Problems reconciling controller temp to cone: way over fired!

It's not strictly temperature. it is temperature over time. If you were to
hold at cone 5 temp for some extended time, cone 6 will drop. If you take
it to cone 5 temp, fast, and shut off, cone 4 will just bend. and 5 will be
unaffected. Cones measure "heat-work," not just temperature so reconciling
temperature to cone will not work. It is like saying I have been driving at
60 KPH (mph), how far have I gone?

Tony

http://tonyolsen.com/up/


"no spam here, thanks" wrote in message
...
I'm having a real problem firing to desired cone using my kiln
controller.

I know my heating rate - it's 60C/hr at 1100-1200 dropping quickly to
40C/hr @1280.

My first firing to Cone 10 was set to 1280C and was way overfired Cone
10 was a horizontal droopy blob - as would be expected with that slow
heating rate (which I couldn't know about until I'd monitored it, of
course).

My second firing to Cone10 was set to 1240C and was a bit over fired,
Cone 10 was bent right over. I had used the Orton Conecalc program to
find that temperature, and it should have been a good Cone 10: it was
close enough. .

My third firing to Cone 6 was set to 1222C (60C / hr at that temp) and
cone 7 was laying flat out - could have been Cone 9 or 10 I suppose. I
used the Orton "wallchart"
(http://www.ortonceramic.com/center/p...rt_degreeC.pdf)
to set that temperature, but it was clearly way wrong.

My fourth firing to Cone 6 set to 1209C (60C/hr) was a perfect Cone 8!
I had used the data in
http://www.ortonceramic.com/center/pdf_files/60C.PDF to set that
temperature, as it was much lower than the one shown in the wallchart!
(Why????) but it was clearly way wrong.

(BTW, yet a 3rd Cone 6 temperature is shown in
http://www.ortonceramic.com/center/cone.chart.C.html as 1220 (OK, not so
far from 1222, but still different!)).

So: I am really at a loss now. There are two things I can think of,
and I'd really appreciate some guidance -

1) The ambient temperature around my controller will be say 40C (well
above 30C anyway, which is what it is after several hours cooling). I
fire overnight in my garage. Is the thermocouple simply not taking
account of the ambient temperature? It should, I thought (it has some
kind of 'compensation lead' at the end).

2) Am I supporting the cones properly (I can't quite decipher what I am
meant to do) - The clay support I press them into is less than ½ inch
thick - I think I saw on one of the Orton Charts that the 'regular
cones' should be "mounted" at 2" above base (footnote to
http://www.ortonceramic.com/center/p...ortoncones.pdf) , which is
odd as they only measure just over 2" anyway!

That's me completely baffled for now. I have no idea what temperature
to fire to to get Cone 6 now, so I'll try for 1182C when I do another
test firing tomorrow. So far I haven't dared fire anything but tests!

Any feedback would be most welcome!

In article , no spam here,
thanks writes
Thanks .... I fully accept that there is something I'm not understanding
- but I don't think it's instantaneous temperature vs heatwork.

That's why I mentioned the rate of temperature increase in the last
period of firing (which is, as I understadn it, the important part -
when the 'useful' or 'necessary' heatwork is done). At 60C/hr, the
heat-work equivalent to Cone 6 should be reached (according to Orton's
website)at temperatures of variously 1209 or 1222C. (At 150C/hr the
temperatures need to be higher for the equivalent heatwork to be done).




Do you have a temperature cut off point on your controller and do you
have peep holes in the Kiln wall? If so I suggest you do what we tell
all our customers to do: Set a cone equivalent to the temperature you
want to achieve opposite a peep hole. Fire the kiln as per normal, but
watch it like a hawk at the latter stages. When the cone goes over, note
the temperature for future setting and over-ride the controller and shut
down.

Steve
Bath
UK
--
Steve Mills
Bath
UK

"Steve Mills" wrote in message
...
In article , no spam here,
thanks writes
Thanks .... I fully accept that there is something I'm not understanding
- but I don't think it's instantaneous temperature vs heatwork.

That's why I mentioned the rate of temperature increase in the last
period of firing (which is, as I understadn it, the important part -
when the 'useful' or 'necessary' heatwork is done). At 60C/hr, the
heat-work equivalent to Cone 6 should be reached (according to Orton's
website)at temperatures of variously 1209 or 1222C. (At 150C/hr the
temperatures need to be higher for the equivalent heatwork to be done).




Do you have a temperature cut off point on your controller and do you
have peep holes in the Kiln wall? If so I suggest you do what we tell
all our customers to do: Set a cone equivalent to the temperature you
want to achieve opposite a peep hole. Fire the kiln as per normal, but
watch it like a hawk at the latter stages. When the cone goes over, note
the temperature for future setting and over-ride the controller and shut
down.

Steve
Bath
UK
--
Steve Mills
Bath
UK

Good idea Steve. No Spam why are you firing so slowly?
I fire for bisque 100C per hr to 600C then flat out to !000C, then half hour
soak. It takes about 9 hours.
For Glaze 150C per hr to 300C then flat out to desired temp with half hour
soak.
For cone 5 1/2 I set my kiln to 1170C and get a perfectly dropped cone.
For cone 6 I set to 1200C
I fire my own work - fairly fine - and childrens work in the same kiln. I
have had only one exploding piece and it really was not dry enough. I
pushed my luck.
Your heat work seems long to me.
A

New elephants always move faster.....
"no spam here, thanks" wrote in message
...
On Tue, 8 Jun 2004 14:25:23 +1200, "annemarie"
wrote:



Good idea Steve. No Spam why are you firing so slowly?

Your heat work seems long to me.
A

That's as fast as my kiln will go at 1200! Might need new elements,
perhaos - I bought it 2nd hand, so I've no idea what it can do.