Lee Love on sat 25 oct 08
On Sat, Oct 25, 2008 at 10:46 AM, Bruce Girrell
wrote:
> Recommendations, anyone?
My super duty softs held up well. I don't know if they are available here.
Can you put fiber blanket on top of the hardbrick arch?
--
Lee Love in Minneapolis
http://togeika.multiply.com/journal
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
Larry Kruzan on sat 25 oct 08
I'm building a gas test kiln right now with a 27" wide arch as well and have
been thinking about using ITC on the interior too. Nils Lou recommended it
in his book but I have heard of others having unspecified issues with it -
if anybody has any experience please pass it along.
I am also curious about your chamber and flu size? Mine is a 27" cube plus
the 6" arch. I'm using a 4.5"x5" exit port with a 4.5"x9" flu that is
adapted the a 6" round pipe above the arch level. The burners are two
MR100s running on high pressure LP.
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Bruce Girrell
Sent: Saturday, October 25, 2008 11:47 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: [CLAYART] Kiln arches
Frederick Olsen states that the minimum rise for a sprung arch is 1 1/2
inches per foot of span and that the maximum is about 3 inches per foot of
span. However, he then immediately adds, "I have raised an arch with a 6"
rise per foot of span with very good results, so no hard and fast rule can
be applied."
I have only a 27 inch span which, at a 3" per foot of span rise, would
result in an arch rise of just over 6", which doesn't sound like much of an
arch.
What factors determine arch rise? Certainly, the flatter it gets, the less
stable it will be, so higher would be better, with the upper limit perhaps
being a semi-circle. But how does arch rise affect heat flow? What other
considerations might there be?
While we're on the topic of arches...
My previous roof was built entirely from IFB. For my arch, I am considering
using hard brick, primarily to minimize the little crumblies that might fall
from the roof as IFB ages over time. But it might be possible to mitigate
that problem with a soak in ITC or by a different method. I would prefer to
use IFB (to decrease heat loss through the roof), but am prepared to use
hard brick. The (propane-fueled) kiln is intended to fire nominally to ^10
reduction, but my experience has been that some firings go a bit further and
I have pushed ^13 at times.
Recommendations, anyone?
Bruce Girrell
getting itchy to get a kiln running again
Vince Pitelka on sat 25 oct 08
Bruce Girrell wrote:
"Frederick Olsen states that the minimum rise for a sprung arch is 1 1/2
inches per foot of span and that the maximum is about 3 inches per foot of
span. However, he then immediately adds, "I have raised an arch with a 6"
rise per foot of span with very good results, so no hard and fast rule can
be applied." I have only a 27 inch span which, at a 3" per foot of span
rise, would result in an arch rise of just over 6", which doesn't sound like
much of an arch.
What factors determine arch rise? Certainly, the flatter it gets, the less
stable it will be, so higher would be better, with the upper limit perhaps
being a semi-circle. But how does arch rise affect heat flow? What other
considerations might there be?"
Bruce -
I do not have my Olson or my AP Green Pocket Refractory Handbook here at
home, but I believe that the highest arch rise they suggest is 2.3 inches
per foot. A 6" rise overall in 27 inches is a pretty high arch, and will be
very stable. Of course there are higher arches, all the way up to a Roman
arch, which is a half circle. That's what I used in 1974 on my very first
kiln, all hardbrick. You need to consult the tables in Olson or in one of
the pocket refractory handbooks. Arch rise is determined by the rigidity of
the buttressing, and the span of the arch. Very low-rise arches are risky
except in situations where the arch buttressing is absolutely rigid, which
occurs only in industry. You might think that a welded steel frame is
absolutely rigid, but it is not by a long shot. So, for arched studio
kilns, a higher-rise arch is always safer.
You wrote:
"While we're on the topic of arches...
