Cynthia Bracker on thu 23 mar 06
Hello Clayarters,
Sorry to take so long to reply to this thread, I'm still catching up =20
from NCECA. Antoinette, the kiln you describe sounds sufficiently =20
similar to ours, (though I don't know if it is or not for certain =20
since I can't tell from your e-mail what school it was originally =20
sold to) that I feel I should reply. I will do so as if it is our =20
kiln. First some basic information: The Bracker Raku Kiln is a =20
lightweight and portable design for firing ceramic pieces in your own =20=
backyard. The kiln we make today was designed by Bill Bracker in the =20
early 1970=92s utilizing the (at that time, new) technology of ceramic =20=
fiber. The kiln is made by lining a cage of wire fence material and a =20=
metal garbage can lid with one-half inch thick fiber blanket. The =20
fiber is then rigidized with a mixture of sodium silicate and water. =20
The use of the fiber allows the ceramicist to have the insulating =20
qualities of 2.5 inches of soft insulating firebrick, yet it is light =20=
enough that anyone is able to pick it up. You can look at pictures =20
of the set up and get more information on our website: http://=20
www.brackers.com/store/results_detail.cfm?cat=3D62&prodid=3DRAKUKILN
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> It had a metal can lid at the top and 3 holes about 3.5 x2.5
> inches on the one side high up on the drum. I cut 3 bricks to close =20=
> the
> holes (ports if you wish).
The ports are cut in accordance with Kiln Design theory (principle 3 =20
as delineated by Fred Olsen in The Kiln Book, p42-43 of current =20
edition) which states that (paraphrased) total number of square =20
inches of inlet area must be equal to the total number of square =20
inches in outlet area. Or in layman terms: What goes in must come =20
out, and they must be equal. However, these can be left open or =20
partially plugged to oxidize or reduce the firing atmosphere.
> On Mar 6, 2006, at 11:13 PM, Lynn Barnwell wrote:
> why 3 ports on the front? There was not a flue opening on the top, is
> this necessary?
The first design Dad did had the holes on the opposite side. =20
However, after observing use in a school setting, Dad moved the =20
venting ports for the purpose of safety. He didn't want anyone =20
walking too close to the kiln and getting hit by flames licking out =20
of the ports. It is not necessary to have a flue opening on top, as =20
long as you don't cover all the port holes on the front. As an added =20=
benefit, the orientation of vent holes on the side rather than in the =20=
top, like many fiber raku kilns have, provides better circulation of =20
heat.
> On Mar 6, 2006, at 11:13 PM, Lynn Barnwell wrote:
> the seam where the kaowool met was not
> overlapped and you could see into the kiln from that point. This =20
> was only
> my second time trying to fire raku and was disappointed
> that this was a top hat fiber kiln that is on the market.
The seam should not be overlapped. The cage is lined with the fiber, =20=
then the wire on the cage is crimped in such a way that the seam is =20
tight. When installed, the fiber is put in a wave pattern to account =20=
for the linear shrinkage and LOI (Loss on Ignition) of ceramic =20
fiber. All non-pre-fired ceramic fiber does this, regardless of =20
manufacturer. See Fiberfrax or Carborundum documentation if you =20
would like more details on this.
> On Mar 6, 2006, at 11:13 PM, Lynn Barnwell wrote:
> Would another layer of fiber blanket wrapped around the
> outside of the wire frame overlapping at a different point
> than the first layer help the kiln?
Adding another layer of fiber, or increasing the thickness of the =20
fiber would slow kiln cooling, but since the pieces are not cooled in =20=
the kiln, it would be unnecessary.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> The floor was firebricks. I used a burner (looked
> like a standard one used for raku in America) with a narrow gas =20
> outlet and
> then the attached metal tub of about 3.5 inches. The shelve was =20
> lifted on
> probes about 5 inches high and a small brick was used to split the =20
> flame.
We include a case of 2600 degree firebricks with our Raku Kiln Kit =20
which provide an excellent way to post the first shelf. Use three =20
insulating firebricks (2.5" x 4.5" x 9") in a triangular formation, =20
with a "point" of the triangle exactly opposite of the burner port, =20
which will baffle (or circulate and mix) the flame and heat from the =20
burner. You can place the posting firebrick on the pad of firebrick =20
(or kiln lid) so that the 9" side is either vertical or horizontal. =20
Either way may work best with your individual, unique set-up. The =20
burner that comes with the kit has an output of 1/2 million BTUs. =20
However, the burner is not a forced-air burner, so a good supply of =20
oxygen to the burner head is imperative. The tip of the burner should =20=
be approximately 1/2" to 1" outside of the kiln, but you can also =20
control the atmosphere and speed of firing by moving the burner =20
slightly towards or away from the kiln. The flame from the burner =20
should be directed so that it is under the shelf. Initial firings in =20=
a cold kiln should take about one hour and successive firings can go =20
as fast as about thirty minutes, depending on how fast you want to =20
fire. If you are using a different burner, or natural gas, you =20
should check into what the needs of that burner are for combustion.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> I think the kiln will be very unsafe
> if a sudden wind comes up. It is too lightweight.
I've never heard of this actually happening. I suppose it is =20
possible since it is lightweight, but I've never had a reported case =20
of it. We use it here in Kansas, which can be VERY windy, very =20
suddently. You can certainly put a hard brick on top of the lid if =20
you are still concerned (which we do here). However, I would not =20
recommend Rakuing in extremely high winds in any kiln. Rakuing in =20
these conditions is unsafe, both to the firers and pieces.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> I think there was too much of a draft, since the flames went =20
> everywhere
> (also unsafe). Even after I used sand to seal off the bottom, the =20
> flames
> still went everywhere, through the ports, through the seams between =20=
> the lid
> and the sides.
