Eric B on wed 6 aug 03
i spoke with a supplier about a kiln i'm thinking of buying, which they would
build. IFB brick downdraft. i asked about K26 bricks instead of K23, so
that i could feel more comfortable taking it to cone 11 on occasion, and they guy
there said that K26 bricks are denser and therefore the kiln would take
longer to get to temperature.
does anyone have any guestimates of how MUCH longer they would take, and
whether it would be worth the extra expense to get the K26s for a higher fire once
in a while?
Eric
SpunMud
Edouard Bastarache on wed 6 aug 03
Hello Eric,
from what I recall from my younger years, K23s have a 100 degree F
safety coefficient, so you can fire up to 2400 with them, more especially
if you make your walls 9 inches thick.
There are 2 problems with K26 in this case :
1-They are quite more expensive than K23s,
2-At C/8-11 they will act as hard bricks
and your firings will be quite more expensive
in fuel.
But, they are good to make peep hole plugs.
Later,
"Ils sont fous ces Quebecois"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
Phil Smith on wed 6 aug 03
You could ask for k26 in the floor only to provide protection at the burner
location. (assuming that's where the burners are).
Phil...
Eric B on thu 7 aug 03
thanks everyone for your input. is sure sounds like K23 is the most popular
and i'll probably go with it (except for maybe around burners as was
suggested).
but it sure leaves me wondering WHY a studio potter would ever build a kiln
out of K26s, especially with the loss of insulative quality at higher temps.
possibly somone who fires only at ^11 and does it a lot?
eric
SpunMud
John Baymore on thu 7 aug 03
i spoke with a supplier about a kiln i'm thinking of buying, which they
would
build. IFB brick downdraft. i asked about K26 bricks instead of K23, so=
that i could feel more comfortable taking it to cone 11 on occasion, and
they guy
there said that K26 bricks are denser and therefore the kiln would take
longer to get to temperature.
This can be calculated if one knows the brick mass and the kiln
configuration. It is some "pain in the butt" math. Don't have to time t=
o
do it right now even if you gave me the data. But some quick thoughts. =
=
While there is some variation brick manufacturer to manufacturer......
generally the 26 has a higher use rating than the 23 but a lower insulati=
ng
value per inch. The 26 has a larger amount of thermal mass....... more
"clay" in the brick and less "air". =
Good in one way....bad in another .
=46rom 32 plus years of kiln building experience professionally.... if yo=
u
are going to a cone 11......... I'd suggest a lining of 26 with a backup =
of
20's.... 26's on the headers. Higher rating in the fireboxes. Better
yet....don't pay for use rating you don't need. Look at 25's instead of
the 26's. That is plenty of brick for the job at 11. You'll get a littl=
e
better insulation value per inch and a little lower thermal mass..... and=
you'll pay slightly less per brick. (Can't say that for sure because I
don't know exactly which manufacturer's bricks you are talking about.....=
..
so it is a generality.) That is if you want the kiln to last a really
long time........ 25-30 years in hard use. 23's to regular cone 11's is
asking for fast deterioration in a periodic kiln......particularly if the=
person(s) firing the kiln are not all that experienced in fuel firing. =
You'd be amazed at the variation in things like firebox temperature and
evenness of the general chamber the person firing the unit can make .
Even though the rating for the brick is for "continuous duty"...... it is=
NOT easier on the brick when it is heated intermittnetly as it is in a
periodic kiln. The frequent heating and cooling is hard on the
refractories and causes micro cracks to form in the tiny clay walls betwe=
en
the little air pockets.
This eventually lowers the insulating value, provides spalling start
points, and so on. Add to this the increases hot face shrinkage duwe to
pushing the use rating...and it deteriorates faster than in something lik=
e
a tunnel kiln.
For many years in the now somewhat distant past, AP Green 23's were reall=
y
over engineered.... and many potters had great service out of them at con=
e
10. I think that resulted in many potters feelings that 23's are great f=
or
cone 10 use. But from the many kilns I have gone in to look at for
repairs....... and from new construction jobs where the client wants to c=
ut
that corner........ I find many current 23's show a lot of deterioration
pretty fast when compared to 25's or 26's. =
I've got some pictures on my website that show what can happen from poor
refractory grading. I have a whole slide collection of "kiln problems"
that I have accumulated over the years .
If a kiln is well designed it should not inherently take longer to
fire....because the lining heat loss and thermal mass is taken into
consideration in the design. The kiln should be fireable at the rate whi=
ch
you determine.... not what IT somehow "inherently" just takes. What it
WILL take is a tad more heat energy to heat it up because of the thermal
mass and the slightly lower insulating value per inch.
