Steel Dome Oven On A Trailer

[Grimaldi]

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]

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]

Re: Steel Dome Oven On A Trailer

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]

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]

Re: Steel Dome Oven On A Trailer

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]

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]

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]

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]

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]

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.

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.

[Grimaldi]

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.

.

Yeah, I may have to reconsider the 4" thickness. If 2.5" will get the job done, and for all the reasons you mentioned... time, weight, money, that may be the new plan. I could also double up with the ceramic insulation and still have the thermal properties.

I appreciate the input.

[metalmaster]

Re: Steel Dome Oven On A Trailer

I will be building an oven using a steel dome inside another steel dome, and it got me to ask why you need to use refractory cement if you have the steel against the fire.
why not use concrete or stucco for the thermal mass?.

[dmun]

Re: Steel Dome Oven On A Trailer

Because the concrete will break down at oven heat.

If you are using two steel domes, why not just pound in foundry sand between the two layers? That will get as hard as it needs to be, and won't crack up in road vibration conditions.

[JoeyVelderrain]

Re: Steel Dome Oven On A Trailer

I read somewhere (gonna look it up again) that low iron clay was used in fire brick because the high iron content would rust and the smell could permeate the food being cooked. Would a steel dome have the same problem?

[Grimaldi]

Re: Steel Dome Oven On A Trailer

I will be building an oven using a steel dome inside another steel dome, and it got me to ask why you need to use refractory cement if you have the steel against the fire.
why not use concrete or stucco for the thermal mass?.

Hey metalmaster...what size metal domes are you planning on using? I had initially considered using a dome inside a dome but ran into the problem of finding a dome large enough to go over my 40" dome...I talked to a manufacturer and they quoted me around $1500 for a 48" dome, if they had it in inventory, because they wouldn't be doing a run for one piece. So, I moved on to creating a refractory layer over my dome and then insulating that, followed by a stucco outer finish.

To answer your question...as Dmun said, concrete will break down under high heat.

I'm interested in how you are planning to put it all together...are you going to weld the domes to steel plate? What kind of insulated base are you planning on making?