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Post by bmeagle on Jan 20, 2012 4:08:44 GMT -8
Hi guys
I am new around here, I have been absorbing as much as I possibly can.
By profession I am a mechanical engineer, with a big interest in thermo fluids and alternative energy.
Peterburg has some awesome stuff and the thread on the drive force behind a RMH is very informative.
I have a stovetec stove which I sometimes use to cook outside with, amazing how little charcoal it uses.
I am from south africa and it is still summer so I want to start experimenting with my idea before winter.
I want to build a clay paving brick (200mm x 100mm x 50mm) based RMH based on a normal type of RMH. I will probable have to use some fire brick for the riser and burn tunnel.
You guys seem to use a reusable mortar mix, clay and sand.
I want to experiment and when it works break if up and rebuild it inside the house, use it for a season or two and then break it up when I move into my own house and rebuild.
Any more details on this mortar mix? I need to find the equivalent materials locally.
The biggest thing I like about peterberg's bell designs is the all brick setup. My wife has ruled out any steel drums for aesthetic reasons.
Now I know the barrel enhances the draw by cooling the gas which increases the density which helps pull the gas down in the barrel section.
Has anyone had any success with a brick "barrel"?
I expect the initial draw to be good when the brick barrel is cold and the draw would probably decrease as the brick barrel heats up.
Maybe one should build the brick barrel with a greater surface area than just a round or square barrel.
Alternatively, I could use a steel barrel and surround it with mortared bricks with a circular gap between the bricks and the drum.
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Post by Deleted on Jan 20, 2012 5:51:14 GMT -8
Homemade refractory concrete formula www.backyardmetalcasting.com/refractories.htmlFor more insulation one could replace the sand with more perlite. Some are recomenting to replace half of the portland cement with hydrated lime or to use white cement. Some are using just saw dust or paper instead of perlite. |
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Post by peterberg on Jan 20, 2012 6:43:16 GMT -8
I've found another source, which says you'll have to rule out silica altogether, so no sand in the mix at all. It's possible to cast a lightweight and insulating concrete by using Portland cement and expanded clay (like hydroton) or expanded shale. This should be fire resistant up to 800 F. www.everything-about-concrete.com/heat-resistant-concrete.html |
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Post by Deleted on Jan 20, 2012 7:24:41 GMT -8
Depends on particle size, which influences the reaction on termal shock and the ability
to react chemicaly with the rest of the mix, either by hydration or ceramic at firing.
Quarz ( SiO2 ) has a melting point of 1670 °C (β tridymite) or 1717 °C (β cristobalite)[1].
Fire clay consists of up to 60% quarz.
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Post by bmeagle on Jan 20, 2012 7:35:17 GMT -8
Thanks for the input thus far.
Here are is a picture of what I have in mind.
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Post by bmeagle on Jan 20, 2012 7:36:18 GMT -8
And a section view.
Learnt to use sketchup today, someone different to traditional CAD.
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Post by bmeagle on Jan 20, 2012 7:37:31 GMT -8
The pictures have some inconsistencies, mainly the barrels, I just stacked two cylinders on top of each other, barrel cut outs should be where you would expect them to be.
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Post by Donkey on Jan 20, 2012 8:28:36 GMT -8
As mortar, I usually just use clay slip. That is clay rich earth, mixed with water, put through a sturdy fly screen.
IMHO, the thinner the joints are the better. Mortar is for holding the bricks apart, NOT sticking them together, gravity holds 'em together (with a remarkable mount of stickiness from the clay, but let's ignore that.)
If I need something thicker than just the slip (big voids or the bricks rock around on a high point) then I'll mix in wood ash (to the slip mixture) to a bread dough consistency. Use as little as you can get away with and still do the job.
The works can then be puttied up from the outside with the clay/ash mix, filling the holes, etc.
That's it. No fancy mixes, no store-bought gunk, no toxics (besides the lye naturally found in wood-ash. Wear gloves)
It'll last for a good long time and when it's time to take things apart again, no problem. You will be surprised how resilient the clay/ash mix can be. If you got good clay, it won't come apart too easy.
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Post by bmeagle on Jan 20, 2012 11:15:32 GMT -8
Looks like I have found a local supplier of bentonite. www.clay.co.za/Comes in 40kg bags, need to get some. I suspect that most of the clay bricks in South Africa is made from this exact same stuff, so hopefully the thermal expansion coefficients will match. Donkey your slip clay method sounds a lot like some guys around here use a product called Blockgrip to glue concrete bricks together with. The clay paver bricks I want to use are usually very uniform in shape, so voids etc shouldn't be a problem. Next week I should have a source for fire bricks. |
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Post by Deleted on Jan 20, 2012 11:34:12 GMT -8
Bentonite is famous for it's strong water absorption and swelling properties,
which will lead to huge shrinkage and lots of cracks when drying to fast.
Kaolin (china clay) does not have these problems and is usualy even cheaper.
There are other kinds of fireclay too.
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Post by bmeagle on Jan 20, 2012 11:46:50 GMT -8
Mmm, thanks I will keep that in mind.
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Post by Deleted on Jan 20, 2012 11:58:24 GMT -8
If you have problems to get other kinds of fire clay:
The huge shrinkake can be prevented by mixing it with cement,
as the cement will make it hard long before all the water is out.
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Post by bmeagle on Jan 20, 2012 22:27:40 GMT -8
Kaolin is available as well, I just need to find a supplier close by.
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Post by bmeagle on Jan 23, 2012 6:34:07 GMT -8
I think I need to clarify something. I want to be able to re-use the bricks while experimenting not necessarily the mortar. I want to be able to get most of the mortar of the bricks. I reckon that rules out cement for a temporary set-up. For experimenting I'll first see how far I can get by just dry stacking. In the mean time I've found some fire bricks: www.durransrms.co.za/both/ds_bricks.gifI think the JM23 type should be good, 1260C rating should suffice for the burn tunnel and heat riser! |
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Post by peterberg on Jan 23, 2012 7:10:53 GMT -8
bmeagle, When reusing the bricks is the goal you're after, use kaolin with sand, volume parts 1:1. It's very easy to dismantle the stove by hand and clean the bricks. Even the clay can be re-used, scrape the clay off the bricks in a bucket, add water and the next day it's clay again. I've done that countless times during the development of the rocket/bell stove. The bricks you've found are nice, insulating fire bricks will make the stove very responsive.
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