High alumina refractory/cement

[TheGreenMan]

Noobie to all this, if you can't tell. Question for you all:

I was wondering about making some high alumina refractory to line a furnace instead of buying some. I have access to different types of alumina (calcined alumia, tabular alumina, and therally reactive alumina) but have no clue what exactally would be needed and how mix it etc.

Anyone here know a recipe or would it be easier to just buy some commercial refractory?


Something similar to this would be cool: High Temperature Adhesives and Epoxies, Ceramics, Insulation

[J. Bennett]

Can't answer your question, but thanks for that link! Jerry

[welder19]

Refractory cements are or can be pretty in depth and complicated however there are some very effective and simple recipe's that work just fine.
I don't know if it matters which alumina you use but if it were me I would use epk kaolin clay and mix in fine shreaded foam or use foam from a bean bag chair, mix in as much foam as you can and still have it stick together 4:1 or so, that will make an isulative refractory, then use some clay and alumina and make a hot face which you will want to make about 1/4"-1/2" thick.
Normally clay and silica sand make up the hot face but in your case use alumina since you have it and it is more refractory than sand.

welder19

[Frosty]

Styrofoam beads don't work very well, they're very hard to mix and pack. Then there's the great stinking clouds of toxic of smoke you get burning it out. You can TRY dissolving it with acetone but that tends to make the styrene residue an evenly divided part of the refractory and pretty much smokes for a long time.

Sawdust is WAY better than styrofoam beads.

Perlite is pretty much industry standard for low (relative term) temp insulating refractories, it's good to 2,000f.

When you say furnace I assume you're talking about a gas, probably propane, furnace. Yes?

Your easiest route is just buy a commercial castable or rammable refractory. $30-50 will buy you enough to make a forge WAY larger than you're going to need for general smithing.

However, the better the insulation the more economical and hotter it's going to be. No, it won't raise the absolute temperature a burner is capable of reaching but the more heat you can keep in the forge chamber the better. It'll use less fuel because it loses less through the walls. This means it will be hotter by the amount of reduced loss.

Pretty much standard practice though certainly not universal is a high temp 2,600f or better ceramic wool blanket liner with a split hard brick or 3,000f kiln shelf floor, coated with ITC-100, Plistex or similar IR reflective coating.

It's a long and well hashed out subject.

Welcome aboard.

Frosty

[TheGreenMan]

After thinking it over some more I'll just go the commercial route. I'm thinking of making a small gas forge out of a .50 cal ammo can. I got plenty of those as I collect rifles. It will be small enough that it may actually be able to fit in my small patch of grass, what some might generously call a "yard". :-)

[philip in china]

Only thing I would add to Frosty is use chain saw sawdust. You need the particle size.

[welder19]

The smaller the better when making an insulating castable from burnable material.
Sawdust or foam is a preference, I prefer foam because it burns out faster and leaves no ash, ash can act as a flux depending on what type of binder you use and how much there is of it.
If you found it too hard to mix or pack then you may have used too much.
The smoke isn't that bad and it doesn't last that long, however it doesn't bother me that much since I'm used to it from all of the lost foam casting that I do, which creates way more smoke than the little bit from insulating refractory.
Do not use acetone to try and dissolve the foam out, if you do let it sit for a long time before fireing it and at that start very slow, like with a light bulb and increase very slowly since there could be pockets of acetone left inside which if your lucky would just blow chuncks out of the walls.
Acetone is used to dissolve foam out when foam is used for creating voids or pockets in fiberglass or plaster or any place where there is not going to be any issue from heat or flame.

welder19