[Stoves] Clay ring maker for various stoves

[Lanny Henson]

I don't want to blather up the list with too many "that a boy's and way to
goes" but I have to say
that a boy and way to go, that looks like a very useful invention.
You work just keeps getting better and better!
Lanny

-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org]On Behalf Of Crispin
Pemberton-Pigott
Sent: Sunday, June 04, 2006 11:20 AM
To: 'Stoves'
Subject: [Stoves] Clay ring maker for various stoves


Dear Stove Builders

The first ProBEC Clay Ring Maker (CRM) is working and you can see it on the
Bioenergylists website. www.bioenergylists.org  The photos are changing
daily as better ones are taken (thanks Tom).  There is a sequence showing
the entire cycle for making a clay ring.

These rings are used in the domestic Rocket Stove being produced by Andreas
Michael in Malawi.  This machine is to increase the production, make a
uniform product and to reduce losses during drying and firing.

I have produced some rings from straight red laterite to test the
compression and the results are very encouraging.  This afternoon one ring
was made with the composition:

79% laterite
11% charcoal powder
10% water added (to air-dry laterite)  The water content is perhaps 15% -
not important at this stage.

The mass will be in the region of 2050 gm after firing for a density of 1.35
depending on how much water is bound in the clay.

The spreadsheet tells me the charcoal powder content would have to be 34% to
get a clay ring with a density of 1.0.  Mixed 50-50 with the clay it would
have a final density of something like 0.83.

The forming pressure is high enough to run the damp clay throughout the mix
and the ring is strong enough to be picked off the mould with one hand and
handled with ease.

As it has only 1/2 the water normally used to form a ring, this one should
dry with a minimum of distortion or cracking.  As it is not extruded at any
time the mix is homogenous inside with no slip zones.  The means it should
shrink evenly in all dimensions (isotropically) and thus crack less.

Interestingly, adding water produced a higher density in some cases.  Air
dry laterite did not flow well enough to expel the air resulting in a porous
ring.  It is not clear if the clay will bind it well enough to be used like
that.  When adding charcoal powder (ground in a manual peanut butter maker)
it can be pressed very hard with sufficient water to make it flow well and
the porosity can still be set to any predetermined level because the
charcoal burns out.

Regards
Crispin

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