Kathy Forer on mon 15 aug 11
I bisque fired my small Skutt K18 for the first time since I quite careless=
l=3D
y way over-fired it to 1230 Celsius aka 2240 Fahrenheit.=3D20
I was more wary this time but found it confusing. I had replaced the broken=
k=3D
iln sitter pyrometer though not the unsheathed thermocouple for the digital=
p=3D
yrometer. Though it bent in a light arc during the firing I thought I'd try=
i=3D
t as I was relying on witness cones.=3D20
After a slow ramp up the kiln sitter kicked off at a pyrometer reading of 1=
8=3D
30 F. But the witness cones were all standing tall. My clay is bisque 04-06=
s=3D
o I am willing to wait until the cones bend. Waiting, waiting over an hour =
u=3D
ntil the kiln gets to 1948, 1955, 1960.... Finally I shut the kiln off thou=
g=3D
h the guide is barely down and the firing cone only slightly bent.=3D20
I realize air may be coming in the peeps cooling the area where I have the =
c=3D
one packs. I had also stuck the pyrometer in the top peep instead of the sm=
a=3D
ll hole in the back and there is a gap of cool air around it affecting the =
t=3D
op witness pack.=3D20
So there is whooshing air, imperfectly placed cone packs, possibly poorly c=
a=3D
librated kiln sitter, difference between bar pyrometric in sitter and large=
c=3D
ones in purchased holder packs, and possible bad pyrometer thermocouple. Wh=
a=3D
t else should I consider?
On the plus side the numbers are beginning to make sense if I think of them=
a=3D
s dates, 1066 and all that.=3D20
I ran the Bailey vent from 180 until about 1750. When should it be run?=3D2=
0
Thanks!=3D20
Kathy Forer
Claypit Creek
Kathy Forer on mon 15 aug 11
Thanks Bill, this is all very helpful!=3D20
Careless again, mildly, not quite reckless, I didn't notice the pyrometer t=
h=3D
ermocouple was in the wrong place until after it was too hot to move. It ha=
d=3D
n't been on my mental checklist as I was loading the kiln. I'm still workin=
g=3D
on proper cone placement. =3D20
See below...
On Aug 15, 2011, at 10:10 AM, William & Susan Schran User =
w=3D
rote:
>>=3D20
> If the thermocouple bent, you might have it sticking too far into the kil=
n=3D
> chamber. It should protrude at least 1", perhaps a bit more, but will ben=
d=3D
> when heated if protruding too far.
>>=3D20
The type K thermocouple is 8" long. The brick is 2-1/2" thick. There's mayb=
e=3D
1" where the wires attach. Should the thermocouple stick into the room an =
e=3D
xtra 3-1/2"? Inquiring minds...
Kathy Forer
Claypit Creek
>=3D20
William & Susan Schran User on mon 15 aug 11
On 8/15/11 7:09 AM, "Kathy Forer" wrote:
> I bisque fired my small Skutt K18 for the first time since I quite carele=
ssly
> way over-fired it to 1230 Celsius aka 2240 Fahrenheit.
> I was more wary this time but found it confusing. I had replaced the brok=
en
> kiln sitter pyrometer though not the unsheathed thermocouple for the digi=
tal
> pyrometer. Though it bent in a light arc during the firing I thought I'd =
try
> it as I was relying on witness cones.
If the thermocouple bent, you might have it sticking too far into the kiln
chamber. It should protrude at least 1", perhaps a bit more, but will bend
when heated if protruding too far.
> After a slow ramp up the kiln sitter kicked off at a pyrometer reading of=
1830
> F. But the witness cones were all standing tall. My clay is bisque 04-06 =
so I
> am willing to wait until the cones bend. Waiting, waiting over an hour un=
til
> the kiln gets to 1948, 1955, 1960.... Finally I shut the kiln off though =
the
> guide is barely down and the firing cone only slightly bent.
It really doesn't matter what the pyrometer reads, especially if the
thermocouple might be damaged. Though I check rate of heat climb with
pyrometer, I only rely on the witness cones. Sometimes ^06 goes over with a
reading in the high 1700's, other times in the mid 1800's - all depends on
load and how fast kiln is firing.
