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Post by patamos on Oct 14, 2017 21:24:15 GMT -8
Hi Folks, Crazy busy summer... and now (finally) time to start lighting up the fires. I have a bead on a big stash of 'kinda soft' fire bricks for not too much cost, that i am hoping to use in shaping a hot horizontal flue run just downstream of a vortex firebox. But i hear some people saying the softer ones are more insulative. I have always tended to assess by weight. Eg, the heavier the brick the more it will absorb and conduct. But i know that is an over simplification. In the past i have gotten 'medium heat duty' fire brick from a company called Clayburn (formerly based here in BC, then based in eastern US, then bought out by a big Texas mega corp), but they are no longer stocking much locally. So, i'm on the sniff for something mid grade, and mid price that can handle the thermal shocks All thoughts are welcome  pat |
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Post by Deleted on Oct 15, 2017 5:29:38 GMT -8
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Post by patamos on Oct 15, 2017 7:57:00 GMT -8
Hi Karl Thanks for the post. And thanks for all that you have shared over the years Good to see you here again. I'm guessing that the mention of lower conductivity in some fire bricks is referring to either the purposefully insulative ones, or the cheapo ones that come as liners in some metal box stoves... will keep reading though and getting a chemical analysis of the bricks in question will no doubt help. thanks  |
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Post by matthewwalker on Oct 15, 2017 16:16:42 GMT -8
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Post by patamos on Oct 16, 2017 7:03:03 GMT -8
Hi Matt, Thanks for the links. Good to hear from you I'm not looking to kiln fire bricks, I'm just trying to sort out a decent enough pre-made brick to handle the fairly high temps just downstream from the fire chamber. I can get France non-spall at a local Supplier (Brock White) but they are pricey. After that all they have are the soft pinkish coloured ones. A place up in Nanaimo has a windfall of firebricks that feel denser than the cheap ones… so i am just trying to nut it all out. That said, I see people like Max and Eva making their own with a cinva ram. But having fire tested a few bricks i've made with my local clay, i don't think it will be good for the higher temps. |
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Post by matthewwalker on Oct 16, 2017 8:07:52 GMT -8
I'm not suggesting you kiln-fire bricks. I'm suggesting you get one of those free kilns which are built of the perfect bricks for you. You could salvage enough for your stove from one medium kiln, most likely. Might also get some good sheet metal and fittings for door or other hardware creation.
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Post by Deleted on Oct 16, 2017 10:19:09 GMT -8
The keys to high thermal shock resistance are low thermal expansion,
high thermal conductivity, porosity, small crystalls,
only low to medium vitrification
and no phase transitions in the required thermal range.
Some of the properties contradict each other.
Avoid quartz like the plague, because quartz has a high thermal expansion,
forms large crystals and has several phase transitions.
The porosity in cheap bricks comes often from perlite or vermiculite,
which makes them weak and brittle.
In high quality bricks the porosity is created with the help of burn out additives.
The problem with home made bricks is that they need to be fired in the range of 900°C - 1200°C
to gain strength.
A LTGS Binder can lower the temperatures required for sintering by several hundred degrees Celsius.
BTW ordinary Portland Cement mixed with 20%-30% pozzolanic materials like aluminium silicate stone flour, clays,
fly ash, blast furnace slag and some quartz free sand can easily resists temperatures up to about 900°C.
Up to 1200°C are possible with commercial portland cement based fire concrete.
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Post by patamos on Oct 21, 2017 22:04:16 GMT -8
I'm not suggesting you kiln-fire bricks. I'm suggesting you get one of those free kilns which are built of the perfect bricks for you. You could salvage enough for your stove from one medium kiln, most likely. Might also get some good sheet metal and fittings for door or other hardware creation. Ahhh, head so busy… slow on the uptake. Concurrent with my looking into Morgan IFB's that a fellow named Dave at Improheat in Vancouver can bring over. It hadn't fully occurred to me that insulative kiln liners would still be in decent shape. But given that the denser kiln shelfs often are... Have you been using these liners? And if, at what point do you see them as too far gone? thanks always for the help |
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Post by patamos on Oct 21, 2017 22:26:42 GMT -8
The keys to high thermal shock resistance are low thermal expansion, high thermal conductivity, porosity, small crystalls, only low to medium vitrification and no phase transitions in the required thermal range. Some of the properties contradict each other. Avoid quartz like the plague, because quartz has a high thermal expansion, forms large crystals and has several phase transitions. The porosity in cheap bricks comes often from perlite or vermiculite, which makes them weak and brittle. In high quality bricks the porosity is created with the help of burn out additives. The problem with home made bricks is that they need to be fired in the range of 900°C - 1200°C to gain strength. A LTGS Binder can lower the temperatures required for sintering by several hundred degrees Celsius. BTW ordinary Portland Cement mixed with 20%-30% pozzolanic materials like aluminium silicate stone flour, clays, fly ash, blast furnace slag and some quartz free sand can easily resists temperatures up to about 900°C. Up to 1200°C are possible with commercial portland cement based fire concrete. Thanks Karl this is valuable information the area of the heater i am most interested in using a lower grade fire brick is the primary flue run after the downdraft chamber and the upper half of the bell backrest that follows. I am thinking of stacking them 4 high on flat in the two sides of the primary flue run, with another layer on flat as the top covering of the 6" wide run. Wanting the gasses to move through there fairly quickly so there is more heat being dumped further downstream and in the bell. the only info i have from the manufacturer is that they are 8% alumina. They feel almost as heavy as the high heat duty clayburn bricks, but they are way softer. There will be another 5" of cob on top of them with a decent amount of fine straw fiber. So my question is: 'Are they going to hold up if cased in cob?' The last vortex i built had a 5 high front row of these bricks on flat with about 3/4" of cob facing and it has shown no signs of trouble after one year of firing. These bricks are about $2 per unit. High Heat Duty ones are about $7 per and 40% alumina. Medium HD were $3.50 per and 29% (or so) alumina So with the middle path apparently out of production, I wonder which way to go... I should get my clays tested for the aspects you have suggested. Been thinking about adding alumina to see what happens. Can you suggest where i might learn more about LGTS binders? many thanks |
