Lkay so first thanks for the advice up front. I’m building a vertical forge for smelting.

 

its made out of Schedule 40 1/4” pipe that’s 12” ID.

So, my question is about the insulation.

im going to do a 2600f ceramic wool and kastolite 30. Do i need to put a rigidizer on the wool? If I did would their be a Benefit?

 

thanks 

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I always rigidize the wool to if nothing else keep the fibers from floating around while the forge is in operation. I know you are going to coat the wool with Kast-O-Lite but I always err on the side of caution. There is a thread about ceramic wool warnings.

Rigidizing the wool first stiffens it up somewhat. This gives a more rigid layer behind the cast refractory layer and helps it to resist the inevitable pokes and bangs a bit better. It may be more important in a forge than in a vertical crucible furnace. You'll need to evaluate your process and equipment to decide if it's a real factor for you.

It's not a magic bullet and it needs a pretty thick rigidized layer to make much difference: you need to evaluate carefully whether you have the time/patience/climate to soak the wool and dry it out FULLY before applying the castable. Most of my forge failures have been down to not drying things out fully before the next stage of the build. Any trapped water when firing flashes off to steam and readily damages all the stuff you've worked so hard to get right.

If you have a rigidized layer behind the cast refractory, you may be able to use a thinner cast layer, reducing the thermal mass and giving faster heat-up and cool-down: often an advantage for the hobby smith, probably less of a consideration for a melting furnace.

 

So you will be smelting ore into metal  and not melting metal for casting?

What ores do you plan to smelt? Have you ever run a bloomery before?

Most casters put an emergency drain hole in the furnace bottom, to keep metal from creating a mess all over the furnace, in case of crucible failure. Such a hole also allows collected water and steam to escape during thermal cycling.

a drain hole to empty flux is very recommended given the purpose is to slag the contents off the metal. Theres a bunch of refractories rated to 3200 mind you liquid iron can be like 2800 or so depending on the content. I personally use satanite because its cheap and easy to remove/replace/patch

"Metal Technology in Medieval India" has a very interesting method of smelting zinc.   Still waiting on clarification that you will be smelting and not melting and what metal(s)?