# Ceramic / refractory material for combustion baffle



## Nofossil (Oct 5, 2007)

I want to build a different combustion chamber baffle for my EKO 25. The insert that comes with the unit is a large block of firebrick with a trough in the top. It's hard to clean ashes from around it, and it doesn't maximize hot gas flow along the walls. I've built a much better design out of 8" square flue tile, but no good deed goes unpunished. It disintegrated from thermal stress. I glued it back together with refractory cement, and coated the whole assembly with fiberglass cloth and refractory cement. Same result. I then built the same thing out of 1/2" steel from snow plow blades and firebrick. Ate right through the steel and cracked the firebrick. Tried again with low-density firebrick, and melted some broken glass bottles on top of the steel to protect it. Kind of works, but ugly.

The structure that I want to build is essentially an 'H' beam about 10" high by 8" wide by 20" long. At present, two courses of firebrick make the sides, and the steel plate makes the web. It's just 'stacked in place'. It's set up so that the secondary combustion happens towards the front of the top channel. Gas flow is front-to-back in the top channel. The back end is sealed, and the back of the web is cut away so that the gas then flows down to the bottom channel, where it then flows back to the front. It then exits to the sides and flows back to the hx at the back end of the boiler. The serpentine path means that all the gas flows along the full length of the boiler walls, and ashes are really easy to clean out.

What materials are available out there for building a structure like this that can withstand 2200 degrees? I've seen what I think is a ceramic based board about 1/2" thick - that might be ideal. I can't find sources accessible to non-industrial buyers.


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## Highbeam (Oct 5, 2007)

My Hearthstone stove uses a ceramic fiberboard type material for the secondary baffle. It's maybe 1/4" thick and lightweight, appears fragile. The board is removable and replacable.


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## Nofossil (Oct 5, 2007)

Cool - any idea where I can buy a sheet of the material? Fragile is OK - it doesn't have to withstand mechanical stress, just thermal abuse.


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## Corie (Oct 5, 2007)

Thermal Ceramics makes a "kaowool" board that would work.  Not easy to find this stuff in small quantities or even find it where joe public can buy a piece.  I had a hell of a time getting some last year.


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## Highbeam (Oct 5, 2007)

nofossil said:
			
		

> Cool - any idea where I can buy a sheet of the material? Fragile is OK - it doesn't have to withstand mechanical stress, just thermal abuse.



No idea where to buy a sheet. Heck, I couldn't even find micore in my state. It was actually suggested by my wife that I buy a spare baffle for my stove from HS to have on hand just in case I break the one in there now. It might take a while to be delivered and the board is right there where a chunk of wood could pop up and hit it.


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## KeithO (Oct 5, 2007)

Unifrax corp Niagra Falls NY
http://www.unifrax.com/web/UnifraxH...18268E0BC11D4A47852569570068EF11?OpenDocument

Remember that there is airflow.   Not the high velocity pulsating stuff found in automotive exhaust, but still airflow, which may tend to carry the board material away over time.  Speak to those folks at Unifrax about the suitability of their board and they will tell you if it is right for your application.  They do sell to the little guy, which is a rare thing these days.

You can also try Thermal Ceramics: http://www.thermalceramics.com/Products/ByCategory.asp

They have everything from fiber to casteable refractory and proper alumina firebrick etc.   If you actually try the real alumina firebrick you will find it is totally incomparable to the vermiculite "junk" that is consumer grade.


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## webbie (Oct 5, 2007)

A little bit of anything can be purchased from McMaster-Carr.......

Is this a component of a gasification system? If so, almost 2000 degrees is possible. Thin stainless covering refractory might be an option.

At Tarm, the gasification bricks were made one by one, in wooden molds using poured refractory cement with stainless fibers in it. I assume that is also how a lot of other similar products are made.

But, off the cuff, I like the idea of thin...bent or rounded stainless steel as a cover to a fragile ceramic board. Might give you the best of both worlds...then again, Keitho and others here are REAL engineers. I just play one in my shop.


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## KeithO (Oct 6, 2007)

The only material that is going to put up with 2000F service for any reasonable amount of time is alumina (Al2O3) or fused silica (artificial quarz glass like used in the space shuttle windows)  Stainless in an oxidising atmosphere will be gone in no time.  Inconel in the right grade may last a while (jet engine parts) but it is hard to get, expensive and hard to work and weld.  Just so you know, I use all of those materials at work in our lab, so I'm not joking.  We test samples of the mat that we use for mounting the substrates of emission control systems up to 1000 deg C in our lab equipment every day of the week.  Some of those materials are 98% alumina too because that is all that will survive the application.

