One last Furnace question

I asked for some help with my furnace design for melting aluminum a week ago
and got some good advice from this group which I am following. In my 18"
diameter tank I've decided to go with 1" of Cera blanket as the outer layer
and then 3" of castable refractory up against that. I've seen other designs
on the web doing this and they also seem to stop about 2" from the top with
the fiber blanket and cover with the castable refractory. This in effect
buries the fiber blanket inside the refractory. Is there any problem with
this i.e air space in the blanket being trapped inside with no where to go?
I could leave the refractory cover off the blanket but then it seems like a
good idea to protect it from potential spills, etc. and it will look better
covered. What do you think?
Reply to
Terry Mayhugh
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Aside from any other insulating qualities, many refractories, such as the ceramic wools or the cements that contain vermiculite, take advantage of the insulating property of trapped air. With that in mind it would seem that you'd want the air space in the blanket to be sealed with the castable material.
I'm not an expert though, and there may be some other principle at work that I'm not aware of.
Reply to
Artemia Salina
I think the Cera should be nearest the heat (as Tim Williams recommended) but can't tell if that's what you mean to do. Here is my reasoning for having it be the inner wall of the furnace: If it's like Kaowool, it has an R value better than 4 per inch (per
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page 4.02), vs the roughly .1 - .2 of concrete (according to
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). If you have the better insulation near the heat the temperature profile in the wall will drop faster, meaning that you have less heat invested in heating the wall when your furnace gets up to heat.
There is a frequently-recommended and quite expensive refractory coating made to be painted on the surface of Kaowool to cut down its wear and tear. Referred to as "rigidizer" in first URL, or as ITC-100 HT Ceramic Coating at
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. -jiw
Reply to
James Waldby
Precicely. And then, since the cement gets little use, being so much more conductive than the fiber, you can just about eliminate it.
If I were going all-out, personally, outside I'd use 2" kaowool or whatever, with 1/2" to 1" of hard 3200°F or so cement inside that, plus a coating of ITC-100 on all inner surfaces. The cement liner provides a hard shell that heats up quick.
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @
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Reply to
Tim Williams

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