vince pitelka on sun 17 mar 02
> I am about to start building a shuttle kiln very soon and i have a quick
> question to anyone with experience in the matter. Is it safe to use only
> hard bricks on the floor of the shuttle, sitting directly on the steel
cart
> with two layers of brick? Or will the bricks get too hot for the steel and
> cause damage to it. I was told to put "wonderboard" or "flex board" under
> the bricks directly on the shuttle, which i plan to do. But i still am
> concerned because i know hard bricks get very hot.
> Any feedback would be greatly appreciated. Thanks!
Paul -
You are right. You do not want to just have two layers (5") of hardbrick.
My favorite kiln-car floor design has two layers of softbrick and a few
inches of AP Green Mizzou castable on top (it is still being made by
Harbison-Walker, and should be available from any good refractory supplier).
Or you could just do one layer of softbrick and a layer of hardbrick on top.
As you know, on any kiln floor the working surface is usually hardbrick or
hard castable to stand up to the weight and abuse of kiln furniture.
Be sure you do a tapered car - tapering about 1/2" in width from the front
to the back, so that it is a wedge fit. That way there will be no leakage
at all along the edge when it is closed. It fits tight when closed, but as
soon as you start to open it there is clearance, with minimal abrasion.
This is the ONLY kind of car floor seal to consider. Of course the edges of
the firebox floors need to taper accordingly. The easiest way to do this is
to just build the kiln with the appropriate taper at the base of the
fireboxes - the surfaces that the sides of the car will seal against when
the car is rolled in place. Once the kiln is done including the fireboxes,
build your track and car, with a sheet steel deck on the car coming out
within 1/2" of the firebox bases and the back of the kiln when the car is
rolled into the kiln. Roll the car into the kiln, and lay the bricks in the
car floor DIRECTLY against the edges of the firebox floors. If you are
doing a layer of castable on the car floor, lay tinfoil or plastic wrap
across the surface of the softbrick layer and up the corresponding outer
edges of the firebox floors, and trowel your castable onto the foil or
plastic, carefully smoothing it level on top. This moisture barrier is
essential, because it will prevent the porous brick from drawing the water
out of the castable before it has a chance to airset.
The car will be hard to pull out the first time, but once you have pulled it
out the first time you can sand the corresponding surfaces a bit, and it
will be easy from then on, but will still give you an airtight fit.
Hope this helps. I kind of went beyond what you asked.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
PBORIAN on sun 17 mar 02
I am about to start building a shuttle kiln very soon and i have a quick
question to anyone with experience in the matter. Is it safe to use only
hard bricks on the floor of the shuttle, sitting directly on the steel cart
with two layers of brick? Or will the bricks get too hot for the steel and
cause damage to it. I was told to put "wonderboard" or "flex board" under
the bricks directly on the shuttle, which i plan to do. But i still am
concerned because i know hard bricks get very hot.
Any feedback would be greatly appreciated. Thanks!
Paul
Falmouth, ky
Brandon Phillips on mon 18 mar 02
Hey Paul, I just finished building my first car kiln a couple weeks ago. 2
layers of hard bricks would only be 5" or 6" depending on your bricks. My
salt kiln is 9" thick hard brick and you can't even stand closeto it at peak
temp. My car is IFB's for the first layer and mixed hard and IFB for the
second layer. The hard bricks are what the shelves are supported on. This
has worked well for us, you might be able to do a layer of soft and a layer
of hard. I put the bricks directly on the car on top of 10 ga. sheet metal,
I can touch the bottom of the car when the kiln is at full temp. Of course
there's the whole ITC thing but you'll have to talk to somebody else about
that.
Extra tip, if you're using v-groove wheels on a track buy the biggest ones
possible, it'll make it a whole lot easier to roll in and out.
Brandon Phillips
(I call these kilns mine, they belong to the university, but the university
didn't shed blood sweat and tears to build them!)
>I am about to start building a shuttle kiln very soon and i have a quick
>question to anyone with experience in the matter. Is it safe to use only
>hard bricks on the floor of the shuttle, sitting directly on the steel cart
>with two layers of brick? Or will the bricks get too hot for the steel and
>cause damage to it. I was told to put "wonderboard" or "flex board" under
>the bricks directly on the shuttle, which i plan to do. But i still am
>concerned because i know hard bricks get very hot.
