A castable burn chamber

Thomas Vogel wrote:Has anyone considered using two adjustable elbows and a short piece of duct to make the interior mold of a castable burn chamber? There's gotta be something wrong with it. Seems too easy.

This!
Whats the word, bird? From other reading I suspect a square chambers sharp edges are preferred, as they create turbulence. do I have this right?

While there may be slight gains from the sharp transition from top of tunnel to riser creating turbulence for mixing, there's also evidence that a sweep at the bottom back of the riser helps a lot, and this method would provide that. I think that this idea would probably work just fine. It sure would be easy! Let us know if you try it out.

Just wanted to mention something a knowledgable source told me the other day. I was buying a bunch of ingredients for my core and stove at a masonry place (in New England) and I was asking about perlite, why they only sold vermiculite. He said it isn't so much the product, it has it's applications, but when it comes to mixing it for masonry projects, adding perlite is more like adding marbles to a mix, essentially weakening the mixture due to a presence of an aggregate that doesn't bond. On the other hand, adding vermiculite to a mix is more along the lines of adding oatmeal, yes it absorbs water, but in that process also bonds with the mix! I found it invaluable info and was glad to be getting vermiculite, masonry grade of course.

Please don't get me wrong, perlite has its applications, but in a castable core thread I wanted to share information that I felt grateful to receive, in fact it was rather revelatory!

Now if I could just find some fire clay! I am swinging by a local potter tomorrow, I'd like to stretch all that furnace cement as well as splurging on a bag of nox-Crete, replete with stainless steel needles!

Hope this helps, make it rockety!

I am not really close to casting anything, but the draw for me is cost saving. Firebricks or better kiln bricks can be pricey.A cheap, malleable substitute can be used in bulk, experimented with, and used for other things like the dome on a bread oven...

Concerning the vermiculite, this feeds into something else I have been thinking about, finding a substitute for the Refractory Mortar, the most spendy part of the formula.
Looking into alternatives, I considered lime plasters and such, but what intrigues me is right now is Water Glass.
I am not sure of the durability but the material is used in metal casting, so it should be able to stand the heat just fine.

Also there is this:

Refractory use[edit source | editbeta]
Water glass is a useful binder of solids, such as vermiculite and perlite. When blended with the aforementioned lightweight aggregates, water glass can be used to make hard, high-temperature insulation boards used for refractories, passive fire protection and high temperature insulations, such as moulded pipe insulation applications. When mixed with finely divided mineral powders, such as vermiculite dust (which is common scrap from the exfoliation process), one can produce high temperature adhesives. The intumescence disappears in the presence of finely divided mineral dust, whereby the waterglass becomes a mere matrix. Waterglass is inexpensive and abundantly available, which makes its use popular in many refractory applications.

William, those "furnace cement" products I use as hardening additive to my mix use sodium silicate as the main hardening ingredient. While it's much more expensive to buy that way, it's easy to find at any hardware store. So yeah, you could just use water glass instead of the furnace cement.

Hi William:
I also was intrigued with the ingenious castable burn chamber videos that Matt posted. Like you I also wanted to integrate sodium silicate (aka: waterglass). I spent may days researching the subject, before I bought the supplies to start experimenting. A word of caution first wear gloves, sodium silicate is a lye solution, and it will burn your skin! Sodium silicate changes the properties of clay when added to it. Sodium Silicate allows for a great decrease in the amount of water necessary to get the correct texture. The advantage being, that there would be less shrinkage of the form, from water evaporation. The decrease in moisture, also in theory, reduces the number of cracks.
So far, in my first experiment, I diluted the sodium silicate and added it to a mixture of mostly perelite with a smaller amount of fireclay. The mixture dried in two days, and I was happy with the hardness and durability. I am waiting to do more experiments using a tank of CO2, or soda water ( which is infused with CO2). CO2 gas would harden the cast very quickly, using the lesser amount of water. I am still in the midst of experimenting. I will start to document more of my experimenting, and posting my results.
Best of Luck,
Diane

Thanks for the replies, very inspiring info in this thread.
I haven't priced every thing out, is thr sodium silicate cheaper strait or as part of a furnace cement?

Also, any thoughts on using baking soda as a source of carbon dioxide for curing?

From what I have found online is that the new Fake TSP hass Sodium Metasilicate as one of the ingredients. I'm going to make a batch of cement, perolite and Fake TSP on monday with a little soda water and see how it holds up.

I am a complete noob and have never worked with any of these materials for these particular applications, but I do know a thing or two about chemistry and cars so I thought I would suggest a source for CO2.

The complete combustion of any hydrocarbon results in heat, CO2 and H2O.

For example if gasoline was completely combusted you would have the following reaction:

Gasoline can be represented by octane C8H18. Its combustion, in the most straight-forward sense is to carbon dioxide and water.

