Steve Dalton on fri 21 apr 00
Greeting,
I'm building my train kiln, now it's time to
build the roof. My first plan was to go with
an arch, but because of the price of arch brick
I was going to make my own. I realize now,
way too time involved with that plan!
I'm thinking of going with a flat top.
My question, is there a way to estimate
the number of needed brick?
Steve Dalton
ferenc jakab on sat 22 apr 00
> I'm building my train kiln, now it's time to
> build the roof. My first plan was to go with
> an arch, but because of the price of arch brick
> I was going to make my own. I realize now,
> way too time involved with that plan!
> I'm thinking of going with a flat top.
I've asked before but not received an answer, What is a flat top kiln, if
it's brick how is it supported?
Would be grateful for knowledge.
Feri.
Cindy Strnad on sun 23 apr 00
Feri,
That is a question with a long and complicated answer. You can find a lot in
the archives, I'm sure. I'm not really qualified to give you much of an
answer, but I suggest you get Nils Lou's book, "The Art of Firing". The
Potters' Shop has it.
Cindy Strnad
earthenv@gwtc.net
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
Fredrick Paget on sun 23 apr 00
Feri,
Flat top the way we use it usually refers to Nils Lou's design where the
kiln ceiling is made of vertical bricks in a very shallow dome shape where
the horizontal force from the dome is taken up by steel threaded rods
that are in tension.
The trick is that a dome partly converts the force of gravity to a force
tangential to the dome structure. By making a very shallow dome most of
this force is horizontal and can be supported by squeezing in the sides of
the dome with the clamping rods.
The dome shape is made by building the ceiling on a well supported piece
of plywood and jacking up the center from below after which the bricks are
grouted with a fireclay - sand mixture, then the tension frame is tightened
before the jack is released. Now you have a dome with only a couple of
inches rise in the center. There is a limit on how wide this can be made as
the crushing strength of the insulating firebrick would appear to limit the
maximum pressure that can be applied.
This works well for a square ceiling. I think it could be made to work
with a long shallow arch made the same way but the clamping method would
have to be worked out.
On a train kiln isn't the ceiling also the door ? If so it would be even
harder to clamp and probably if it is not too wide some sort of a door
could be made with stainless steel rods inside the bricks close to the cold
face to support the bricks. I used this method on my small luster kiln and
I once fired it to cone 10 and the roof is still up although it is only
about 2 feet wide.
I have seen in the Harbison Walker (A. P. Green formerly) catalog some
brick support modules that can be welded to an external steel framework to
make wide flat top kilns. Some of these use fiber modules, some are brick.
These are no doubt used in large commercial tunnel kilns, etc.
Fred Paget
>----------------------------Original message----------------------------
>> I'm building my train kiln, now it's time to
>> build the roof. My first plan was to go with
>> an arch, but because of the price of arch brick
>> I was going to make my own. I realize now,
>> way too time involved with that plan!
>> I'm thinking of going with a flat top.
>
>I've asked before but not received an answer, What is a flat top kiln, if
>it's brick how is it supported?
>Would be grateful for knowledge.
>Feri.
>From Fred Paget, Marin County, California, USA
Stephen Grimmer on sun 23 apr 00
Feri,
A (Minnesota) Flat Top kiln is a kiln designed by Nils Lou which
incorporates a very low dome (2" rise) rather than a traditional arch. The
top is laid up on a flat plywood support on the kiln and compressed with
steel brackets. Some flat tops are now being made with monolithic fiber
modules, as well. Nils's new edition of The Art of Firing is very good and
has more information.
With regard to estimating the number of brick for the top, calculate the
area of the whole top and divide by the area of the end of one your bricks.
For example, if your kiln is 63"x63" (3969 square inches) and you are using
standard 2.5" fire brick, the end is 11.25 square inches. Dividing gives an
estimate of 352.8 bricks. Remember to add the hard brick for the corners.
The new Art of Firing has an improved layout for brick which is interesting.
--
Steve Grimmer
Bowling Green State University
Bowling Green, OH
> From: ferenc jakab
> Reply-To: Ceramic Arts Discussion List
> Date: Sat, 22 Apr 2000 21:20:57 EDT
> To: CLAYART@LSV.UKY.EDU
> Subject: Re: estimating flat top brick
>
> ----------------------------Original message----------------------------
>> I'm building my train kiln, now it's time to
>> build the roof. My first plan was to go with
>> an arch, but because of the price of arch brick
>> I was going to make my own. I realize now,
>> way too time involved with that plan!
>> I'm thinking of going with a flat top.
>
> I've asked before but not received an answer, What is a flat top kiln, if
> it's brick how is it supported?