>Any feedback would be greatly appreciated. Thanks!
>Paul
>Falmouth, ky
>
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ThePottery@AOL.COM on mon 18 mar 02
Paul, You need to have as much insulation on the floor of your kiln as the
walls. I use two layers of IFB bricks (5") below the floor of the cars hard
brick to protect the iron. The use of concrete board "wonder board" will
help in any migration of air and give you a good flat surface to start laying
the car bricks. What kind of doors are you going to use? Tracy
The Pottery
Penland NC
thepottery@aol.com
John Baymore on mon 18 mar 02
Paul,
Hi. Hopefully I can share some useful thoughts with you on this one. Be=
en
building kilns professionally and teaching it at the college level for ov=
er
25 years. =
I am about to start building a shuttle kiln very soon and i have a quick
question to anyone with experience in the matter. Is it safe to use only
hard bricks on the floor of the shuttle, sitting directly on the steel ca=
rt
with two layers of brick? Or will the bricks get too hot for the steel an=
d
cause damage to it. I was told to put "wonderboard" or "flex board" under=
the bricks directly on the shuttle, which i plan to do. But i still am
concerned because i know hard bricks get very hot.
There is an unfortunate persistent myth that "heat rises" that has led to=
the floors of countless kilns of all types ending up terribly
underinsulated. Then the potters wonder why the bottom of their kiln ten=
ds
to fire cold . If you have decided that the walls and arch area of yo=
ur
kiln need to have a certain insulating value ..... then the floor should
have about that same insulating value. Heat energy moves in all directio=
ns
equally and it knows no directional reference. Heat transfer is based on=
the temperature differential (Delta T) and the physical nature of the
material(s) (K value) through which it is passing. It doesn't care if it=
is going throught he arch or the wall or the floor.
Building a good tight shuttle kiln is about having close tolerances in th=
e
clearance between the rolling car and the kiln itself. A single 1/4 inch=
open seam four feet long is the same thing as having a single
"uncontrolled" hole into/out of the chamber of 12 square inches. That =
is
a lot of space for radiant energy to radiate out through, for hot gases t=
o
leak through, or for air to inflitrate into. So you want to build with a=
s
much precision as you can........ the tighter the clearances, the better.=
=
Don't have "line of sight" cracks in the car heat seal...... use offsets
and/or a sand seal. HOWEVER........... with really tight clearances a
slight shifting of the refractories can cause the car to hang up as the
refractories rub against each other. So you don't want the car bed
shifting at all. This takes good planning and design.
First of all, remember that seemingly rigid steel is pretty darn flexible=
. =
Many, many kiln designs I have seen and gone in to fix "after the fact" a=
re
somewhat under-engineered in the steel department. As a generality... us=
e
thicker steelwork for the car load bearing structure than you think you
need. Use shorter spans between wheels than you think you can. You want=
to make sure that the steel members you are using do not deflect (bend)
under load (weight of car itself plus the load of ware) MORE than the
amount of clearance that you have available in your design. Your steel
supplier can help you calculate the deflection between two supported poin=
ts
(the wheels) for a given span, type of steel structure material, and the
load.....it's not rocket science . =
And DON'T let steel get hot..... it loses strength, warps (ala the World
Trade Center), and eventually also rusts. The last thing you want is the=
car to bind up with a load on it when it is IN the kiln .
In building shuttle cars I tend to use channel steel (U shaped legs
pointing down) as the main structural members for carrying the weight of
the car refractories and the setting of ware and shelves. Then on top of=
these two main load bearing struts, a rigid welded ladder chassis is
constructed from angle steel that has cross members spaced to match the o=
n
center dimension of the floor refractories (ie. -9" on center). This
allows each of the bottom course of the floor brick to sit firmly support=
ed
at each end on a steel cross member. No need for flexboard or wonderboar=
d
or plate steel to support the brick. This also allows good air circulati=
on
to dissapate the cold face heat. It is important to note that the weld
beads on the working surface (where the brick goes) of the ladder structu=
re
need to be ground flush with the top of the angle steel surface ..... so
that all the brick can lay FLAT onto the steel.
