Rigid insulation for small ovens

Constructing an oven from combustible materials is a bad, bad idea.

I'm guessing 375°F is what you expect for the maximum cooking/heating temperature. The heating elements will have to exceed that due to normal losses, therefore the insulation will experience localized heating quite a bit higher than 375°F. 

McMaster-Carr has a good selection of insulations with helpful descriptions.

When I mentioned plywood, I was refering to ease in cutting and drilling, etc, not it's flamable characteristics. Thanks for the McMaster-Carr link. Their high-strength cement might work. I could build a metal box and then insulate it with the cement.

Thanks,

PAPADOC

Find here

You could use cement backer board which is 1/2 inch thick, can be fabricated much like plywood and is non-combustible. If you create a hollow, double wall, the cavity can be filled with mineral wool and provide insulation which will reduce your heat losses and reduce your electric bill. All of these items are readily available at larger home improvement centers. Another solution would be to cast the walls in a single piece using vermiculite (gardening centers), chopped glass fibers and cement.

If you provided information on use of the ovens, location, etc., additional suggestions could be given.

The cement backer board might work. I could build a steel frame, then, add the backer board to the frame with screws, bolts, or rivets. I might have to glue the boards together to get an inch of thickness. This oven is to be used to cook briskets and other roasts with continous hickory smoke. The heat will be supplied by electric heating elements. I am presently using an old bakers oven. I use a temperature controller and it exceeds expectations. I would like to build one from scratch. Also, I'm planning to build a wood fired oven with automatic damper control.

Thanks very much for your help,

PAPADOC

The best cement to bond cement backer boards together would be a silicate type which can be found in the fireplace and wood burning stove section of larger home improvement centers or hardware stores. Silicate cement is available in caulk gun tubes for convenience. Silicate cements are used in the foundry industry.

More expensive would be high performance silicone adhesive used in the automotive industry for engine and exhaust systems.

Sounds like you have a delicious application for engineering.

Thanks. You ain't justa kidding. I've go a fresh pork picnic roasting right now. As I walk by the oven, the smoke escapes with that hickory aroma. It's got 3 more hours to go and I'm really getting hungry!

It all depends on the final use: food processing, make sure that everything used has a correct approval.

To calculate the heat needs you can download and use Tracecalc, it has a vessel function. Attention: it calculates the heat needed to keep it's temperature. For heat up you need to add extra according the mass you want to heat up.

Hello PAPADOC,

As a safety note: don't breath the refractory silicate dust, use proper PPE. It is probably not enough to hurt you but why take the chance. If you already know this , if you didn't.

From an MSDS

Crystalline silica is listed by IARC as a Group 1 Carcinogen "sufficient evidence of carcinogenicity in humans",

and is listed by NTP as K, "Known To Be A Human Carcinogen".

· Information pertaining to particular dangers for man and environment:

May cause cancer by inhalation.

Irritating to eyes, respiratory system and skin.

Danger of serious damage to health by prolonged exposure.

Just got a 55lb pail of refractory cement from http://www.anhrefractories.com/ but the 3200⁰F is over kill for this but if you need something refractory they should have it.

Brad

At a max. of 375 F. gypsum wall-board, (sheet rock), is a possibility.

You would, as a prvious poster suggested, have to SHIELD the G.B. from

the heating elements, but this could easily be done with a sheet metal strip & air gap.

I thought of that. However, this oven will be located outside. Is there a gypsum board that is suitable for outside service? If I have to put a metal shield around it, I may as well use fiberglass insulation and make the unit lighter. Do you have any suggestions?

Thanks for your comments,

PAPADOC

Gb can be bonded to plywood, some adhesive can with stand 1100° F, may be worth your time eh? Two 1/2 sheets green board (exterior or marine grade) sheet rock bond to ACX?

TRY USING RED CLAY, WHEN COOKED AT HIGH TEMPRATURES IT TURNS TO CREAMIC WHICH IS EXCELLENT FOR INSULATING HIGH HEAT OUTPUT BOXES, OR YOU MAY WANT TO TRY CALLING YOUR LOCAL FIREBRICK COMPANY (USED TO LINE INTERIOR FIRELACES). BUT TRUST ME PLYWOOD NO!

Just finished a brick outdoor oven last month. (40" x 40" x 36") and it's great.

All the suggestions above are great BUT beware. Differential thermal expansion might cause cracking of any sheet material that you use. For any largish oven there needs to be expansion joints.

Maybe if you use two overlapping layers of sheeting with the join lines between sheets staggered, then the cracks that might happen would be unlikeluy to exactly correspond and the oven will maintain it's integrity.

There are some really interesting "smoke" alternatives that I've seen, including some "out there" stuff using essential oils. Have fun!