Steel Dome Oven

[christo]

Re: Steel Dome Oven

Hey Wiley -

How are you coming on the paint? I used some smooth Stucco-type finish from Dryvit that remains flexible. So far so good. There was one area on the foundation that had a hairline crack and I have not seen it since I coated it.

The color seems to be holding it's own.

Good luck.

[Wiley]

Re: Steel Dome Oven

Christo, Actually I haven't gone any further with that problem. We've been busy....

I've been getting ready to haul my boat. We're hauling out tomorrow and hopefully we will only be out a week. Lots of lost time what with weekly parent visit and grandkid's birthday on the weekend so it might be longer. That's of course assuming we don't find any major problem(s). But we took her to the dock today and off loaded extra diesel and water and sails and such like, both my wife and I agreed we need to spend more time on the water. We want to work my/our schedule so we get more time on the boat. Priorities!

I also cleaned the mooring chain last week and decided I want to replace it before winter. So once we are back in the water I will be replacing the top pennant of her mooring (20 ft of 1/2 inch chain) and probably add an additional 3 to 4 ft of the heavy chain (1 1/2 inch / 9+ lbs per link stuff) so I don't have to make these swaps at low low tide.

But soon as that's done I plan on finishing up the pavilion and finding some sort of elastomeric paint, how thick (viscosity not film thickness) is the Dryvit material? I looked at some hypalon paint, which I know is tough and which will accept an overcoat of the paint I have. A bit on the pricey side though.

Bests,
Wiley

[christo]

Re: Steel Dome Oven

Good to talk to you. I've been away too long!!!

The stuff I used has some sand in it - more like a smooth stucco finish. I'm not sure if they have a smoother finish.

I'm hating I sold my boat - but not so much....

I'm heading down to FL soon to do some sailing and fishing with some old friends (who still have their boats!!)

Please send some pics of the pavillion - sounds very cool.

Take care,

Christo

[firebug]

Re: Steel Dome Oven

Hey wiley,

I'm new to this thread and you have answered many of my questions, I plan on building a trailer mounted wfo,my plan is to build metal base welded to trailer, them form up base with cement and perilite then one layer firebricks for the floor, take 1/2 steel bent for a big barrel vault 4x6'.build a dog house around it fill it with 6'' or more of perilite,I want to do a hearth in the front,,,,all done with fire rated materials I want few moving parts I think this could work ,what are your thoughts?

[Wiley]

Re: Steel Dome Oven

Hi Firebug,
OK, first thoughts and assumptions on your query:

It would appear you are considering using no other heat retaining medium other than the steel plate bent to form the barrel vault for the ceiling. Without knowing the exact shape you are envisioning it would be hard to get an precise weight. However, steel weighs about 40.8 lbs per sq ft one inch thick (board ft). So a flat sheet 4' x6' and 1/2 inch thick would weigh about 490 lbs and in the interest of getting some sort of figure with which to work (ball park figures) doubling that for the curve of the ceiling and the ends etc would give us a figure under 1000 lbs. My gut feel is that that is too little a heat reservoir/ heat sink for that large a volume. I suspect it would heat up fairly quickly but also cool down quickly as well. We don't get something for nothing. BTUs need to be liberated; the heat transferred into the heat sink then released back. It's the released back that we are using to bake with in addition to the heat from a ongoing fire to maintain a certain searing/reflection/direct radiation in the case of baking a pizza. I am not a thermodynamics engineer so alot of what I am saying and thinking is "gut feel" (and we all know how much that "gut feel" can get us into trouble). But if one knew the heat capacity of steel and compared it to the heat capacity of firebrick/stone/clay/terracotta one might be able to produce a better answer as to "Would this work?" And by "heat capacity" I mean how much heat (BTUs) can this material soak up/contain/hold? and how fast does the material cool down, give up that stored heat?

So, I suspect such an oven would heat up very fast and but that controlling the heat might prove problematic.

I'm sorry that is not much of an answer. I used the steel dome of my oven as an uncrackable, unspallable, hard to damage and smooth interior form to support the heat reservoir, not as a heat sink itself. I suspect that my steel interior more quickly distributes heat to a larger surface area of the heat reservoir than straight bricks do, however, that is once again, "gut feel" and I have no hard evidence to support that supposition. I do have evidence that a steel dome doesn't crack, that in advertantly striking the interior with a peel results in minimal (read that as no) damage.

Hope this helps,
Wiley

[firebug]

Re: Steel Dome Oven

Wiley,

Thank you for you response,I guess I was hoping the perilite on top of the steel would help retain the heat keeping the dome hot I planned on 6 inches on the sides and 12'' on top of the barrel,but it sounds like what I need is fire bricks on the inside of the barrel as a heat sink,or do you think lots of insulation on top of the dome would suffice? another ideal I had was to weld some channel inside the dome so i could slip in firebricks throughout the entire inside, all the brick would be free from mortar etc,this means no cracking and falling apart.I need a oven that can do major volume and fast,and I have heard to many horror stories with all brick ovens busting apart on the road.thanks for all your insight and look forward from hearing back.