The link I provided for the Thermal Ceramics site shows Alumina firebrick to be about $32/brick compared to $5-6 each for "regular" firebrick.  Its a matter of how much do you need and what are the alternatives.   Alumina brick will go on in that application forever, so you will certainly get your money's worth.

In case you want to give Inconel a go, try these guys: http://www.hightempmetals.com/techdata/hitempInconel706data.php  Info on Inconel 706
Materials thay have in inventory in that grade: http://www.hightempmetals.com/hightemp/hitemp07.php#A020

They will cut to order and will sell any amount to anyone and I find them as reasonable as anyone else considering the exotic nature of the material.  GE and Williams etc will of course get better deals....


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## webbie (Oct 6, 2007)

1500 is probably more the norm.....but I once used a temp sensor in the top of catalytic converter (in an early stove). It generally stayed at 1400 or so until one day when I put a small piece of heavy pine (probably southern yellow) from our barn floor into the stove. This stuff had been seasoned since 1898. That probe hit over 1800 degrees F. Of course, this is just the gas stream inside the honeycomb, and no materials of the stove ever reached anything much over 1000....still not a temp that makes regular plate steel happy.

Stainless is used in many applications where it glows a very bright red on a full-time basis - I would assume 1200-1400? Probably more toward the lower end of that.

All in all, your best bet is to use factory replacements....or, get yourself an inexpensive temperature monitor thingy and see what the actual temps you are dealing with are. As Keith says, 2200 or 2000 are near impossible to deal with, but that might be just an advertised temp or the temp of a flame somewhere in the middle of the air...not that material temp your boiler sees inside.


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## BrotherBart (Oct 6, 2007)

Ceramic fiber board:

eBay item number 160100314489    

1 x 24 x 36 fifty bucks plus shipping.


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## Nofossil (Oct 8, 2007)

Thanks for all the suggestions. This is in fact a gasification application, and peak temperatures appear to be in the 2200 degree F range. I've attached an instrumented run from last year - the combustion temp is divided by 10 to get it to fit on the graph. The combustion probe is an Omega Inconel jacketed thermocouple, and all the other channels are glass encapsulated thermistors. Looks like I'll be doing some combination of alumina firebrick and ceramic board. I'll post pictures when it's done.


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## KeithO (Oct 9, 2007)

Just so you know, most of the ceramic board materials are alumina silicate.  Silicate is basically glass.   Unless the alumina content is at least 80% or more, it loses its mechanical properties fast at any temperature over 600 deg C.  600 C is enough for many "conventional" combustion processes (like some of the OWB modification projects to get a secondary burn).  Alumina board is generally called alumina and not ceramic, because they don't want to be compared to the cheap stuff.

If you get the alumina bricks, ask them if they have alumina board, more than likely they do.  Otherwise, you will be rebuilding after a relatively short time and fired refractory is always more difficult to handle without damage compared to the "green" state when it is delivered.  If you do the board, think about cutting it into shorter pieces to allow for expansion and also to allow sections to be replaced without tearing up the whole thing.   It will generally also get you a higher yield from the board you buy.

Best of luck...


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## webbie (Oct 9, 2007)

I know I may sound like I am repeating myself, but the combustion temps can differ vastly from the material temps - example would be the temp at the tip of the candle flame and the temp of the wax. So the real temp you need is exactly in the board or bricks that are being used. Any way you look at it, you need some good material!


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## Nofossil (Oct 9, 2007)

Thanks. Someone provided a link to an eBay vendor who has 'ceramic' board that they claim is good to 2300 F. They also have different grades of alumina bricks rated a various temps from 2000 to 2600F. I'll ask the alumina question about their ceramic board.

I was planning on building the structure as a 'stack of blocks'. Sounds like that will meet your suggestion. Of course, the proof will come in another month or so....


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## KeithO (Oct 9, 2007)

Craig:
If the insulator forms a barrier to a cold surface, then obviously there will be a big gradiant across the material and the average temperature will be lower.   What Nofossil is proposing is a labrynth combustion chamber with the gas flowing over 1 side in 1 direction and then back over the other side in the opposite direction.  What that means in practical terms is that the baffle will see the full combustion temperature since it is "immersed" and is not going to cooled by any means other than direct radiation.  Thats a pretty nasty application and he has already shown that ceramic (flue liner) can't take it.    The gradient BTW is also no piece of cake for a rigid material like firebrick, since the differential expansion on the hot vs the cold side can easily cause it to crack.  For felt type materials that have minimal stiffness this problem doesn't exist.



