The Potter's Edge on sun 27 jul 03
Howdy all.
My name is Christopher; however my pottery ego is Victor X-Ray (long story)
I'm a relatively new potter and am seeking to complete my studio in a time
and cost efficient manner. At present, I have a wheel, extruder and an
Evenheat 6320XL that will be used for bisque only. At present, I'm glaze
firing at a community college's car kiln doing cone 10 reduction. (I'm done
with oxidation cone 5-6. It is not my bag. I've also been "gifted" a
gutted 30"X30" electric that I want to convert to gas (using propane as
we're moving from AZ to PA next year and don't want to spend the change
installing a gas line). I've been doing some research but have a number of
issues to address.
Because I would have to use this as a bisque, raku and cone 10 kiln what
difficulties if any have you encountered with each process (aside from the
previously discussed issue with heat loss and an addition of an extra layer
of brick)?
Even though the interior brick is in good repair, do you believe that it
would be an advantage to also provide an additional layer of 1" to 2"
refractory blanket encircling the entire outside and then held in place with
a compression fitting of durable "chicken wire" or metal sheeting? (My
freebee is the typical light porous refractory brick). I'm a bit concerned
about the efficiency of the fire (as most older electrics were only rated
to cone 8) I know that within reason brick is brick (not to be confused with
casted refractory, blankets, porous or dense) but I want to keep operating
costs down over time and am concerned about the possibility of a too rapid
cool coming down from cone 10.
Have you tried to Raku out of yours? The way that I'm envisioning this
project is that I'll have the base, 2 rings, the optional 3rd. Aside from
having a possibly awkward time pulling ware (if the third ring is added for
depth) what about the "heat blast" when the lid is removed? For the record,
the lid that I have is a lightweight fiber wool lid (but I'm in the process
of casting a thicker refractory lid to handle cone 10 temps.)
Regarding the size of the flu, I realize that bigger is better (as it can
always be narrowed) but any thoughts? I've read a number of articles and
there seems to be so many different opinions on what is adequate that I
can't get a norm. (still have not spoken to the supplier of the conversion
kit though)
Would you believe that a chimney would be of benefit (to ensure proper
negative pressure during the initial heat ramp/oxidation and then with the
flu closed some, the positive pressure of reduction)? Or do you think that
this is just over engineering (which I'm known to do)?
Any answers, suggestions would be of help and greatly appreciated.
psci_kw on mon 28 jul 03
----- Original Message -----
From: "The Potter's Edge"
To:
Sent: Monday, July 28, 2003 12:32 AM
Subject: Electric to Gas Kiln Conversion Questions
...but I want to keep operating
> costs down over time and am concerned about the possibility of a too rapid
> cool coming down from cone 10.
>
I don't know how anyone else does their raku, but this is my procedure:
I have an old, gutted electric from which I have removed the bottom (base)
It sits on a "platform" of sorts made up from a combination of firebrick
surrounded by cinderblock filled with sand.
The "kiln" such as it is, has attached to the top two 1/4" steel cables,
running together to one (to form a triangle) about four feet over the top of
the kiln, in which I have punched a 6" hole more or less centered in the
top.
The cable runs up to a pulley, horizontally to another pulley, and then
vertically down to a few pieces of steel and cinderblock as counterweight.
Pull the counterweight down, voila, the kiln goes UP, and vice versa. In
the "platform" under the kiln (and on which the kiln rests when in the down
position) is a "slot" in the top layer of firebrick, in which sits the gas
burner, with the shut off valve located close to the counterweight about
five feet away. The burner looks like an industrial version of those "weed
torches" you see in catalogs...you know the type. It can be pushed in
closer to the kiln, or pulled further out (reduction or oxidation). The
burner blows against a piece of firebrick under the piece I'm firing, which
is sitting on stands and shelf over it. All very primitive, but works well
for me.
Once the firing is completed, which is determined by sight through a peep in
the side of the kiln, as well as looking in through the top hole (which can
be closed off with a shelf as well), and a glance at the thermocouple temp.,
I turn off the gas, raise the kiln, and as quickly as I can grab the piece
with tongs and transfer it (for post-fire reduction) to my pit...more
cinderblocks enclosing sawdust, wood shavings, seaweed or whatever I'm
using. Sprinkle more on top of the piece, and cover. For oxidation, I
simply place it on a nearby kiln shelf and let it cool. Or just leave it on
the shelf I fired it on, and leave the kiln hanging in the air above it.
I estimate I lose no more than 5% to cracking, and then only if I've gotten
lazy about wedging. I have no pug mill (but oh is it on my wish list).
Clay either arrives premade, or if I get a bee in my bonnet, is mixed in an
old cement mixer.
Why worry about too rapid cooling? Our ancestors never did.
