Donovan Palmquist on mon 23 jul 12
Hi all,
I'd like to add my opinion although belatedly to the thread on the bourry=
=3D
box=3D20
kiln and the flue channels and the use of expansion joints in kilns.
At last count I have built 12 (modified to my standards) bourry box kilns=
=3D
. The=3D20
flue channels in the floor act as a way to distribute the fire more evenl=
=3D
y=3D20
throughout the kiln. By placing your kiln shelves on these channels and u=
=3D
p=3D20
against the exit flues you will force the fire to find its way through th=
=3D
e floor.
This will negate most of but not all of the crossdraft effect in the kiln=
=3D
. The=3D20
result is less "one sided" pots from the kiln. The original design of Em=
=3D
ile=3D20
Bourry's in the late 19th early- 20th century kiln was to protect the wor=
=3D
k from=3D20
coal/wood ash. The bag wall was completely solid to almost the arch. Th=
=3D
is=3D20
forced the heat to the top of the kiln and then down through the floor. =
=3D
This=3D20
would allow you to fire wares with a minimum of ash contacting the work.=3D=
20=3D
=3D20
Some work out of bourrys this style look as though they were gas fired. =
=3D
In=3D20
the bourry box kilns I have built the bag walls can be opened to a more o=
=3D
r=3D20
less degree to allow some flame and ash to come in contact with the work.=
=3D
=3D20=3D20
The flue channels in the floor allow you to direct the flame down through=
=3D
the=3D20
floor. In my bourry the flame path is almost vertical to the pots, depos=
=3D
iting=3D20
ash on the backside of work. It looks as though the ash is raining down =
=3D
on the=3D20
pots. The effect is fewer one sided pots.=3D20=3D20
If you remove the flue channels you will have more crossdraft effect and =
=3D
more=3D20
one sided pots. Another function flue channels have is to act like a "co=
=3D
llection=3D20
flue" for hot gasses as they cool and leave the kiln. This expansion and=
=3D
=3D20
contraction of air and combustion products is what drives the kiln....sor=
=3D
t of a=3D20
venturi effect. Most wood kilns without some kind of collection flue wil=
=3D
l stall=3D20
at high temperatures.
There was a thread on the use of expansion joints when building kilns. I=
=3D
=3D20
would also like to ad my opinion here.=3D20=3D20
Based on my experience of about 350 kilns I can say that the only place I=
=3D
=3D20
have ever used them is in long anagama type tube kilns. Primarily becaus=
=3D
e=3D20
they are made of hardbrick and there is a large coefficient of expansion =
=3D
with=3D20
that material. That being said I have dry stacked kilns (bad idea for=3D2=
0=3D
longevity although you can pound the bricks back into place), completely=3D=
20=3D
mortared a kiln together, another bad idea that can cause a kiln to tear =
=3D
itself=3D20
apart, to using a bedding mortar of fireclay and sand to level and seal t=
=3D
he=3D20
brick joints. This also has an effect of when fired the fireclay and san=
=3D
d=3D20
shrinks slightly it seems to let the bricks move a little without causing=
=3D
wall=3D20
cracks. I have seen these kilns with over 200 firings and they are as st=
=3D
raight=3D20
and true as the day I built them. I am also an advocate of welding a sol=
=3D
id=3D20
steel frame on the kiln. Using valve springs and threaded rod may work fo=
=3D
r a=3D20
while but the kiln WILL move eventually. If you imagine the frame of a k=
=3D
iln=3D20
with threaded tie rods without the brick in it you will see a frame that =
=3D
is=3D20
wobbly and unstable. ALL industrial and commercial kilns have solid weld=
=3D
ed=3D20
frames and do so for a reason.
jonathan byler on mon 23 jul 12
Hi Donovan,
Thanks for your input. Are you saying that expansion joints in the
walls and floor of a smaller kiln (say 30-45 cu ft) with hard brick
interior and IFB exterior are pretty much unnecessary if you use a
rigid welded frame?
-jon byler
On Jul 23, 2012, at 12:15 PM, Donovan Palmquist wrote:
> Hi all,
>
> I'd like to add my opinion although belatedly to the thread on the
> bourry box
> kiln and the flue channels and the use of expansion joints in kilns.
>
> At last count I have built 12 (modified to my standards) bourry box
> kilns. The
> flue channels in the floor act as a way to distribute the fire more
> evenly
> throughout the kiln. By placing your kiln shelves on these channels
> and up
> against the exit flues you will force the fire to find its way
> through the floor.
> This will negate most of but not all of the crossdraft effect in the
> kiln. The
> result is less "one sided" pots from the kiln. The original design
> of Emile
> Bourry's in the late 19th early- 20th century kiln was to protect
> the work from
> coal/wood ash. The bag wall was completely solid to almost the
> arch. This
> forced the heat to the top of the kiln and then down through the
> floor. This
> would allow you to fire wares with a minimum of ash contacting the
> work.
> Some work out of bourrys this style look as though they were gas
> fired. In
> the bourry box kilns I have built the bag walls can be opened to a
> more or
> less degree to allow some flame and ash to come in contact with the
> work.
> The flue channels in the floor allow you to direct the flame down
> through the
> floor. In my bourry the flame path is almost vertical to the pots,
> depositing
> ash on the backside of work. It looks as though the ash is raining
> down on the
> pots. The effect is fewer one sided pots.
> If you remove the flue channels you will have more crossdraft effect
> and more
> one sided pots. Another function flue channels have is to act like
> a "collection
> flue" for hot gasses as they cool and leave the kiln. This
> expansion and
> contraction of air and combustion products is what drives the
> kiln....sort of a
> venturi effect. Most wood kilns without some kind of collection
> flue will stall
> at high temperatures.
>
> There was a thread on the use of expansion joints when building
> kilns. I
> would also like to ad my opinion here.
> Based on my experience of about 350 kilns I can say that the only
> place I
> have ever used them is in long anagama type tube kilns. Primarily
> because
> they are made of hardbrick and there is a large coefficient of
> expansion with
> that material. That being said I have dry stacked kilns (bad idea
> for
> longevity although you can pound the bricks back into place),
> completely
> mortared a kiln together, another bad idea that can cause a kiln to
> tear itself
> apart, to using a bedding mortar of fireclay and sand to level and
> seal the
> brick joints. This also has an effect of when fired the fireclay
> and sand
> shrinks slightly it seems to let the bricks move a little without
> causing wall
> cracks. I have seen these kilns with over 200 firings and they are
> as straight
> and true as the day I built them. I am also an advocate of welding
> a solid
> steel frame on the kiln. Using valve springs and threaded rod may
> work for a
> while but the kiln WILL move eventually. If you imagine the frame
> of a kiln
> with threaded tie rods without the brick in it you will see a frame
> that is
> wobbly and unstable. ALL industrial and commercial kilns have solid
> welded
> frames and do so for a reason.
| |
|