			
				Webmaster said:
			
		

> I know I may sound like I am repeating myself, but the combustion temps can differ vastly from the material temps - example would be the temp at the tip of the candle flame and the temp of the wax. So the real temp you need is exactly in the board or bricks that are being used. Any way you look at it, you need some good material!


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## Nofossil (Oct 9, 2007)

Webmaster said:
			
		

> I know I may sound like I am repeating myself, but the combustion temps can differ vastly from the material temps - example would be the temp at the tip of the candle flame and the temp of the wax. So the real temp you need is exactly in the board or bricks that are being used. Any way you look at it, you need some good material!



Yeah, it's a little tough to know for sure. In this case, there is a 'blowtorch' effect and the flame/combustion fills the upper chamber of my baffle pretty well. I put my inconel probe on the surface of the bottom panel of the combustion chamber and measured 2200F. It's certainly hot enough to melt glass....


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## Nofossil (Oct 9, 2007)

KeithO said:
			
		

> Craig:
> If the insulator forms a barrier to a cold surface, then obviously there will be a big gradiant across the material and the average temperature will be lower.   What Nofossil is proposing is a labrynth combustion chamber with the gas flowing over 1 side in 1 direction and then back over the other side in the opposite direction.  What that means in practical terms is that the baffle will see the full combustion temperature since it is "immersed" and is not going to cooled by any means other than direct radiation.  Thats a pretty nasty application and he has already shown that ceramic (flue liner) can't take it.    The gradient BTW is also no piece of cake for a rigid material like firebrick, since the differential expansion on the hot vs the cold side can easily cause it to crack.  For felt type materials that have minimal stiffness this problem doesn't exist.



Exactly right. However in Craig's defense, the temperature of the return path (bottom side of the same panel) seems to peak out at around 1600 F. The floor and walls of the top section are incandescently hot, but by the time the gases make the turn and come back, they've cooled considerably. Of course, this adds to the thermal gradient problem.


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## Nofossil (Oct 19, 2007)

*New alumina brick / ceramic wool board labyrinth ready to go!*

Many thanks to KeithO for the technical information and BrotherBart for noticing a useful item on eBay. I've built my new labyrinth and it's ready to go. Of course, it's almost 70 outside. I'll post results when it gets cold enough for another fire, but I'm very optimistic.

The alumina bricks and the ceramic board are rated for 2300F. The bricks are cool - they're very light, and can be cut easily on my beater bandsaw with a wood blade. The ceramic board is very fragile - you can easily gouge it with a fingernail. It's almost like lightly compressed wood pulp. It also cuts easily on the bandsaw. I was able to attach the ceramic board to the bricks with stainless steel drywall screws. Almost like driving them into styrofoam. The screws don't have to support any load at all - they just keep the vertical sheet from tipping over.

In operation, the combustion nozzle empties into the top channel. The hot gases flow toward the right end, then downwards through the opening. They then flow back to the left end. At that point, they'll split and flow back along each side, around the vertical 1" baffle. and out.

In the photo of the remains of the old baffle, you can easily see the badly eroded plates of hardened plow blade steel as well as the melted glass slag, broken firebrick, and a pile of gravel that used to be a 'C' shaped section of flue tile.


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## Eric Johnson (Oct 19, 2007)

That's awesome, nofossil. How much did it cost in materials, and is there any danger of the ss screws disintegrating? I'm curious to see how it works out for you.

BTW, are you familiar with the new BioMax boilers that New Horizon is selling? Like the Atmos, it has a curved refractory chamber and what looks like a curved (on the top) firebox. Looks like an Atmos knockoff to me. Presumably there's a good reason for the shape, but I'm not in a position to say what that would be, other than facilitating the heat distribution in the chamber.


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## Nofossil (Oct 19, 2007)

Eric Johnson said:
			
		

> That's awesome, nofossil. How much did it cost in materials, and is there any danger of the ss screws disintegrating? I'm curious to see how it works out for you.
> 
> BTW, are you familiar with the new BioMax boilers that New Horizon is selling? Like the Atmos, it has a curved refractory chamber and what looks like a curved (on the top) firebox. Looks like an Atmos knockoff to me. Presumably there's a good reason for the shape, but I'm not in a position to say what that would be, other than facilitating the heat distribution in the chamber.



