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Old 04-01-2011, 09:20 AM
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Default Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Hey All, this is the first of what I hope will be a series of posts about the project I am about to embark upon. Currently I am in the beginning stages of my project for the summer, which will be to design and build a mobile pizza truck out of the side of a step van (think Fed Ex style truck).

I built my first fire brick oven last fall in Ancram NY, following the Pompeii Build instructions. (see below)

The oven works well, the draw is good, it holds heat for hours, etc. However, as I contemplate starting up a business, I am thinking it will be really helpful to have a two chamber oven (a 'white oven' as opposed to a 'black oven') for two reasons. One, in my experience, firing more than three pizzas in quick succession drains the hearth of its heat and the subsequent pizzas have crusts that are slightly doughy for my liking. It would be nice to avoid pulling coals back across the hearth as often as I do. Two, the fire takes up valuable floor space in the baking chamber, and cannot be tended to while pizzas are firing. My initial design ideas are below.





1. I am curious if anyone knows of sources for design plans or rules of thumb regarding the relative volumes of the chambers, the vents between them, and the chimney.

2. I would also like feedback regarding the feasibility of casting most of this thing in refractory concrete, including the hearth which spans several gaps. Specifically:
A. Strength of the cast: Will I need to use Stainless Steel Needles or other strengtheners?
B. How do you determine where to put expansion seams, if any? Would I use a refractory mortar between seams?
C. Can cast pieces spanning gaps as load bearing elements? Do I use rebar or will I run into issues with expansion?
If you can leave responses in a like format (i.e. "2.A. I would suggest....") that might be helpful because I'm asking so many broad questions. Thanks very much in advance!
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Old 04-01-2011, 01:02 PM
david s's Avatar
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Location: Townsville, Nth Queensland,Australia
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Your design looks very much like the Ancient Roman pottery kilns, only they had their flue at the top of the dome(updraft) rather than at the front (crossdraft).
Google search Roman kilns
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Old 04-01-2011, 03:59 PM
david s's Avatar
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

A. Stainless steel needles are the industry recommendation for reinforcing castable refractory. Presumably rebar has been tried and found unsuitable. Stick with the recommendation.

B. The positioning of seams is usually determined by trial and error, ie. a seam is put in where a crack develops. I found when making a floor cast in one piece that a crack occured right down the middle from front to back so now make the floor in two pieces with the join down the middle.
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Old 04-01-2011, 04:04 PM
david s's Avatar
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

C. Your cast pieces can span gaps but you would be advised to place a number of supports under the floor to minimise the span of the gaps, but not too much that will impede the fire.

You have no guarantee that that this design will work well, the floor may actually get too hot. The extra weight will also be a major consideration and may be the difference between using a four or eight cylinder to haul it.
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Old 04-01-2011, 04:31 PM
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

This is actually a guillard style oven. In a white oven the flame and smoke would never enter the cooking chamber. I'm currently building a small oven that is very similar to this that can fit in the back seat of my hatchback compact car, so I don't want to come across as if I think it can't work, but my design has some key differences. The biggest difference is it's small size compared to the relatively large fire box, the fire box in my oven is larger then the 20x20 oven chamber. Personally I think you would be better off with a more traditional guillard style design where you have a normal insulated hearth with a hole coming up through it from the firebox bellow. I'm not sure you would hit super high temperatures in it but I would bet with a big enough fire box you could hit 650 or 700. I personally did a lot of research on wood fired kilns while working out the design of my little oven and based it off the theory of operation of the olson fast fire kiln. If I were you I would study up on the olson kiln and and pollaine guillard style ovens for some design ideas.
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Old 04-01-2011, 06:06 PM
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Before you embark on this, have you checked with the state health department (or whoever licenses food trucks) to see if they approve of the design and materials? I know in Minnesota, it wouldn't. Can't use anything that's not NSF, ETL, ANSI approved.
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Old 04-19-2011, 05:09 PM
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Thanks for the word of caution. I'm from Minnesota, too! But out here in Columbia County, NY, they don't seem to be so concerned. The department of health only asked that I use non-toxic building materials. The refractory materials should be fine.

I've also checked with the building inspector, and the fire chief, and neither of them seemed concerned. My last obstacle is the NY DOT, and they will hopefully be getting back to me soon.

***Just talked to Doug at the Commercial Vehicle Safety branch of the NY State DOT. He gave me the green light, as long as the fires are out before I'm driving.

Last edited by HudsonHearth; 04-20-2011 at 12:45 PM.
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Old 04-20-2011, 12:55 PM
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Thank you guys for the responses. I looked into Frederick Olsen's fast fire kilns, and according to his book he lets stress cracks develop by themselves, instead of engineering expansion joints. I'm think I'm going to do this thing as a single cast. I'll use the sand mold method for the dome and then, pulling from my fiberglass experiences in the past, I think I'll shape the vent and opening using Styrofoam. That stuff is great for creating smooth, irregular shapes. I can probably coat it with some cheap bondo/ fiberglass mix for strength before laying down the castable.

There are two major questions I still have:

1. How low can I go with the height of my dome? I'm doing a 36" internal diameter oven, and I'm wondering if I can go as low as 10" for my maximum height. I know this is pretty flat but I've seen some of the old french bread ovens that have massive spans and are almost totally flat.

2. Is there a rule of thumb for the ratio in volumes between fire box, baking chamber, and flue size? I know the usual rule is that the cross-section area of the flue should be 10% of oven opening area, but I am assuming that is immaterial in my case because the oven will be breathing in a totally different way, due to the firebox opening below.

In case anyone needs one, there is a great tool for computing ellipsoid volumes here, for REF mix quantity estimates: ABE VOLUME CALCULATORS, SPHERE

Thanks again,
Sam
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Old 04-20-2011, 01:04 PM
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Also, I managed to pick up a truck to build the oven into, in Baltimore. Here he is! His name is Edwin:


Last edited by HudsonHearth; 04-20-2011 at 01:15 PM.
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Old 04-21-2011, 02:17 PM
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Default Re: Refractory Cast Mobile Pizza Truck Oven ("White Oven" Design)

Quote:
Originally Posted by HudsonHearth View Post

There are two major questions I still have:

1. How low can I go with the height of my dome? I'm doing a 36" internal diameter oven, and I'm wondering if I can go as low as 10" for my maximum height. I know this is pretty flat but I've seen some of the old french bread ovens that have massive spans and are almost totally flat.
I think the lower the better given the design. The oven is going to want to be hotter on the deck then the dome, which is gonna be your biggest fight. Keeping the dome low and the fire close to the pie is your best bet for a balanced bake at high temperatures. 10" isn't ridiculously low either, my oven has a 13" dome.

Quote:
Originally Posted by HudsonHearth View Post
2. Is there a rule of thumb for the ratio in volumes between fire box, baking chamber, and flue size? I know the usual rule is that the cross-section area of the flue should be 10% of oven opening area, but I am assuming that is immaterial in my case because the oven will be breathing in a totally different way, due to the firebox opening below.
I think standard flue guidelines would still apply. 8" round should be plenty for a 36" oven. I would make the throat from the fire box to the oven have the same cross sectional area as the flue. I would also make the door as small as you can while still being able to work inside the oven. I would also highly recommend building a tight fitting insulating door that you use for firing. There is no need for the oven opening to be opened during heat up of this oven and without the cold air rushing in it should heat up much more efficiently.
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