EARL ROBERTS OR ARNOLD HOWARD on thu 16 jul 98
Dear Friends:
I would appreciate your views on kiln overfiring. What safeguards do
you take to avoid it? Has it ever happened to you? What did you learn
from it?
I appreciate your feedback.
Sincerely,
Arnold Howard
Paragon Industries, Inc.
Stuart Ridgway on fri 17 jul 98
In response to Arnold Howard's query overfiring has happened to me. I was
firing a load in an electric kiln that had power controls on each ring that
controlled power by cycling the power on time. When on a bimetallic strip
was heated and opened the circuit, it then cooled closed the circuit and
power came on again. The time on/time off ratio was adjusted by a
continuous control knob. I had left the power set at medium which would not
have overfired the load even if left on for a long time, and then the
Northridge January 1994 earthquake insurance adjuster arrived. Several
hours went by in intense negotiation and the kiln was unattended. Finally
the adjuster left and I went to the kiln and saw from the color of the light
leak around the peeps that there was a severe overfire, probably cone 12 or
13. A cone 5 pot had completely slumped, and the shelf and the kiln floor
was severely damaged. What had happened is that the power control contacts
had welded, and did not open as they should have in the cycling.
The unit had seen many years of service, and the ring controlled by
the power control unit had a heavier winding and drew a larger current than
the controller was rated for and was therefore in an overload condition.
I replaced the controller with a triac adequately rated, and timed
by the controller on another ring.
I am the kiln sitter, and check the temperature every hour, and have
not had an overfire in the past 4 years. But I don't like kiln sitting, and
am in the market for a good flexible kiln controller. Programmable in
basic, Pascal, or Fortran would be OK.
Stuart Ridgway
>----------------------------Original message----------------------------
>Dear Friends:
>
>I would appreciate your views on kiln overfiring. What safeguards do
>you take to avoid it? Has it ever happened to you? What did you learn
>from it?
>
>I appreciate your feedback.
>
>Sincerely,
>
>Arnold Howard
>Paragon Industries, Inc.
>
Arturo M DeVitalis on fri 17 jul 98
>From my teaching experience all of the few over firings were caused by
shelf being placed so that the kiln siter rod was prevented from
dropping, either because the shelf physically touched the rod, or the
shelf touched the cone and prevented it from deforming until it had
melted and dripped, obviously at a much higher temp,
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tmartens on fri 17 jul 98
My kiln was over firing and I could not figure out why. Finally
nailed it down to a broken ceramic tube (have no idea what the damn
thing is called) in the kiln sitter, replaced that and bought a
digital pyrometer and thermo couple. Now watch the thing like a hawk,
vacillate between trusting the pyrometer or the cone in the sitter
and usually judge somewhere in between the pyrometer and the colour of
the fire ( then the cone bends minutes after or just before I
switch off.)
Makes for neurotic glaze firings....
Toni Martens pondering this odd obsession with clay she has.
> ----------------------------Original message----------------------------
> Dear Friends:
>
> I would appreciate your views on kiln overfiring. What safeguards do
> you take to avoid it? Has it ever happened to you? What did you learn
> from it?
>
> I appreciate your feedback.
>
> Sincerely,
>
> Arnold Howard
> Paragon Industries, Inc.
>
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