 2550F it is about 2340F.
because i have used the same kiln and same
pyrometer for thirty years....the bimetal
pyrometer is accurate for my observation needs.
it will not set with the setscrew to 2340...not even
close. i just leave it right where it is.
it is helping me know what the heat work is doing.
it is sort of like having a wire hook on your screen door.
`first line of defense`.
the cones are what potters with gas kilns use to
determine when the kiln is done, along with the clock on
the wall.
observation. the mechanical tool helps us get there.
it is like being mindful of the length of the flame coming
from the middle front spy hole. that observation is
critical..and, of course, noting the atmosphere inside the
kiln..how well can one observe the pots, three rows back?
what color is the inside...has it turned to yellow white yet?
the thing that changes from firing to firing is the stacking
of the kiln...shelf placement. and that makes each
firing unique to itself. that is why i never change the
location of the pyrometer, spy holes, cones and oxyprobe.
they remain the same. all for observation purposes.
of course the world changes around us each time we fire.
rain, snow, cold, heat, wind. any potter worth their
terra sig knows this, and lives within the confines of
being a human, in nature.
we do live in a time when many want to give up their human,
natural instincts. they want mechanical help to trust rather
than their own skills and observation.
when i go outside this morning, and the heat and humidity
smack me in the face, and the wind is gone...i feel like
a wet blanket just got tossed in my face...i need not turn
on the weather channel to let me know about the day.
i am automatically crabby. i think i will go down behind
the garagette, take off my shirt and pee into the weeds.
remind myself that i belong in nature. my golden
retriever chutney, will do the same...but, i will turn
my back to her, she is a lady you know. and, she does not have a shirt.
eve brown knew when she found hiedi casto at the airport
for a hay creek pickup....heidi had on `bright orange crocs`.
`HEY, THERE YOU ARE.` observation.
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link: http://www.visi.com/~melpots/clayart.html
Edouard Bastarache Inc. on wed 26 jul 06
Hello Mel,
" when my gas kiln pyrometer reads:
2550F and the kiln has been on for 8 hours...
i know that cone 10 will be going over soon.
the kiln is not at 2550F it is about 2340F."
Here are the differences between the readings on
a
"S" system with a 2,400 dollar digital readout
I got for free from a local steelmill.
I use a "K" thermocouple and 2 "S" per firing.
The "K", even if a technician formerly working
for our federal governement garanteed it was good
for very high temperatures, is only good up to
C/4.
The "S" are connected to different readouts for
comparison.
At the begining of the life of my last gas kiln I
decided to fire without a pyrometer for a certain
number of years, and I learned the behaviour of
the kiln.
Later I decided to fire with thermocouples and
noted the readings on the expensive readout for
many firings and made averages of these numbers.
Andre, an engineer in physics, told me he could
recalibrate my readouts so there would not be
any difference between the cones and the readout.
I said "NO", I do not need to, I already have
at hand the differences between the 2 systems.
Now I can say at 2084 F C/4 is down
or very close to that position; and so on for the
other cones.
Écarts Cone/Thermocouple
(Differences Cone/Thermocouple)
Ste-Anne de Sorel, QC
C/08 = nil
C/02 (2050 F) = -47
C/3 (2138 F) = -87
C/4 (2174 F) = -90
C/6 (2245 F) = -91
C/8 (2300 F) = -123
C/9½ ( 2363 F) = -154
Later,
Edouard Bastarache
Le Français Volant
The Flying Frenchman
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.pshcanada.com/Toxicology.htm
http://www.flickr.com/photos/potier/172943983/
http://www.flickr.com/photos/potier/172941969/
Ivor and Olive Lewis on thu 27 jul 06
Dear Mel,
I would not dare to dispute your observations. Heat at the tip of your =
pyrometer is what gives the energy which is processed to give either a =
digital or analogue readout. If you were to have ten Pyrometers =
scattered around the cavity of your gas kiln you would get ten differing =
values. But each reading is accurate.
It is what the Cone does that is the important thing.=20
One Pyrometer will tell us only about "Progress". Trust it ! !. If need =
be, keep records of Time V Temperature for a few firings and get Excel =
to print out a Graph to mount and hang by your kiln once you are =
satisfied
I would suggest that people ignore the difference between the Kiln Pyro =
Reading and the Cone Value Equivalent Temperature, as you are doing. =
This is reality you are measuring. There are ways of testing a pyrometer =
probe but this is difficult to do without having a the facility and =
ability to record phase changes in molten metals and as I said earlier, =
you have to have two reference points, one for the hot junction and one =
for the cold..=20
When I was compiling Phase Change data for Steel samples the whole =
specimen, a rod of metal about 5 mm dia and 100 mm long, was part of the =
electric circuit. The rod was slotted at each end and the Pyro wires =
were forged into the slots to establish continuity.
Best regards,
Ivor
Tom at Hutchtel.net on thu 27 jul 06
Subject: ivor/pyrometers
it ! !. If need =
> be, keep records of Time V Temperature for a few firings and get Excel =
> to print out a Graph to mount and hang by your kiln once you are =
> satisfied
We graph every firing...temp read on a pyrometer, with indications of change
made in settings (gas kiln power burners) pressures, etc. Yes, they are
mostly the same, but if one varies, we know something's going on early
rather than later. Nils Lou recommended this in "Art of Firing and
published a blank graph there for repro.
Tom Wirt
William & Susan Schran User on thu 27 jul 06
On 7/27/06 2:22 AM, "Ivor and Olive Lewis" wrote:
> I would suggest that people ignore the difference between the Kiln Pyro
> Reading and the Cone Value Equivalent Temperature, as you are doing.
I agree and I would add, for folks with programmable kilns, your
kiln/controller is also a pyrometer reading a thermocouple. One can't
completely rely on this device to provide an accurate picture of what is
happening in the kiln to the clay & glazes. This is especially true if there
is only one thermocouple at the midpoint of the kiln.
We have L&L programmable kilns at school for our crystalline firings. These
kilns have a sheathed thermocouple in each section, that helps to even out
the temperature throughout the kiln. But we still put cone packs at each
level for that critical accurate record after the firing is completed.
I'll grant you, a few test firings with cones, will assist in narrowing in
on a temperature reading that may closely match the reading on the
controller and the bending of the firing cone, but I would suggest the only
way to truly understand the results of a firing is witness cones.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Ivor and Olive Lewis on fri 28 jul 06
Dear Tom Wirt,=20
Thanks for confirming the need for good practice.
Best regards,
Ivor
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