Martin Howard on sun 1 jul 01
The cone 3 in my electric kiln is bending right over now.
In earlier firings it stayed upright. I want to fire at 1 or 2 and not
really hit 3. It is there as a guard cone.
So, one simple answer is to adjust the temperature scale. OK. Done.
But my question to the list is this:-
What is likely to be causing this change in temperature (or heat work to be
precise)?
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
william schran on sun 1 jul 01
Martin - If you want to fire to cone 1 or 2, why not use a cone 1 or
2 witness cone on the kiln shelf and shut off the kiln when cone 1 or
2 bends over? Any other "devices" simply complicate the whole issue.
Bill
David Hewitt on mon 2 jul 01
Martin,
Not sure that I really understand your situation, but as your elements
get older the heat up rate slows down, all other aspects staying the
same such as amount of pots in the kiln and regulator settings. An Orton
cone table gives cone 3 at 60 C heating rate/hr as 1152 and at 150 C
rate/hr as 1168. When you replace elements, of course, the reverse
happens.
David
In message , Martin Howard writes
>The cone 3 in my electric kiln is bending right over now.
>In earlier firings it stayed upright. I want to fire at 1 or 2 and not
>really hit 3. It is there as a guard cone.
>So, one simple answer is to adjust the temperature scale. OK. Done.
>But my question to the list is this:-
>
>What is likely to be causing this change in temperature (or heat work to =
>be
>precise)?
>
>Martin Howard
>Webb's Cottage Pottery
>Woolpits Road, Great Saling
>BRAINTREE, Essex CM7 5DZ
>England
>
>martin@webbscottage.co.uk
>http://www.webbscottage.co.uk
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Martin Howard on mon 2 jul 01
Thanks William for that idea.
But I now keep the spyholes in the front of the kiln closed and do not look
at the cones until I open.
I found that leaving those holes open caused a draft upward which distorted
the action of the cones and made the bottom two cones cooler than the top.
I now place the cones further back, away from the spyholes; so there are
pots between the cones and the spyholes in any case.
The system runs by thermostatic probes in the rear wall, linked to a Fireman
control panel where I can set full ramp temperature (500C), top temperature
(1100C) and dwell time (one hour).
My question is really:- What part of the system is likely to be causing this
change in work done as shown by the cones?
and should it be replaced?
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Frederich, Tim on mon 2 jul 01
Martin,
The change is probably due to the aging of the thermocouples and they are
starting to drift in temperature. This is common with Type K thermocouples
and they will need to be replaced at some point. In the meantime you can
adjust your setpoint the way you are now.
Best regards,
Tim Frederich, Orton Ceramic Foundation
-----Original Message-----
From: Martin Howard [mailto:martin@WEBBSCOTTAGE.CO.UK]
Sent: Monday, July 02, 2001 2:08 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Electric Kiln Temperature
Thanks William for that idea.
But I now keep the spyholes in the front of the kiln closed and do not look
at the cones until I open.
I found that leaving those holes open caused a draft upward which distorted
the action of the cones and made the bottom two cones cooler than the top.
I now place the cones further back, away from the spyholes; so there are
pots between the cones and the spyholes in any case.
The system runs by thermostatic probes in the rear wall, linked to a Fireman
control panel where I can set full ramp temperature (500C), top temperature
(1100C) and dwell time (one hour).
My question is really:- What part of the system is likely to be causing this
change in work done as shown by the cones?
and should it be replaced?
Martin Howard
Webb's Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
England
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
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william schran on mon 2 jul 01
Martin - The probes, just as elements will degrade and change over
time, thus causing changes in your readings. That's why I only rely
on & use witness cones for the most accurate measurement.
Bill
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