Wrapping up the Furnace

Posted: September 13, 2010 in Furnace Body


As mentioned in Casting the Base, I added in the Inswool blanket around the refractory shell.  At the very bottom, there’s not enough room for the full 1″ wrap, just .5″.  Then 1″, then 2″ at the top.  My last-minute decision to widen the crucible chamber for big pours has reduced total insulation value.  Still, there’s a lot of insulating refractory even with NO extra inswool in the bottom couple of inches (about 1.5″ of highly insulated refractory + 1″ of inswool for the outer liner), so I’m ok, I’m sure.

After that, I added a refractory “cap” to stabilize everything and give a surface for the lid to sit on and provide a surface to seal against if I discover that I need to add a wool gasket to keep the flames from coming out the sides at the junction.

I needed a bit more work on the hinge mechanism to get it to hold the lid straight and allow the lid to fully descend.  The angled reinforcing bar does wonders for rigidity.   Here’s the end product (prior to painting the base.)

Here’s a picture of the lid  moved to the side as if I were going in to retrieve the crucible.  The top is large enough that the base can still support the lid while the hole is fully open, relieving me of hoping that the arm doesn’t deform over time, or generating a “stand” to hold the lid when it’s moved off to the side. 

I’ve painted the base, and will be doing a firing tomorrow night to bake the paint and to drive out the water and solidify the refractory.

Then… well, inserting the burner, hooking it up to the propane tank and doing its virgin melt.

  1. cicciorusso says:

    Hello, I am a puppet builder, to build some tools I made my molds but I have the exact formula of the refractory, you can give it to me?

  2. kcrucible says:

    I’m afraid that I won’t be able to help much. I purchased the base castable refractory (Kastolite 3000) from http://elliscustomknifeworks.hightemptools.com/castablerefractory.html

    To that I added half as much shredded foam/sawdust/coffee grounds to increase insulation values further.

    The net effect is 2 unit per volume of refractory powder to 1 unit per volume of additional burn-out material. Once mixed, I added water to get the proper consistancy (too little is better than too much, because otherwise some of the cement will run through the mixture and puddle at the bottom of the mold leaving the top weak.)

    If you don’t have access to refractory, you could probably make due with Refractory Cement (used for mortering refractory bricks together) of 2500-3000 degrees and add 3 units of sawdust/foam to 1 unit of cement to give you some decently insulative cement.

    If you can do a “rammable” refractory that you want to make yourself, I’ve seen this recipe out there (but can’t vouch for it.)

    33% fireclay
    33% silica sand
    33% perlite

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