The problem is that since you said you blocked all the outflow ports, =20=
there was NO DRAFT. The pressurized kiln was trying to let the =20
combusted gas out while the burner was supplying new gas. Since =20
there was no oxygen in the kiln, the gas seeped out of the kiln and =20
immediately combusted and ignited in the oxygen atmosphere. =20
(ANALOGY: If you light a fire in your fireplace, then close the flue, =20=
where are the flames going to go? Into your house, because it is the =20=
only place it can get to that has oxygen.)
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> After 2 efforts to reach temperature (one 1.5 our period and
> then after adjusting some things, another 45 minute period) I =20
> realized that
> I will not be able to reach temperature in this kiln. We ended up =20
> with some
> melting on the inside of 2 pieces, but the rest was just one big =20
> black smoke
> mess.
Again, since you had the vent ports all plugged, you were probably in =20=
reduction the entire time, thus accounting for the inability to reach =20=
temperature and the black smoke mess. You can refire the kiln empty =20
to clear the carbon, though you'll never get it ALL out.
> On Mar 6, 2006, at 2:45 PM, William & Susan Schran User wrote:
> One of my students bought one of these kilns some time back.
> She also could not get up to temperature.
>
> I had her:
> Build a 9" high wall of IFB. Original design had top of kiln =20
> sitting right
> on the floor.
> Had her raise the shelf to 9". I think it will work lower though.
> Had her make certain the burner was not in or touching the burner =20
> port.
> Had her set it back about an inch from the opening.
> Had her get a pressure gauge and use less pressure.
> She was going through a 20# tank of propane for one or two firings.
> Had her cover one of the three flue holes with fiber blanket.
> Had her get smaller diameter shelf.
> She tried each thing, one at a time, but ended up doing all of the =20
> above to
> get to raku temperature in less than 1/2 hour and several firings =20
> out of a
> 20# tank of propane.
The problem in this situation was the tank. Had she switched to at =20
least a 30# tank (minimum, larger is recommended), she would not have =20=
needed to Build a 9" high wall of IFB, raise the shelf to 9" or get =20
smaller diameter shelf. Having the burner outside the opening is a =20
necessity in order to mix the gas with oxygen and get combustion. =20
Covering one of the port holes is optional and sometimes can be helpful.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> In my view this is a poorly designed kiln and I will state that in =20
> my report
> unless some of you clayarters will tell me what I=92ve done wrong.
I claim no objectivity on this personally, as it is my dad's design, =20
and, by the way, the oldest design for a Fiber Raku Kiln around (It =20
was presented at the Flagstaff NCECA in 1973. There were no other =20
known Fiber Raku Kilns at that time), so of course, I think it is an =20
exceptional design. However, I can provide the name of one person in =20=
particular who IS objective and has experience with MANY Raku kilns =20
over the years, and that would be Robert Piepenburg (author of Raku =20
Pottery and several other titles). He did a workshop here last fall =20
and went out of his way to complement the design of this kiln at the =20
close of the workshop. I spoke to him just know on the phone to make =20=
sure it was ok with him that I use his name. He said "Absolutely! =20
That's a great kiln, I have no problem endorsing it. It's such a =20
unique design, too, espeically with those vent ports on the side. I =20
really liked it." I'd be happy to provide names of others who have =20
used the kiln and can speak objectively. If anyone is curious, =20
please contact me off-list.
Lastly, I do have a question. Why did you not call the manufacturer =20
(whether that's us or someone else) when you had problems? Who would =20=
be better than the designer to troubleshoot your problems and help =20
you have success?
And in more generality, I'd like to add that many manufacturers/=20
suppliers are not on Clayart. I feel like I can safely speak for the =20=
vast majority of us when I say that we NEED to hear things like this =20
first hand. If there is a problem with the design of any piece of =20
equipment, it cannot get fixed unless the manufacturer knows about =20
it. I think Clayart is a wonderful thing and a great place to get =20
lots of input, ideas, and solutions from a lot of people with varying =20=
degrees of expertise & experience. But no one on this list can =20
answer the kinds of construction and design questions that the actual =20=
manufacturer of a piece of equipment can answer. I think William =20
Schran said it best (On Jan 15, 2006, at 4:20 PM specifically =20
referring to problems with a Bailey Gas kiln):
> Always - first call goes to manufacturer/supplier when one =20
> encounters any
> problems with equipment. They should have somebody available to =20
> answer your
> questions and walk you through the process.
>
> If you want to start a fire, push the kiln up against a wall made of
> combustible materials, then....
>
> I'm sorry, I couldn't help myself.
I welcome further commentary or questions, on or off list.
Cindy (on behalf of myself, Anne W. Bracker and Anne M. Bracker)
Cindy Bracker
Bracker's Good Earth Clays, Inc.
888-822-1982
http://www.brackers.com
Antoinette Badenhorst on thu 23 mar 06
Thank you Cynthia, now I know at least what kind of kiln we're talking
about. I will try your instructions and see if I can manage it better. I
will still not use it around children. Sorry if this offended you, but I =
had
no where to turn to as to my old claybuds. Thank you guys.