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Post by Deleted on Oct 22, 2017 5:41:07 GMT -8
Fire clays are kaolinitic clays. Kaolinite Al2Si2O5(OH)4 39.50 % Al2O3 without water 46% 46.55 % SiO2 without water 54% 13.96 % H2O Thermal Conductivity Al2O3 ~ 12-38.5 W/m*K SiO2 ~ 1.3-1.5 W/m*K as quartz up to 12 W/m*K Contrary to common sense bricks with higher silica content will have a higher thermal conductivity. Higher silica content will also make more prone to thermal shock Kaolin fired to less than 1050 °C has a low thermal conductivity of about 0.3 W/m*K, which can be considered as insulative. At higher temperatures the thermal conductivity strongly increases up to about 3 W/m*K. LTGS binder donkey32.proboards.com/thread/2070/karls-brick-cheap-geopolymer-refractory |
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Post by patamos on Oct 26, 2017 8:07:29 GMT -8
Thanks Karl. I think for this application in the primary flue run the structural strength will be the bottom line. This is a tunnel 9" tall by 6" across, with a row of 9" x 4.5" x 2.5" bricks spanning the top. Max temps probably no more than 600c I get the sense that low grade firebricks handle the thermal shocks well enough, But they have low structural integrity. So in this case i will stick with the High Heat Duty bricks that have more appropriate chemical make up. I look forward to experimenting with portland cement and 20 - 30% pozzolanic materials |
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Post by pyrophile on Oct 27, 2017 14:01:55 GMT -8
Hi!
I would say that a common cheap brick especially made to build bread oven would fit everywhere except in the firebox and the flame.
Those bricks generally have a rather low alumina content and are burnt at rather low temperature (according to their own melting point). Those bricks, often underfired, have a rather high porosity which helps a lot to limit thermal shocks.
Before, common bread ovens were built with cheap underfired bricks made with appropriate (adequate)clay. Care! Other underfired bricks could, maybe, not fit but cheap bread oven bricks should.
Those bricks are not sold in shops anymore (to cheap and to little demand). You must find the little brickyard which has the good clay and makes these bricks with rather old technology. I can find those bricks at 150 km from where I am, far away then, but rather cheap (5-6 cents a brick). Those are dark red but in old bread ovens they were often clear red or orange. But the colour is not a sign, find rather the good little articanal brickyard! Masons who sometimes build or rebuild bread ovens can help.
The problem with modern common bricks is that they usually aim to other properties than thermal shock resistance (exact dimensions, high structural resistance, conformity to building codes,etc.)and they are also expensive, thanks to highly industrial manufacturing. Your money doesn't go to workers but to the bank!
Benoit
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Post by Deleted on Oct 28, 2017 9:55:25 GMT -8
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Post by patamos on Oct 29, 2017 8:26:45 GMT -8
Hi! I would say that a common cheap brick especially made to build bread oven would fit everywhere except in the firebox and the flame. Those bricks generally have a rather low alumina content and are burnt at rather low temperature (according to their own melting point). Those bricks, often underfired, have a rather high porosity which helps a lot to limit thermal shocks. Before, common bread ovens were built with cheap underfired bricks made with appropriate (adequate)clay. Care! Other underfired bricks could, maybe, not fit but cheap bread oven bricks should. Those bricks are not sold in shops anymore (to cheap and to little demand). You must find the little brickyard which has the good clay and makes these bricks with rather old technology. I can find those bricks at 150 km from where I am, far away then, but rather cheap (5-6 cents a brick). Those are dark red but in old bread ovens they were often clear red or orange. But the colour is not a sign, find rather the good little articanal brickyard! Masons who sometimes build or rebuild bread ovens can help. The problem with modern common bricks is that they usually aim to other properties than thermal shock resistance (exact dimensions, high structural resistance, conformity to building codes,etc.)and they are also expensive, thanks to highly industrial manufacturing. Your money doesn't go to workers but to the bank! Benoit Thanks Benoit, Yes i am always on the look out for older bricks. Around here (west coast Canada) there are very few old bread ovens. And the ones made have been built with common red clay bricks. But these bricks vary in quality, depending on the raw materials from the various brick yards. Even ones from the same brick yard can vary over the years as their source of raw materials varied. So i usually test by clanging two bricks together. If they make higher pitch ringing sound i guess higher alumina content. A lower pitch thud sound indicates lower quality - and these ones are usually already much the worse for wear. I think what i will do for this build is return to cobbing together a bunch of old red clay bricks and then parging the inside of flue with fire-clay, sand, and roxul mineral wool fibre. Or maybe make a mortar/parge using Karl's recommendation with portland cement and additives. On another note, i remember old threads in which you were making a tall narrow bell chamber. I will be building a narrow bell chamber for the bench backrest of this next heater. But i wonder how narrow can we get before we lose the free stratification. The last bell backrest i made was about 7" wide at the top, and 10" wide at the bottom, but i wonder if that was too narrow. thanks pat |
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Post by Deleted on Oct 29, 2017 9:45:55 GMT -8
A higher pitch ringing sound mainly indicates a higher vitrification,
which in turn indicates a higher sensitivity for thermal shock.
If you want to test for thermal shock resistance use a high power gas torch
and heat spots of a brick until it starts to glow yellow orange.
If a brick can resist several minutes without to crack it has a good thermal schock resistance.
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