My previous roof was built entirely from IFB. For my arch, I am considering
using hard brick, primarily to minimize the little crumblies that might fall
from the roof as IFB ages over time. But it might be possible to mitigate
that problem with a soak in ITC or by a different method. I would prefer to
use IFB (to decrease heat loss through the roof), but am prepared to use
hard brick. The (propane-fueled) kiln is intended to fire nominally to ^10
reduction, but my experience has been that some firings go a bit further and
I have pushed ^13 at times."
There is absolutely no reason to use hardbrick in order to avoid "crumblies"
falling on the ware. Hardbrick in such a situation is a huge thermal mass,
and it will take as much energy to heat up those arch brick as it will to
fire the ware. We cannot afford such waste of fossil fuels. In the case of
salt or soda it is necessary, but the hotface on a highfire reduction or
oxidation kiln should be all IFB except for the firebox, bagwall, burner
ports, floor, and flue channel.
Blow off your softbrick with compressed air before laying up the arch. If
you cut any brick for the keystone course, blow them off extra thoroughly.
Coating the inside with ITC-100 or some other thermal coating is a good
idea, and should help reduce the minute amount of sifting you might
experience. If it is a problem initially, just place a shelf above the top
layer of ware.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Hank Murrow on sat 25 oct 08
On Oct 25, 2008, at 9:46 AM, Bruce Girrell wrote:
> Frederick Olsen states that the minimum rise for a sprung arch is 1
> 1/2 inches per foot of span and that the maximum is about 3 inches
> per foot of span. However, he then immediately adds, "I have raised
> an arch with a 6" rise per foot of span with very good results, so
> no hard and fast rule can be applied."
>
> I have only a 27 inch span which, at a 3" per foot of span rise,
> would result in an arch rise of just over 6", which doesn't sound
> like much of an arch.
>
> What factors determine arch rise? Certainly, the flatter it gets,
> the less stable it will be, so higher would be better, with the
> upper limit perhaps being a semi-circle. But how does arch rise
> affect heat flow? What other considerations might there be?
>
> While we're on the topic of arches...
> My previous roof was built entirely from IFB. For my arch, I am
> considering using hard brick, primarily to minimize the little
> crumblies that might fall from the roof as IFB ages over time. But
> it might be possible to mitigate that problem with a soak in ITC or
> by a different method. I would prefer to use IFB (to decrease heat
> loss through the roof), but am prepared to use hard brick. The
> (propane-fueled) kiln is intended to fire nominally to ^10
> reduction, but my experience has been that some firings go a bit
> further and I have pushed ^13 at times.
Dear Bruce;
I have had some success building arches with a very shallow catenary
curve. This allows for a stronger curve at the top, so the arch does
not 'flatten out' as Roman arches tend to do. It is very easy to
spray can to leave an outline of your proposed rise and stretch on a
piece of butcher paper. I start with straights at the skews and add a
#1 then a straight, then 2 #2s etc. with either #2s or a #3 at the
top of the rise. I like around a 10" rise for 40" span. Easy to form
up, and easy to maintain.
Cheers, Hank
www.murrow.biz/hank
Bruce Girrell on sat 25 oct 08
Frederick Olsen states that the minimum rise for a sprung arch is 1 1/2 inc=
hes per foot of span and that the maximum is about 3 inches per foot of spa=
n. However, he then immediately adds, "I have raised an arch with a 6" rise=
per foot of span with very good results, so no hard and fast rule can be a=
pplied."
I have only a 27 inch span which, at a 3" per foot of span rise, would resu=
lt in an arch rise of just over 6", which doesn't sound like much of an arc=
h.
What factors determine arch rise? Certainly, the flatter it gets, the less =
stable it will be, so higher would be better, with the upper limit perhaps =
being a semi-circle. But how does arch rise affect heat flow? What other co=
nsiderations might there be?
While we're on the topic of arches...