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Cynthia =
Bracker
Sent: Thursday, March 23, 2006 2:28 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Analyzing this raku kiln
Hello Clayarters,
Sorry to take so long to reply to this thread, I'm still catching up =20
from NCECA. Antoinette, the kiln you describe sounds sufficiently =20
similar to ours, (though I don't know if it is or not for certain =20
since I can't tell from your e-mail what school it was originally =20
sold to) that I feel I should reply. I will do so as if it is our =20
kiln. First some basic information: The Bracker Raku Kiln is a =20
lightweight and portable design for firing ceramic pieces in your own =20
backyard. The kiln we make today was designed by Bill Bracker in the =20
early 1970's utilizing the (at that time, new) technology of ceramic =20
fiber. The kiln is made by lining a cage of wire fence material and a =20
metal garbage can lid with one-half inch thick fiber blanket. The =20
fiber is then rigidized with a mixture of sodium silicate and water. =20
The use of the fiber allows the ceramicist to have the insulating =20
qualities of 2.5 inches of soft insulating firebrick, yet it is light =20
enough that anyone is able to pick it up. You can look at pictures =20
of the set up and get more information on our website: http://=20
www.brackers.com/store/results_detail.cfm?cat=3D62&prodid=3DRAKUKILN
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> It had a metal can lid at the top and 3 holes about 3.5 x2.5
> inches on the one side high up on the drum. I cut 3 bricks to close =20
> the
> holes (ports if you wish).
The ports are cut in accordance with Kiln Design theory (principle 3 =20
as delineated by Fred Olsen in The Kiln Book, p42-43 of current =20
edition) which states that (paraphrased) total number of square =20
inches of inlet area must be equal to the total number of square =20
inches in outlet area. Or in layman terms: What goes in must come =20
out, and they must be equal. However, these can be left open or =20
partially plugged to oxidize or reduce the firing atmosphere.
> On Mar 6, 2006, at 11:13 PM, Lynn Barnwell wrote:
> why 3 ports on the front? There was not a flue opening on the top, is
> this necessary?
The first design Dad did had the holes on the opposite side. =20
However, after observing use in a school setting, Dad moved the =20
venting ports for the purpose of safety. He didn't want anyone =20
walking too close to the kiln and getting hit by flames licking out =20
of the ports. It is not necessary to have a flue opening on top, as =20
long as you don't cover all the port holes on the front. As an added =20
benefit, the orientation of vent holes on the side rather than in the =20
top, like many fiber raku kilns have, provides better circulation of =20
heat.
> On Mar 6, 2006, at 11:13 PM, Lynn Barnwell wrote:
> the seam where the kaowool met was not
> overlapped and you could see into the kiln from that point. This =20
> was only
> my second time trying to fire raku and was disappointed
> that this was a top hat fiber kiln that is on the market.
The seam should not be overlapped. The cage is lined with the fiber, =20
then the wire on the cage is crimped in such a way that the seam is =20
tight. When installed, the fiber is put in a wave pattern to account =20
for the linear shrinkage and LOI (Loss on Ignition) of ceramic =20
fiber. All non-pre-fired ceramic fiber does this, regardless of =20
manufacturer. See Fiberfrax or Carborundum documentation if you =20
would like more details on this.
> On Mar 6, 2006, at 11:13 PM, Lynn Barnwell wrote:
> Would another layer of fiber blanket wrapped around the
> outside of the wire frame overlapping at a different point
> than the first layer help the kiln?
Adding another layer of fiber, or increasing the thickness of the =20
fiber would slow kiln cooling, but since the pieces are not cooled in =20
the kiln, it would be unnecessary.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> The floor was firebricks. I used a burner (looked
> like a standard one used for raku in America) with a narrow gas =20
> outlet and
> then the attached metal tub of about 3.5 inches. The shelve was =20
> lifted on
> probes about 5 inches high and a small brick was used to split the =20
> flame.
We include a case of 2600 degree firebricks with our Raku Kiln Kit =20
which provide an excellent way to post the first shelf. Use three =20
insulating firebricks (2.5" x 4.5" x 9") in a triangular formation, =20
with a "point" of the triangle exactly opposite of the burner port, =20
which will baffle (or circulate and mix) the flame and heat from the =20
burner. You can place the posting firebrick on the pad of firebrick =20
(or kiln lid) so that the 9" side is either vertical or horizontal. =20
Either way may work best with your individual, unique set-up. The =20
burner that comes with the kit has an output of 1/2 million BTUs. =20
However, the burner is not a forced-air burner, so a good supply of =20
oxygen to the burner head is imperative. The tip of the burner should =20
be approximately 1/2" to 1" outside of the kiln, but you can also =20
control the atmosphere and speed of firing by moving the burner =20
slightly towards or away from the kiln. The flame from the burner =20
should be directed so that it is under the shelf. Initial firings in =20
a cold kiln should take about one hour and successive firings can go =20
as fast as about thirty minutes, depending on how fast you want to =20
fire. If you are using a different burner, or natural gas, you =20
should check into what the needs of that burner are for combustion.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> I think the kiln will be very unsafe
> if a sudden wind comes up. It is too lightweight.
I've never heard of this actually happening. I suppose it is =20
possible since it is lightweight, but I've never had a reported case =20
of it. We use it here in Kansas, which can be VERY windy, very =20
suddently. You can certainly put a hard brick on top of the lid if =20
you are still concerned (which we do here). However, I would not =20
recommend Rakuing in extremely high winds in any kiln. Rakuing in =20
these conditions is unsafe, both to the firers and pieces.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> I think there was too much of a draft, since the flames went =20
> everywhere
> (also unsafe). Even after I used sand to seal off the bottom, the =20
> flames
> still went everywhere, through the ports, through the seams between =20
> the lid
> and the sides.
The problem is that since you said you blocked all the outflow ports, =20
there was NO DRAFT. The pressurized kiln was trying to let the =20
combusted gas out while the burner was supplying new gas. Since =20
there was no oxygen in the kiln, the gas seeped out of the kiln and =20
immediately combusted and ignited in the oxygen atmosphere. =20
(ANALOGY: If you light a fire in your fireplace, then close the flue, =20
where are the flames going to go? Into your house, because it is the =20
only place it can get to that has oxygen.)