Wayne in Key West
The Potter's Edge on tue 29 jul 03
Wayne, thanks for the response. All taken to heart and will keep them in
mind as I move forward. For the record, I've also considered your same
method (slightly different but general principles apply) The way I see it
is for a one man operation the counterweight is a must. My GF is available
but she has an aversion to fire (which essentially strikes her from the raku
equation LOL)
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of psci_kw
Sent: Monday, July 28, 2003 5:55 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Electric to Gas Kiln Conversion Questions
----- Original Message -----
From: "The Potter's Edge"
To:
Sent: Monday, July 28, 2003 12:32 AM
Subject: Electric to Gas Kiln Conversion Questions
...but I want to keep operating
> costs down over time and am concerned about the possibility of a too rapid
> cool coming down from cone 10.
>
I don't know how anyone else does their raku, but this is my procedure:
I have an old, gutted electric from which I have removed the bottom (base)
It sits on a "platform" of sorts made up from a combination of firebrick
surrounded by cinderblock filled with sand.
The "kiln" such as it is, has attached to the top two 1/4" steel cables,
running together to one (to form a triangle) about four feet over the top of
the kiln, in which I have punched a 6" hole more or less centered in the
top.
The cable runs up to a pulley, horizontally to another pulley, and then
vertically down to a few pieces of steel and cinderblock as counterweight.
Pull the counterweight down, voila, the kiln goes UP, and vice versa. In
the "platform" under the kiln (and on which the kiln rests when in the down
position) is a "slot" in the top layer of firebrick, in which sits the gas
burner, with the shut off valve located close to the counterweight about
five feet away. The burner looks like an industrial version of those "weed
torches" you see in catalogs...you know the type. It can be pushed in
closer to the kiln, or pulled further out (reduction or oxidation). The
burner blows against a piece of firebrick under the piece I'm firing, which
is sitting on stands and shelf over it. All very primitive, but works well
for me.
Once the firing is completed, which is determined by sight through a peep in
the side of the kiln, as well as looking in through the top hole (which can
be closed off with a shelf as well), and a glance at the thermocouple temp.,
I turn off the gas, raise the kiln, and as quickly as I can grab the piece
with tongs and transfer it (for post-fire reduction) to my pit...more
cinderblocks enclosing sawdust, wood shavings, seaweed or whatever I'm
using. Sprinkle more on top of the piece, and cover. For oxidation, I
simply place it on a nearby kiln shelf and let it cool. Or just leave it on
the shelf I fired it on, and leave the kiln hanging in the air above it.
I estimate I lose no more than 5% to cracking, and then only if I've gotten
lazy about wedging. I have no pug mill (but oh is it on my wish list).
Clay either arrives premade, or if I get a bee in my bonnet, is mixed in an
old cement mixer.
Why worry about too rapid cooling? Our ancestors never did.
Wayne in Key West
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David Coggins on tue 29 jul 03
There is one major problem with your idea - the light refractory bricks used
in electric kilns are usually rated to 2300 degrees max. - if you fire to
cone 10 with a gas burner you WILL melt the bricks. At cone 10 the temp near
a burner would be well over 2500 degrees.
Also, if you put a layer of fibre around the outside of a stainless steel
encased kiln (as I assume it is) you will destroy the stainless steel very
quickly.
Old electric kilns are OK for Raku kilns, but definitely not cone 10.
Dave
David & Elaine Coggins
dcoggins@bigpond.com
www.users.bigpond.com/dcoggins
----- Original Message -----
From: "The Potter's Edge"
Sent: Monday, July 28, 2003 2:32 PM
Subject: Electric to Gas Kiln Conversion Questions
I've also been "gifted" a
> gutted 30"X30" electric that I want to convert to gas
>
> Even though the interior brick is in good repair, do you believe that it
> would be an advantage to also provide an additional layer of 1" to 2"
> refractory blanket encircling the entire outside and then held in place
with
> a compression fitting of durable "chicken wire" or metal sheeting? (My
> freebee is the typical light porous refractory brick).
psci_kw on tue 29 jul 03
----- Original Message -----
From: "The Potter's Edge"
To:
Sent: Tuesday, July 29, 2003 3:36 AM
Subject: Re: Electric to Gas Kiln Conversion Questions
> Wayne, thanks for the response. All taken to heart and will keep them in
> mind as I move forward. For the record, I've also considered your same
> method (slightly different but general principles apply) The way I see it
> is for a one man operation the counterweight is a must. My GF is
available
> but she has an aversion to fire (which essentially strikes her from the
raku
> equation LOL)
My S.O. too had an aversion to getting too close to "anything that roars" as
he put it. I got him over that quickly by explaining that if he would
"prepare" dinner, we could cook it on the kiln while firing (suitably
covered of course). No more hot kitchen! His raku chili is hot enough to
melt a cone 11 glaze off a pot at 300 feet :>)
Sometimes it's just a matter of making them aware of the economy of it, or
the fact that you CAN multi-task, or something to prove it beneficial to
THEIR interest :>)
Good Luck!
