mel jacobson on sat 1 oct 11
nils has a section in his book
where he has industrial specs on firing
speed and the amount of ware, posts, shelves etc in the
kiln.
he says:
`take a scale and weigh all your shelves and
posts, then weigh all your pots.
that total weight should indicate how long
your kiln should fire.`
makes sense to me.
oft times people have kilns that just take a long time
to reach temp...and often that kiln can be modified
to work faster.
if the kiln fires in 16 hours that becomes the bench
mark for firing. that information is passed to others
and it becomes dogma.
most folks are introduced to firing in a college or art center.
those kilns are often very big and stuffed with pots.
so, that 20 hour firing becomes your bench mark.
does not have to be that.
if you have a 20 cubic foot kiln...it may fire in half that time.
just makes sense.
from: minnetonka, mn
website: http://www.visi.com/~melpots/
clayart link: http://www.visi.com/~melpots/clayart.html
Ron Roy on mon 3 oct 11
Someone from Alfred once told me - about speed of firing - there is a
speed at which the fuel is used most economically - not too fast and
not too slow.
When you fire fast - does more heat go up the chimney?
RR
Quoting ivor and olive lewis :
> Mel comments...
> "nils has a section in his book where he has industrial specs on firing
> speed and the amount of ware, posts, shelves etc in the
> kiln. he says: `take a scale and weigh all your shelves and
>
> posts, then weigh all your pots. that total weight should indicate how lo=
ng
> your kiln should fire.'. makes sense to me."
>
> Good sense if you pay due regard to the assumptions. Firing duration may
> depend on the rate of heat input as well as the retention of energy.
>
> Nils also says " The more critical part of the firing is in the cooling -
> not the heating" (p 16) in his criticism of fibre refractories.
>
> Regards,
>
> Ivor Lewis,
> REDHILL,
> South Australia
>
ivor and olive lewis on mon 3 oct 11
Mel comments...
"nils has a section in his book where he has industrial specs on firing
speed and the amount of ware, posts, shelves etc in the
kiln. he says: `take a scale and weigh all your shelves and
posts, then weigh all your pots. that total weight should indicate how long
your kiln should fire.'. makes sense to me."
Good sense if you pay due regard to the assumptions. Firing duration may
depend on the rate of heat input as well as the retention of energy.
Nils also says " The more critical part of the firing is in the cooling -
not the heating" (p 16) in his criticism of fibre refractories.
Regards,
Ivor Lewis,
REDHILL,
South Australia
ivor and olive lewis on tue 4 oct 11
Dear Ron,
That is something upon which I cannot comment without evidence and it would
cost a lot to set up the lab to test that hypothesis. (we did a lot of
calorimetric determinations in sixth form physics)
But having used a dilatometer, heated by electricity, where I could apply
uniform rates of heating and cooling in the quest for the determination of
phase changes in ferrous metals I know if the heating or cooling is rapid
the effects we expect may be suppressed. Phase changes may be delayed and
some ingredients in clay and glaze require both time as well as heat energy
to accomplish chemical transformation to useful ceramic compounds.
After firing my small (4cu ft) fibre kiln almost four hundred times I know =
I
can reach 500 C in five hours with a two to three inch neutral flame and a
minimum damper gap. But I have never though to weigh my LPG bottle. During
the first firing I plotted time against temperature at the point where burn=
t
gas exited the chamber into the flue.
One idea I have considered is to rethink a kiln in terms of a vessel in
which a fluid is contained by an impervious barrier, analogous to the
puddled clay of a water dam. Such a barrier is saturated with water yet
little escapes into the surrounding earth or air. Similarly, a dense fire
brick is saturated with heat at cone maturity. After that it is a question
of arresting thermal radiation, convection and conduction.
Note the firing rate of Orton Small Cones, fast firing is not an unusual
process when the makers give such information. 300 deg C per hour gives
well over cone 8 in four and a half hours.
All the best,
Ivor Lewis,
REDHILL,
South Australia
Ron Roy comments
> Someone from Alfred once told me - about speed of firing - there is a
> speed at which the fuel is used most economically - not too fast and not
> too slow.
>
> When you fire fast - does more heat go up the chimney?
>
> RR
>
>
>
>
> Quoting ivor and olive lewis :
>
>> Mel comments...
>> "nils has a section in his book where he has industrial specs on firing
>> speed and the amount of ware, posts, shelves etc in the
>> kiln. he says: `take a scale and weigh all your shelves and
>>
>> posts, then weigh all your pots. that total weight should indicate how
>> long
>> your kiln should fire.'. makes sense to me."
>>
>> Good sense if you pay due regard to the assumptions. Firing duration may
>> depend on the rate of heat input as well as the retention of energy.
>>
>> Nils also says " The more critical part of the firing is in the cooling =
-
>> not the heating" (p 16) in his criticism of fibre refractories.