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> After 2 efforts to reach temperature (one 1.5 our period and
> then after adjusting some things, another 45 minute period) I =20
> realized that
> I will not be able to reach temperature in this kiln. We ended up =20
> with some
> melting on the inside of 2 pieces, but the rest was just one big =20
> black smoke
> mess.
Again, since you had the vent ports all plugged, you were probably in =20
reduction the entire time, thus accounting for the inability to reach =20
temperature and the black smoke mess. You can refire the kiln empty =20
to clear the carbon, though you'll never get it ALL out.
> On Mar 6, 2006, at 2:45 PM, William & Susan Schran User wrote:
> One of my students bought one of these kilns some time back.
> She also could not get up to temperature.
>
> I had her:
> Build a 9" high wall of IFB. Original design had top of kiln =20
> sitting right
> on the floor.
> Had her raise the shelf to 9". I think it will work lower though.
> Had her make certain the burner was not in or touching the burner =20
> port.
> Had her set it back about an inch from the opening.
> Had her get a pressure gauge and use less pressure.
> She was going through a 20# tank of propane for one or two firings.
> Had her cover one of the three flue holes with fiber blanket.
> Had her get smaller diameter shelf.
> She tried each thing, one at a time, but ended up doing all of the =20
> above to
> get to raku temperature in less than 1/2 hour and several firings =20
> out of a
> 20# tank of propane.
The problem in this situation was the tank. Had she switched to at =20
least a 30# tank (minimum, larger is recommended), she would not have =20
needed to Build a 9" high wall of IFB, raise the shelf to 9" or get =20
smaller diameter shelf. Having the burner outside the opening is a =20
necessity in order to mix the gas with oxygen and get combustion. =20
Covering one of the port holes is optional and sometimes can be helpful.
> On Mar 6, 2006, at 10:53 AM, Antoinette Badenhorst wrote:
> In my view this is a poorly designed kiln and I will state that in =20
> my report
> unless some of you clayarters will tell me what I've done wrong.
I claim no objectivity on this personally, as it is my dad's design, =20
and, by the way, the oldest design for a Fiber Raku Kiln around (It =20
was presented at the Flagstaff NCECA in 1973. There were no other =20
known Fiber Raku Kilns at that time), so of course, I think it is an =20
exceptional design. However, I can provide the name of one person in =20
particular who IS objective and has experience with MANY Raku kilns =20
over the years, and that would be Robert Piepenburg (author of Raku =20
Pottery and several other titles). He did a workshop here last fall =20
and went out of his way to complement the design of this kiln at the =20
close of the workshop. I spoke to him just know on the phone to make =20
sure it was ok with him that I use his name. He said "Absolutely! =20
That's a great kiln, I have no problem endorsing it. It's such a =20
unique design, too, espeically with those vent ports on the side. I =20
really liked it." I'd be happy to provide names of others who have =20
used the kiln and can speak objectively. If anyone is curious, =20
please contact me off-list.
Lastly, I do have a question. Why did you not call the manufacturer =20
(whether that's us or someone else) when you had problems? Who would =20
be better than the designer to troubleshoot your problems and help =20
you have success?
And in more generality, I'd like to add that many manufacturers/=20
suppliers are not on Clayart. I feel like I can safely speak for the =20
vast majority of us when I say that we NEED to hear things like this =20
first hand. If there is a problem with the design of any piece of =20
equipment, it cannot get fixed unless the manufacturer knows about =20
it. I think Clayart is a wonderful thing and a great place to get =20
lots of input, ideas, and solutions from a lot of people with varying =20
degrees of expertise & experience. But no one on this list can =20
answer the kinds of construction and design questions that the actual =20
manufacturer of a piece of equipment can answer. I think William =20
Schran said it best (On Jan 15, 2006, at 4:20 PM specifically =20
referring to problems with a Bailey Gas kiln):
> Always - first call goes to manufacturer/supplier when one =20
> encounters any
> problems with equipment. They should have somebody available to =20
> answer your
> questions and walk you through the process.
>
> If you want to start a fire, push the kiln up against a wall made of
> combustible materials, then....
>
> I'm sorry, I couldn't help myself.
I welcome further commentary or questions, on or off list.
Cindy (on behalf of myself, Anne W. Bracker and Anne M. Bracker)
Cindy Bracker
Bracker's Good Earth Clays, Inc.
888-822-1982
http://www.brackers.com
_________________________________________________________________________=
___
__
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.
Cynthia Bracker Sturm on fri 24 mar 06
Hmmmm. I'll have to ask Mom for certain why we continue with the
current burner. I know Dad started with that because he used one for
burning weeds, and it was inexpensive. Perhaps at that time, it was
the only one available - ? It was a long time ago. I think there are
smaller ones in that same brand now. Next time we order burners, I'll
see if I can get one of those. I have some things I need to Raku
anyway, so I could test it and see how it works.
Good suggestion! Thanks
Cindy
On Mar 24, 2006, at 9:28 PM, William & Susan Schran User wrote:
> On 3/24/06 6:05 PM, "Cindy Bracker" wrote:
>
>> What was the BTU output of the burner you used in school? If it was
>> a smaller burner, say 100,000 BTUs or even 1/4million BTUs, then they
>> don't require as much pressure behind them to achieve their BTUs, and
>> thus, would operate just fine on a 20# tank. This torch, which is
>> 1/2million BTUs requires a 30# tank in order to fire a kiln of this
>> size correctly.
>
> Cindy - You are correct. I did not take into account the burner size.
> I'm working with a burner of about 75,000 btu capacity.
>
> May I ask why a burner of 1/2 million btu is used with your raku
> set-up?
>
> Just curious.
>
> Our Geil 24 cu. ft. gas fired kiln using 8 burners has a total
> capacity of
> 300,000 btu. It would seem a 1/2 million btu in a small kiln is
> perhaps a
> bit much. Have you tested your kiln with a smaller burner to see if it
> would
> fire as well?