A typical car bed floor refractory layout that I use employs a graded
rating system. This lets you have a brick with a higher insulating value=
(but lower use rating) on the outer cold face surfaces....and a higher us=
e
rating (but lower insulating value) toward the hot face. It also allows
you to utilize the structural qualities of certain refractories to your
advantage. This helps you keep as much heat as possible from reaching th=
e
steelwork of the car and also to make a durable refractory structure. =
(BTW..... the grading of refractories in walls and arches also is a good
general practice.)
I am assuming that you are talking high fire here.... a cone 10 ish kiln.=
=
The first layer that is sitting on the steel is often a layer of medium
duty hard refractory brick, in the configuration called "thin splits". =
These are typically 1 inch thick as opposed to the "normal" 2 1/2 inches =
of
the "standard" brick that potters tend to use. These are used mainly for=
their physical stregnth and durability.........not insulation........ in=
spanning the open spaces in the steelwork ladder construction and in taki=
ng
years of vibration against the steel frame as the car is rolled in and ou=
t.
Next is a 2 1/2 inch thich layer of 2000 F rated IFB. On top of this is=
a
2 1/2 thick layer of 2300 F rated IFB. The "working surface" of the kiln=
car floor (hot face) is then a 2 1/2 inch layer of either Greenlite 28's =
or
high duty hardbrick. The GL 28's provide a good compromise between
insulating value and resistence to abrasion. Another alternative layout =
is
to use another layer of 2300's and then top it with a layer of high duty
hardbrick splits. So the typical floor refractory thickness described he=
re
is about 8 1/2 inches .....mostly of IFB........ although one option coul=
d
make 3 1/2 inches of that total being hard brick.
If the car is carrying the structure of the exit flues for a true downdra=
ft
setup....... the construction gets FAR more complicated due to the flue
channels located in the car bed. Let's skip all that right now .
The brickwork in the area of the heat seals should be mortared in place
with a good commercial heat/air setting mortar. Make sure that all brick=
joints are well offset in all dimensions so that the construction is real=
ly
solid. You DON'T want these places to shift. All it takes is a very sma=
ll
amount of contact in the heat seal to make the car "jam" and become
completely hung up. You can also use laminated ceramic fiber felt as a
replaceable compressive heat seal on the end faces where the car hits the=
kiln structure. (Beware the significant dangers of airborne fiber!!!)
Take a look at the couple of photos of the 67 cubic foot car kiln on
JohnBaymore.com/p0001347.htm on my website and you'll see a shot or two
that might be useful. It is part of sort of a "kiln gallery"....so it'll=
take a while to load .
No matter what you do........ 5 inches of hardbrick is pretty inadequate
for just about ANY kiln floor......... particularly for a car kiln.
Hope all this is of help. Good luck with the new kiln. New kilns are
always exciting!!!!!!!
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
"DATES SET: Earth, Water, and Fire Noborigama Woodfiring Workshop Augu=
st
16-25, 2002"
cyberscape on mon 18 mar 02
I would sandwich a layer of softbrick between the two layers of hard
brick. You will be glad that you have that insulation between the
interior of the kiln and the steel. Hard brick conducts heat and so
does steel. You will cook the frame and the wheels. I don't think that
your kiln will last long without the soft brick layer. It is not so
expensive to add this layer. Good luck.
Harvey Sadow
Marcia Selsor on tue 19 mar 02
> Dear Paul,
I, too, have been building kilns for over 30 years for college programs and
potters including self. For the shuttle I have used fiber between the layer of
hardbricks to insulate the floor. It will get very squished, but it works.
Marcia Selsor
professor emerita, Montana Sate University-Billings
>
> I am about to start building a shuttle kiln very soon and i have a quick
> question to anyone with experience in the matter. Is it safe to use only
> hard bricks on the floor of the shuttle, sitting directly on the steel cart
> with two layers of brick? Or will the bricks get too hot for the steel and
> cause damage to it. I was told to put "wonderboard" or "flex board" under
> the bricks directly on the shuttle, which i plan to do. But i still am
> concerned because i know hard bricks get very hot.
>
>
>
> ______________________________________________________________________________
> 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.
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