My previous roof was built entirely from IFB. For my arch, I am considering=
using hard brick, primarily to minimize the little crumblies that might fa=
ll from the roof as IFB ages over time. But it might be possible to mitigat=
e that problem with a soak in ITC or by a different method. I would prefer =
to use IFB (to decrease heat loss through the roof), but am prepared to use=
hard brick. The (propane-fueled) kiln is intended to fire nominally to ^10=
reduction, but my experience has been that some firings go a bit further a=
nd I have pushed ^13 at times.
Recommendations, anyone?
Bruce Girrell
getting itchy to get a kiln running again
Bruce Girrell on sun 26 oct 08
Thanks to all who answered my arch questions both on and off list. I can se=
e I was worrying about it too much.
Hank - This very afternoon I was just this side of nodding off in bed and =
I thought, "Why wouldn't a catenary be a better arch? The shape difference =
wouldn't be much, but the dead load and the expansion forces would be handl=
ed better." I think I'll do that. Thanks for the final push.
Vince - Yes, it's the same kiln that I was talking with you about. Sometime=
s the design process forces us to make difficult decisions. In the end, we =
are deciding what is more important to us. I talked myself back and forth e=
nough that I finally refused to think about it for a couple of months. But =
not having _any_ kiln was far worse than possibly making a poor decision, s=
o I decided to forego the increased capacity in return for a simpler design=
. At least I can move forward again.
Bruce Girrell
Karin Givon on sun 26 oct 08
Lee:
Re: blanketing your arch--yes, you can! I've done it, and it worked
very well for me. Kaowool is the best stuff ! Easy to work with and
altho it eventually falls apart, I think it's pretty cost-effective.
Karin
DancingDragonPottery.net
On Oct 25, 2008, at 10:09 PM, Lee Love wrote:
On Sat, Oct 25, 2008 at 10:46 AM, Bruce Girrell
wrote:
> Recommendations, anyone?
My super duty softs held up well. I don't know if they are available
here.
Can you put fiber blanket on top of the hardbrick arch?
--
Lee Love in Minneapolis
http://togeika.multiply.com/journal
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
jonathan byler on mon 27 oct 08
the kilns we have from bailey have softbrick floors and fireboxes
too, but he uses 2800 or 3000 degree rated bricks for the firebox
area. The only hardbricks are over the burner ports and the flue to
manage the extra stress from the unsupported spans in those areas.
The 3000 degree bricks are pricey, however, I think we paid either $4
or $5 each for them when buying some recently. compare that to $1.50
for the k23's, and $2.44 for the hard bricks.
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Oct 25, 2008, at 8:12 PM, Vince Pitelka wrote:
> Bruce Girrell wrote:
> "Frederick Olsen states that the minimum rise for a sprung arch is
> 1 1/2
> inches per foot of span and that the maximum is about 3 inches per
> foot of
> span. However, he then immediately adds, "I have raised an arch
> with a 6"
> rise per foot of span with very good results, so no hard and fast
> rule can
> be applied." I have only a 27 inch span which, at a 3" per foot of
> span
> rise, would result in an arch rise of just over 6", which doesn't
> sound like
> much of an arch.
> What factors determine arch rise? Certainly, the flatter it gets,
> the less
> stable it will be, so higher would be better, with the upper limit
> perhaps
> being a semi-circle. But how does arch rise affect heat flow? What
> other
> considerations might there be?"
>
> Bruce -
> I do not have my Olson or my AP Green Pocket Refractory Handbook
> here at
> home, but I believe that the highest arch rise they suggest is 2.3
> inches
> per foot. A 6" rise overall in 27 inches is a pretty high arch,
> and will be
> very stable. Of course there are higher arches, all the way up to
> a Roman
> arch, which is a half circle. That's what I used in 1974 on my
> very first
> kiln, all hardbrick. You need to consult the tables in Olson or in
> one of
> the pocket refractory handbooks. Arch rise is determined by the
> rigidity of
> the buttressing, and the span of the arch. Very low-rise arches
> are risky
> except in situations where the arch buttressing is absolutely
> rigid, which
> occurs only in industry. You might think that a welded steel frame is
> absolutely rigid, but it is not by a long shot. So, for arched studio
> kilns, a higher-rise arch is always safer.
