Problems reconciling controller temp to cone: way over fired!

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"

formatting link
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
formatting link
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
formatting link
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

formatting link
, 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!

Reply to
no spam here, thanks
Loading thread data ...

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

Reply to
tony

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).

Reply to
no spam here, thanks

In article , no spam here, thanks writes

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

Reply to
Steve Mills

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

Reply to
annemarie

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.

Reply to
no spam here, thanks

Reply to
Eddie Daughton

InspirePoint website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.