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
> _______________________________________________________________________
> _______
> 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.
>
William & Susan Schran User on fri 24 mar 06
On 3/23/06 3:28 PM, "Cynthia Bracker" wrote:
> The problem in this situation was the tank. Had she switched to at
> least a 30# tank (minimum, larger is recommended), she would not have
> needed to Build a 9" high wall of IFB, raise the shelf to 9" or get
> smaller diameter shelf. Having the burner outside the opening is a
> necessity in order to mix the gas with oxygen and get combustion.
> Covering one of the port holes is optional and sometimes can be helpful.
IMHO I don't think the tank IS the problem. Too much pressure is more likely
the issue.
We used 20# tanks at school for many years, getting as many as a dozen
firings out of one tank. We kept the tank in a tub of water to prevent
freeze up. We now use 30# tanks simply for the convenience of not having to
refill them as often.
Too much gas pressure creates too much back pressure that will stall the
temperature climb.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Cindy Bracker on fri 24 mar 06
What was the BTU output of the burner you used in school? If it was
a smaller burner, say 100,000 BTUs or even 1/4million BTUs, then they
don't require as much pressure behind them to achieve their BTUs, and
thus, would operate just fine on a 20# tank. This torch, which is
1/2million BTUs requires a 30# tank in order to fire a kiln of this
size correctly. Recently, we sold a Raku kiln kit to a school where
they believed as you do that they could use a 20 pound tank, because
that's what they'd always done (on a different kiln, using a
different burner). They could never get to temperature. They even
went as far as to manifold 4 20# tanks together, which only increase
the amount of gas, not the amount of pressure. The next week, after
speaking to us, they fired using 1 - 30 pound tank and got 10 perfect
firings in one day and had enough gas to fire the next day had they
wanted to.
Our raku kiln and burner set up does require at least a 30# tank.
Period. 20# is insufficient.
Cindy
Cindy Bracker
Bracker's Good Earth Clays, Inc.
888-822-1982
http://www.brackers.com
On Mar 24, 2006, at 7:47 AM, William & Susan Schran User wrote:
> On 3/23/06 3:28 PM, "Cynthia Bracker" wrote:
>
>> The problem in this situation was the tank. Had she switched to at
>> least a 30# tank (minimum, larger is recommended), she would not have
>> needed to Build a 9" high wall of IFB, raise the shelf to 9" or get
>> smaller diameter shelf. Having the burner outside the opening is a
>> necessity in order to mix the gas with oxygen and get combustion.
>> Covering one of the port holes is optional and sometimes can be
>> helpful.
>
> IMHO I don't think the tank IS the problem. Too much pressure is
> more likely
> the issue.
>
> We used 20# tanks at school for many years, getting as many as a dozen
> firings out of one tank. We kept the tank in a tub of water to prevent
> freeze up. We now use 30# tanks simply for the convenience of not
> having to
> refill them as often.
>
> Too much gas pressure creates too much back pressure that will
> stall the
> temperature climb.
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
> ______________________________________________________________________
> ________
> 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.
William & Susan Schran User on fri 24 mar 06
On 3/24/06 6:05 PM, "Cindy Bracker" wrote:
> What was the BTU output of the burner you used in school? If it was
> a smaller burner, say 100,000 BTUs or even 1/4million BTUs, then they
> don't require as much pressure behind them to achieve their BTUs, and
> thus, would operate just fine on a 20# tank. This torch, which is
> 1/2million BTUs requires a 30# tank in order to fire a kiln of this
> size correctly.
Cindy - You are correct. I did not take into account the burner size.
I'm working with a burner of about 75,000 btu capacity.
May I ask why a burner of 1/2 million btu is used with your raku set-up?
Just curious.
Our Geil 24 cu. ft. gas fired kiln using 8 burners has a total capacity of
300,000 btu. It would seem a 1/2 million btu in a small kiln is perhaps a
bit much. Have you tested your kiln with a smaller burner to see if it would
fire as well?
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
William & Susan Schran User on sat 25 mar 06
On 3/24/06 11:12 PM, "Cynthia Bracker Sturm" wrote:
> I know Dad started with that because he used one for
> burning weeds, and it was inexpensive. Perhaps at that time, it was
> the only one available - ? It was a long time ago. I think there are
> smaller ones in that same brand now. Next time we order burners, I'll
> see if I can get one of those. I have some things I need to Raku
> anyway, so I could test it and see how it works.
I'm sure your Dad, in developing the raku kiln system, certainly had cost as
a high priority and the relatively inexpensive, readily available weed
burner would be an attractive solution.
I would think that many folks purchasing your raku set-up would think a 20#
tank would work simply because that is the size tank that is most readily
available to them. It's also easy - they can just the exchange tanks because
of the convenience and they don't have to make the investment in purchasing
a larger tank.
We've been using the MR-750 venturi burner for about 20 years with very good
results. We use a 0 - 15 psi regulator at the tank. Our firing time is about
one hour for the initial heat up, but after a few firings, can get to
temperature in as little as 15 minutes. I prefer this set-up because we can
control the heat rise depending on the type of ware being fired. We can fire
on as little as 1/4lb. Pressure if we need to go slow, but rarely go over
2lbs. Pressure.
Here's a link that shows a picture with specifications of the burner:
http://www.gasapplianceco.com/pdf/venturi_spec.pdf
The burner sells for about $50.
Let us know how your tests go. Maybe we'll find out what your father used is
the best choice.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
dewitt on sat 25 mar 06
>
> I would think that many folks purchasing your raku set-up would think a 2=
0#
> tank would work simply because that is the size tank that is most readily
> available to them. It's also easy - they can just the exchange tanks beca=
use
> of the convenience and they don't have to make the investment in purchasi=
ng
> a larger tank.
