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Theresa Zelazny
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Can rocket mass stove technology be applied to firing ceramics? Has anyone tried this, if so how?
 
Cindy Mathieu
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At Dragon Heaters, we kiln our products using a large box lined with fireclay brick we made and a 6" Dragon Heater. However, we are not trying to get the heat to a certain cone level or anything else very particular. The exhaust goes directly into the box and the smoke discolors the products in a random (it seems to me) manner. This would probably not be acceptable for firing ceramics. So, you might have to do some air to air heat exchange (so that the smoke is excluded) to get consistent results. You would also have to really feed the fire continually to heat up all the bricks.
 
allen lumley
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Theresa Zelazny : With a rocket mass heater that has come up to temperature a downstream kiln should see little if any smoke ever ( unless a little smoke was
simply not objectionable), which Is what Cindy Mathieu meant I Think !

It was recently pointed out to me that cyclone dirt catcher will work with air flow and it does not matter if the air flow is natural draft-pushing, or vacuum assisting
pulling, this should reduce any airborne fly ash greatly, again, for some 'objects d'art' that might be a plus !

FIRE BRICKS I really need to start a thread called fake fire bricks > > >

The best Fire brick as we configure bricks in Rocket stoves are generally 9'' x 4.5'' x 2.5/3'' and weigh 28-30 ounces Less than a quart of milk, the are very
insulating returning or reflecting, much of the heat energy of our Burn Tunnel and Heat Riser / Combustion Chamber back into the 'heart of the fire' !

The second best brick to use to surround and make our Burn Tunnel/ Combustion chamber is 100 yr old soft, red/red orange House Brick!!!

There is a 2nd kind of 'FIRE BRICK" that comes in the same size as regular Lightweight Firebrick and is the same nominal size as well as many others, and
generally weighs more that 7 Pounds, almost a gallon of milk.

This 2nd class of brick is very hard and dense, and is used in industrial kilns because it is extremely durable absorbs and holds heat like the Dense Thermal
Mass it is, and functions to hold the kiln at high temperatures to allow ether further annealing or hardening to take place !

As a choice for use in our Rocket burner core it is a poor choice, not worth its premium price and should be watched for and avoided !

Any one having access to these Hard Dense fire bricks for free or very cheep will recognize that they fit the bill exactly for a good type of Thermal Mass for
our Cob Bench or to line the inside or the outside of a ''Rocket Bell' I I hope this was clear as many people have gone to Lowes' or HO-DE's or a big box
store and got the wrong thing ! For the good of the craft ! Big AL
 
Cindy Mathieu
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Some clarification:

About the smoke, if you are not watching the fire very closely, it will become smokey as the bulk of the wood gets burned up. I believe its because there is too much air for the amount of combustion going on which cools the fire. Cooler fire...volatiles don't get burnt up... smoke is produced. This could be alleviated if you were right there watching it and adding more fuel or closing off some of the feed tube, etc. However, I have admitted that this is not how this kiln is being used. It is outside and not closely supervised, not in our living room.

About the fireclay bricks, we are using the dense refractory kind as the walls of the kiln. The bricks do build up heat and hold it for several hours. Our burn tunnel is cast refractory and is insulative. In addition, it is designed to be surrounded by 2" of perlite on all sides.

As with all refractory materials, there is a range of density and other qualities available suiting different purposes in a hi-temperature environment. This does not mean either kind of fire bricks are fake; it just means they were designed either for insulating or for conducting (and storing) heat. Allen's concept of weighing the bricks will indicate generally whether the bricks insulate or store heat.

We have one pyrometer in there so we know the approximate temperature, but coning is another matter. Our kiln does not have any windows and if we opened it up to check the cones, a lot of heat would leave.

Our kiln box is mounted up off the ground so that the exit from the heat riser flows directly into it.
 
allen lumley
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Cindy Mathieu : I plead guilty of (on an other post ) using the term ''fake fire brick '' It was Grand Standing at its finest, Meant only to grab the attention of people
browsing the rocket and wood stoves forum Threads and make sure that they were not purchasing the heavier Fire brick at a premium price, when it is the lighter
Sub 2 pound type or the 'Split-' sub 1 pound type (equal to a pint of milk) that they should be using if constructing D.I.Y. units, Only time will tell if my grab for
sensationalism works for good, my primary intention, (or not!)

If my best intentions of spreading the word about the inadvertent use of the wrong fire brick works to create disinformation, and poorly built rocket stoves on any
level or form I am sure that we will both be working to restore the correct order to The Rocket/Dragon Worlds. BIG AL !
 