The ceramic board was about $50 delivered, and a box of 12 firebricks was about $45. I used a bit less than half the sheet of ceramic board, and I have one firebrick left over.

The SS screws are on the back side - almost the coldest place in the whole structure. I'm hoping they hold up. They don't have to do much - just keep the end panel from tipping away from the firebricks. I tried to glue the panel to the bricks with refractory cement, but no joy. The refractory cement definitely does not stick to the ceramic board.

Haven't seen the BioMax. I'd be interested to see if it performs better in any way.


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## Eric Johnson (Oct 19, 2007)

One of our members, rreinhart, just bought one, I believe. He said he considered both and concluded that the Max had a slightly better feature set. I hope he lets us know more about it once he gets it installed. Or before. Not having a working model has never stopped me from pontificating.


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## Gooserider (Oct 19, 2007)

Very cool thread, but seems more appropriate to the Boiler Room, so I have moved it accordingly.

Hope the new baffle works well!

Gooserider


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## Nofossil (Oct 19, 2007)

> Very cool thread, but seems more appropriate to the Boiler Room, so I have moved it accordingly.
> 
> Hope the new baffle works well!
> 
> Gooserider



I wondered how long it would take to get moved. I agree, by the way.

Policy / acceptable conduct question for you and/or Eric and/or Craig:

Over the past few years, I've put together a site that has a bunch of information, pictures, notes, and data from my personal experience in doing the wood / solar / heat storage thing. It's purely informational, not commercial. I'm egotistical enough to think that it's a useful resource, but I don't want to cross any written or unwritten boundaries between being helpful versus shameless self-promotion (Look how smart I am!).

I suspect it's also of interest to only a small subset of members. I realize that 'roll your own' control systems are a pretty small minority.

For these reasons, I haven't posted a link to it in the 'Links to Articles and Resources' topic and I haven't started a thread to discuss what I've done. I have on occasion linked to a picture or a page within a thread when appropriate.

The site is http://www.nofossil.org/. Have I found the right balance? Too self-effacing? Too something-or-other?


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## Eric Johnson (Oct 19, 2007)

I think it's a great resource, 'fos. Lots of good information and some insight into the man behind the avatar.

Ken "slowzuki" McFarland has a nice one, too. 

http://www.onthefarm.ca


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## Gooserider (Oct 19, 2007)

nofossil said:
			
		

> > Very cool thread, but seems more appropriate to the Boiler Room, so I have moved it accordingly.
> >
> > Hope the new baffle works well!
> >
> ...



Threads that are active tend to get moved sooner  :coolsmirk:  I look mostly at new posts, and activity brings the thread up onto my radar - inactive threads tend to get buried and if I don't see them I won't do anything about them unless asked.

As to the link question, I actually did look at some of your site, and *I* think that it is perfectly reasonable to post a link to a personal detailed site like yours, both as a general resource and to point to relevant subsections when talking about what you've done - it saves repeatedly typing the same long answers if you can say "I did thus and such, see <link> for details"  I would add it to the L&R;thread, otherwise I'd say you've hit about the right balance.  Craig sets the rules, but seems to me like even commercial activity is OK as long as it's kept low key - I would say the perfect example is Mike from Englander - it's no secret that he wants to sell stoves, and I hope his postings here helps him do so, but he doesn't make a big deal about it and doesn't say an Englander stove is the solution to everybody's needs...

I would even say that a link to a commercial site isn't objectionable if it's relevant - for instance a list of boiler makers, and other useful parts manufacturers with links that lead to "meaty" stuff like technical references, spec sheets and so forth could be useful.  A link to a dealers sales site (unless it has a really good technical reference section like Tom Oyen's shop does) is less valuable...

Just my opinion, I figure Eric is more the chief boilermaker.   

Gooserider


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## Eric Johnson (Oct 19, 2007)

I'm just trying to get this forum up and running with lots of contributions and ideas for people interested in central heat. So the more the merrier.

I'll really have to hunt down some Tarm guys and get them over here. Tarm makes great boilers and gasifiers and it would be nice to compare notes. There's a small group of Tarm 60 owners over on Yahoo who taught me a lot about storage and gasifiers when I was thinking about getting one. They might want to stop by.

And there's a few Hearth.com members with OWBs, and I hope they'll feel welcome here as well. They do some interesting things with heat exchangers and heating garages and outbuildings that most indoor boiler people don't get into. And in-floor radiant--that's a pretty hot new technology that the "big box burners" seem to know something about. Most OWB's aren't pressurized, which I find interesting, since I've always had closed loop pressurized systems. 

