Michael Wendt on wed 14 sep 11
I will add to Paul Herman's comments that the thermal
conductivity of hard refractory brick is still fairly poor
(compared to metals for example).
I measured the specific heat of some hard brick and found
it to be
approximately 0.35 (water is the reference material and is
1 calorie per gram of water per degree Celsius). From this
you can see that rapid heating is just as Paul describes
because hard brick is a poor conductor so the inner brick
surface heats up fast if enough heat is applied and it only
requires about 1/3 the heat water needs to increase its
temperature.
I always fire my kilns full on as fat as they will go after
I pass red heat.
Slow firing wastes fuel.
Regards,
Michael Wendt
dianamp@COMCAST.NET on wed 14 sep 11
Dear Clayart:
This question is for those who fire hard brick kilns, such as salt.
I was told long ago that you can't rush a hard brick kiln and if you try to=
, you
are just wasting gas. Because hard brick can only absorb Only so much heat =
at a time,
which therefore should set the pace for your gas input.
Do you agree?? What is your experience trying to rush a hard brick, gas fir=
ed, kiln?
Thanks,
Diana Pancioli
E.M.U.
Vince Pitelka on wed 14 sep 11
Diana Pancioli wrote:
"I was told long ago that you can't rush a hard brick kiln and if you =3D
try to, you are just wasting gas. Because hard brick can only absorb =3D
Only so much heat at a time, which therefore should set the pace for =3D
your gas input.
Do you agree?? What is your experience trying to rush a hard brick, gas =3D
fired, kiln?
Hi Diana -=3D20
There is no truth to that at all. What a strange concept. The opposite =
=3D
is true. If you fire at a normal rate, or even if you fire faster than =3D
normal, the hardbrick is slowly absorbing heat while the wares are being =
=3D
fired. The slower you fire, the more heat is absorbed by the hardbrick =3D
and the more expensive the firing. Ultimate that is true of any form of =
=3D
refractory - they absorb heat over time, and in a long firing a greater =3D
amount of heat penetrates deeper into the refractory wall, but it just =3D
happens much more slowly with an insulating refractory than with =3D
hardbrick. In a quick firing, less heat penetrates the walls than in a =3D
slow firing, whether the walls are softbrick or hardbrick. That said, =3D
of course hardbrick absorbs a lot more energy in comparison to =3D
softbrick, but even in an all-hardbrick kiln, a reasonable-length firing =
=3D
is still going to be more efficient and less-expensive than a slow one. =
=3D
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu=3D20
http://iweb.tntech.edu/wpitelka
Paul Herman on wed 14 sep 11
Hi Diana,
I do fire a hard brick kiln, but wood burning, not gas. However, we
have found it possible to raise the temperature in our catenary salt
chamber very quickly. Many times it has gotten too hot, too fast and
we have had to struggle to keep it under control.
Whoever said this: " Because hard brick can only absorb Only so much
heat at a time" sounds like they didn't know what they were talking
about. I wonder what their faulty reasoning is based on. You can heat
up a hard brick kiln as fast as you like, if you have powerful enough
burners or a powerful enough wood burning firebox. Just dump enough
BTUs on it to do the job. That said, of course hard bricks take a lot
more fuel than soft bricks to get to any particular temperature.
Good firings,
Paul Herman
Great Basin Pottery
Doyle, California US
www.greatbasinpottery.com/
On Sep 14, 2011, at 11:38 AM, dianamp@COMCAST.NET wrote:
> Dear Clayart:
>
> This question is for those who fire hard brick kilns, such as salt.
>
> I was told long ago that you can't rush a hard brick kiln and if you
> try to, you
> are just wasting gas. Because hard brick can only absorb Only so
> much heat at a time,
> which therefore should set the pace for your gas input.
>
> Do you agree?? What is your experience trying to rush a hard brick,
> gas fired, kiln?
>
> Thanks,
>
> Diana Pancioli
> E.M.U.
ivor and olive lewis on thu 15 sep 11
Dear Diana Pancioli,
Adsorption of heat depends partially upon several factors
which include; the temperature difference between the temperature of the
flames and the temperature of the refractory. Then consider the thermal
conductivity of material being heated and the area of the exposed internal
faces of the kiln chamber. In addition, the physical density (Kg/Cu Metre)o=
f
the refractory has to be taken into account.
When I was gas firing Salt Glaze in a hard brick kiln I used the same rate
of temperature rise as I did when firing Stoneware in hard brick with Oil o=
r
porcelain with gas (LPG)in my fibre kiln, My target was 100 degrees Celsius
rise per hour
Sincere regards,
Ivor Lewis,
REDHILL,
South Australia
Snail Scott on thu 15 sep 11
On Sep 14, 2011, at 1:38 PM, dianamp@comcast.net wrote:
> I was told long ago that you can't rush a hard brick kiln and if you =3D
try to, you
> are just wasting gas...