>
Have to say that I'm puzzled by the earlier comment that a 30# tank is
required because it provides more pressure than a 20# tank. I don't
believe that's the case. While a 30# tank might provide a slightly
higher flow rate before there is a pressure drop, properly ganging
together 2 or more 20# tanks should provide as high or higher pressure
/ flow rate as a single 30# tank.
Also, earlier it was noted that the air inlet and flue area of this
kiln is 1:1. Because of the way raku kilns are fired, they generally
benefit from a larger flue. Steven Branfman recommends that the flue
area for raku kilns be 50% larger than the inlet. e.g., if the inlet
area is 16 sq inches, the flue opening should be 24 sq inches. One of
the most common reasons raku kilns don't reach temperature is because
they are starved for air which is helped by a larger flue area.=20
Turning down the gas also often helps.
deg
Antoinette Badenhorst on sat 25 mar 06
I am going to sound very stupid here but I am trying to find out if I
understand the # sign correctly. If you talk about a 30# tank, does that
refer to the LB it holds? If so, I used a 100lb tank for the firing of =
this
kiln. If it refers to the pressure: I did not use a pressure gauge, but =
I
also make it out that the lb create a pressure by itself.Am I right? =
Maybe
if I can figure that out, I will be able to get to the bottom of what I =
am
doing wrong. I already figured out that I had the setup of the bricks
different from the way Cindy described. I used a brickwall inside the =
gas
port. Her lay out shows the brick wall on the furthest end across from =
the
gas port.=20
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of William & =
Susan
Schran User
Sent: Saturday, March 25, 2006 8:16 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Analyzing this raku kiln
On 3/24/06 11:12 PM, "Cynthia Bracker Sturm" =
wrote:
> I know Dad started with that because he used one for
> burning weeds, and it was inexpensive. Perhaps at that time, it was
> the only one available - ? It was a long time ago. I think there are
> smaller ones in that same brand now. Next time we order burners, I'll
> see if I can get one of those. I have some things I need to Raku
> anyway, so I could test it and see how it works.
I'm sure your Dad, in developing the raku kiln system, certainly had =
cost as
a high priority and the relatively inexpensive, readily available weed
burner would be an attractive solution.
I would think that many folks purchasing your raku set-up would think a =
20#
tank would work simply because that is the size tank that is most =
readily
available to them. It's also easy - they can just the exchange tanks =
because
of the convenience and they don't have to make the investment in =
purchasing
a larger tank.
We've been using the MR-750 venturi burner for about 20 years with very =
good
results. We use a 0 - 15 psi regulator at the tank. Our firing time is =
about
one hour for the initial heat up, but after a few firings, can get to
temperature in as little as 15 minutes. I prefer this set-up because we =
can
control the heat rise depending on the type of ware being fired. We can =
fire
on as little as 1/4lb. Pressure if we need to go slow, but rarely go =
over
2lbs. Pressure.
Here's a link that shows a picture with specifications of the burner:
http://www.gasapplianceco.com/pdf/venturi_spec.pdf
The burner sells for about $50.
Let us know how your tests go. Maybe we'll find out what your father =
used is
the best choice.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
_________________________________________________________________________=
___
__
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.
Antoinette Badenhorst on sat 25 mar 06
And this might be the reason why I had no trouble with my old burner 10
years ago....only, I was lucky to get it to work correctly from the
beginning, because I start realizing now, I had no idea what I was =
working
with.
Do you need sharp trimming tools that will not wear out quickly? Contact =
me
for information.=20
Antoinette Badenhorst
105 Westwood Circle
Saltillo MS, 38866
662 869 1651
www.clayandcanvas.com
www.southernartistry.org
=20
=20
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Cynthia =
Bracker
Sturm
Sent: Friday, March 24, 2006 10:13 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Analyzing this raku kiln
Hmmmm. I'll have to ask Mom for certain why we continue with the
current burner. I know Dad started with that because he used one for
burning weeds, and it was inexpensive. Perhaps at that time, it was
the only one available - ? It was a long time ago. I think there are
smaller ones in that same brand now. Next time we order burners, I'll
see if I can get one of those. I have some things I need to Raku
anyway, so I could test it and see how it works.
Good suggestion! Thanks
Cindy
On Mar 24, 2006, at 9:28 PM, William & Susan Schran User wrote:
> On 3/24/06 6:05 PM, "Cindy Bracker" wrote:
>
>> What was the BTU output of the burner you used in school? If it was
>> a smaller burner, say 100,000 BTUs or even 1/4million BTUs, then they
>> don't require as much pressure behind them to achieve their BTUs, and
>> thus, would operate just fine on a 20# tank. This torch, which is
>> 1/2million BTUs requires a 30# tank in order to fire a kiln of this
>> size correctly.
>
> Cindy - You are correct. I did not take into account the burner size.
> I'm working with a burner of about 75,000 btu capacity.
>
> May I ask why a burner of 1/2 million btu is used with your raku
> set-up?
>
> Just curious.
>
> Our Geil 24 cu. ft. gas fired kiln using 8 burners has a total
> capacity of
> 300,000 btu. It would seem a 1/2 million btu in a small kiln is
> perhaps a
> bit much. Have you tested your kiln with a smaller burner to see if it
> would
> fire as well?
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
> =
_______________________________________________________________________
> _______
> 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.
>
_________________________________________________________________________=
___
__
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.
William & Susan Schran User on sat 25 mar 06
On 3/25/06 1:03 PM, "Antoinette Badenhorst" wrote:
> I am going to sound very stupid here but I am trying to find out if I
> understand the # sign correctly. If you talk about a 30# tank, does that
> refer to the LB it holds?