Check out nofossil's website if you get the chance. A lot of knowledge and thought obviously went into it. Leaddog has the same boiler I do, and I've already learned a lot from him. And slowzuki's got three of these really cool, obsolete gasifiers that you load vertically and go like the speed of sound, or some such. My boiler has a little electronic controller that's so small the mfg. houses it in a big pyramid on top of the boiler so that it looks impressive. Slowzuki's rig has what looks like a utility substation bolted to a big piece of plywood.

So it's all good.


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## Nofossil (Oct 30, 2007)

I have two fires with the new ceramic baffle now. Definitely faster startup - my last one was six minutes from lighting the match to gasification. It runs with a bypass damper open during startup, and flue temperature measured 24" from the boiler was less than 225F when I switched to gasification mode. Water jacket temp was 30C (86F).

With this setup, I get through startup faster and at lower temperatures than before. Life is good. Thanks for the help.


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## sled_mack (Jan 16, 2008)

Nofossil,

This thread is pretty old.  I was hoping for some feedback on how this setup has held up for you?  I do like the idea a lot.

I guess the other question is how effective it has been after using it for a while.  Zenon told me I should keep the "tunnel" as large as possible for better burning.  But your setup is effectively cutting the tunnel in half.  

I've also thought of doing something like this, but turned on it's side.  Block off the front of the tunnel, forcing all gasses to the rear.  Block off the rear, but have an opening to one side (let's say the left).  Gasses now have to come back to the front, around the end of the tunnel, then along the other side to the rear.

Just curious what you think if that idea as well.

Thanks.


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## Nofossil (Jan 16, 2008)

sled_mack said:
			
		

> Nofossil,
> 
> This thread is pretty old.  I was hoping for some feedback on how this setup has held up for you?  I do like the idea a lot.
> 
> ...



The lightweight alumina bricks are toast. My current version uses high-density half bricks that are rated for 3000 degrees. Good so far, but the 2300 degree ceramic board is getting eaten. I'm looking for a replacement. If I can't find it. I think I'll just lose the tunnel floor and be happy. I cut the tunnel in half to create more turbulence and a longer 'hot' path before the gases see the cold water jacket.

Works good in that I get gasification reliably in 6 minutes from the match. Since I build a fire almost every day, clean and quick starts are important to me. Others may not care as much.

I'm trying to make sure that I have symmetric flow, so that all the HX pipes get their fair share. My rear panel is about 1 1/2" from the HX tube water jacket so that flow from both sides has a little more chance to get to the center tubes. I'd be worried that you approach would starve the HX tubes on the far side.

Now that I have secondary combustion and flue temp monitoring, I can fiddle and see what makes a difference.


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## rsnider (Jan 16, 2008)

were can you get the ceramic board? thanks ryan


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## begreen (Jan 16, 2008)

eBay, often has some for sale. Search on insulation board. 

I see some Marinite in 4 x 8 sheets, $6 per sheet. This looks like it would be a good insulation board. I'm checking with the manufacturer to see if they agree and to get it's insulation values translated into R and/or K units. 

http://stores.ebay.com/HIGH-TEMP-REFRACTORY-STORE_W0QQ_trksidZp284Q2em158QQtZkm


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## Nofossil (Jan 16, 2008)

With a 1200 degree rating, it won't last but a few minutes. The board that I bought was from eBay as well. It was rated for 2300 degrees, and it failed too. I'm working on sources and specifications for something with a little more strength at temperature.


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## begreen (Jan 16, 2008)

You're right.  The provider in the link might be worth contacting. It looks like they sell a broad range of ceramic insulation products.


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## swestall (Jan 16, 2008)

I do not recall the name of the product, but a few years back I purchased a bag of refractory material through a local company that relines large scale boilers. My application was to reline the inside of an old Antique Oak coal/wood stove where the bottom half has a refractory pot poured in. To make the pot I needed to line the inside of the stove with the cement, using 1/4 inch cage wire, and let it harden. 
They told me the interior of the boilers they reline gets to very high temps; so perhaps this type product cast to your need might do the trick.


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## KeithO (Sep 28, 2008)

Mr Nofossil

If you will send me a PM with a mailing address and the size of board that you need, I could send you an alternative material to try that is not very stiff mechanically, but quite erosion resistant, will never crack and will sustain the temperatures you are looking at.

How are the heavier firebricks holding up ?

Keith



			
				nofossil said:
			
		

> With a 1200 degree rating, it won't last but a few minutes. The board that I bought was from eBay as well. It was rated for 2300 degrees, and it failed too. I'm working on sources and specifications for something with a little more strength at temperature.


