Fw: [Stoves] Clay ring maker for various stoves

[ken goyer]

Dear Crispin, While I haven't properly digested everything you have 
recently written, I would like to add a couple of comments. Your machine 
looks great and by the time you get the clay formula worked out you can 
put a motor on it and really turn out the discs. In Ghana they converted 
an old shoe leather die stamp machine to stamp out ceramics. I'll bet 
you could use a "iron worker" machine also. Dry pressing ceramics does 
have certain advantages but I'm waiting to see how you can exert 
pressure and end up with a light weight insulative ceramic. It is 
important to eventually get the density down below one gram per c.c.  or 
the stove won't have the necessary insulation. Finding some non 
compressive organic material that will  burn out would be the path to 
take. Charcoal comes to mind but it might take a high temperature and a 
long time in the kiln to adequately oxidize. Regular bricks that are 
inadequately burned are "black cored"  from the remaining carbon in the 
clay. That said, the carbon itself might make a good insulator in high 
enough  quantities.  Some organic material is less "squishy" than 
others. I like rice husks very much even though I am on the other end of 
the water equation. I have found success with wet slop mixtures. But 
rice husks don't seem to absorb as much water as say, sawdust. Other 
hard hulls (millet?) might work. In the end it depends on what you have 
available in large quantities. Ceramic microspheres are another 
possibility. These come from fly ash and presumably are a disposal 
problem for power generation plants. Larry and I have been talking about 
making insulation by coating rice hulls with clay slip and "popping" it 
like you make perlite. Then you could use these as the lightweight 
component of your ring.  If you try it, give Larry some credit for this 
idea. Larry says that the best, lightest brick he has seen was made by 
Damon using graded pumice with clay binder compressed (I think kind of 
dry) and then fired.
    As to the water content and shrinkage. Don't forget that after the 
superficial water has been evaporated there is still the water of 
hydration. The water of hydration of the clay accounts for a lot of the 
shrinkage when this water is driven off. Remember the High School 
demonstration where the blue copper sulfate crystals, CuSO4.5H2O is 
heated, driving off the 5H2O and leaving a white powder. Then there is 
the the Quartz inversion when the alpha- beta inversion takes place 
around 550o C. and changes the volume by 15%.  A potter has to contend 
with this once or twice, but we might have to contend with it once or 
twice a day in a stove, I think that this is what contributes the most 
to spalling. Finding a zero expansion clay formula would be nice :-) . 
And they do exist, just expensive and problematical.
    The reason that I have come to like the SixBricks is that the 
expansion and contraction can take place in a linear fashion and the 
bricks provide the pre-cracks to allow for the change.  When you go 
around corners you get into trouble. As an analogy, think of heating up 
a steel washer. Does the hole in the center get larger or smaller? Now 
what happens when you heat up your ceramic body?
    I'm sorry that we haven't met. I would (will) invite you to come to 
stove camp sometime, but unfortunately, this year I will be in Africa.
Best regards and keep on experimenting,
Ken Goyer

Crispin Pemberton-Pigott wrote:

>Dear Lanny
>
>Thanks!  All encouragement is appreciated.  I work in my little troll-house 
>on my own surrounded by what I call opportunities.
>
>One thing it gives me is 'perspective from a distance' but I also have to 
>thank my wife Margaret who lives in Waterloo Ontario for letting me have 
>LOTS of time to burn my fingers (in more ways than one!)
>
>Where do you live?  I would like to visit sometime soon.
>
>Keep on stovin'
>Crispin
>
>
>----- Original Message ----- 
>From: "Lanny Henson" <lanny at roman.net>
>Subject: RE: [Stoves] Clay ring maker for various stoves
>
>
>
>I don't want to blather up the list ... 
>
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