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Playing with castable refractory

Michael Newby


Joined: Apr 06, 2011
Posts: 152
Location: Mount Shasta, CA Zone 8a Mediterranean climate
    
    7
While it's not technically for a rocket stove, I thought I would share my experiences using castable refractory cement. This mold and casting are for a high temp forge but I plan on using the exact same techniques to cast rocket stove parts.

I was using Kast-O-Lite 3000 from a Portland OR supplier that you can buy from through e-bay.

For the mold I used 5/8" plywood with one smooth side (can't remember the trade term for that) and one 10' 2x6 ripped on a tablesaw to the depth I wanted the refractory panels - in this case 2". I then wrapped all the separate mold pieces with the thin plastic sheeting you can get from most hardware stores. I basically wrapped them like I would a present, using duct tape and making sure that the taped edges weren't going to be exposed to the refractory surface. Once all surfaces were wrapped I assembled the whole thing using deck screws. With all the pieces screwed into place so that they were pretty sturdy I ran a small bead of caulking along all the seams to ensure a water-tight seal.




[Thumbnail for Refractory Mold - Bare.jpg]


[Thumbnail for Refractory Mold Assembled.jpg]


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I like trees because they seem more resigned to the way they have to live than other things do.  ~Willa Cather, 1913

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Michael Newby


Joined: Apr 06, 2011
Posts: 152
Location: Mount Shasta, CA Zone 8a Mediterranean climate
    
    7
Once the caulking had cured I coated all the mold surfaces with a thin coat of veggie oil - just wiped it on with a paper towel then used another to wipe up the excess, leaving only a thin film.



[Thumbnail for Refractory Mold - Oiled.jpg]

Michael Newby


Joined: Apr 06, 2011
Posts: 152
Location: Mount Shasta, CA Zone 8a Mediterranean climate
    
    7
If I could only change one thing about the whole process I used, it would be using an actual mixer for mixing the refractory, not a trashcan and shovel! As far as mixing the actual product went I just followed the very thorough instructions that came with the refractory.

To say I poured the refractory would be misleading - the working mixture seemed very dry but the instructions were extremely clear that you should not exceed their threshold for water used in the mix. What I ended up doing was shoveling the mix into the mold then used my fingers and a pencil to pack it into the corners and remove as much air as I could. If I hadn't been stuck doing this whole thing in my living room next to the wood stove (you need at least 60 deg F for proper curing) with my infant daughter sleeping in the next room I would have used an air impact wrench on the sides of the mold to vibrate the whole thing for better settling and air removal. As it was I'm very happy with the results. The instructions say not to trowel the surface smooth to ensure better moisture release but I did use a piece of scrap wood to screed the whole thing for level.

Once the refractory was cast the whole thing was covered with a sheet of plastic and allowed to cure next to the wood stove for about 36 hrs.



[Thumbnail for Refractory Mold - Filled.jpg]

Michael Newby


Joined: Apr 06, 2011
Posts: 152
Location: Mount Shasta, CA Zone 8a Mediterranean climate
    
    7
After curing I just unscrewed the mold and everything separated so easily! I'll even be able to reuse the mold if/when I want to. The only minor problem I've encountered so far is that the caulking wasn't fully cured like I thought and it stuck to the refractory better than to the plastic. It just peels off where it's thicker and the rest comes off pretty easily with a stiff plastic bristle brush (used hard toothbrush). If you look closely at the edges of the piece that's been pulled you can see the white caulk all around.



[Thumbnail for Refractory Mold - First Piece.jpg]

Michael Newby


Joined: Apr 06, 2011
Posts: 152
Location: Mount Shasta, CA Zone 8a Mediterranean climate
    
    7
Here's a final shot of all the pieces mocked up into the forge. The refractory still needs to be brought up to operating temperatures according to the instructions but it's already pretty darn solid - think cinder block. I have a little machining to do on the blocks before I fire them so I'll have a good idea of how workable the green refractory is in a few more days.



[Thumbnail for Looking Into the Forge.jpg]

Ken Peavey
steward

Joined: Dec 21, 2009
Posts: 2202
Location: FL
    
  58
Well Done

Working Tip
To get the material to move tightly into corners, use a poorman's vibrator.
Place a small board on top of the mold. Apply a random orbit sander to the board. The vibration of the sander will work with a thin casting.
The mold can be covered with plastic or a towel for easy cleanup.

Seed the Mind, Harvest Ideas.
http://farmwhisperer.com
Prescott H. Paine


Joined: Feb 28, 2013
Posts: 15
How much was the material (and brand name would be handy to as I am scouting materials), and what sort of shipping did it set you back? It must have added up to less than a local price, or your "local price" included traveling to a city or the like. Love the idea, and good man for not using the impact wrench with baby napping. Trade offs! (though the air pockets could be beneficial as insulation!)