Miles Flansburg
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Hey Cindy, would you mind posting a picture of that kiln?
 
Cindy Mathieu
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Here are 2 pictures of the kiln. The first one shows it after we had fired some pieces and were starting to unload. You can see some discoloration on the burn tunnels. They go in gray with no brown.

The second one shows the 6" combustion system on the ground on the right hand side. The feed tube is inside a short 13" x 13" chimney flue liner. The heat riser is right under the kiln in another chimney flue liner. You can see the old pyrometer (with a handle) on a cement block in front with a wire going inside which is the thermocouple.

The sides and top are wrapped with 5" thick Roxul and then Hardie siding on the outside. There is a piece of metal roofing coming off the building to which it is adjacent to keep the rain off. This was a big project to build...lots of heavy fireclay bricks to lay, built a form to do the arch on the top, etc.
Kiln_Front_open_web.JPG
[Thumbnail for Kiln_Front_open_web.JPG]
Kiln_Front_closed_web.JPG
[Thumbnail for Kiln_Front_closed_web.JPG]
 
Erica Worhatch
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thanks for asking the question Theresa, I was wondering the same thing as there are already wood fire kilns for pottery.
 
Miles Flansburg
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Thanks Cindy !
Are the big steel doors insulated with anything?
 
Cindy Mathieu
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Yes, the big steel doors have 1" ceramic fiber blanket on the inside. The blanket has to be attached with special anchors welded on to the steel plate.
 
Katrin Kerns
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Just curious, but does anyone know if you could build a pottery kiln that would work effectively using only cob (not fire bricks) and build in a rocket stove feature right in? I mean like building a cob pizza oven (only bigger) with like a rocket stove type firebox built into it. I don't know if I'm making my self clear here or not.
 
Joe Braxton
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I've never built one, but the "groundhog" style kilns look to me to be the best candidates for a rocket heat source. Perhaps these will inspire you.

https://www.google.com/search?q=groundhog+kiln&safe=off&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X&ei=5CXcU8amLpSeyATD1oG4Dw&ved=0CB4QsAQ&biw=1534&bih=83
 
Katrin Kerns
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Joe Braxton wrote:
I've never built one, but the "groundhog" style kilns look to me to be the best candidates for a rocket heat source. Perhaps these will inspire you.

https://www.google.com/search?q=groundhog+kiln&safe=off&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X&ei=5CXcU8amLpSeyATD1oG4Dw&ved=0CB4QsAQ&biw=1534&bih=83


I'm not sure if this is quite what I was thinking of but it certainly gives me some ideas. Thanks for posting the link Joe.
 
allen lumley
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Katrin K. : I see a lot of assumptions/presumptions of what you mean by using the word 'KILN' , can you come back and tell us do you want to bake- bread, wood, or clay ?

Or something else altogether ? While each of these projects require a "KILN" , there is considerable difference in the need to hold ether/both high and constant temperatures !

Hopefully we will get a diverse group of craftsmen to weigh in on your next answer ! For the good of the craft ! BIG AL !
 
Katrin Kerns
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allen lumley wrote:Katrin K. : I see a lot of assumptions/presumptions of what you mean by using the word 'KILN' , can you come back and tell us do you want to bake- bread, wood, or clay ?

Or something else altogether ? While each of these projects require a "KILN" , there is considerable difference in the need to hold ether/both high and constant temperatures !

Hopefully we will get a diverse group of craftsmen to weigh in on your next answer ! For the good of the craft ! BIG AL !


So sorry that I wasn't clear enough BIG AL, I meant a pottery kiln for firing clay stone ware and bisque ware. I'm interested in finding out if one could be built out of cob (not brick) but with like a rocket stove type design.
 
allen lumley
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Katrin K. : O.K., Lets try this, to start with there are three types of ' COB ' - Structural COB, with hay, straw, animal hair, material that helps lock the cob into a
monolithic single piece ! Much, if not most of a COB House is made this way ! Generally we use equal parts non structural COB (no binders in the mix ) and local dense
rock or possibly urbanite to make up the bulk of the Thermal Mass of the rocket mass heater RMH!

Preferably the second to last layer or shell created to surround both the rocket mass heater and its Thermal Mass is a structural layer to give some physical protection
to the Whole RMH/Thermal Mass against knocks, jars, and things falling on it ! The Extreme outside layer also contains fiber and additional waterproofing materials !

