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#1
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Heat Work Problem
Last week we did a 1280 firing mainly for tile tests. The kiln has had
14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. My supplier told me to try aiming for a lower temp with a longer soak. The next planned firing was a 1250 so I programmed 100/hr to 600 then full power to 1240 (10 lower) then a 30 min soak. I put cones 8 and 9 on the middle shelf to test heatwork and the result was that both cones were, again, all the way down. The ware, on this occasion, including a terracotta with a firing range up to 1250, stayed stable with no visible distortion. Is it plausible that 9+ can equate to a 1240 firing, as in the above example or is there something wrong with the controller? We're getting a bit desperate here as we've got our first market at the end of November and without an accurate kiln we're up a goat's ass without a paddle! Help thanks again pete (For those of you in the UK who know Potterycrafts we are using a P5976 4cub.ft Topworker with an Ipco 3000 controller.) |
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#2
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"pete" wrote in message news Last week we did a 1280 firing mainly for tile tests. The kiln has had 14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. My supplier told me to try aiming for a lower temp with a longer soak. The next planned firing was a 1250 so I programmed 100/hr to 600 then full power to 1240 (10 lower) then a 30 min soak. I put cones 8 and 9 on the middle shelf to test heatwork and the result was that both cones were, again, all the way down. The ware, on this occasion, including a terracotta with a firing range up to 1250, stayed stable with no visible distortion. Is it plausible that 9+ can equate to a 1240 firing, as in the above example or is there something wrong with the controller? We're getting a bit desperate here as we've got our first market at the end of November and without an accurate kiln we're up a goat's ass without a paddle! Help thanks again pete (For those of you in the UK who know Potterycrafts we are using a P5976 4cub.ft Topworker with an Ipco 3000 controller.) 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 |
#3
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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 Last week we did a 1280 firing mainly for tile tests. The kiln has had 14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. My supplier told me to try aiming for a lower temp with a longer soak. The next planned firing was a 1250 so I programmed 100/hr to 600 then full power to 1240 (10 lower) then a 30 min soak. I put cones 8 and 9 on the middle shelf to test heatwork and the result was that both cones were, again, all the way down. The ware, on this occasion, including a terracotta with a firing range up to 1250, stayed stable with no visible distortion. Is it plausible that 9+ can equate to a 1240 firing, as in the above example or is there something wrong with the controller? We're getting a bit desperate here as we've got our first market at the end of November and without an accurate kiln we're up a goat's ass without a paddle! Help thanks again pete (For those of you in the UK who know Potterycrafts we are using a P5976 4cub.ft Topworker with an Ipco 3000 controller.) -- David David Hewitt Pottery 7 Fairfield Road, Caerleon, Newport, South Wales, NP18 3DQ. Tel:- +44 (0) 1633 420647 Fax:- +44 (0) 870 1617274 Web:- http://www.dhpot.demon.co.uk |
#4
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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 Last week we did a 1280 firing mainly for tile tests. The kiln has had 14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. My supplier told me to try aiming for a lower temp with a longer soak. The next planned firing was a 1250 so I programmed 100/hr to 600 then full power to 1240 (10 lower) then a 30 min soak. I put cones 8 and 9 on the middle shelf to test heatwork and the result was that both cones were, again, all the way down. The ware, on this occasion, including a terracotta with a firing range up to 1250, stayed stable with no visible distortion. Is it plausible that 9+ can equate to a 1240 firing, as in the above example or is there something wrong with the controller? We're getting a bit desperate here as we've got our first market at the end of November and without an accurate kiln we're up a goat's ass without a paddle! Help thanks again pete (For those of you in the UK who know Potterycrafts we are using a P5976 4cub.ft Topworker with an Ipco 3000 controller.) -- David David Hewitt Pottery 7 Fairfield Road, Caerleon, Newport, South Wales, NP18 3DQ. Tel:- +44 (0) 1633 420647 Fax:- +44 (0) 870 1617274 Web:- http://www.dhpot.demon.co.uk |
#5
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my kiln (gas 9+cu ft) reads 1240 on the thermo when ^10 is going down, I
would imagine that with 1280 on the thermo + a 15 min soak you could warp crank...... Love and stuff (when in doubt fire on cones they tell you the truth.....) Eddie ps. yes packing does make a difference..... Loose packs go a tad higher on the thermo (say 1255) for the same effect on the cones...... "David Hewitt" wrote in message ... 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 Last week we did a 1280 firing mainly for tile tests. The kiln has had 14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. My supplier told me to try aiming for a lower temp with a longer soak. The next planned firing was a 1250 so I programmed 100/hr to 600 then full power to 1240 (10 lower) then a 30 min soak. I put cones 8 and 9 on the middle shelf to test heatwork and the result was that both cones were, again, all the way down. The ware, on this occasion, including a terracotta with a firing range up to 1250, stayed stable with no visible distortion. Is it plausible that 9+ can equate to a 1240 firing, as in the above example or is there something wrong with the controller? We're getting a bit desperate here as we've got our first market at the end of November and without an accurate kiln we're up a goat's ass without a paddle! Help thanks again pete (For those of you in the UK who know Potterycrafts we are using a P5976 4cub.ft Topworker with an Ipco 3000 controller.) -- David David Hewitt Pottery 7 Fairfield Road, Caerleon, Newport, South Wales, NP18 3DQ. Tel:- +44 (0) 1633 420647 Fax:- +44 (0) 870 1617274 Web:- http://www.dhpot.demon.co.uk |
#6
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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 "pete" wrote in message news Last week we did a 1280 firing mainly for tile tests. The kiln has had 14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. |
#7
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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 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 "pete" wrote in message news Last week we did a 1280 firing mainly for tile tests. The kiln has had 14 firings so it should be at its optimum. I use a fairly good controller which, the suppliers tell me, is very accurate. On this occasion we also used cones 8,9 & 10 to test heatwork. The result was that all three cones were all the way down and there was warping amongst the tiles which should have been good for the temperature. The controller has a automatic cutout and will flash a retrospective warning if the kiln overfires - this didn't happen. The cycle used was 100C/hr to 200 then full power to 1280 then a 15min soak. -- Steve Mills Bath UK |
#8
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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 |
#9
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In article , potty
writes 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 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 -- Steve Mills Bath UK |
#10
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Just recently I programed a controller for a new kiln, Cone 6 Oxidation,
1240/60 oC, and set cone packs on every shelf. this tallish electric had a "cool" bottom, "hot" top... variations: 2 cones. so I programmed in a "lag" and lowered the heat rate from 150 oC/hour to 100 oC/h after we passed 573 oC. result: more uniform firing and pots properly fired to maturity and not overfired. if you do not push the heat input too high, the pyro and the controller will come closer to meshing. good pots. peace. Tom B. Tom Buck aa563 at hwcn.org) -- primary address. Tom.Buck at hwcn.org "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 |
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