An Open Call to Ceramic Engineers- Reverse Engineering Biscotto di Sorrento

[shuboyje]

Ive thought about this a lot. My ideal would be a 5 piece floor that is the four pie pieces with a square center piece sized so they fit in the door.

I've long guessed and recently been told that the Neapolitan builders rare the entire front facia off the oven to replace the floor.  It's a major undertaking.

[PizzaJerk]

It must be quite an arduous task indeed! It makes even more importance lay upon treating your tools with the utmost care.

Could the wear of the floor in particular almost be inevitable due to the volume of pies having been made in it during the oven's lifetime? Or is it more of an issue of rough practices going on by the oven operator (as I am thinking)?

[TXCraig1]

I've long guessed and recently been told that the Neapolitan builders rare the entire front facia off the oven to replace the floor.  It's a major undertaking.

I find that very difficult to believe. How would that not entail rebuilding the entire top half of the oven? I would have sworn that Frank at Vesta told me the new floor goes in through the door. Maybe they are designed so that all the steel in the front of the oven can be removed without structural damage to the oven, and that is enough?

[TXCraig1]

Maybe they are designed so that all the steel in the front of the oven can be removed without structural damage to the oven, and that is enough?

I just looked at my oven, and this is basically how it is designed. I never paid any attention before to why they did it this way, but the steel in the front is two pieces. The outer piece is the outcropping of the oven's steel frame, and the center portion that includes the door (shaded yellow below) is tacked into place. It can easily be removed by cutting a few small welds, and it does not support any of the brick structure.  With it out, there is plenty of room for the full size floor tiles to pass through.

[shuboyje]

You will find the conversation here where I was told about the floor replacement.  I would guess you are going to trust the source as much as I do:

http://www.pizzamaking.com/forum/index.php/topic,14506.msg222514.html#msg222514

As you'll see I also always assumed it was as simple as removing the castings to access the oven, but I guess that isn't the case.  There is masonry around the cast iron arch behind the cast iron plate in all the builds I have seen, so I guess once you remove that it get's pretty involved.

[TXCraig1]

You will find the conversation here where I was told about the floor replacement.  I would guess you are going to trust the source as much as I do:

http://www.pizzamaking.com/forum/index.php/topic,14506.msg222514.html#msg222514

As you'll see I also always assumed it was as simple as removing the castings to access the oven, but I guess that isn't the case.  There is masonry around the cast iron arch behind the cast iron plate in all the builds I have seen, so I guess once you remove that it get's pretty involved.

I think I misinterpreted what you meant by "the entire front facia." It sounds like the process in the SF is not all that different from mine.

[Tscarborough]

I am not sure of the mathematics, but I am sure of the process.  An extruded brick body is not by any means what you would consider to be "wet", it is about 1/3 the moisture level of commercially sold wet clays, and to a normal eye and hand is hard as a rock.  There are methods to achieve a dry pack with any (fine) granular material and minimal moisture and no specialized machinery, that is how most cast stone is made.

I have no specific knowledge of the floor tiles made in Italy, but my guess from seeing them and knowing what is available would be a high ratio of volcanic pozzolans, inert (not hydraulic) clays, and ground tufa aggregate (which is also slightly hydraulic).  They are probably wet cast and then fired.

All of that begs the question of whether or not they are the ideal floor for a WFO, I would say they are not, as they are soft and delicate, as well as too large to have all the cracks pre-engineered.

[scott123]

forgive me if you guys already know this, or its obvious,  but I have heard numerous people who work with, own, or sell real neapolitan ovens talk about how fragile and quick to wear down the biscotto de sorrento is.    Simply having an oven operator thats not gentle with their peel could cause it to need replacing in just a few years.    Of course, in a home environment it would take a lot longer than that to wear down and become hard to manage.  I am speaking of a commercial setting.

I am aware of this as well.  The low conductivity materials we currently have access to (fibrament, quarry tiles), though, wouldn't last for years in a WFO, they'd start breaking down in a matter of hours. If we could get years out of a domestic product in a commercial WFO setting, I think that would make for some pretty happy oven owners.

[scott123]

Ive thought about this a lot. My ideal would be a 5 piece floor that is the four pie pieces with a square center piece sized so they fit in the door.

I've been thinking about tile size, and, if we do end up with something with questionable resistance to thermal shock, smaller pieces, as Tom mentioned, would pre-engineer cracks and allow for better thermal expansion.

[scott123]

I am not sure of the mathematics, but I am sure of the process.  An extruded brick body is not by any means what you would consider to be "wet", it is about 1/3 the moisture level of commercially sold wet clays, and to a normal eye and hand is hard as a rock.  There are methods to achieve a dry pack with any (fine) granular material and minimal moisture and no specialized machinery, that is how most cast stone is made.

Thanks, Tom, this is helpful information. I've seen these types of bricks being made, and sensed that, because the moisture level wasn't that much higher than dry pressing, that the final porosity (and corresponding conductivity) wasn't that much lower than dry pressed brick. I can't find any conductivity numbers for extruded firebrick, but I still feel pretty strongly that they aren't that low.

I could be wrong here, but it seems to me that there's no free lunch.  It looks like the only way to achieve sub .6 W/m-K conductivity in a refractory material is by adding air- and by adding air, you're potentially decreasing hardness/abrasion resistance as well as potentially lowering resistance to thermal shock.