I disagree. Why waste time and fuel letting the heat=3D20
penetrate the brick? Heat the air and the work, and=3D20
get 'er done. Obviously, the brick will act as thermal=3D20
mass and slow the firing whether we like it or not,=3D20
but slowing down on purpose just to heat the brick=3D20
seems pointless.
-Snail
gary navarre on thu 15 sep 11
So this returns me in part to my question about load =3D
Hey Folks,=3D0A=3D0A=3D0A=3DA0So this returns me in part to my question abo=
ut load =3D
density and the mass of the setting. It seems more stuff in the kiln would =
=3D
absorb more of whatever heat entered the chamber before the walls got too h=
=3D
ot and became saturated. I covered my 4.5" hardbrick chamber with insulatin=
=3D
g blanket and 2.5" IFB. I thinking of another inch of blanket over the IFB.=
=3D
Being 65cu.ft. this kiln is not going to fire fast like a 20'-30', it take=
=3D
s at least a day to get the good draft going. If I can find out how fast I =
=3D
can increase temperature this next firing I might not waste much fuel but b=
=3D
ut I expect at least a 10% loss compared to gas or oil. I'd say I wasted a =
=3D
lot of fuel in the last firing because there was more space between pieces =
=3D
and fewer pieces so the heat soaked into the walls or went out the stack. =
=3D
=3DA0 =3D0A=3D0A=3D0A=3DA0Mentioning oil, my pal Rick said he has an oil bu=
rner from =3D
a furnace I haven't seen yet but I wonder if I could stick one in the crown=
=3D
of my kiln and take a break from stoking to get a final soaking flame if n=
=3D
eeded. I don't know anything about hooking up an oil assist except the meta=
=3D
l plate drawings of the passive drip feed in Leach's book. I might have eno=
=3D
ugh natural draft with 16.5' but forced air would work better. Still, I thi=
=3D
nk the load mass is a major factor in efficient usage of fuel.=3D0A=3D0A=3D=
A0=3D0AG=3D
ary Navarre=3D0ANavarre Pottery=3D0ANavarre Enterprises=3D0ANorway, Michiga=
n, USA=3D
=3D0Ahttp://www.NavarrePottery.etsy.com=3D0Ahttp://www.youtube.com/GindaUP=
=3D0Aht=3D
tp://public.fotki.com/GindaUP/=3D0A=3D0A=3D0A=3D0A_________________________=
_______=3D
=3D0AFrom: Snail Scott =3D0ATo: Clayart@LSV.CERA=
MICS=3D
.ORG=3D0ASent: Thursday, September 15, 2011 8:09 AM=3D0ASubject: Re: [Claya=
rt] =3D
Hard Brick Kilns=3D0A=3D0AOn Sep 14, 2011, at 1:38 PM, dianamp@comcast.net =
wrot=3D
e:=3D0A> I was told long ago that you can't rush a hard brick kiln and if y=
ou=3D
try to, you=3D0A> are just wasting gas...=3D0A=3D0A=3D0AI disagree. Why wa=
ste time=3D
and fuel letting the heat =3D0Apenetrate the brick? Heat the air and the w=
or=3D
k, and =3D0Aget 'er done. Obviously, the brick will act as thermal =3D0Amas=
s an=3D
d slow the firing whether we like it or not, =3D0Abut slowing down on purpo=
se=3D
just to heat the brick =3D0Aseems pointless.=3D0A=3D0A-Snail
Larry Kruzan on fri 16 sep 11
Hi Gary,
Could you use that furnace burner to assist in preheating the kiln flue? =
=3D
I'd
question if the was enough BTU output to make much difference in your =3D
kiln,
but as a aid in warming the flue, it might help a lot. Do you have an
opening in the flue to stick a burner in? Just some random thoughts, =3D
pal.
Best always,
Larry
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of gary =3D
navarre
Sent: Friday, September 16, 2011 12:26 AM
To: Clayart@LSV.CERAMICS.ORG
Subject: Re: Hard Brick Kilns
<<<<<<<<<<<<>>>>>>>>>
=3DA0Mentioning oil, my pal Rick said he has an oil burner from a furnace =
=3D
I
haven't seen yet but I wonder if I could stick one in the crown of my =3D
kiln
and take a break from stoking to get a final soaking flame if needed. I
don't know anything about hooking up an oil assist except the metal =3D
plate
drawings of the passive drip feed in Leach's book. I might have enough
natural draft with 16.5' but forced air would work better. Still, I =3D
think
the load mass is a major factor in efficient usage of fuel.
=3DA0
Gary Navarre
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