Wayne in Key West
The Potter's Edge on tue 29 jul 03
David thanks for the response. I too was worried about this; however the
car kiln that we use at the college appears to be made of the same brick. I
know it isn't a castable refractory and definitely isn't the hard brick
either as I've scratched it/tested it. What are your thoughts on going to
cone 8 with 10 glazes? I definitely don't want to suffer from China
Syndrome in my back yard but also don't want to only go to 5 because I'm
using 10 clay. Any suggestions? What about spraying some super cool
something or other on the bricks to make them more suited?
TTUL
CD
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of David
Coggins
Sent: Tuesday, July 29, 2003 12:01 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Electric to Gas Kiln Conversion Questions
There is one major problem with your idea - the light refractory bricks used
in electric kilns are usually rated to 2300 degrees max. - if you fire to
cone 10 with a gas burner you WILL melt the bricks. At cone 10 the temp near
a burner would be well over 2500 degrees.
Also, if you put a layer of fibre around the outside of a stainless steel
encased kiln (as I assume it is) you will destroy the stainless steel very
quickly.
Old electric kilns are OK for Raku kilns, but definitely not cone 10.
Dave
David & Elaine Coggins
dcoggins@bigpond.com
www.users.bigpond.com/dcoggins
----- Original Message -----
From: "The Potter's Edge"
Sent: Monday, July 28, 2003 2:32 PM
Subject: Electric to Gas Kiln Conversion Questions
I've also been "gifted" a
> gutted 30"X30" electric that I want to convert to gas
>
> Even though the interior brick is in good repair, do you believe that it
> would be an advantage to also provide an additional layer of 1" to 2"
> refractory blanket encircling the entire outside and then held in place
with
> a compression fitting of durable "chicken wire" or metal sheeting? (My
> freebee is the typical light porous refractory brick).
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
The Potter's Edge on wed 30 jul 03
Thanks Steve.
Looks like this should be relatively easy and is workable. As always,
appreciate the input. Just one final question on scale, does small for you
= 30"X30"? If so then I'm golden.
Well the verdict is in, I have one neutral, two positives, one beer drinker
who may know a lot but I couldn't understand him, and one negative. (No
offense to the beer drinker, it lubes my soul too) I'm going for it. On a
side bar, this discussion didn't sound much different than the Senate or
House LOL. Seriously, thanks to everyone who responded. Time to go spend
some money....figured I could also hit the Executive branch while I was at
it.
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of steve
harrison
Sent: Wednesday, July 30, 2003 4:10 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Electric to Gas Kiln Conversion Questions
> Hi there CD,
I've used the American "Thermal Ceramics" K23 insulating fire bricks in
all my own small kilns for many years. I've had very many hundreds of
firings with them and they are very good. The hot face gets a number of
shrinkage cracks, because they are technically overfired. However,
after half an inch in they are still in good nik. I would'nt use
anything else fro a small test kiln at cone 10. Their great advantage
is their light weight and fuel efficiency, compared to the RI 26. twice
as good as RI 26. But not as light as fibre, only about half as good. (
in general terms)
You will save a small fortune in fuel costs over the life of the kiln.
BUT, they do shrink and so are only good for small kilns. 8 courses max.
ALSO. don't get confused with the Thermal Ceramics JM23. This is a very
different brick, coming out of Italy. It does not take the hot face
work. It will spall (crack - up ) very badly.
Trust me, I've done it.
Steve Harrison
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
steve harrison on wed 30 jul 03
> Hi there CD,
I've used the American "Thermal Ceramics" K23 insulating fire bricks in
all my own small kilns for many years. I've had very many hundreds of
firings with them and they are very good. The hot face gets a number of
shrinkage cracks, because they are technically overfired. However,
after half an inch in they are still in good nik. I would'nt use
anything else fro a small test kiln at cone 10. Their great advantage
is their light weight and fuel efficiency, compared to the RI 26. twice
as good as RI 26. But not as light as fibre, only about half as good. (
in general terms)
You will save a small fortune in fuel costs over the life of the kiln.
BUT, they do shrink and so are only good for small kilns. 8 courses max.
ALSO. don't get confused with the Thermal Ceramics JM23. This is a very
different brick, coming out of Italy. It does not take the hot face
work. It will spall (crack - up ) very badly.
Trust me, I've done it.
Steve Harrison
steve harrison on thu 31 jul 03
Small kilns for me means "8 courses max"
by this, I meant 8 courses of brickwork. ie. 24"
which is close, but no cigar.
remember, shrinkage is a real problem.
Steve
On Thursday, July 31, 2003, at 04:58 PM, The Potter's Edge wrote:
> Thanks Steve.
>
> Looks like this should be relatively easy and is workable. As always,
> appreciate the input. Just one final question on scale, does small
> for you
> = 30"X30"? If so then I'm golden.
>
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