Robert on wed 28 nov 07
Hi All,
Been off list a while. Last November I walked away from 10 years of
accumulated equipment and am starting again from scratch. Over the
summer I researched a local deposit of high alumina (30% average) flint
fireclay which is primarily kaolinite in its mineralogy. Hank has been
kind enough to fire a couple of test bricks for me in determining a
suitable castable recipe. The basic recipe is 4pts flint fireclay,2
pts. saw dust to 1 pt calcium alumina cement (70% alumina) The deposit
is quite large and has boulder size pieces down to gravel and fines. In
my first set of tests I screened two different sizes of fire clay
1/2"-1/4" and 1/4" to fines and used them in equal parts for one set and
1/4" to fines exclusively in another set. The test came out looking
very much like commercial IFB's with some spalling/shrinkage cracks and
zero fusion at cone 10. The tests with the larger aggregate were
obviously more crumbly. In addition my saw dust was a fairly coarse fir
end grain shaving which seemed to contribute to a lack of mechanical
strength. I have since dug enough material to build a 30 cu ft kiln and
just received word from Hank today that the second set has been fired.
For this test I used only 1/4" to fines and I varied the proportion of
saw dust as well as using sifted table saw sawdust with a more
vermicular shape. I have yet to see the tests to assess them but have
been considering over the months the possible need to calcine all or a
portion of the kaolinite. The kiln I am constructing will be fire to
cone ten. Cast as separate largish blocks. The brick will be air set
only and with a 7" wall thickness the temperature differential between
the hot face and exterior will be significant.
So the question is: what advantage, in terms of mechanical strength,
would be gained by calcining all or a portion of the kaolinite. It
would not be a simple thing to calcine the volume of material I'm
dealing with (about 2 cu. yds.) Or, alternatively, what other additions
might you suggest to increase the mechanical strength of the castable.
I am trying to use primarily local materials but this kiln will not be
purist in that sense. Any other thoughts or comments would also be
appreciated. So... TIA
Robert
Hank Murrow on thu 29 nov 07
On Nov 28, 2007, at 4:45 PM, Robert wrote:
> Hi All,
> Been off list a while. Last November I walked away from 10 years of
> accumulated equipment and am starting again from scratch. Over the
> summer I researched a local deposit of high alumina (30% average)
> flint
> fireclay which is primarily kaolinite in its mineralogy. Hank
> Murrow has been
> kind enough to fire a couple of test bricks for me in determining a
> suitable castable recipe. The basic recipe is 4pts flint fireclay,2
> pts. saw dust to 1 pt calcium alumina cement (70% alumina) The
> deposit
> is quite large and has boulder size pieces down to gravel and
> fines. In
> my first set of tests I screened two different sizes of fire clay
> 1/2"-1/4" and 1/4" to fines and used them in equal parts for one
> set and
> 1/4" to fines exclusively in another set. The test came out looking
> very much like commercial IFB's with some spalling/shrinkage cracks
> and
> zero fusion at cone 10. The tests with the larger aggregate were
> obviously more crumbly. In addition my saw dust was a fairly
> coarse fir
> end grain shaving which seemed to contribute to a lack of mechanical
> strength. I have since dug enough material to build a 30 cu ft
> kiln and
> just received word from Hank today that the second set has been fired.
> For this test I used only 1/4" to fines and I varied the proportion of
> saw dust as well as using sifted table saw sawdust with a more
> vermicular shape. I have yet to see the tests to assess them but have
> been considering over the months the possible need to calcine all or a
> portion of the kaolinite.
Hank replies........ that the newest samples looked like bricks, did
not shrink that much, and fired white at cone 11 in Reduction. Looks
like a smidge of modification will nudge the newest samples into
serious contention with factory brick. Kudos, Robert!
> The kiln I am constructing will be fire to
> cone ten. Cast as separate largish blocks. The brick will be
> air set
> only and with a 7" wall thickness the temperature differential between
> the hot face and exterior will be significant.
> So the question is: what advantage, in terms of mechanical strength,
> would be gained by calcining all or a portion of the kaolinite. It
> would not be a simple thing to calcine the volume of material I'm
> dealing with (about 2 cu. yds.) Or, alternatively, what other
> additions
> might you suggest to increase the mechanical strength of the castable.
> I am trying to use primarily local materials but this kiln will not be
> purist in that sense. Any other thoughts or comments would also be
> appreciated. So... TIA
If the cast blocks are not fired throughout to at least bisque temp,
they may prove fragile on the exterior. Of course, one could 'mud'
the kiln with Insulating Cement(good to 1200F) to insure that the
outer layer of the cast blocks reaches bisque.
Cheers, Hank
www.murrow.biz/hank
Duff bogen on thu 29 nov 07
Robert
sounds great
In my recent experience I used a mix of equal volumes of alumina and OM4 I've used before to make small items (buttons for fiber tie down, spy holes) I tried to up scale it and had massive failure of parts larger than a half pound of clay- 40 years in clay and I"d never seen anything like it!
If I had made grog and had it half and half would it have worked????
Cardew and Davis both recommend high grog content. Making bricks at Cardew's gave me the impression that they are passing on to us SOP for saggar making from "The tradition"and poetics of mullite crystals felting together.
As for firing see brick making in the appendix - make a crude kiln with raw bricks and fire a batch of bricks to be ground for grog...
Keep up the good fight
Duff
Robert wrote:
Hi All,
Been off list a while. Last November I walked away from 10 years of
accumulated equipment and am starting again from scratch. Over the
summer I researched a local deposit of high alumina (30% average) flint
fireclay which is primarily kaolinite in its mineralogy. Hank has been
kind enough to fire a couple of test bricks for me in determining a
suitable castable recipe. The basic recipe is 4pts flint fireclay,2
pts. saw dust to 1 pt calcium alumina cement (70% alumina) The deposit
is quite large and has boulder size pieces down to gravel and fines. In
my first set of tests I screened two different sizes of fire clay
1/2"-1/4" and 1/4" to fines and used them in equal parts for one set and
1/4" to fines exclusively in another set. The test came out looking
very much like commercial IFB's with some spalling/shrinkage cracks and
zero fusion at cone 10. The tests with the larger aggregate were
obviously more crumbly. In addition my saw dust was a fairly coarse fir
end grain shaving which seemed to contribute to a lack of mechanical
strength. I have since dug enough material to build a 30 cu ft kiln and
just received word from Hank today that the second set has been fired.
For this test I used only 1/4" to fines and I varied the proportion of
saw dust as well as using sifted table saw sawdust with a more
vermicular shape. I have yet to see the tests to assess them but have
been considering over the months the possible need to calcine all or a
portion of the kaolinite. The kiln I am constructing will be fire to
cone ten. Cast as separate largish blocks. The brick will be air set
only and with a 7" wall thickness the temperature differential between
the hot face and exterior will be significant.
So the question is: what advantage, in terms of mechanical strength,
would be gained by calcining all or a portion of the kaolinite. It
would not be a simple thing to calcine the volume of material I'm
dealing with (about 2 cu. yds.) Or, alternatively, what other additions
might you suggest to increase the mechanical strength of the castable.
I am trying to use primarily local materials but this kiln will not be
purist in that sense. Any other thoughts or comments would also be
appreciated. So... TIA
Robert
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