Heat Work Problem

Pete: It sounds like you have a funky thermocouple attached to that controller. Clean the contacts and test it to cone 06 empty, with a witness cone in the middle of the kiln. Keep an eye on the cone, and when it's down, see what the controller says the temp is. Cheaper than losing a kiln full. Wayne in Key West

I have always worked to witness cones so have no experience of relying on a controller. I do know, however, that my temperature indicator gives a much lower reading than one would expect from the witness cones. I have always understood that this was quite common, i.e. thermocouples and temperature indicators as used in kilns are not that accurate. Perhaps others could comment on this.

Would it not be possible for you to fire to witness cones rather rely on the controller initially to compare the results?

A problem that I have always envisaged if relying entirely on a controller is that consistent results depend on the 'loading/packing' of the kiln being consistent. By 'loading/packing' I mean the amount of clay being fired and hence the heat work required to get up to the set temperature. I would be interested to hear from those who use controllers if this is a real or imagined concern on my part.

David In article , pete writes

I have always worked to witness cones so have no experience of relying on a controller. I do know, however, that my temperature indicator gives a much lower reading than one would expect from the witness cones. I have always understood that this was quite common, i.e. thermocouples and temperature indicators as used in kilns are not that accurate. Perhaps others could comment on this.

Would it not be possible for you to fire to witness cones rather rely on the controller initially to compare the results?

A problem that I have always envisaged if relying entirely on a controller is that consistent results depend on the 'loading/packing' of the kiln being consistent. By 'loading/packing' I mean the amount of clay being fired and hence the heat work required to get up to the set temperature. I would be interested to hear from those who use controllers if this is a real or imagined concern on my part.

David In article , pete writes

This is the age old problem again - pyrometers measure temperature, cones measure heat work. It doesn't matter how accurate the pyrometer is, it can never replace cones as an indicator of glaze maturity. You have to "calibrate" your controller to suit your work, loading and firing schedule, and then use cones as well to be sure. There is no other option.

Dave

In addition to the excellent advice you've had from all who have responded to your post, I would like to add that I have never yet seen the need to soak a cone 9 firing; by the time the kiln has got that hot, the firing curve has flattened off so much that the last 40 odd degrees are as good as a soak, so the heat-work is greater than the rise in temperature over that period. When we sell any kiln with a controller (I am a Potter first and a Supplier second) we ALWAYS give the customer enough cones to, as Dave rightly puts it, *calibrate* the controller to THEIR needs. A firing like the one you describe is going to go way over the cone unless you watch it. Fire to the cone, note the indicated temperature when it goes over, then adjust the controller end-point to that, and remember to check it every dozen or so firings. Thermocouples degrade, very slightly over the first 5 years, then it starts to accelerate!

Steve Bath UK

In article , David Coggins writes

Thanks Guys

I guess I'm just going to have to calibrate my controller to the cones initially as Dave C. suggested; we fire overnight cos the kiln's in the workshop so we're not around when the cones go down - I guess we're not the only ones who have to do this. I can't see any major problems so long as we calibrate to standard loads so, thanks again everybody.

pete

Thanks for that, Steve. It's only through getting advice from you guys (and, of course, guyesses) in the group that I'm able to fill in the gaps the books and websites don't cover. Is there anywhere I can find graphs for firing cycles? Unfortunately, we have to fire overnight because the workshop's too small so we're not around to observe them going over. We'll just have to do it the other way round by firing lower with a range of cones and seeing which ones are still upright. Will this work or does the cone-related heatwork include the cooling cycle? Thanks again Pete

In article , potty writes

There is sometimes a small continuation of heatwork after shut-down but it's not drastic. The thought occurs that since you know the duration of your firing from the program (or have the prospect of being able to calculate it) how about a Saturday night firing (Sunday for recovery!), setting your alarm clock in time to watch the last hour of it; could save time and work!

Steve

Just recently I programed a controller for a new kiln, Cone 6 Oxidation,

Tom Buck ) -- primary address. "alias" or secondary address. tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada). mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada

Hello,

Sorry if I make some mistakes, I'm French and my English is not perfect.

For the Pete's problem, I would say as Tom : maybe the firing is too quick at the end. I begin to fire myself and I learn. But in my school, we made some firings. For the glaze, with a gas kiln, we went quite quickly at the beginning, 350°C/h until 1000°C. But after, we went slower, 80°C/h. About 1100°C, the glaze begin to melt and if you go too quickly, the temperature is not homogeneous in the kiln and you will have differences. In an another firing we made, also in a gas kiln, we went very quickly (all the firing last 5 hours), went a little higher than

I don't know if you can use the same speed in a electric kiln than a gas kiln. The maker of the one I have since two days told me not to reach 1000°C in less than 7 h, to protect bricks from too fast wear....

Corinne Beurdine #1, MLB#1, ....#1 Pour me répondre, faites moi descendre de ma moto