[Tscarborough]

Adding air decreases abrasion resistance but it increases the ability to withstand thermal shock.

[shuboyje]

I received the data on the Whitacre Greer light duty buff firebricks I use today.  I guess this explains why I have never had the burning issues others experience.  Looks like the quest is over and Whitacre Greer holds the key.  I have sent a follow up email inquiring about their capacity to produce larger tiles.  I don't know what makes them so different from other firebricks, but they do mention they are vacuum dry pressed.  Is that normal Tom or could the Vacuum account for their low conductivity in some way? 

[Tscarborough]

I have not been to their plant to see the process, but I would assume that the point of using vacuum in a dry press process is to further reduce entrained air in the clay body, although it is normally very low already.  It is also possible that they are using vacuum as the method of dry pressing, I do not know.  I will call them on that tomorrow.  I do not know of any other brick being vacuum pressed, the normal method is vibratory dry pressed.

[scott123]

Adding air decreases abrasion resistance but it increases the ability to withstand thermal shock.

http://www.pdhonline.org/courses/m158/m158content.pdf (page 22)

Insulating fire bricks often suffer from thermal spalling problems, particularly in an environment of rapidly changing temperature. Since these bricks are good insulators, a substantial temperature gradient will occur between the hot and the cold face of each brick. The hot face will expand more than the cold face. The thermal gradient thus, gives rise to a mechanical stress in the body of the brick.

[Tscarborough]

Are we discussing insulating firebrick or thermal mass (dense) firebrick? 

[shuboyje]

These are not an insulating brick, they are a dense brick weighing somewhere in the 7 pound range.  I've run hundreds of fires on them in two ovens and have yet to have a brick spall, crack or chip. 

[scott123]

Are we discussing insulating firebrick or thermal mass (dense) firebrick?

Jeff is discussing a dense firebrick with abnormally low conductivity. While the W-G bricks are extremely encouraging, I'm still holding out hope for something a bit lower, something that can match the lower end of the .3-.6 W/m-K spectrum that Craig references for biscotto.  Unless I'm missing something, the only way that I can see a .3 W/m-K material is by adding air- and thus creating something between a dense and insulating brick. Once you enter this middle ground, though, it seems impossible to achieve the features we're looking for: abrasion resistance, thermal shock resistance, very low conductivity.

If insulating bricks are in the .2 W/m-K realm and dense bricks typically clock in around 1 W/m-K, then, if the Italians have managed to create a .3 W/m-K brick with abrasion resistance and thermal shock resistance, it's some pretty major alchemy, imo.

I brought up insulating bricks as an extreme example of what happens when you add air to firebricks- the conductivity drops, and, as the conductivity drops, you have very hot areas next to far cooler areas, which, in turn, produces thermal expansion issues/spalling.  As you add air to a dense firebrick and take it in an insulating direction, it's thermal shock resistance drops.

[scott123]

These are not an insulating brick, they are a dense brick weighing somewhere in the 7 pound range.  I've run hundreds of fires on them in two ovens and have yet to have a brick spall, crack or chip.

Jeff, I've been examining the formula, density and porosity of the W-Gs and comparing it to other firebricks and, I have to admit, I can't find anything that would explain the lower conductivity.  The vacuum aspect is odd, but, if it is impacting air in the bricks, it's only drawing it out and creating a denser brick, not a more porous one, so the vacuum aspect can't be responsible for the freakishly low conductivity.

These are dense bricks, and density should bring conductivity- unless the formula is atypical- and there doesn't seem to be anything atypical about the W-G formula.

[shuboyje]

Jeff is discussing a dense firebrick with abnormally low conductivity. While the W-G bricks are extremely encouraging, I'm still holding out hope for something a bit lower, something that can match the lower end of the .3-.6 W/m-K spectrum that Craig references for biscotto.  Unless I'm missing something, the only way that I can see a .3 W/m-K material is by adding air- and thus creating something between a dense and insulating brick. Once you enter this middle ground, though, it seems impossible to achieve the features we're looking for: abrasion resistance, thermal shock resistance, very low conductivity

Why?  What positive do you see from a lower conductivity at the cost of strength?  I cook on these at traditional Neapolitan temperatures and get traditional Neapolitan results.  I see no positive out of an even lower conductivity.  With my experience and the data I now have on these If I could get them in larger slabs I would take them over Biscotto any day. 

Jeff, I've been examining the formula, density and porosity of the W-Gs and comparing it to other firebricks and, I have to admit, I can't find anything that would explain the lower conductivity.  The vacuum aspect is odd, but, if it is impacting air in the bricks, it's only drawing it out and creating a denser brick, not a more porous one, so the vacuum aspect can't be responsible for the freakishly low conductivity.

These are dense bricks, and density should bring conductivity- unless the formula is atypical- and there doesn't seem to be anything atypical about the W-G formula.

I agree, I don't see anything out of the ordinary, but again, we have data from a major brick and tile laboratory at a major university that directly correlates to every cooking experience I have on this material.  For a couple years I have been baffled by people complaining about their firebrick hearths be too hot and burning while mine worked perfectly.  Now it all makes sense. 

[Tscarborough]

The reason I ask is that up to a point, air entrainment is a good thing, but in the amounts found in insulating fire brick it is not (in relation to durability).  

I don't think the Italians are performing magic, see if you can find the physical properties of tufa and volcanic pozzolons since I am almost certain that those are the main constituents of their product (and it probably has an air entrainment of around 20%).