It is very important that the layer of COB closest to the core of the RMH be insulating, or physically holds insulating materials against the "Firebrick" that surrounds the
actual combustion zone of a RMH, as such this Cob can contain various amounts of Perlite or Zonolite, along with its normal Sand and Clay materials,* with enough
thickness this cob can be highly insulating !

Even more insulating are various amounts of pure clay slip mixed with Perlite or Zonolite, however this mixture is extremely fragile and does not take the bumping into
common in unloading and loading a Pottery Kiln !

So structural cob is insulating and will help hold heat within the Thermal mass, slowly letting heat energy 'leak out from the core of the thermal mass !

Regular cob -mostly sand in a sand clay mixture that while not as dense as Rock, will provide a Solid core transporting the heat energy easily through itself to the Dense
Rock that can both hold and transport large amounts of Heat energy !

Finally, there are types of highly insulating cob that have additional materials in them to help create and maintain the high Temperatures 2000dF + , that allow us to burn
the wood cleanly, efficiently, and Totally !

A quick review of "Fire Brick'', which comes in two types and we can wrap this up !

"Soft Fire Brick " is highly insulating and we say it comes up to temperature quickly " Hard Fire Brick " absorbs a lot of heat this is because it is more Dense than the
other Soft(er) Fire Brick ! Both get their name from the fact that neither one expands or contacts much as it absorbs heat, or as it cools, not how much 'heat it can take '

In 'firing' Pottery^ the higher the temperature the Clay can survive in, the more durable (Generally ) the final product is !

The hotter the temperature that the Pottery is 'fired to' the slower you want the whole KILN to cool down !

Most Commercial Kilns have their interior walls lined with 'Hard Fire Brick'' that will absorb large amounts of Heat Energy at High Temperatures, and these Dense bricks
are glued, Cemented, Sealed to the interior walls and then between them and the Kilns Exterior there are large amounts of insulating materials to help retain the Heat
Energy trapped within or High Temperature Hard/Dense "Fire Brick " !

While you certainly can build a workable kiln out of COB, and fire it with a rocket mass heater RMH, Conventional/Traditional Wisdom says that You Need ether a Dense
/Heavy" Fire Brick " or other dense stone to maintain the High Core Temperatures you need over the extended period necessary to reliably fire and Save your Pottery
pieces !

For further reading I can recommend www.traditionaloven.com ! I hope you found this to be Timely and helpful ! For the Crafts !

Think like fire, Flow like a Gas! Don't be a Marshmallow ! As always, your comments, or questions are Solicited and Welcome ! Big AL !

* sawdust too has been used to make a very light insulating material, when 1st fired it will turn to charcoal and in subsequent firings much will burn away, leaving empty
'cells' where the sawdust was ! This too is very fragile !

^ The Fire bricks are themselves fired this way ! Buy fire bricks rated for the temperature you expect to fire at ! Higher Temperature fire bricks are not worth the extra
cost ! A.L.
 
Katrin Kerns
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Hi Allen.

Thank you for the information. I'm a complete novice and haven't actually done any pottery or kiln building before. It's something that I'm highly interested in and actually hope to do some day though. I like the artistic way that cob can be shaped and used and hate the traditional large square brick oven style of kiln. Yes, I know that there are also round-ish kilns, but all of the one's that I've seen are very small in comparison to what I was envisioning. I was just wondering if it would be at all possible to build a large kiln out of cob because it's shape-able and I could be creative with the design and size. But then I wondered if you could build a wood fired cob kiln and that of course led me to the question of whether or not it was possible to build an all in one cob RMH type of kiln. LOL, you never know what you can or can't do if you don't ask, so I asked. You have given me a great deal of information to work with and an excellent link. So thank you very much for helping to educate a novice such as myself. Take care,

Kat
 
allen lumley
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Kat K. : A rising tide floats ALL Boats ! We are all in this together, keep coming back, with over 25,000 Fellow Members World Wide you should be able to come here 24 / 7 and
talk to someone who wants to talk about what you want to talk about ! For the good of the Krafts ! Big AL
 
Glenn Herbert
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Katrin - If as you say you have never even done any pottery, let alone built a kiln, you need to start there first. Find a community studio or something where you can take classes and see all the operations. A good teacher (live) will help you avoid innumerable errors and frustrations. There is also a considerable amount of expensive equipment you can use before buying your own.

