#11  
Old 07-25-2011, 12:01 PM
Serf
 
Join Date: Mar 2011
Location: Utah
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Default Re: Mobile oven design Buoy...HELP

I appreciate the comments. The dome was welded after I gave instructions not to do so; the "friend" was trying to rush the job thinking he knew better. It does seem logical that the heat transfer will be a problem, even after the dome has its insulating layers. What about increasing the fire brick insulating layer from 3 inches up to 6 inches? Would that help keep heat in the oven and off the trailer? Or perhaps building a suspended poured masonry deck an inch or two off of the steel plate? I could weld a rebar frame into (but not attached to) the bottom 3 inches of the buoy steel plate using FB insulation board as the first one inch to keep the masonry deck elevated off the steel deck, then place fire brick deck, thus minimizing the heat transfer from the fire. Though I'm guessing much of the heat will be transferred from the flames rising up to the dome itself and transferring to the trailer.

Or recommendations on a better fix?

Last edited by P712; 07-25-2011 at 12:44 PM.
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  #12  
Old 07-25-2011, 01:28 PM
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Join Date: Aug 2010
Location: MN, USA
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Default Re: Mobile oven design Buoy...HELP

More insulation in the floor will help, but I don't think that is the major issue. I'm thinking that you are correct and heat will go through the dome and into the trailer. You'd have to put a smaller dome INSIDE the buoy and insulate between the two.
I wonder if the perlite/vermiculite mix is strong enough that you could plaster it on the inside a for a couple inches? Then use insulation blanket, then a new dome? Certainly doesn't sound fun. Cutting the weld while you still can would probably be the best course of action. Although I know you don't want to hear that.
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  #13  
Old 07-28-2011, 09:16 PM
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Default Re: Mobile oven design Buoy...HELP

So update...had a smackdown with "friend" and it ended with me hooking up my trailer and drove off huffing. Oh well, friends are over rated. So I set up shop in my Dad's garage. Bought a torch and took the dome off at 5 inches up from weld. Managed to find some fire brick and rented a brick saw from HD for $50, it made fast work of those bricks. My plan is to lay down FB board from Forno Bravo store (2 inches) then lay the bricks on top (3 inches). After that I'm stumped as to connecting the dome back on while keeping it separated from the trailer some how.
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  #14  
Old 07-28-2011, 09:18 PM
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Location: Utah
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Default Re: Mobile oven design Buoy...HELP

sorry those photos are wrong side up
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Last edited by P712; 07-29-2011 at 03:46 AM.
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  #15  
Old 07-28-2011, 10:41 PM
Il Pizzaiolo
 
Join Date: Jan 2007
Location: Tampa, FL
Posts: 1,446
Default Re: Mobile oven design Buoy...HELP

I'm going to side with dmun on the foil, it has been noted on many past threads that cement/concrete (portland cement) is highly corrosive to aluminum foil. In theory, a slip plane seems like a good idea, aluminum foil is not the answer. In no time the cement based product (vermiculite concrete) will be in direct contact with the steel dome, with the vermicrete layer moving with the steel. Many have said that foil is the reason for reduced cracking, science says that other variables are at play, its not the foil.

RT
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  #16  
Old 07-29-2011, 04:09 AM
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Location: Utah
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Default Re: Mobile oven design Buoy...HELP

I guess I assumed the foil was a temporary barrier anyway, to keep the thermal layer from bonding with the steel dome. What are the negative effects of losing the foil after the cement layer has cured?
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  #17  
Old 07-29-2011, 10:34 AM
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Join Date: Mar 2008
Location: Washington State USA
Posts: 768
Default Re: Mobile oven design Buoy...HELP

"I guess I assumed the foil was a temporary barrier anyway, to keep the thermal layer from bonding with the steel dome. What are the negative effects of losing the foil after the cement layer has cured?
Yesterday 10:41 PM"

Correct, the foil is simply acting as a "parting film". That it is corroded away is no problem as it is quite thin and so doesn't pose problems with expansion as it corrodes. I never made a case for any thermal increase nor for reduced cracking (I included it between the polygonal sections of refractory so that it would crack where I desired rather than randomly) . I included it in my build primarily to keep the calcium aluminate concrete from sticking to the steel dome during the construction and first firings. It was placed so that the two (refractory and steel dome) are in intimate contact yet not bonded. The intimate contact allows for rapid and efficient heat transfer from the steel dome to the refractory. The "not bonded" is so that stresses due to differences in expansion between the two materials can be accommodated.

Whether this same action is desirable in the construction of a more traditional brick domed WFO is for each to decide for themselves. Each builds their own WFO. When one diverges from the tried and true path (Forno Bravo Pompeii plans) one suffers or gains from their decisions.

Hope this helps,
Wiley

I disagree, friends are not over-rated. Sorry if your WFO has cost you a friendship, WFOs usually bring friends together.
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  #18  
Old 07-29-2011, 04:39 PM
Il Pizzaiolo
 
Join Date: Jan 2007
Location: Tampa, FL
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Default Re: Mobile oven design Buoy...HELP

Guys, my apologies if I insinuated you didn't have a clue what you were doing with the foil.
Foil seems to raise its ugly head every few months, its roots going back a long time with old school builders. From what I have read, their intention was a slip plane that would allow the layers to move independently, thus reducing movement of outer layers and reducing cracks. Problem is, even if the foil does not corrode, the slip plane would only work in one direction (like rubbing your palms together) and would do nothing for outward expansion.
In your application, stopping adhesion of the layers, I see no reason not to use it...foil is cheap.

RT
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  #19  
Old 07-30-2011, 04:40 AM
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Default Re: Mobile oven design Buoy...HELP

Back to the main issue. For the life of me I can't see how you haven't painted yourself into a corner. Are you still planning to use the steel dome as your interior oven surface? Without any thermal mass? Sitting on what?

Your firebrick floor still touches the metal trailer housing? I work with metal a lot, and believe me, that stuff conducts heat.

I think you need to do some serious thinking at this point. If it were me, I'd be thinking in the direction of using your steel sphere as a waterproof covering to a real oven, with proper insulation all around. That sphere is immense by brick oven standards. You really don't need anything like that much interior cooking space for a portable pizza oven.
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  #20  
Old 07-30-2011, 07:29 AM
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Default Re: Mobile oven design Buoy...HELP

Quote:
Originally Posted by dmun View Post
Back to the main issue. For the life of me I can't see how you haven't painted yourself into a corner. Are you still planning to use the steel dome as your interior oven surface? Without any thermal mass? Sitting on what?

Your firebrick floor still touches the metal trailer housing? I work with metal a lot, and believe me, that stuff conducts heat.

I think you need to do some serious thinking at this point. If it were me, I'd be thinking in the direction of using your steel sphere as a waterproof covering to a real oven, with proper insulation all around. That sphere is immense by brick oven standards. You really don't need anything like that much interior cooking space for a portable pizza oven.
I concur,
Wiley
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