> Would be grateful for knowledge.
> Feri.
Dave Finkelnburg on mon 24 apr 00
Feri,
The flat top is too simple! It really is just a flat top, rather than a
sprung arch.
If you visualize the kiln walls, all the same height, ready for the
skewbacks on two sides, and you put a form inside, top of form flush with
the walls, form set solidly on legs, then you're ready to build the flat
top. The bricks are dipped in high-temp mortar (there should be a post in
the archives describing just how this is done) and laid on end, vertically,
so the kiln dome is 9-inches thick. The brick, in the plans I've seen,
aren't all laid parallel, some are at right angles to break up the straight
lines along the joints.
When the brick are all in place four pieces of angle iron, one at each
corner, and connected by rod, are pulled toward each other by tightening
nuts at the ends of the rods. This really is very much like the roof on a
common electric kiln, only usually larger. It's really quite strong.
The flat top can be "sprung," quite literally, an inch or so, to
increase its strength, by jacking the center up when the brick are just
laid, and the frame not yet pulled tight. Raising the center of the form
creates small gaps between the top end of the bricks. If those gaps are
then filled with high temperature mortar, the dome effectively becomes a
VERY flat arch.
Hope this helps answer your question.
Dave Finkelnburg
-----Original Message-----
From: ferenc jakab
To: CLAYART@LSV.UKY.EDU
Date: Saturday, April 22, 2000 7:22 PM
Subject: Re: estimating flat top brick
>----------------------------Original message----------------------------
>> I'm building my train kiln, now it's time to
>> build the roof. My first plan was to go with
>> an arch, but because of the price of arch brick
>> I was going to make my own. I realize now,
>> way too time involved with that plan!
>> I'm thinking of going with a flat top.
>
>I've asked before but not received an answer, What is a flat top kiln, if
>it's brick how is it supported?
>Would be grateful for knowledge.
>Feri.
>
ferenc jakab on mon 24 apr 00
Steven, Thank you for your reply. I include my thank you to Fred Paget.
I applogise for the misconception that I was trying to build one. I hijacked
a previous poster's query and appended mine. Never the less your details
have considerably further enlightened me.
Feri.
Fred,
Thank you for the extended reply. I now understand what a flat top kiln is.
I've not seen any in Australia, though I am sure there are some. I also
haven't seen any books by Nils Lou, though again I'm sure that the big city
libraries migh have some. I tried the archives and while there were many
posts about problems etc. There was nothing which I could find which
explained it so well. Bruce Girrel explained the bricks were on end and put
under compression but he did not explain the doming. This and the fire clay
mortar would be what allows expansion and contraction with heating and
cooling.
I still have doubts about optimum hot gas flow. Would you get many cold
spots? I suppose it would be similar to a shallow sprung arch in
aerodynamics.
Gratefully yours,
Feri.
ferenc jakab on mon 24 apr 00
> Feri,
> Flat top the way we use it usually refers to Nils Lou's design where the
> kiln ceiling is made of vertical bricks in a very shallow dome shape where
> the horizontal force from the dome is taken up by steel threaded rods
> that are in tension.
> The trick is that a dome partly converts the force of gravity to a force
> tangential to the dome structure. By making a very shallow dome most of
> this force is horizontal and can be supported by squeezing in the sides of
> the dome with the clamping rods.
> The dome shape is made by building the ceiling on a well supported piece
> of plywood and jacking up the center from below after which the bricks are
> grouted with a fireclay - sand mixture, then the tension frame is
tightened
> before the jack is released. Now you have a dome with only a couple of
> inches rise in the center. There is a limit on how wide this can be made
as
> the crushing strength of the insulating firebrick would appear to limit
the
> maximum pressure that can be applied.
> This works well for a square ceiling. I think it could be made to work
> with a long shallow arch made the same way but the clamping method would
> have to be worked out.
> On a train kiln isn't the ceiling also the door ? If so it would be even
> harder to clamp and probably if it is not too wide some sort of a door
> could be made with stainless steel rods inside the bricks close to the
cold
> face to support the bricks. I used this method on my small luster kiln and
> I once fired it to cone 10 and the roof is still up although it is only
> about 2 feet wide.
> I have seen in the Harbison Walker (A. P. Green formerly) catalog some
> brick support modules that can be welded to an external steel framework to
> make wide flat top kilns. Some of these use fiber modules, some are
brick.
> These are no doubt used in large commercial tunnel kilns, etc.
> Fred Paget
Fred,
Thank you for the extended reply. I now understand what a flat top kiln is.