Once you have some experience, you can think about building a kiln. You said you wanted a big kiln, but think about how much work you need to make to fill it up (a half-empty kiln fires inefficiently and poorly). Unless you get into production quantities (making a living at it), it will be unreasonable to have a kiln much bigger inside than a three-foot cube or the equivalent.

As for actually building a kiln, I have annually for the past decade or so built and fired an experimental version of an English medieval kiln, using local clay with dried grass temper... essentially cob. The usual location has very silty, sandy native clay which fires out easily, but my local native clay (gravelly with little sand) has also worked well.
The mechanics of a kiln require lots of heat input at a steady and controlled rate. Too fast at the start and your pottery no matter how dry will explode as its residual water boils... this stage is very sensitive. Earthenware/bisque temperatures are relatively easy to get, but stoneware needs much higher temperatures and specialized design skills. Also, native clays may not be able to stand stoneware temperatures, and you might find the inside of your kiln melting. My local clay makes porous earthenware at cone 06, is semi-vitrified at cone 6 and turns to a runny glaze at cone 10.

As a rocket heater is designed to burn fast and hot, it is inherently at odds with pottery kiln requirements. I have heard of research involving multiple rocket heaters for a large kiln, with baffles and staging to attain the necessary slow temperature rise. It would be interesting to find out more about the subject. I encourage you to go ahead... with your eyes open.
 
Katrin Kerns
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Thanks Glenn. Very good advice all.
 
Jason Learned
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Years ago I saw a video of a rocket stove brick kiln made in the Phillipines I believe. I searched but cannot find the video. I do remember that they switched to using rice husks and also used a blower to get the heat up. It seemed to work. They had the riser go into the kiln about a third up and then exhaust through two ports on the bottom of the bell/kiln then up the chimney. I would think you could build one up on a platform and have a 6 feet heat riser and make it a ten inch system. According to what I heard from Ernie say on a podcast that should make the temperature extremely hot and give you the airflow you might not need a blower.

The kiln might function better if you could twist the riser as it goes up and then shape the top of the kiln to direct the flow in a spiral so it will swirl around the ceramics and evenly heat the kiln.

Just a thought.
 
Jason Learned
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Okay I drew a crude sketch-up picture of one of the kiln ideas(sorry, I don't have a huge amount of time to make it perfect). The idea is the tube is slanted to get the flow to go in on the tangent to get the spiral going around the clay then the middle is hollow to let the exhaust go out through the center to the chimney. If this would not work. I would have the riser go straight up through the bottom and then have two exhaust ports on the tangent going out to two chimneys of the appropriate diameter to match the in flow. This should get the hot gases to flow around the kiln in a similar way that they do in a blast furnace with a blower. If you want to melt metal you blow the hot air around the crucible from the bottom to the top. With this I would try to get it to flow down for a bit to trap as much heat in the kiln. Also I would add a small port where you could aim a laser thermometer to check your temps.

So to see the bad scale. The inside of this kiln is 6' diameter and 6' high. That is about how big the one I saw in Asia was, but it was square.
kiln.jpg
[Thumbnail for kiln.jpg]
 
Jason Wright
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https://picasaweb.google.com/Jonnygms/RocketStoveKiln#

I posted this link in another thread, but it seems that you are looking for the same answer. These pictures show the build of an inexpensive kiln made with cob materials and a dual rocket stove setup. There were some problems but they address these in the photo captions.

Does anyone see any issues with building a pottery kiln of this design? I am not experienced with cob or rocket stove building, so I would like some input on this design.
 
Glenn Herbert
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Not "issues" as deterrents, but a kiln built this way will require careful firing to start the temperature rise slowly and evenly (as does any wood-fired kiln). It is extremely easy to get the fire running away and getting hot too fast, causing the residual water in the dry but unfired pots to flash to steam and explode. This is unlikely to be a personal hazard, but a large part of the pottery load can be destroyed this way either directly or by shrapnel. The character of the pottery clay will influence this greatly; porous clay with considerable sand or grog may let the water escape easily, while porcelain or other dense, tight clay bodies require extreme care.

A kiln built from local clay is likely to be unable to withstand stoneware temperatures, as the one in the example shows. 1000 C (1830 F) which damaged that kiln is equivalent to cone 06, or earthenware bisque temperature. Obviously they are firing those stoves to a very low earthenware temperature which would not be suitable for any reasonable American style use. But if you build a kiln with material tested to withstand stoneware temperatures, there should be no reason you can't use the rocket firing technology with appropriate care.
 
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