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"
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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
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to set thattemperature, 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
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as 1220 (OK, not sofar 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
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, which isodd as they only measure just over 2" anyway! That's me completely baffled for now. I have no idea what temperatureto fire to to get Cone 6 now, so I'll try for 1182C when I do anothertest firing tomorrow. So far I haven't dared fire anything but tests! Any feedback would be most welcome!