I've not seen any in Australia, though I am sure there are some. I also
haven't seen any books by Nils Lou, though again I'm sure that the big city
libraries migh have some. I tried the archives and while there were many
posts about problems etc. There was nothing which I could find which
explained it so well. Bruce Girrel explained the bricks were on end and put
under compression but he did not explain the doming. This and the fire clay
mortar would be what allows expansion and contraction with heating and
cooling.
I still have doubts about optimum hot gas flow. Would you get many cold
spots? I suppose it would be similar to a shallow sprung arch in
aerodynamics.
Gratefully yours,
Feri.
Tom Wirt/Betsy Price on mon 24 apr 00
Feri...
Strongly suggest you get Nils Book ( as others have suggested). He ahs a
new layout for the top using 3" brick. It seems to be a big improvement in
strengthening the lid. Also, the current edition shows plans for widening
the door....again a major improvement.
tom Wirt
>Subject: Re: estimating flat top brick
> ----------------------------Original message----------------------------
> Feri,
> A (Minnesota) Flat Top kiln is a kiln designed by Nils Lou which
> incorporates a very low dome (2" rise) rather than a traditional arch. The
> top is laid up on a flat plywood support on the kiln and compressed with
> steel brackets. Some flat tops are now being made with monolithic fiber
>
> > From: ferenc jakab
> > Reply-To: Ceramic Arts Discussion List
> > Subject: Re: estimating flat top brick
> >
> > ----------------------------Original message----------------------------
> >> I'm building my train kiln, now it's time to
> >> build the roof. My first plan was to go with
> >> an arch, but because of the price of arch brick
> >> I was going to make my own. I realize now,
> >> way too time involved with that plan!
> >> I'm thinking of going with a flat top.
> >
> > I've asked before but not received an answer, What is a flat top kiln,
if
> > it's brick how is it supported?
> > Would be grateful for knowledge.
> > Feri.
>
Dannon Rhudy on mon 24 apr 00
.....
>I was going to make my own. I realize now,
>way too time involved with that plan!
>I'm thinking of going with a flat top.
>
>My question, is there a way to estimate
>the number of needed brick?
..................
Steve, for a flat-topped train-kiln you can use kiln
shelves to span the width (providing the width works
with your shelves) covered by a fiber blanket during
firing. Works well.
regards
Dannon Rhudy
potter@koyote.com
ferenc jakab on tue 25 apr 00
> ----------------------------Original message----------------------------
> Feri...
>
> Strongly suggest you get Nils Book ( as others have suggested). He ahs a
> new layout for the top using 3" brick. It seems to be a big improvement
in
> strengthening the lid. Also, the current edition shows plans for widening
> the door....again a major improvement.
>
> tom Wirt
I thank every body who has replied to my query and every body who will.
There is a time lag between posting and reply because of the time difference
between North America and Australia. I have posted replies to some of the
people who got in early, but the number is escalating. So I post this as a
big thank you to every body. This response demonstrates the best of Clayart,
good will and a desire to help.
I want to apologise to every body who thought I want to build such a kiln,
my question was out of curiosity only, for I could not visage such a beast.
My query was appended to another person's query and I apologise to that
person and for any confusion and hope they have seen the posts that I have
received.
Gratefully yours,
Feri.
Hank Murrow on tue 25 apr 00
>----------------------------Original message----------------------------
>Fred,
I now understand what a flat top kiln is.
>I've not seen any in Australia, though I am sure there are some. Snip.....
>I still have doubts about optimum hot gas flow. Would you get many cold
>spots? I suppose it would be similar to a shallow sprung arch in
>aerodynamics.
>
>Gratefully yours,
>Feri.
The experiences of potter friends of mine who use the MFT design; is that
they promote very even reduction, due to the turbulence created by the Flat
Top. Also, they maximize stacking capacity vs. overall cubic capacity.
Regards, Hank in Eugene
John Neely on tue 25 apr 00
> I'm building my train kiln, now it's time to build the roof. My first
> plan was to go with an arch, but because of the price of arch brick I
> was going to make my own. I realize now, way too time involved with
> that plan! I'm thinking of going with a flat top.
>
> My question, is there a way to estimate the number of needed brick?
Steve,
As Dannon has pointed out, most folks just span the things with kiln
shelves and cover the shelves with fiber and/or soft brick. Estimating
ought to be pretty simple - divide the area to be covered by the area that
one brick covers. Or do I misunderstand the question?
As far as I know, no one has done one with a Nils Lou style flat top, but
it seems to me that it should work. In fact for a hinged lid like we have
here, it might work even better than a more conventional arch. If you use
soft brick it is just about imperative that you use some sort of coating to
protect the brick.
John Neely
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