High duty fire bricks

[Johnny the oven man]

Re: High duty fire bricks

I think Varnon are made by AP Green?

[fornax hominus]

Re: High duty fire bricks

I built my oven with a combination of med and hi-duty bricks .. all salvaged and some vintage from steamship boilers.. I did come across some ''chief'' #1 arch bricks which I used on row 6 , they are the last bricks to lose their soot as they have more mass the further they go into the dome , and I mortared them in . After parging with mortar I put a layer of extreme heavy duty aluminum foil [shiny side in ] over the whole oven , before the ceramic fiber layer. I also have a floor of 3x5x7in. hi dutys and they do hold their heat!!
One aspect that hasn't been mentioned so far is that hi-dutys weigh more! so they have to take longer to heat up , and longer to cool .
I am tossing a handful of snow in these days to add moisture for the bread.. it vapourizes fast!!

[fornax hominus]

Re: High duty fire bricks

I think Varnon are made by AP Green?

I may be wrong [what? Again?] but I think AP green is no longer with us.
tim

[dmun]

Re: High duty fire bricks

There was a big consolidation of the refractory industry a few years back, I think partly because of asbestos liabilities. I think AP green was absorbed into the Harbison-Walker refractory conglomerate. Now HW is about the only game in town in the US.

[fornax hominus]

Re: High duty fire bricks

Oh! Asbestos! ... great! I bought and am still using on my kiln a stash of AP Green's EPG50 insulating cement .. grey , fluffy and they claimed no asbestos... they claimed.. sigh!! .. Anybody heard a discouraging word on this?
tim

[Johnny the oven man]

Re: High duty fire bricks

If they "claimed" no asbestos , your widow will be able to sue them.lol

[altamont]

Re: High duty fire bricks

Hate to admit it, but I spent almost 15 years with AP Green. As the USA stopped manufacturing this and making that, demand dropped. And fast. The remainders of APG and Harbison-Walker and Kaiser basically ended up consolidating into one. And that one is much smaller now than any one of the originals were. And I personally have concerns about the health aspects too - I crawled in and out of thousands of furnaces over those years.

Back to the original train of thoughts in this thread though:

For our WFO's we all will see just a little difference in the heat retention (and rate of heat-up) between low heat duty, medium heat duty and super duty bricks.

If the information is available, compare the density (weight per unit volume). For our purposes we can assume a greater density will store more heat. On the other hand that means a little more fuel being burned to supply those calories. Then, to get even more rententive, we could start considering the thermal conductivity - a VERY rough generality is the denser material will conduct heat a little bit faster which could imply a slightly higher heat loss.
Concentrate on following the great plans provided here, and INSULATE - bottom, sides and top - any place a firebrick is located: insulate. If in doubt and can afford it, add more insulation.

[gsp]

Re: High duty fire bricks

Looking for a good source for high duty firebrick in WA. Any leads would help me get my oven built!

[peterbennett]

Re: High duty fire bricks

High Duty, when the alumina content is high it makes the bricks more resistant to very high temperatures and erosion/hot corrosion. The reason is that the other constituent in them is silica. On the net you can find the alumino-silicate phase diagram, essentially at the high alumina end the brick's melting point is extremely high 1828C, whereas once the silica content is above 30% this drop down to a mere 1587C (and stays there unless fluxed lower by other contaminating oxides, e.g. calcia).

So that is the duty side of things clarified, a non-starter for cooking ovens, but what about when in direct contact with the fire, what is the max. temp?


Heat retention is a completely different matter, here we are talking about thermal mass and thermal conductivity. If you want the brick to store a lot of heat you want it to have a high thermal mass (and not lose it by conducting it away to cooler regions), in simple physics terms you want it to have a high specific heat capacity, i.e. the heat/energy required to raise a unit mass, Kg by 1 degree, now here is where densification comes in. If the product is quite dense it will have a higher thermal mass per unit volume than a less dense version. Now replacing alumina by silica or vice versa will [B]not[B] necessarily improve or reduce the thermal mass, it depends on their relative specific heat capacities (& how dense the brick is made when you consider this on a volumetric rather than a weight basis, as noted above). My guess is that their specific heat capacities are probably quite similar, so probably a non-issue?

From tables, an engineering brick has a specific heat capacity of about 1.0 kJ/KgK, whereas a firebrick has a specific heat capacity of about 1.05 kJ/KgK.

So unless you plan to melt steel the high duty firebrick could be a bit of an overkill, or is it?

I have updated another post on this type of topic with info on typical thermal conductivities of firebricks, engineering bricks and a couple of red /buff common bricks (not concrete common bricks). Not an issue if you choose the right brick.

I hope this is helpful and helps clears up the various issues involved (but I don't know the max duty temps.)