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## Adios Pantalones (Sep 28, 2008)

Castable refractory cement will withstand very high temps.  I got mine from Cutter Atlantic refractories- Woburn, MA.  I have cast a number of shapes that withstand good temps (2300 F).  I know folks that add metal fiber to give it crack resistance, but I cast a 1" thick 22x22" kiln chimney cap that has withstood 4 firings without it, and know folks that cast larg portions of high fire kilns with it.

Ceramic fiber board is held together with a starch.  You can add rigidizer- silica or alumina based, that holds to higher temps.  You could also treat it with ITC100 and it will rigidize, withstand higher temps, and withstand erosion better.  The material and coatings are available from a number of pottery supply sores- Sheffield pottery, MA is a good starting place.

Super duty brick will withstand well over 2600F sustained and is high alumina.  It's available in a number of configs- 2" thick fire tile, 9x4.5x2.5 straight brick, 9x4.5x1.25" splits, and several custom sizes.  Check refractory suppliers.


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## steam man (Sep 28, 2008)

My woodstove has castable ceramic plates. The top plate gets blasted by the flames. Its about 1.5" thick and is only supported by the edges. Its been on there for 18 years with no problem and its the hottest stove going. I've made castable stuff for industrial boilers. Typically styrofoam forms are used to make odd shapes. I think you can get the 3000 deg stuff and reinforcing stainlees "needles" on ebay. I think you just need to leave some expansion by making it out of separate pieces. It has to fire slowly to get the moisture out or it will disintegrate. If you can find a kiln oven..........

Mike


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## Nofossil (Sep 28, 2008)

This thread is back from the dead! 

KiethO, sent you a PM - thank very much. The new firebricks are holding up quite well.

Mike and AP: Thanks for the encouragement. I know there has to be something out there that will work.


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## Brian VT (Nov 7, 2008)

Ok if I revive this thread again ? You guys seem to know your materials.
I'd like to make a replacement "everburn" secondary combustion box for my woodstove rather than pay $250 for the o.e.m. replacement.
I was just at a local HVAC supply house and saw Kaowool boards 1/2"x18"x36" that I could work with. Do you think this would be suitable for my purpose ?
The salesman said it is commonly used where a flame from an oil burner contacts it directly so he thought it’d be fine for my application. There’s no specs. on the manufacturer’s website (Lynn). What about adding these coatings you refer to ? Would those help or even be necessary ? I don't know what temps. occur in this box.


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## trehugr (Nov 7, 2008)

NoFo, I was a ladle maker in a foundry years ago. We used a product called coral plastic. It has a consistency like modeling clay. We lined all ladles with it. Its tough stuff. http://www.refwest.com/index.asp?PageAction=VIEWPROD&ProdID=75 It withstood 3000 + for long periods of time. ( we poured armor for the M1 tank ) Just a thought.


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## trehugr (Nov 7, 2008)

Data Sheet for Coral Plastic 
http://www.hwr.com/products/datasheetsv1/CORAL_PLASTIC_28-82_ADTECH.pdf


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## Gooserider (Nov 7, 2008)

Ditto...  I'm going to be trying to make it through the winter on my existing refractory box that I've tried to patch back together with stainless wire and refractory cement, but wouldn't mind finding suitable stuff to make a new one out of come spring...

Gooserider


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## Nofossil (Nov 8, 2008)

Wow - more materials! This is great!

I just got some castable material as a free sample from a local industrial boiler service outfit. I'll try anything. I'd love to get a durable solution that's also easy to clean ashes from.


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## j.w.young (Nov 8, 2008)

I get ceramic fiberboard from my Maple syrup equipment supplirs. They will sell a box or 1 sheet at a time, about $10 per 1"x12"x36" We use it to insulate behind the firebricks in the eaporators. Easy to cut with a construction box knife. Google Maple syrup equipment supplies for a great list of places, yes they will sell to anyone.


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## Nofossil (Nov 8, 2008)

enchantedforest said:
			
		

> I get ceramic fiberboard from my Maple syrup equipment supplirs. They will sell a box or 1 sheet at a time, about $10 per 1"x12"x36" We use it to insulate behind the firebricks in the eaporators. Easy to cut with a construction box knife. Google Maple syrup equipment supplies for a great list of places, yes they will sell to anyone.



Thanks - I think that's the type of ceramic board that I have now. A bit soft and crumbly before firing?