[JoeyVelderrain]

Re: Steel Dome Oven

Wiley,
I need a oven that can do major volume and fast,and I have heard to many horror stories with all brick ovens busting apart on the road.thanks for all your insight and look forward from hearing back.

sounds like this would be perfect for you.
2stone Pizza Pro portable high heat pizza oven (propane)

[Wiley]

Re: Steel Dome Oven

Firebug,
First , thanks for the brain teaser, I have enjoyed messing with the figures in my head :-) And now to try and put them on paper.... So,

Some further thoughts and assumptions:
Let's assume a semicircle x-section for the proposed WFO, with the 6 ft being the long dimension and the 4 ft being the diameter. Pi x D = 12.56 ft. and that divided by 2 gives the length of the half circumfrence. And that times the 6 ft length gives us 37.7 sq ft of 1/2 inch plate. Dividing that by 2 gives us 18.8 square ft of one inch plate and then taking that times 40.8 lbs/sq ft gives us 769 lbs.

So just for comparison lets take that same square footage of ceiling and make it out of 4 inch thick refractory. So 37.7 sq ft x .333 ft results in 12.55 cu ft. Now once again ball parking: a cubic yard of stone weighs a ton. So 2000 divided by 27 gives us 74 lbs per cu ft. 74 times 12.55 gives us a figure of 929.6 lbs. We're ball parking so lets say 930 lbs for the refractory and 770 lbs for the steel. 160 lbs difference. Really not that much. It wouldn't take but two 80 lb bags of concrete to have them the same weight.

So do you have a 6 ft "pup" of the pipe used in the Trans Alaska Pipeline? If memory serves that was just over one half inch thickness and 48 inches in diameter? Although a graph of heat up and cool down versus time would, I suspect, be more peaked and show a shorter "linger time" at the top for the steel, all in all it might actually work. "Gut feeling" being inaccurate once again better "to put a pencil to it" and get some numbers.

Bests,
Wiley

[firebug]

Re: Steel Dome Oven

Hey Wiley,

Your giving me some more good info,fist I thought about a large pipe cut into half,but I don't want a 1/2 round arch I want an elliptical arch which is more suitable for a barrel vault (correct me if I'm wrong) my legs on each side will come up 12'' and come up 10'' more in the center creating the barrel arch,I think this is proper for the size of my oven 4x6 deck.there is a company in Portland that will bend the steel for me and weld the back on , the front will have a smaller opening in it then welded on.then I will build brick hearth and chimney,then the task of covering the metal vault begins,what would you recommend I use to do that?thanks again for your help

[Wiley]

Re: Steel Dome Oven

Firebug,
When you say "covering the metal vault" I'm thinking you are meaning the welded up firebox? And do you mean after it is placed upon the base (firebrick over perlite/cement insulation)? If that is what we're discussing, and since this is an experimental WFO, I think I would be prone to make things simple and in such a manner that one could easily get back to the steel vault should you find that you need more thermal mass. I like your idea to build the enclosure such that you can fill it with loose perlite. It's not as expensive as kaowool or other ceramic blanket and if you need to do work on the vault all you would need is a clean shop vac and some plastic trash bags and you can get the stuff out and still have it reuseable. Space isn't a concern so 8 or more inches of dry loose perlite might be all you would need.

Your mention of Portland brought this to mind.....and this is a wild idea in that it was something that came up last winter and I have no idea what the situation is regarding it at present. But there was an offering for free supersacks filled with perlite at the airport. If I remember the story right somebody had the stuff (100,000 lbs) stored there and couldn't pay storage they wanted/needed it gone and fast. Had the weather been better I and a friend were going to participate in the deal. I think I would give a call to the airport and ask a few questions as to who got the stuff and where did it go. There is the off chance that somebody scooped up the deal and would like to be rid of it themselves. Or perhaps sell what you need less expensively than retail, because I think you are going to need alot. Check archives for 11/19/08 a posting by Jed. The Craigslist posting is dead but somebody will know something at the airport, (and I'm fairly certain it was at the airport. But then again my memory is good, just short).

You might start your own thread as this will be a WFO alot of people I think will be interested in following.
Bests,
Wiley

[firebug]

Re: Steel Dome Oven

Thanks wiley I will do that,can you tell me a little about the ciment fondu,does it become a heat sink,does it hold on to the heat well?how much does the stuff cost?and where can I find some....thank you very much for you help.

[Wiley]

Re: Steel Dome Oven

Firebug, The Fondu is simply the binder, in my WFO the principle heatsink is the crushed basalt. In lieu of basalt any dense rock would probably work. Fondu is a trade name for calcium aluminate cement.