Yes, the # sign refers to lb.
But the gas is sold by the gallon in the US.
Depending on who's filling the tank,
the 20# holds 4 gallons of liquid propane,
the 30# holds about 6 gallons,
if my memory serves me correctly.
I still think you are using too much pressure,
but you won't know unless a pressure gauge is used.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
dewitt on tue 28 mar 06
On 3/28/06, Cindy Bracker wrote:
> The way that LPG (Liquefied Petroleum Gas) is supplied to the burner
> is in the form of a vapour that is drawn off through a vapour valve
> at the top of the tank. As this vapour is released (through
> combustion), the remaining liquid will "boil off" and replace the
> vapour at the top of the tank. If the draw is too fast for the "boil
> off" to replace the vapour in the tank, then the burner will
> experience a drop in pressure. This is the equivalent of turning the
> burner "down". Suffice it to say, the less vapour that is supplied
> to the burner, the lower the output of the burner in BTUs.
>
> Further, the burners themselves have a BTU rating that is also based
> on a normal operating pressure range. So it is important to run the
> burner on the size tank that it is designed for.
>
> Ganging 2 or more tanks together does not increase pressure, it just
> increases the volume of gas that is available before the tank is
> "empty". In your example, 2-20# tanks will contain twice as much
> gas, but not increase the available pressure. 1 30# tank increases
> available pressure, which will increase flow velocity and combustion
> rate (higher BTU output.
>
I suggest you contact Marc Ward to discuss this. His website is
http://www.wardburner.com/ and you can find his email address there.
Feel free to copy any of my text on the issue to him. I'm confident
that a 30# tank doesn't provide more pressure than a 20# tank and that
two 20# tanks ganged together properly will provide at least as much
pressure / flow rate as a 30# tank, but I can't say that I'm an expert
and doubt that my opinion will carry much weight with you in any case.
However, your customers deserve accurate info and you certainly don't
want to post questionable info to Clayart.
deg
Cindy Bracker on tue 28 mar 06
The way that LPG (Liquefied Petroleum Gas) is supplied to the burner
is in the form of a vapour that is drawn off through a vapour valve
at the top of the tank. As this vapour is released (through
combustion), the remaining liquid will "boil off" and replace the
vapour at the top of the tank. If the draw is too fast for the "boil
off" to replace the vapour in the tank, then the burner will
experience a drop in pressure. This is the equivalent of turning the
burner "down". Suffice it to say, the less vapour that is supplied
to the burner, the lower the output of the burner in BTUs.
Further, the burners themselves have a BTU rating that is also based
on a normal operating pressure range. So it is important to run the
burner on the size tank that it is designed for.
Ganging 2 or more tanks together does not increase pressure, it just
increases the volume of gas that is available before the tank is
"empty". In your example, 2-20# tanks will contain twice as much
gas, but not increase the available pressure. 1 30# tank increases
available pressure, which will increase flow velocity and combustion
rate (higher BTU output.
I must agree with Steve Branfman that most raku kilns benefit from
larger flue sizes. This is due to the fact that most raku burner
systems are over-powered for the size of the kiln available.
According to Nils Lou, The exit flue has a maximum "flow rate" in
BTUs and an over-powered kiln can overwhelm the flue. Increasing the
dimensions of the exit flue will draft the kiln quicker.
Cindy Bracker (with help from David Sturm)
Cindy Bracker
Bracker's Good Earth Clays, Inc.
888-822-1982
http://www.brackers.com
On Mar 25, 2006, at 11:15 AM, dewitt wrote:
>>
>> I would think that many folks purchasing your raku set-up would
>> think a 20#
>> tank would work simply because that is the size tank that is most
>> readily
>> available to them. It's also easy - they can just the exchange
>> tanks because
>> of the convenience and they don't have to make the investment in
>> purchasing
>> a larger tank.
>>
>
> Have to say that I'm puzzled by the earlier comment that a 30# tank is
> required because it provides more pressure than a 20# tank. I don't
> believe that's the case. While a 30# tank might provide a slightly
> higher flow rate before there is a pressure drop, properly ganging
> together 2 or more 20# tanks should provide as high or higher pressure
> / flow rate as a single 30# tank.
>
> Also, earlier it was noted that the air inlet and flue area of this
> kiln is 1:1. Because of the way raku kilns are fired, they generally
> benefit from a larger flue. Steven Branfman recommends that the flue
> area for raku kilns be 50% larger than the inlet. e.g., if the inlet
> area is 16 sq inches, the flue opening should be 24 sq inches. One of
> the most common reasons raku kilns don't reach temperature is because
> they are starved for air which is helped by a larger flue area.
> Turning down the gas also often helps.
>
> deg
>
> ______________________________________________________________________
> ________
> 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.
Cindy Bracker on thu 30 mar 06
Dave and I have both spoken to Marc Ward as well our local Heetco
(propane supplier) franchise. The ultimate findings are:
A 20# tank has 20# of LP Gas in it. A 30# tank has 30# of LP Gas in
it. When brand new and completely full, a 30# tank DOES have more
pressure than a 20# tank, for about an instant once you turn it on.
At that point, the issue of the tank's ability to fuel a burner and
get a kiln up to temperature has less to do with the pressure in the
tank and more to do with the ability of the gas in the tank to make
up the loss of vapor. (The loss rate is dependent primarily on the
burner, but also on the current atmospheric pressure and the
temperature of the tank.) Because of the increased VOLUME of Propane
in a 30# tank, it can make up for the loss from combustion faster
than a 20# tank can, and therefore does not freeze up as fast. What
this means is that you must use the proper tank size for the burner
that you are using. (Any propane dealer will have a chart that will
help you determine what size tank you need for your burner,
elevation, temperature and necessary BTU output.) You must also
factor in the weather where you are located. For instance, if you
are in Minnesota in January you will need a larger tank (or smaller
burner that is still adequate for the kiln that you are using) than
you would if you were in Arizona in January. Similarly, your
elevation will also factor in to the size tank you need. If you are
at a higher elevation, you will need a larger tank than at sea level.