It gets eaten away where the flames touch it, and it gets very brittle after firing. Probably good for insulation if protected by firebrick, but not strong enough for my application.


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## Brian VT (Nov 8, 2008)

nofossil said:
			
		

> It gets eaten away where the flames touch it, and it gets very brittle after firing.


Is that the Kaowool board I asked about ? Kinda tan in color ?


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## Nofossil (Nov 8, 2008)

Brian VT said:
			
		

> nofossil said:
> 
> 
> 
> ...



I'd say more like off-white. Rated for 2300 degrees.


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## DaveBP (Nov 8, 2008)

Nofossil, have you looked at kiln furniture? The shelves and posts that are stacked in ceramic pottery kilns to hold all those bowls and mugs. Some of those things are fired to 2300F and higher with all that weight on them. Silicon Carbide and alumina are used. Try googling "Nitride Bonded Silicon Carbide Kiln Shelves" and you'll get lots of brags about tough and hot. Some pottery is fired closer to 2500F and some kilns are run on wood. I used to mess with that stuff but that was 30 years ago.


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## Nofossil (Nov 8, 2008)

I don't know the actual temperatures in the flame zone. Ruined an inconel jacketed type K thermocouple - the signal went screwy after the indicated temp hit about 2500. The research I've done suggests that the max temp is right around that, and in the flame zone it oscillates between reducing and oxidizing as the gases swirl around. Hadn't thought about kiln shelving - sounds worth pursuing.


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## Nofossil (Nov 8, 2008)

Did a little research on 'ash fusion' - the temperature at which ash residue starts to fuse and clump together. Looks like that's around 2700 degrees. I'm definitely seeing a bit of that phenomenon.


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## j.w.young (Nov 9, 2008)

Yep, kinda tan or mixed tan to darker, I hide it behind firebrick. My Maple arch isn't as fierce flames as a gasifer.


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## Brian VT (Nov 9, 2008)

So...should I build my VC Everburn box out of 1/2"  Kaowool board or not ?


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## Medman (Nov 14, 2008)

NoFossil - anything to update here?  I would like to make improvements to the secondary chamber as well.  What luck have you had with new materials?


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## Nofossil (Nov 16, 2008)

Medman said:
			
		

> NoFossil - anything to update here?  I would like to make improvements to the secondary chamber as well.  What luck have you had with new materials?



Nothing I'd recommend yet. I'll report back when I get done with this round of tests. Life is busy just now.


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## verne (Feb 16, 2009)

anyone have any updates on this? My curved blocks have cracked after one season. I found high alumina castable refractory rated at 3000 deg. I think the brand was Kaolite.I can get 20 lb bags shipped for about $30. Any thoughts ? thanks scott


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## Adios Pantalones (Feb 16, 2009)

Silicon carbide kiln shelves are a bad bet for this- they do not withstand thermal shock well (I use them in my kiln- need to raise temp slowly).  High alumina shelves may work, but buying a bag of castable refractory and just casting them would be cheapest.

Kaowool boards need to be rigidized with alumina, silica, or ITC100 rigidizer or they are very brittle.  ITC100 is great stuff, but pricey.  All are available through pottery supply houses- Sheffield pottery, or the Big Ceramics Store.


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## Nofossil (Feb 16, 2009)

Interesting that this thread resurfaced just now. I had failure of one of my high alumina / high density 2300 degree firebricks yesterday. I also made a tentative discovery. Due to impending structural failure of various combustion labyrinth component, I had added some additional support which had the effect of increasing the flow restriction in the secondary chamber. I had really pronounced problems with 'puffing' mini-explosions in the primary chamber - something that I generally don't see, and which I had always attributed to excessive gas-generating surface area such as too much kindling.

I'll be burning tonight with a revised labyrinth that's much simpler and offers virtually no flow resistance. Reports to follow.

I have a bag of castable refractory that I'll do up if I ever get some spare time to make the forms.


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## Fred61 (Feb 16, 2009)

Nofossil,

I see you're in Addison county. When I had my Woodgun I found a place in Montpelier that sold all kinds of refractory material. I can't recall the name at this time but I do remember they were on Barre Street. 

You could ask these guys some questions: http://www.cotronics.com/vo/cotr/cm_castable.htm


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## kabbott (Aug 31, 2009)

I'll bring this old thread back to life.
Any news on the castable refractory?
The choices are bewildering, I assume material for the secondary tunnel that withstands extreme temps would be a poor choice
for the nozzle itself. I am thinking the nozzle wont be near as hot but will take more mechanical abuse? 
Any thoughts on what to use?


