Heat Work Problem

Last week we did a 1280º 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 100ºC/hr
to 200º then full power to 1280º 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 1250º so I programmed 100º/hr to 600º then
full power to 1240º (10º 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 1250º, stayed stable with no
visible distortion.
Is it plausible that �9+ can equate to a 1240º 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" wrote in message
news
Last week we did a 1280º 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 100ºC/hr
to 200º then full power to 1280º 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 1250º so I programmed 100º/hr to 600º then
full power to 1240º (10º 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 1250º, stayed stable with no
visible distortion.
Is it plausible that �9+ can equate to a 1240º 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

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 1280º 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 100ºC/hr
to 200º then full power to 1280º 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 1250º so I programmed 100º/hr to 600º then
full power to 1240º (10º 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 1250º, stayed stable with no
visible distortion.
Is it plausible that �9+ can equate to a 1240º 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

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 1280º 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 100ºC/hr
to 200º then full power to 1280º 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 1250º so I programmed 100º/hr to 600º then
full power to 1240º (10º 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 1250º, stayed stable with no
visible distortion.
Is it plausible that �9+ can equate to a 1240º 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

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 1280º 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 100ºC/hr
to 200º then full power to 1280º 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 1250º so I programmed 100º/hr to 600º then
full power to 1240º (10º 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 1250º, stayed stable with no
visible distortion.
Is it plausible that �9+ can equate to a 1240º 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

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 1280º 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 100ºC/hr
to 200º then full power to 1280º then a 15min soak.

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 1280º 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 100ºC/hr
to 200º then full power to 1280º then a 15min soak.



--
Steve Mills
Bath
UK

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

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

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