As to the properties of the Fondu itself, it is darker grey in color than usual Portland type cement and to my eye I detect a slight greenish tint to the color. It sets quite quickly and so small batches were the rule for my mixing.

Using crushed (1/4 minus) basalt just as it came from the pit I mixed by volume 5 parts crushed basalt to one part Fondu. I used a 1 quart plastic yogurt container for measuring and if memory serves the biggest batch I mixed was two containers of Fondu and 10 of basalt for a total of 12 quarts. I mixed by hand in a wheel barrow. I also used separate containers for the cement and the basalt and for the water as I didn't want cross contamination.

The material is sensitive to the amount of water added and quickly goes from a too stiff to a too wet consistancy. I started with one part of water to my 1 to 5 mix and then added slowly water by hose, adding and mixing and adding and mixing to get the right consistancy. Once at the right consistancy it is easy to work but like I said it sets quite quickly, with an ambiant temp of around 70 to 75 degrees it becomes stiff/"goes off" in about 20 minutes. Re "tempering" by adding more water and quick mixing will give you a few more minutes once it starts to harden but is something the directions on the bag do not reccommend.

Fondu is not cheap, in fact I would say it is fairly expensive so in the interest of economy, if you are building a stationary WFO I sort of feel that the Fondu may be overkill. So if money is tight I think one might possibly get away with using another mix, perhaps using lime and a little Portland cement as the binder. There is a company in AU that builds WFOs with two domes and they use dry sand as their heatsink so one isn't asking too much of the binder, just to hold the crushed refractory together. When completed the sections are supported by the steel dome and are not subject to abuse by oven tools. One would be breaking new ground going with a cement other than what I used but all life is more or less an experiment. Using a lime and Portland binder one should also have a longer working time although the downside is the Fondu allowed one to work without waiting for the previously poured/trowled sections to harden. By the time one cleaned the wheel barrow and the tools and started measuring out another mix the section just completed was quite hard and could easily support the new material. One might have to work with a stiffer mix and/or wait a day or so between sections if one used a Portland lime mix.

As for availability, I purchased my Fondu from Glacier Northwest and they have recently been purchased by another company, CalPortland. I see that you are in the Portland area, here's a link to their outlet in the Portland area:


CalPortland Company

I noticed in their list of products a type of cement which I am unfamiliar with called type "G". They say it is for higher temperatures than usual Portland cement (not furnace, however). I do not know its properties but depending upon its price it might be worth trying in some combination with lime.

Sorry to run on so, but hope this helps,
Wiley

[firebug]

Re: Steel Dome Oven

Wiley,

I think the route I will be going will be building a barrel dome out of half inch steel, place it on my trailer on a prebuilt base with 5'' of perilite portland cement base with fire bricks on top,deck size will be about 4'x6'.then I will build a steel frame around oven leaving about 8'' from inside of wall to outer shell of oven,on the inside of wall I will wrap several layers of kaowool it will be 3 or 4 inches thick,there should be about a 4'' hole from dome shell to kaowool insulation,then for the heat sink I will fill up the hole with dry sand.I don't think the insulation will compress much. and i will do something similar for for the roof.so to recap steel dome 4 to 5 inches of sand for heat sink then 3 to 4 inches of insulation.do you think this could work? thanks so much.

[Wiley]

Re: Steel Dome Oven

Firebug, I think I would want a steel sheet (something on the order of 16 guage) on the inside of that steel framework and attached to it. That way over time the kaowool would not be compressed to a thinner layer by the sand as it is shaken and settles during travel. It would also keep a more consistant thickness of the heatsink over the outside of the barrel. I don't know how familiar with kaowool you are but it is in consistancy much like wool such as one used to be able to get for dressings for wounds. Kaowool has a curious feature in that it squeaks when one squeezes it. The sound is faint but definitely audible if you listen close for it. If you simply poured the sand between it and the inner barrel I think it would definitely compress.

Also I would want to have an access hole on the top so that you could top up the sand as it settles. For sand I would see if I could find spent greensand from a local foundry. It's usually olivine, a high temp mineral that would be perfect for a heatsink. I would think you could get it for free or for very little cost.

I think it would work well. I suspect it will be a heavy WFO and need a significant trailer to hold it and truck to pull and more importantly, stop it.

Bests,
Wiley

[firebug]

Re: Steel Dome Oven

Wiley

I was thinking something similar with the metal,What if I built my enclosure walls out of 2x6 metal studs put the kaowool in between the studs and put dura rock (or equivalent) on both sides of the 2x6 walls then fill it up with sand that way its protected from collapsing the insulation. the oven should weight about 5-6 k lb max and my traileris rated for 10k lb so I'm good there, the trailer also has brakes but who knows how they work, thanks for the reminder I better look into that.Again thanks for all your support and knowledge.