OOPs.......... read your post again........ =
If this is a prefab commercial unit that uses a single layer of 4 1/2
inches of IFB for the total wall thickness........ then you will possibly=
find that if you change that and nothing else about the unit...... your
heat loss and thermal storage figures may impact the firing rate IF the
manufacturer runs the total heat input figure "tight to the wire" based o=
n
the heat loss and thermal mass of the 23's. It will also cost you more p=
er
firing to fire it than with the 23's. But the hot face lining will last
far longer.... so the payback is likely there in teh end . But you al=
so
need to look a the cold face temperature of the lining in the prefab unit=
with your proposed change and make sure that you are not going to damage
some other aspect of the unit because of this increase in temperature.
With a prefab unit...... LISTEN to the manufacturer. They know THEIR uni=
t.
If they say it is a bad idea..... listen. It may not be a "bad idea" in=
the generic sense....... but it probably is a bad idea with THEIR unit >.
My $0.02 worth.
best,
....................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086-5812 USA
JBaymore@compuserve.com
http://www.JohnBaymore.com
603-654-2752 (studio)
800-900-1110 (studio)
"Earth, Water, and Fire Noborigama Woodfiring Workshop: August 15-24,
2003"
Bruce Girrell on thu 7 aug 03
> but it sure leaves me wondering WHY a studio potter would ever
> build a kiln out of K26s
Because K26 is stronger. K23s just about crumble in your hand.
Let's inject some actual science in here. The figures for IFB are from BNZ's
site. The hard brick numbers come from thermalceramics (thermalceramics
reports an even lower thermal conductivity for IFB, but I couldn't find a 26
number for them). Modulus of rupture is an indication of the resistance to
breaking when supported only at the ends with a load in the middle.
Thermal conductivity Crushing Modulus
at 2000 deg F strength of rupture
(BTU-in/sq. ft.) (PSI) (PSI)
PA23 2.6 140 115
PA26 2.9 240 180
Hard ~13.5 ? (a lot) ? (a lot)
As you can see, the 26 is almost twice as strong when it comes to crushing
loads and is more than 50% stronger when it has to support weight over an
open area (burner ports, for example).
The hard brick has a thermal conductivity roughly 5 times greater than the
IFB. To put it another way, let's assume that hard brick is R-19 like the
insulation in your roof. On the same scale K23 bricks would have an R value
of 99 and K26 would have an R value of 88. So, does K23 do a better job of
insulation than K26? Yes. Is K26 similar to hard brick in its heat loss? No
way. K26 does a great job of insulation. For a modest increase in heat lost
(11%), there is a substantial gain in the strength of materials.
Bruce "just the facts, ma'am" Girrell
who thinks it is almost always clearer to include just a little bit of text
from the original message with the response below that - just in case anyone
is keeping track of the votes
steve harrison on fri 8 aug 03
Hi Eric,
If they build the kiln well it wont take any longer to fire with RI26
lining because they should up the energy input as well to match that
required. The firing time need not be any different, but the RI26
bricks will use more energy to get to the same temperature in the same
time. What you have to ask your self is, Do I want to spend 10 to 15%
extra on fuel costs for the rest of my life, just so that I can do a
few firings to cone 11 with out some shrinkage on the hot face of the
kiln? The American K23 from Thermal Ceramics is a very good brick.
(used to be the BNZ and before that it was marketed as the Babcock &
Wilcox 23. It has been a very reliable brick for many years now. Don't
let them build your kiln out of JM 23's that is a very different brick
being produced in the Thermal Ceramics factory in Italy. It just wont
hack it.
With fuel costs set to rise for the next few decades, it's a very
serious question.
Only you can decide.
But I know what I'd do
Regards
Steve Harrison
On Thursday, August 7, 2003, at 09:30 AM, Eric B wrote:
> i spoke with a supplier about a kiln i'm thinking of buying, which
> they would
> build. IFB brick downdraft. i asked about K26 bricks instead of K23,
> so
> that i could feel more comfortable taking it to cone 11 on occasion,
> and they guy
> there said that K26 bricks are denser and therefore the kiln would take
> longer to get to temperature.
>
> does anyone have any guestimates of how MUCH longer they would take,
> and
> whether it would be worth the extra expense to get the K26s for a
> higher fire once
> in a while?
>
> Eric
> SpunMud
>
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