what is best type of brick for TOP of burn tunnel?

[kirkerik]

I'm new to the forum so hello! It's great to find some other tinkerers w/ rocket's and mass heaters. I love the rocket/bell stoves and had a great time at the MHA (masonry heaters assoc.) gathering at Wildacres building two R/B prototypes w/ Max Edleson, David Ludt, Joe Heenan, Alex chernov, Carol Jackson, and Dave French just to name a few. It was a priveledge to work w/ so many interesting and creative masons, artist's, builders etc. Anyone got their ears on? ;D

I've been tweeking my stove for about four years now here and there when i get the chance.

The Rocket stove i built in my home has a core made of insulating fire bricks "soft bricks". The bricks have performed very well in regards to a very fast warm up time except the thermal shock at the top of the burn tunnel must be too much for them.

the IFB's were laid on edge. My theory is that since the bricks transfer heat so slowly the hot face get's much hotter than the cool face and sets up enough stress within the brick itself that it cracks right down the middle.

has any one used IFB's laid flat instead of on edge in the burn tunnel? Perhaps with less brick and therefore less insulation between the two faces of the brick they may heat more evenly and not shock? I doubt these IFB's were made to handle thermal cycling. So....

I think maybe i'll use std. duty fire bricks.

What have you folks used for thermal shock resistance and would you lay the brick flat (warm up faster) or set the bricks on edge (stronger)

oh, and the bricks hot face has some white or transparent deposits condensing on them - mostly on the top of the tunnel. Is that minerals from the wood?

thanks,
kirk

[Donkey]

Aug 21, 2009 14:40:12 GMT -8 kirkerik said:

I'm new to the forum so hello! It's great to find some other tinkerers w/ rocket's and mass heaters. I love the rocket/bell stoves and had a great time at the MHA (masonry heaters assoc.) gathering at Wildacres building two R/B prototypes w/ Max Edleson, David Ludt, Joe Heenan, Alex chernov, Carol Jackson, and Dave French just to name a few. It was a priveledge to work w/ so many interesting and creative masons, artist's, builders etc. Anyone got their ears on? ;D

I've been tweeking my stove for about four years now here and there when i get the chance.

The Rocket stove i built in my home has a core made of insulating fire bricks "soft bricks". The bricks have performed very well in regards to a very fast warm up time except the thermal shock at the top of the burn tunnel must be too much for them.

the IFB's were laid on edge. My theory is that since the bricks transfer heat so slowly the hot face get's much hotter than the cool face and sets up enough stress within the brick itself that it cracks right down the middle.

As far as I can tell, all bricks will do this. The top of the burn tunnel, especially that first or second brick just gets slammed and not much can be done about it.
Oddly enough, I've noticed that plain OLD red-brick (the older the better, like from hundred year old chimneys) tends to stand up well here, even better than fire-brick.. Usually.

has any one used IFB's laid flat instead of on edge in the burn tunnel? Perhaps with less brick and therefore less insulation between the two faces of the brick they may heat more evenly and not shock? I doubt these IFB's were made to handle thermal cycling. So....

I haven't done this, but it seems like it's worth a try.

I think maybe i'll use std. duty fire bricks.

What have you folks used for thermal shock resistance and would you lay the brick flat (warm up faster) or set the bricks on edge (stronger)

I've placed a sheet of steel under the bricks. I still layed bricks on top of the steel (not really sure I have a GOOD reason why). The steel didn't keep the bricks from cracking but it does keep them from falling. Might be a good idea to use pearlite/clay on top of the steel instead of bricks then cover that up with cob.

I've thought about casting the top portion out of refractory, either store bought or home-made. I've considered making my own clay brick, to the shape and size of the top of the tunnel, loaded with grog for heat resistance, letting the heat of the stove "fire" it. Seems to me that this is (yet another) an area for experimentation. Please, fiddle with it and let us know how it goes.

oh, and the bricks hot face has some white or transparent deposits condensing on them - mostly on the top of the tunnel. Is that minerals from the wood?

thanks,
kirk

?? Dunno.

Welcome to the board.

[kirkerik]

thanks,

kirk

[kirkerik]

My latest thought on this is the more dense or the more K value the brick has would certainly make it take longer to heat but would heat more evenly and hold it's temperature longer before the next fire. Therefore, less swing in temp and therefore less shock than an insulating firebrick. This thought in regards just to IFB's.

I also came acrosss this discussion: I don't know how this link thing works but here it goes: mha-net.org/docs/v8n2/docs/Firebrick%20high-duty%20vs%20low%20duty.htm

in the article :
"the commonly available low-alumina, low-duty brick will better
withstand thermal cycling/thermal shock better than high-duty, and a conversation I had with the sales manager for Mt. Savage seemed to confirm this idea. And there are no doubt many 30 year-old heaters out there built of low-duty brick that are still doing fine."

" It doesn't have to be particularly strong and it doesn't have to withstand temperatures of more than 1800 degrees F. What's needed is a limit to the linear expansion when heated in order to describe brick that actually performs well as residential firebox brick. And that is my answer to the question about whether low duty or high duty firebrick performs better in a heater. The difference between low and high duty firebrick is basically the PCE which I think is irrelevant. The best brick for a firebox will be the brick that expands the least when heated up to 1800 degrees F."

perhaps this backs up your experience Donkey! probably the older the better red bricks being superior. This is great news because I just took down an old chimney on my friends little old house. Abundance everywhere! I bet those old brick makers knew what they were doing in regards to common life needs rather than industrial needs. You said they "usually hold up better". Do you recall specifically what type of brick characteristic contributed to better longevity?

And the thing on green bricks in the article - I don't know - maybe not firing in the stove but like some traditional Native Americans fire pottery. Place the pot or "brick" in a big bed of coals and keep a fire going on top for a while then let the fire and coals burn out slowly while the ash insulates everything for a slow cool. Not sure that's how they did it - just guessing. I am certain they knew what they were doing back in the day and hopefully still do. Imagine - possibly thousands of generations perfecting pottery

kirk