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Grimaldi 01-19-2009 12:20 PM

Steel Dome Oven On A Trailer
 
Hey Everybody~ I'm preparing to build a steel dome wood-fired oven on a trailer using a used propane end cap...40" (thanks Wiley ;)).

One of the issues I am trying to consider is heat loss from the steel dome connected to a metal support frame (base). I want to securely attach the steel dome to a base...at first I was thinking of welding the dome to a steel plate laid across the base and insulating underneath (vermiculite concrete and insulating board) and on top of the steel plate, but I think the heat will be drawn from the oven using this method? Or, I could build a steel base with a few welded attachment points recessed within the base frame and buried in light-weight concrete or vermiculite-concrete?

The propane tank I have is still intact and I was thinking I might cut it leaving about 6" or so below the seam where the hemispherical end cap is welded to the cylinder and use that space for a double fire brick oven floor and insulating board (including 2" or so of the dome/cylinder walls buried in the base vermcrete)...the seam would be flush with the top of the oven floor.

I'm still trying to figure it all out...but I have the propane tank, a 5' x 10' single axle (3000#) trailer. Forno Bravo has the ref-mix, insulating board, and ceramic blanket insulation, and I can locally source the fire-brick.

The idea is to use the Forno Bravo ref-mix (4" or so) over the steel dome, followed by ceramic insulating blankets and then stucco.

Any ideas to think this through would be appreciated.

Thanks,
Bob

pacoast 08-19-2009 09:40 AM

Re: Steel Dome Oven On A Trailer
 
I'm sure that someone like Wiley who has already done this would have a lot more useful information. If you haven't already, do read his thread on building a steel dome oven. I haven't read Wiley's thread, so I'm just posing a few questions off the top of my head.

1. Make sure that you know how to safely cut open a propane tank. Having it explode wouldn't be fun.
2. Compare the thermal properties of steel to firebrick.
3. What is the expansion rate of steel compared to firebrick? You will probably have to make some allowance for two different rates. Possibly expansion joints.
4. Go read Wiley's thread again & any threads by anyone else who has built a similar oven.

Good luck.

.

Gromit 08-19-2009 09:59 AM

Re: Steel Dome Oven On A Trailer
 
Quote:

Originally Posted by Grimaldi (Post 49311)
The idea is to use the Forno Bravo ref-mix (4" or so) over the steel dome, followed by ceramic insulating blankets and then stucco.

That works out to about 50 bags of Refmix. I sure hope you can work out a bulk-buy discount.

Grimaldi 08-19-2009 10:23 AM

Re: Steel Dome Oven On A Trailer
 
I had forgotten about this thread until I received an emailed that there was a response.

The project is unfinished, but I hope to get it done this Fall. I cut the tank...that was a lot of fun. I let it air for a good while and then filled it half way with water (once it was filled with water up to the openings where the fittings previously were, I blew it out with compressed air) and started cutting. No issues at all.

Basically, I have just collected materials and tools, mostly from Craigslist. I picked up some real nice firebrick with "MO FLINT" markings and some light weight insulating bricks. Also found several boxes of Durablanket ceramic insulation, steel plate, cutting torch, welder, 10" brick saw. Still need 2" square tubing for the frame, vermiculite, and refractory.

I started this with zero metal working equipment and have spent a lot of money on all of this stuff, but more to go...and then get the thing built!

Thanks for the reminder. I need to get this project back on track.

Grimaldi 08-19-2009 10:33 AM

Re: Steel Dome Oven On A Trailer
 
Quote:

Originally Posted by Gromit (Post 62054)
That works out to about 50 bags of Refmix. I sure hope you can work out a bulk-buy discount.

50 bags???!!!! I was guessing more like about 5 bags or less. The dome is a 40" diameter hemisphere approximately 27" tall.

dmun 08-19-2009 01:22 PM

Re: Steel Dome Oven On A Trailer
 
The volume of 48" sphere is 57906 cu. in.
minus
the volume of 40" sphere, 33510 cu. in.
equals 24396 divided by two (hemisphere) equals 12198 cu. in.
divided by 1728 equals 7 cubic feet more or less.

I get fifteen sixty pound bags of concrete from this website:

Concrete Volume Calculator

Refmix comes in 22 pound bags so you would need 41 of them.

There may be cheaper castable refractories than refmix, which is, after all, a mortar not a castable. Still. Yikes.

pacoast 08-19-2009 04:02 PM

Re: Steel Dome Oven On A Trailer
 
Is the desire for 4" refractory a compensation for thermal properties of the steel? I'm asking because a lot of ovens, particularly those intended for pizza or live fire cooking have walls a lot closer to 2.5", which would save a lot of cost & weight. Usually only retained heat (bread) ovens would have walls of 4" or more.

.

dmun 08-19-2009 07:21 PM

Re: Steel Dome Oven On A Trailer
 
The steel doesn't retain heat, it transmits it. You need thermal mass, and if it were me, i'd use a thin layer of refractory blanket over the steel so it doesn't expand and break your masonry layer (metal has a much higher co-efficient of expansion than masonry) There's a quarter inch refractory blanket that the masonry heater guys use between the core and the outer layer because of the same problem.

Pretty much every brick built oven (except mine) has a four inch wall thickness. You may not need it for thermal mass, but a thinner layer would be much more likely to break apart in a vibrational situation like a mobile oven. Modular ovens are 2.5 inches thick, it's true, but I think fired ceramic units are MUCH more strong than anything you are going to cast out of concrete.

pacoast 08-19-2009 10:04 PM

Re: Steel Dome Oven On A Trailer
 
Yes steel has a greater thermal flux density, hence the question about whether the thick walls were a compensation or not. The majority of brick ovens have 4" walls. But a lot of ovens, specifically mobile ones that use cast refractory or ceramic prefab have 2.5" walls & are generally regarded to work just fine. So it's a valid option to consider using 2.5" walls. If it suits the OP goals, it would save him a lot of time, money & weight.

.

Grimaldi 08-20-2009 09:10 AM

Re: Steel Dome Oven On A Trailer
 
Quote:

Originally Posted by dmun (Post 62076)
The volume of 48" sphere is 57906 cu. in.
minus
the volume of 40" sphere, 33510 cu. in.
equals 24396 divided by two (hemisphere) equals 12198 cu. in.
divided by 1728 equals 7 cubic feet more or less.

I get fifteen sixty pound bags of concrete from this website:

Concrete Volume Calculator

Refmix comes in 22 pound bags so you would need 41 of them.

There may be cheaper castable refractories than refmix, which is, after all, a mortar not a castable. Still. Yikes.

Thanks for the calculations...so 50 bags is not that far off after all. I'm going to need to rethink this aspect and come up with a cheaper alternative...I know there are homemade recipes for refractory using fireclay, I'll have to do some research on that.


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