>
> You wrote:
> "While we're on the topic of arches...
> My previous roof was built entirely from IFB. For my arch, I am
> considering
> using hard brick, primarily to minimize the little crumblies that
> might fall
> from the roof as IFB ages over time. But it might be possible to
> mitigate
> that problem with a soak in ITC or by a different method. I would
> prefer to
> use IFB (to decrease heat loss through the roof), but am prepared
> to use
> hard brick. The (propane-fueled) kiln is intended to fire nominally
> to ^10
> reduction, but my experience has been that some firings go a bit
> further and
> I have pushed ^13 at times."
>
> There is absolutely no reason to use hardbrick in order to avoid
> "crumblies"
> falling on the ware. Hardbrick in such a situation is a huge
> thermal mass,
> and it will take as much energy to heat up those arch brick as it
> will to
> fire the ware. We cannot afford such waste of fossil fuels. In
> the case of
> salt or soda it is necessary, but the hotface on a highfire
> reduction or
> oxidation kiln should be all IFB except for the firebox, bagwall,
> burner
> ports, floor, and flue channel.
>
> Blow off your softbrick with compressed air before laying up the
> arch. If
> you cut any brick for the keystone course, blow them off extra
> thoroughly.
> Coating the inside with ITC-100 or some other thermal coating is a
> good
> idea, and should help reduce the minute amount of sifting you might
> experience. If it is a problem initially, just place a shelf above
> the top
> layer of ware.
> Good luck -
> - Vince
>
> Vince Pitelka
> Appalachian Center for Craft
> Tennessee Tech University
> vpitelka@dtccom.net; wpitelka@tntech.edu
> http://iweb.tntech.edu/wpitelka
jonathan byler on mon 27 oct 08
we have few if any actual crumbles from the arches in our bailey gas
kilns. it seems like if you leave it alone, it will leave you
alone. the problem of a hardbrick roof on a soft brick kiln is not
only one of the extra weight on the walls, which may or may not be an
issue, but also of the added thermal mass at the top of the kiln,
which will not help you fire evenly. I would buy the best bricks you
can afford for the arch, from a reputable manufacturer, and make sure
that they have not been left wet though freeze and thaw cycles, and
you will get good life out of them. I have not tried ITC, but it is
supposed to help with crumbly surface bits if applied properly.
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Oct 25, 2008, at 11:46 AM, Bruce Girrell wrote:
> Frederick Olsen states that the minimum rise for a sprung arch is 1
> 1/2 inches per foot of span and that the maximum is about 3 inches
> per foot of span. However, he then immediately adds, "I have raised
> an arch with a 6" rise per foot of span with very good results, so
> no hard and fast rule can be applied."
>
> I have only a 27 inch span which, at a 3" per foot of span rise,
> would result in an arch rise of just over 6", which doesn't sound
> like much of an arch.
>
> What factors determine arch rise? Certainly, the flatter it gets,
> the less stable it will be, so higher would be better, with the
> upper limit perhaps being a semi-circle. But how does arch rise
> affect heat flow? What other considerations might there be?
>
> While we're on the topic of arches...
> My previous roof was built entirely from IFB. For my arch, I am
> considering using hard brick, primarily to minimize the little
> crumblies that might fall from the roof as IFB ages over time. But
> it might be possible to mitigate that problem with a soak in ITC or
> by a different method. I would prefer to use IFB (to decrease heat
> loss through the roof), but am prepared to use hard brick. The
> (propane-fueled) kiln is intended to fire nominally to ^10
> reduction, but my experience has been that some firings go a bit
> further and I have pushed ^13 at times.
>
> Recommendations, anyone?
>
> Bruce Girrell
> getting itchy to get a kiln running again
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