Thinking about forge wall Construction materials

[kraythe]

Greetings,

I have finally gotten around to working on my new forge. I spend the weekend last weekend welding up the frame out of 2" x 1/8" wall angle iron and flat stock. The forge is essentially a cube with a missing bottom. Its meant that the forge bottom will be one layer of insulating firebrick and a second layer of hard firebrick. The whole idea is that you can replace the brick when borax eats the floor or even take out one insulating layer and increase volume. The whole forge will sit on a table top composed of insulating firebrick for the same reason

The construction involves welding up modules that make up the walls and roof and then assemble them. I have done this step already and i am now ready to assemble. Each of the modules are designed to have 2" of insulation between hot faces and the metal shell. The whole thing will be powered by a ribbon burner placed in the top. So basically I need to put insulation on the 2" thick walls and I have been debating what would be the best strategy. Id appreciate other opinions if some have them to offer. With any strategy, the hot faces will get a good coating of ITC-100 for efficiency.

IDEA #1) Create a complex insulation structure with KAO Wool. In this idea, I can take 2 layers of KAO Wool, one at 1" and the other compressed to half height. Both would be "glued" to the metal shell using refractory mortar bonding agent. First I would cut the panels to size. Then I would soak them in rigidizer and then the compressed layers would but put under a compression jig which would be basically backer board with a 1/2" high frame to get the correct compression. This would give me a wall thickness of 1.5 inches. The final half inch could be either 3200 Degree Refractory Mortar or 3000 Degree Castolyte Castable Refractory.

The advantages are that the outer insulation would be uncompressed and should retain a ton of its insulating power even though the inside layer might be somewhat diminished in insulating capability. Since the hot faces are coated with mortar or castable and then ITC-100, releasing harmful fibers into the air if accidentally poked will simply not happen.

The concerns i have about this are achieving appropriate bonding of the insulation to the metal wall. I worry that the stress from heating and cooling might separate the insulation from the metal wall and separation of the rigidized KAO wool from each other. Although this structure would be the lightest in thermal mass, it is much more complex than the others.

IDEA #2) Take the module parts of the wall and pour them in solid castable refractory, perhaps mixed with stainless steel needles to inhibit catastrophic cracking. The benefit of this is that adhesion with the wall wouldn't be an issue because the wall would be cast right into the castable. The disadvantage I see is that the forge will have significant thermal mass and that could make it less fuel efficient. Also that structure would be considerably heavier than the KAO Wool insulate version. However the solid wall might be less complex.

IDEA #3) Cut only 1" panels from KAO wool, rigidize the panels and then pour 1/2" stainless needle reinforced castable, place the now rigid kao wool board on the poured castable, then top off the rest with more castable. One advantage is that the castable would find all the pockets in the rigidized KAO wool and bond it solidly to the outer layer of castable. In adition, there would be areas that the castable would go all the way through (such as corners) so the structure would be very solid. The fiber blanket core would reduce the thermal mass and use the better insulating capability of KAO wool. Again the construction is complex and this idea would have more castable refractory than IDEA #1.

So ... any opinions out there? Any other ideas?