>>
>> Regards,
>>
>> Ivor Lewis,
>> REDHILL,
>> South Australia
>>
>
>
>
>
Ron Roy on tue 4 oct 11
Hi Ivor,
Well I think there must be a point at which the most heat is
transferred to the furniture and ware in the most efficient way -
slower or faster than that and you have to use more fuel to get the
same result.
I do know that when programing my dilatometer I do have to go slow
enough to prevent gradients that would affect the readings - not the
same as the problems for potters I know but there will be some affect
on kiln furniture, shelves and bricks when fast fired.
RR
Quoting ivor and olive lewis :
> Dear Ron,
> That is something upon which I cannot comment without evidence and
> it would cost a lot to set up the lab to test that hypothesis. (we
> did a lot of calorimetric determinations in sixth form physics)
> But having used a dilatometer, heated by electricity, where I could
> apply uniform rates of heating and cooling in the quest for the
> determination of phase changes in ferrous metals I know if the
> heating or cooling is rapid the effects we expect may be suppressed.
> Phase changes may be delayed and some ingredients in clay and glaze
> require both time as well as heat energy to accomplish chemical
> transformation to useful ceramic compounds.
> After firing my small (4cu ft) fibre kiln almost four hundred times
> I know I can reach 500 C in five hours with a two to three inch
> neutral flame and a minimum damper gap. But I have never though to
> weigh my LPG bottle. During the first firing I plotted time against
> temperature at the point where burnt gas exited the chamber into the
> flue.
> One idea I have considered is to rethink a kiln in terms of a
> vessel in which a fluid is contained by an impervious barrier,
> analogous to the puddled clay of a water dam. Such a barrier is
> saturated with water yet little escapes into the surrounding earth
> or air. Similarly, a dense fire brick is saturated with heat at cone
> maturity. After that it is a question of arresting thermal
> radiation, convection and conduction.
> Note the firing rate of Orton Small Cones, fast firing is not an
> unusual process when the makers give such information. 300 deg C per
> hour gives well over cone 8 in four and a half hours.
ivor and olive lewis on fri 7 oct 11
No doubt about it Ron, you do not have to do many firings with a kiln befor=
e
you develop a subjective appreciation of the way things will go. Much can
be leaned from having a pyrometer located away from the flame pathway. On
the kiln I have used for the past twenty years, which is designed to
redirect the exhausted atmosphere under the hearth of the kiln, the
pyrometer is near the floor within the exit flue. During the firing, even a=
s
the cones are bending, the pyrometer reading is always less than the given
temperature of the maturity cone. Towards the end of a firing careful
adjustment of the damper is necessary to ensure all my fuel is used to
generate heat by maintaining neutral atmosphere. If my subjective assessmen=
t
of the gas and damper settings are good the pyrometer reading continues to
rise without increasing fuel flow or changing damper setting until the cone
drops.
Regards,
Ivor
---- Original Message -----
From:
To: "ivor and olive lewis"
Cc:
Sent: Wednesday, October 05, 2011 9:18 AM
Subject: Re: firing speed and weight of ware
> Hi Ivor,
>
> Well I think there must be a point at which the most heat is transferred
> to the furniture and ware in the most efficient way - slower or faster
> than that and you have to use more fuel to get the same result.
>
> I do know that when programing my dilatometer I do have to go slow enoug=
h
> to prevent gradients that would affect the readings - not the same as th=
e
> problems for potters I know but there will be some affect on kiln
> furniture, shelves and bricks when fast fired.
>
> RR
>
>
>
> Quoting ivor and olive lewis :
>
>> Dear Ron,
>> That is something upon which I cannot comment without evidence and it
>> would cost a lot to set up the lab to test that hypothesis. (we did a
>> lot of calorimetric determinations in sixth form physics)
>> But having used a dilatometer, heated by electricity, where I could
>> apply uniform rates of heating and cooling in the quest for the
>> determination of phase changes in ferrous metals I know if the heating
>> or cooling is rapid the effects we expect may be suppressed. Phase
>> changes may be delayed and some ingredients in clay and glaze require
>> both time as well as heat energy to accomplish chemical transformation
>> to useful ceramic compounds.
>> After firing my small (4cu ft) fibre kiln almost four hundred times I
>> know I can reach 500 C in five hours with a two to three inch neutral
>> flame and a minimum damper gap. But I have never though to weigh my LPG
>> bottle. During the first firing I plotted time against temperature at
>> the point where burnt gas exited the chamber into the flue.
>> One idea I have considered is to rethink a kiln in terms of a vessel i=
n
>> which a fluid is contained by an impervious barrier, analogous to the
>> puddled clay of a water dam. Such a barrier is saturated with water yet
>> little escapes into the surrounding earth or air. Similarly, a dense
>> fire brick is saturated with heat at cone maturity. After that it is a
>> question of arresting thermal radiation, convection and conduction.
>> Note the firing rate of Orton Small Cones, fast firing is not an unusua=
l
>> process when the makers give such information. 300 deg C per hour gives
>> well over cone 8 in four and a half hours.
>
>
>
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