Did the material come with a burn rate temp? I have seen 2500 and 3000, the latter being about 10 more bucks for 25 lbs (@~$42)

Peace, you care for those trees the way I do, too many aren't~p
                        


Joined: Oct 21, 2010
Posts: 32
I've been working with the casta-lite 35 refractory, cost is $48.00 for 50# 3200deg F w/4BTU loss per square inch @1 inch thickness.(per hour)
50# is enough to pour 2 risers 6"x24"@1" thick or 1 riser and 1 fire box (complete stove hot section) I started using the refractory after melting and carbonizing my first stove that was built using rock wool and 16 ga SS, having to do a quick rebuild with more conventional fire brick for the fire box and replacing the riser's inner sleeve, to keep us warm through that winter, being very careful about what I feed it.
Observations:
The smaller the fuel the greater the surface area, the faster it gives up its BTU's
RMH will try to eat everything you give it as fast as it can get the air to do so
When stove starts glowing orange/yellow you may have a problem?

When I get camera thing sorted out will post pics of mod 2 and 3 with full explanations of methods and reasoning
David
Prescott H. Paine


Joined: Feb 28, 2013
Posts: 15
Tarkus, wow, you def have some serious draft going!

Would you be able to share some of your measurements? (ideally all, but the basics work like > >

> 8" system, 6"?
> feed tube CSA (square inches, or measurement thisxthat is cool too)
> burn tunnel (csa and or length)
> heat riser (csa and or height)
> barrel over it (height x width)
> length of pipe in bench, or did it head into a chimney?

Any info helps, I am sorting out the equation for my own space and looking for good pull, max efficiency. You obviously had draft galore, I wan't your recipe!

Glad you patched things up to stay warm. Be good~p
                        


Joined: Oct 21, 2010
Posts: 32
I'm just getting the camera up and functioning again and on a new computer, my first Mac (new to me)
The photos are of Mod 3 portable RMH parts and pieces
the first is the fire box and lower body, the fire box is again 16ga SS the tubes are the feed tube and riser collar also SS welded to fire box, this sits inside the lower body and will be surrounded on all sides by refractory. Two channels run down either side of fire box with screened openings to allow air at floor level to enter body flowing up into upper stove body (convection or forced) around the "Barrel"
the square box with all the fins (heat exchanger) and then out the top of stove. The upper stove body is offset to the rear of the lower body to allow for exhaust (insulated 6" 90deg elbow) out to portable mass?. The riser or catalytic chimney is 24" of 8" HVAC duct with a 1" layer of castable refractory that was poured around a waxed paper tube (6"), allowed to harden and then paper removed, this is slipped over the collar on the fire box after the "Barrel" is installed and screwed to the bottom of the barrel so to say.
In one of the photos Lt-Rt Upper stove body (upside down to show exhaust connection) "Barrel" w/heat exchanger fins then the top that will eventually sleeve the outside of upper body and inside of barrel.



[IM000253.JPG]

[IM000256.JPG]

[IM000257.JPG]

                        


Joined: Oct 21, 2010
Posts: 32
Sorry missed some photos, here's the rest for better clarity. I call it portable because it's a stand alone unit and should be movable with a hand truck, mass not included


[IM000255.JPG]

[IM000258.JPG]

Michael Newby


Joined: Apr 06, 2011
Posts: 152
Location: Mount Shasta, CA Zone 8a Mediterranean climate
    
    7
Prescott H. Paine wrote:How much was the material (and brand name would be handy to as I am scouting materials), and what sort of shipping did it set you back? It must have added up to less than a local price, or your "local price" included traveling to a city or the like. Love the idea, and good man for not using the impact wrench with baby napping. Trade offs! (though the air pockets could be beneficial as insulation!)

Did the material come with a burn rate temp? I have seen 2500 and 3000, the latter being about 10 more bucks for 25 lbs (@~$42)

Peace, you care for those trees the way I do, too many aren't~p


I used Kast-o-lite 3000 which is rated to 3000 deg F and it cost a little over $90 per 55lb bag shipped. The base price is half that if you can pick it up locally (Portland, OR) According to the directions, it takes ~90 lbs per cu. ft. so I needed 2 bags for the forge, I'm thinking I'll need three bags for casting the Rocket Stove I want to build.

Ken - Talk about a forehead slapping moment: A palm sander would have worked great for settleing and the baby would have slept right through it!
 
 
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