Lois Ruben Aronow on sun 16 apr 00
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We recently bought a barely used Skutt 1227, with a computer
controller and envirovent. Did the first full test firing the other
day (cone 6).
On the positive side: love this kiln. Easy to use. Pretty even
temperature throughout.
I fired the kiln on its standard cone 6 program, medium speed, no
hold. The kiln was full of different kinds of ware (class stuff).
The shelves were staggered. I placed cone packs throughout - cones
5,6,7. The kiln fired for 9 hours 45 minutes, according to the
timer. All spies were plugged.
It was a very successful kiln. Lots of lovely ware. My question is
this: my cone packs were all bent flat, except for the very bottom
one, which had the 7 pointing at 3 o'clock. My question is this: did
this kiln overfire? Now, I realise the cones continue to bend after
the kiln turns off. And I thought I understood the temperature/work
heat relationship. I guess I don't.
I'd really like to fully understand what my cone packs should look
like, so I can monitor the firings and the deterioration of the
elements. I'm just getting to know this kiln, and would appreciate
any insights.
Cindy Strnad on mon 17 apr 00
Lois,
I have a kiln like yours, though not the same brand. I think the
thermocouple is not as accurate as might be hoped for. To get a ^6 to bend
to almost touching, I fire to ^4 on the controller, with a 45 minute soak
time.
I understand that heat work is not the same as temperature, but am told that
the computer in this kiln is programmed to adjust for the speed at which the
target temperature is approached (that is, when the kiln is set to stop at a
specific cone, rather than a specific temperature, which is what I do). I
can only assume, if this information is correct, that the thermocouple is
registering higher than the actual temperature of the kiln.
I seem to remember from the instruction manual, that there is a way to
adjust for this, but haven't looked into it yet. My kiln is only recently
cured of being severely underpowered, so it hasn't been an issue before, as
the kiln wouldn't reach ^6 temperatures anyway. At any rate, look through
your book and see if you can't adjust your kiln for a more accurate reading.
Jonathan Kaplan on mon 17 apr 00
You will need to understand that the controller is a binary device: if the
thermocouple senses the need for heat according to your program input, the
controller turns the kiln on. With enough heat, the kiln cycles off. Of
course this depends on your program, rate per hour, end point, etc. etc.
The controller doesnt take into consideration the kiln load....ware,
shelves, and furniture. WIth a heavy load, more heat is needed, hence
perhaps a higher end point.
The pre-programmed firing cycles also do not take this load factor into
consideration. Hence, if you have a tightly stacked kiln and use a
pre-programmed firing cycle, the kiln will probably underfire. In my
experience, these firing programs as well as the built in cone end points
are based on an empty chamber with a certain rate of climb per hour.They
only serve as a refrence point for you.
The solution is simple. After several firings, you will get the feel of
what the end points need to be. Using these as a reference, program the
kiln to fire slightly under that end point and build in a 30 minute soak
time.
These numbers are of course specific to your kiln and load factors. For
instance, on one of our TnF-28-3 kilns, a cone 06 firing with a full stack
is 1800 degrees with a 30 minute hold, based on 250 degrees per hour rise.
In another of our TnF-28-3 kilns, the end point is 1825 degrees. Our large
40 cubic Olympic front loader is 1875 degrees with a 40 minute soak at the
end.
Understanding the load factor and the soak, as well as programming the
controller to fire UNDER the set point will provide you with reliable,
even, and consistant firings.
Good Luck!
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
jonathan@csn,net
http://www.sni.net/ceramicdesigin
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, FEd
Ex, etc.)
chris@euclids.com on mon 17 apr 00
>I fired the kiln on its standard cone 6 program, medium speed, no
hold.
>I placed cone packs throughout - cones 5,6,7.
>my cone packs were all bent flat, except for the very bottom
>one, which had the 7 pointing at 3 o'clock. My question is this: did
>this kiln overfire
Hi Lois,
Yes the kiln overfired, but not by much. The cones are bent a bit too far.
It is also a little cooler in the bottom. You may be able to adjust the
bottom zone to fire a little hotter ... this will even out the temperature,
top to bottom.
Try backing off the firing temperature 30 degrees or so ... this should fix
the overfiring problem.
At the same time, if you like the results in your work ... don`t change a
thing (except to use cones 6,7,8 instead of 5,6,7). Also, some potters take
advantage of kilns with hot & cool spots ... placing ware strategically to
get different glaze finishes in the same firing, with the same glaze. This
may, or may not, be a benefit to you.
chris
chris@euclids.com
www.euclids.com
800-296-5456
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