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## Nofossil (Aug 31, 2009)

kabbott said:
			
		

> I'll bring this old thread back to life.
> Any news on the castable refractory?
> The choices are bewildering, I assume material for the secondary tunnel that withstands extreme temps would be a poor choice
> for the nozzle itself. I am thinking the nozzle wont be near as hot but will take more mechanical abuse?
> Any thoughts on what to use?



That's a tough one. I've had a very hard time getting real advice on castable materials. My brother got some pretty expensive castable material for the floor of his, and had it kiln-fired (a very long and slow process for a large and heavy piece). It cracked anyway.

The 2300 degree high density / high alumina firebricks don't hold up indefinitely either.

The EKO appears to have a cast nozzle that's a different material than the floor of the primary chamber. It's very close-grained - more like ceramic than brick. However, ceramic tiles turn to gravel when used as a flame target. You may be right that the nozzle doesn't see the full fury of the flame, but the bottom side certainly comes close.


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## KeithO (Sep 1, 2009)

NoFossil, I didn't send the low densiy alumina material when I read of some of your failures.  Doesn't appear to have enough structural properties.   Recently found this site: http://www.sentrotech.com/ceramictube.php

They have no prices online, so don't know what to expect.  But the stuff they have is very high grade and super dense (specific gravity of 3.9).

They DO have silicon carbide products also, but as one poster mentioned one has to reduce thermal shock or it can easily crack due to the high expansion.

"SentroTech offers Sintered Alpha Silicon Carbide Products. Alpha silicon carbide material is most commonly used in sintered products in industrial application. It is formed by mixing very fine silicon carbide powder with non-oxide sintering additives at sintering temperature between 2000oC to 2600oC under vacuum or inert atmosphere to form very dense products. Silicon carbide parts can be formed by dry press, extrusion, isostatic press and injection moulding. Various complicated shapes can be formed by these process technologies. Due to its very fine gain size and high density, sintered alpha silicon carbide product has excellent surface finishing and tight dimensional control that require non or minimum after-sintering machining."

There is also this place: http://www.advaluetech.com/alumina-tubes.html   Size limited (largest is 3" OD) but price seems OK, depending on how much you need.

There is also this place : http://www.graphitestore.com/items_list.asp?action=prod&prd_id=348&cat_id=42&curPage=1
Larger tube sizes available, gets expensive as the diameter and length go up.   Maybe the right way to go is a high grade alpha aluminum tube inside the low density insulation (will slow the cooling rate) and then a firebrick "box" around the outside.

Best regards
Keith


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## Nofossil (Sep 1, 2009)

Thanks for the links - I'll follow up on them as time permits. One problem I have is that none of the high-tech materials places are all that excited about selling 25 pounds to an eccentric like myself. I have to pretend to be authentic, and the strain takes its toll.


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## fabguy01 (Sep 1, 2009)

You need to talk to these guy's http://www.indfirebrick.com/ Not only do they know there products but they also have a service department that services the product. they do our furnaces at work and I have nothing but good to say of them


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## KeithO (Sep 1, 2009)

Outside Diameter:    4" (10.16cm) 
Inside Diameter:    3.625" (9.21cm) 
Length:    24" (60.96cm) 
99.8% Alumina Furnace Tube - Open Both Ends. Inert to hydrogen, carbon and refractory metals; can be used at operating temperatures to 1950°C in both oxidizing and reducing atmospheres. Dimensional Tolerances:+/-4% or +/- .050" min.

$500 = expensive.   

Not sure whether you need 4" or 2x3" (for path there & back)

Outside Diameter:    3" (7.62cm) 
Inside Diameter:    2.75" (6.99cm) 
Length:    24" (60.96cm)   a mere $345 per 2 ft.

Don't recall how much you need, but if they have the right dimensions for you and it is better than what ECO sells, it may be the ticket.


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## KeithO (Sep 1, 2009)

Same guys also have castable alumina in sensible volumes (from pint to gallons) http://www.graphitestore.com/items_list.asp?action=prod&cat_id=15&prd_id=143
I can send you alumina fiber to use as re-inforcement but don't know if their mix already has it.  They describe the curing process in some detail.

Physical address:
GraphiteStore.com, Inc.
1348 Busch Parkway
Buffalo Grove, IL  60089
US 
Phone: 800-305-1664 (Toll Free US only)
847-279-1619 
Fax: 847-279-1926 
E-mail: support@graphitestore.com


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