This research, along with the very helpful information from William
Schran, has led Bracker's to order a 100,000 BTU burner to test in
our Raku set-up. I, personally, feel strongly that it probably will
work just as well on the larger tanks and will enable people to use
the smaller, more convenient 20# tanks. If anyone on Clayart would
like to hear the results, please e-mail me off list. As soon as
we've done the tests (probably won't be until May or June when my in-
laws are taking my kids for the weekend), I'll e-mail you privately
(unless a whole bunch of people are interested, in which case, I'll
just post it here)
Thank you to everyone who posted information and suggestions. I take
everyone's opinion seriously when it comes to product improvement.
Cindy
Cindy Bracker
Bracker's Good Earth Clays, Inc.
888-822-1982
http://www.brackers.com
On Mar 28, 2006, at 5:19 PM, dewitt wrote:
>
> I suggest you contact Marc Ward to discuss this. His website is
> http://www.wardburner.com/ and you can find his email address there.
> Feel free to copy any of my text on the issue to him. I'm confident
> that a 30# tank doesn't provide more pressure than a 20# tank and that
> two 20# tanks ganged together properly will provide at least as much
> pressure / flow rate as a 30# tank, but I can't say that I'm an expert
> and doubt that my opinion will carry much weight with you in any case.
> However, your customers deserve accurate info and you certainly don't
> want to post questionable info to Clayart.
>
> deg
>
> ______________________________________________________________________
> ________
> 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.
>
Cindy Bracker
Bracker's Good Earth Clays, Inc.
888-822-1982
http://www.brackers.com
Marcia Selsor on thu 30 mar 06
From experience I have to chime in here.
I think a regulator is significantly helpful when firing with small
tanks. I recommend using one.
I had Marc Ward build a two burner system for me that hooks up to
three 20# tanks pf propane. I teach
a summer workshop in Red Lodge, MT
which is at 6000 ft. about sea level. I fire two fiber kilns
simultaneously for two days with one burner each.
I fire at 2.5-3 pounds pressure. My kilns reach temperature in 15-20
minutes after the initial first firing.
I also use both burners to fire my larger pulley kiln in Billings at
3000 Ft. above sea level.
When the tanks get below 1/2- 1/3 full, that start to show a little
frost line but that is usually after a day of firing or more.
I can fire them down to two pounds or almost empty. The gas company
employee where I refill them,
is always amazed that they are exactly the same to fill up..
Marcia Selsor
http://marciaselsor.com
On Mar 30, 2006, at 7:54 AM, Cindy Bracker wrote:
> Dave and I have both spoken to Marc Ward as well our local Heetco
> (propane supplier) franchise. The ultimate findings are:
> A 20# tank has 20# of LP Gas in it. A 30# tank has 30# of LP Gas in
> it. When brand new and completely full, a 30# tank DOES have more
> pressure than a 20# tank, for about an instant once you turn it on.
> At that point, the issue of the tank's ability to fuel a burner and
> get a kiln up to temperature has less to do with the pressure in the
> tank and more to do with the ability of the gas in the tank to make
> up the loss of vapor. (The loss rate is dependent primarily on the
> burner, but also on the current atmospheric pressure and the
> temperature of the tank.) Because of the increased VOLUME of Propane
> in a 30# tank, it can make up for the loss from combustion faster
> than a 20# tank can, and therefore does not freeze up as fast. What
> this means is that you must use the proper tank size for the burner
> that you are using. (Any propane dealer will have a chart that will
> help you determine what size tank you need for your burner,
> elevation, temperature and necessary BTU output.) You must also
> factor in the weather where you are located. For instance, if you
> are in Minnesota in January you will need a larger tank (or smaller
> burner that is still adequate for the kiln that you are using) than
> you would if you were in Arizona in January. Similarly, your
> elevation will also factor in to the size tank you need. If you are
> at a higher elevation, you will need a larger tank than at sea level.
> This research, along with the very helpful information from William
> Schran, has led Bracker's to order a 100,000 BTU burner to test in
> our Raku set-up. I, personally, feel strongly that it probably will
> work just as well on the larger tanks and will enable people to use
> the smaller, more convenient 20# tanks. If anyone on Clayart would
> like to hear the results, please e-mail me off list. As soon as
> we've done the tests (probably won't be until May or June when my in-
> laws are taking my kids for the weekend), I'll e-mail you privately
> (unless a whole bunch of people are interested, in which case, I'll
> just post it here)
> Thank you to everyone who posted information and suggestions. I take
> everyone's opinion seriously when it comes to product improvement.
> Cindy
>
>
> Cindy Bracker
> Bracker's Good Earth Clays, Inc.
> 888-822-1982
> http://www.brackers.com
>
>
> On Mar 28, 2006, at 5:19 PM, dewitt wrote:
>
>>
>> I suggest you contact Marc Ward to discuss this. His website is
>> http://www.wardburner.com/ and you can find his email address there.
>> Feel free to copy any of my text on the issue to him. I'm confident
>> that a 30# tank doesn't provide more pressure than a 20# tank and
>> that
>> two 20# tanks ganged together properly will provide at least as much
>> pressure / flow rate as a 30# tank, but I can't say that I'm an
>> expert
>> and doubt that my opinion will carry much weight with you in any
>> case.
>> However, your customers deserve accurate info and you certainly
>> don't
>> want to post questionable info to Clayart.
>>
>> deg
| |
|
