High Temp Material

What we are trying to avoid is conducting heat from the oven & surrounding heating element to the outside so we have been avoiding metals.

The outside of the oven is metal, right? The weight of the oven is supported through the metal structure of the oven, I would guess.

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Affordable high temperature materials that are good thermal insulation are usually not very tough. If you can separate the task of support and insulation, it becomes much more simple.

One possible route would be a metal support that aligns with the metal frame of the oven. The center metal support under the nonmetallic part of the oven should be recessed or completely hollow. That space should be filled with an insulator, perhaps a firebrick or one of the earlier materials already tried. Some form of gasket will be needed so that this are sealed without the full weight of the oven being supported by the high temp insulator.

Aerogels?

Rockwool insulation over a substrate?

Maybe NASA has some shuttle tiles that they are not using anymore.

Many years ago Corning (I think it was) developed machinable ceramics. Other companies now make these materials (or buy the stock from a company like Corning). The machinable ceramics can withstand high temperatures, often have low thermal conductivity, and are usually chemically inert.

Here is just one company I found doing an internet search. You can find others - maybe a place close to your company that will work with you.

http://www.cotronics.com/vo/cotr/cm_machinable.htm

We use similar material, they can be a bit brittle & tend to degrade with repeated temperature cycling.

You might give these guys a call:

Hi Temp Ceramic Adhesives - ellsworth.com‎

Adwww.ellsworth.com/HiTemp/Adhesives‎ Ceramic Adhesives from Sauereisen.

Hi Temp Heat Restance to 3000 F

They deal in high temperature "stuff" and may know of something you could use.

That Zircar has a much higher max temp. I'd give it a try as long as it's adequately supported underneath. As it seems to be intended more as an insulating panel, it may have low crush strength. Get some and give it a try.

Looks like you were running Sindanyo at its max temp. Probably why it didn't last.

Have you also considered something like alumina refractory tiles?

We were pushing the Sindanyo to its limit. We will try the Zircar if we can't think of any better options. Alumina would probably work but is a bit expensive to have machined.

Zircar is a ceramic fiber which is the best way to go. Do a search for ceramic fiber boards. They come in 2' by 4' by 1 or 2 inch thickness.

Pay attention to how your insulation is held in place. You may have to weld some stainless steel studs (threaded on the inside) to the case. You can also get wet ceramic fiber that hardens the first time it is heated, but it is a bit chunky and harder to work with. Fills holes very nicely though.

Stainless steel plate on the bottom to protect the insulation is also a good idea depending on what you are processing.

The only thing i can think of that will take the weight is the shelving used in ceramic kilns. My kiln fires to 1350degC. To keep the top surface cool to the touch add a layer of woven ceramic cloth. The woven cloth isn't as friable as the ceramic board.

Try Durock, available at Lowes, Home Depot, etc. It's Class A fire rated. Not that difficult to cut or drill, stack it up to whatever thickness you need. Not expensive.