2C8H18 + 25O2 ~> 16CO2 + 18H2O

Modern day vehicles do a fantastic job of completely burning gasoline, once they have reached operating temperature, so you could just pipe some in from your exhaust pipe.

There are a myriad of other way cool chemical reactions that would release CO2, but this is about as cheap. simple and readily available as you can get.

What exactly is 'fireclay'? Isn't all clay fireclay?
I have access to pottery supplies in my area so I have several clays from which to choose like here
http://trinityceramic.com/dry-clays

I have the rocket mass heater book and will re-read it so the answer may be in there.

Here is the answer to my own questions about fireclay.
http://www.traditionaloven.com/articles/101/what-is-fire-clay-and-where-to-get-it

I am still researching the best mix and methods for RMH core stuff

DIY Refractory Compositions thread out at the Alloy Avenue forums has a number of recipes for refractory. I made my first furnace and a few prototype stoves using a home made fire clay based refractory. There are far too many possible variations to effectively cover in a single post, but there are a few points that are helpful.

Obviously the first point is to use a high firing clay. Adding grog also helps a great deal. Grog is basically bits of clay that have previously been fired and then broken up. Having grog in your mix, preferably with a multitude of sizes as opposed to finely sifted dust, will reduce shrinkage. Being that this previously fire clay has already shrunk it makes a great addition to a fire clay hot face.

Another thing that can be helpful is the shape and design. Given that these clays can and probably will crack, it makes sense to shape it in such a way that it can't fall in on itself or easily topple over. You can use a knife or similar to add 'dashed lines' so it will more likely crack in places you designate as opposed to wherever it feels like cracking. If you wrap a more insulating material around your hot face (insulating refractory, ceramic blanket, home made insulation) this can also be shaped and designed to hold the hot face in shape. I have even seen people make special shaped bricks out of refractory and stack them up. any of the shrinkage or cracking would happen at the brick stage as opposed to happening in the finished product.

Given the possible temperatures of these heaters I would avoid using sand in the hot face, particularly if you are going to be adding insulation. It will turn to glass, and this molten glass will act as a flux and slump your hot face like an ice cream cone on a hot day. While I was fairly fortunate with the first furnace I built, I only got it up to aluminum melting temperatures. As temperatures increase the chance that a home made refractory mix will fail over time increases, be it hours or years. Something made to withstand intense temperatures like Missou Castable Refractory would be better. I have heard of guys on Alloy Avenue destroying Missou with a good oil burner when melting cast iron, but it is supposed to be one of the best refractories available. You could use this as a hot face and make your own insulation. A lot of the furnace construction threads over there use the same principles as building a rocket stove/RMH.

They have brought up some rocket stove stuff over at those forums and they have very experienced people there, including people who worked in proper foundries for a living. I'm sure if you can't find the information you need through searching that the people there would be capable of giving you plenty of help and ideas.

Thomas Vogel wrote:Has anyone considered using two adjustable elbows and a short piece of duct to make the interior mold of a castable burn chamber? There's gotta be something wrong with it. Seems too easy.

I decided to give that a try last winter, when it was too cold in the greenhouse (which is what the RMH is for) to cast anything. Using 6" round duct, I created an interior mold, and squeezed the straight section to try to make an approximation of the vertical port in the Peterberg designs. This is a 6" system, so I was able to make it in the basement -- compact and just light enough that my middle-aged son and I could get it up the basement stairs and outside.

It was only early this month that I was able to get enough time to actually complete the heater (and connection to the duct through the greenhouse bench) enough to start running it. I can report that it does work, but the feed tube/burn tunnel is frustratingly small for the amount of wood I need to burn to heat the bench. After less that two weeks' use, the metal is noticeably burning away as expected. I'm now trying to work out a way to convert to a batch box style. I already know that the perlite, castable furnace cement, and poor man's aircrete mixture of the casting can be cut with an old pruning saw, so it shouldn't be difficult to cut away the feed tube and open up the area. That should allow for a firebrick liner and better vertical port. I'll also be able to see how the back part and the insulated chimney section I used for the riser have fared.

With another cold night, I'd better go feed the fire again.

It's been a few years since the beginning of this thread and I'm looking for an update.  Has anyone done a successful castable mix using anhydrous sodium metalsilicate in league with portland, perlite, and wood ash?  Or this blend without the wood ash but with aircrete?  And really, wouldn't the wood ash be redundant with the water glass?

I've built a form to cast one half of the length of the column at a time and have heard that regular old white glue added to the mix will help the cement bond with it's other half much better during multiple pours.  I wonder if 2 vertical halves will bond or if I should just do a vertical pour and be done with it.  Probably the later.

As an aside; I have found that I don't need steel wool inside the pvc of a foam generator and can stuff it with organza and old sheer curtains to make super thick fine foam (just an observation).  Also I cook a lot so having a bolt of freezer paper worked out well for wrapping the casted objects to free them of their molds without breaking the final form.