> I realize air may be coming in the peeps cooling the area where I have th=
e
> cone packs. I had also stuck the pyrometer in the top peep instead of the
> small hole in the back and there is a gap of cool air around it affecting=
the
> top witness pack.
Why don't you have the thermocouple in the small hole? Having pyrometer
stuck loosely in the spy hole would lead to bending and inaccurate readings
- put it back in the proper hole.
The kiln I bisque in has a vent set up where a hole is in the wall of the
bottom section of kiln. The top spy hole plug is left out during the firing=
.
My cones are in front of this top spy hole, but set back so that there is
little effect from the air entering the kiln.
> So there is whooshing air, imperfectly placed cone packs, possibly poorly
> calibrated kiln sitter, difference between bar pyrometric in sitter and l=
arge
> cones in purchased holder packs, and possible bad pyrometer thermocouple.=
What
> else should I consider?
The bar cone in the sitter should be a cone or two higher than your witness
firing cone. You should fire by witness cone and use the kiln sitter just a=
s
a back up in case something prevents you from getting to the kiln - use it
only as a safety back-up.
> On the plus side the numbers are beginning to make sense if I think of th=
em as
> dates, 1066 and all that.
Here is Orton's site where you can download a kiln chart with temperature
equivalents and hang near your kiln:
http://www.ortonceramic.com/resources/reference/cone_ref.shtml
There is also a download titled "Using Orton cones and temperature chart
that will be helpful to you understanding all this.
> I ran the Bailey vent from 180 until about 1750. When should it be run?
I also have a Bailey vent that vents two kilns. I run the vent when I turn
on the kiln until I turn off the kiln.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Arnold Howard on mon 15 aug 11
On 8/15/2011 6:09 AM, Kathy Forer wrote:
> So there is whooshing air, imperfectly placed cone packs, possibly poorly=
calibrated kiln sitter, difference between bar pyrometric in sitter and la=
rge cones in purchased holder packs, and possible bad pyrometer thermocoupl=
e. What else should I consider?
I would place the cones away from the peepholes. They are much easier to
see when they are at least 12" away from the peephole than when they are
close.
Are you sure the witness cones are slanted 8 degrees from vertical? That
makes a difference in accuracy, too.
Generally, I trust the witness cones more than a pyrometer.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
William & Susan Schran User on mon 15 aug 11
On 8/15/11 11:24 AM, "Kathy Forer" wrote:
> Careless again, mildly, not quite reckless, I didn't notice the pyrometer
> thermocouple was in the wrong place until after it was too hot to move. I=
t
> hadn't been on my mental checklist as I was loading the kiln. I'm still
> working on proper cone placement.
Try to always plan loading in such a way that there will be a clear path to
an element behind the cones across the shelf. Having the brightness of the
element behind the cones will allow you to see them better.
>> If the thermocouple bent, you might have it sticking too far into the ki=
ln
>> chamber. It should protrude at least 1", perhaps a bit more, but will be=
nd
>> when heated if protruding too far.
> The type K thermocouple is 8" long. The brick is 2-1/2" thick. There's ma=
ybe
> 1" where the wires attach. Should the thermocouple stick into the room an
> extra 3-1/2"? Inquiring minds...
Sticking the thermocouple in the kiln chamber at least 1" is the minimum - =
1
1/2" - 2" is fine. Longer than that inside the kiln you will find the
thermocouple will bend from the heat over time, making it impossible to pul=
l
out when needed. Does no matter how much sticks out into the room as long a=
s
it's not in a location where it could be hit/damaged as you walk by or when
loading the kiln.
Bill
Kathy Forer on tue 16 aug 11
On Aug 15, 2011, at 12:40 PM, Arnold Howard wrote:
> Are you sure the witness cones are slanted 8 degrees from vertical? That
> makes a difference in accuracy, too.
I used one of those pre-made cone holders but even with that aide the cones=
n=3D
eed to be placed carefully. It's challenging to place them so far away with=
l=3D
arge pieces but a necessary effort it seems. =3D20
This firing got me several steps closer to easy firing at will. My former c=
h=3D
ildhood terror of electricity is fading and I look forward to having fun wi=
t=3D
h kiln(s). Thank you for your help.=3D20
Kathy Forer
Claypit Creek
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