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I Forge Iron

Using Castalite Refractory Cement and KOA Wool


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I am considering buildign a forge with a 12" x 12" interior floor that has a 4" straight height and ends in a dome that extends up to 7" in height max. Think of it like a cut arch design. I can easily make sheet metal do this for me without a problem One sheet of 1/8th, a torch to heat and some angle iron will bend the sides up and a dome is pretty easy with bent sheet metal welded to front and back forms. The problem is when we get to insulation design. The forge would be powered by two 3/4 inch with propane burners with 1" flares entering from the right side along at the top of the flat rise off the floor. Finally I want the inside 1/2 to 1 inch be catalite 3000deg refractory and that would be wrapped with 3" of kaowool on the top and sides with 2" to 3" of castalyte on the floor.

The problem comes in trying to fugure out how to put the KAO Wool on the outside ad castalite on the inside without compromising either. I had thought about starting with the KAO Wool and then wrapping that inside with a 2" tube cutouts for the burners. Then I would tip the shell on its end (so the two open ends are up and down and then take mixed castalite and put a half inch layer over one end, flip it over and put a half inch layer over the other end and then line the walls with it and finally line the tubes welded for the burners with half an inch of castalyte as well. Finally the entire interior would be lined with ITC-100 coating.

The problems and questions start there. First of all would I be damaging the KAO wool blanket by placing castalite right up against the KAO Wool? I dont know what the water content in the cement would do. Naturally I would let the whole thing thouroughly dry and SLOWLY fire it the first time but I wouldnt want to damage the blanket with the moist cement. I also dont want to crush the blanket and lose its insulation powers. When it comes to the floor I thought about putting another inch or two so of kaowool under the floor and cutting holes in the KAOWool and filling the holes with castalyte. When it dries the holes would form pilars that would hold up the floor from crushing the KAO wool. I could then weld the bottom on after all has dried.

Questions:
1) What do you think? Am I nuts?
2) Do I have to worry about water or crushign the KOA Wool when forming the roof?
3) How logn will I have to work with the castalyte after mixed? Will I be able to mix it like putty and hand sculpt it or is it a pour type material?
4) Any tips for getting a good smooth cast wall? I had thought of inserting a final heavy cardstock wall to the inside shape after the cement is on. This wall could burn away in the forge if needed. Also another material like super thin sheet aluminum was considered given aluminum's low melting point.
5) Anythign else I am missign?



One other thought I have would be to pull off the current flare on my torch and replace it with one lined with 1/2 inch of castalyte and have that be the flare rather than some metal. I dont know how well that would work.

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Working time with the castolite is pretty long, never had it "turn" on me. 1/2 - 1" is kinda thin, it will get lotsa cracks in it. Consider making your dimensions to accomadate a multiple of standard bricks for the floor, maybe 9 X 13-1/2 (the bricks are 4-1/2 X 9). They get slagged up and it's nice to be able to replace them easily. The arch shape is a good idea. Consider pointing your burners upward a little, so they are tangent to the arch, you want to heat the roof and the radiant heat will heat the steel.

Friend of mine builds forges by making a "soupy" mix of castolite and running the wool through it, kinda like a doctor putting on a cast. Then slathers more castolite on the inside. Makes a fiber reinforced shell, packs down some, but works very well. No reason to put wool under the floor.

Castolite is rather slumpy and can't be molded like clay. More like working with concrete. It's a castable not a moldable. I've built small forges using a 10 - 12" pipe and a carpet tube for the inside and just cast the material.

Welcome back Robert!

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Working time with the castolite is pretty long, never had it "turn" on me. 1/2 - 1" is kinda thin, it will get lotsa cracks in it. Consider making your dimensions to accomadate a multiple of standard bricks for the floor, maybe 9 X 13-1/2 (the bricks are 4-1/2 X 9). They get slagged up and it's nice to be able to replace them easily. The arch shape is a good idea. Consider pointing your burners upward a little, so they are tangent to the arch, you want to heat the roof and the radiant heat will heat the steel.

Friend of mine builds forges by making a "soupy" mix of castolite and running the wool through it, kinda like a doctor putting on a cast. Then slathers more castolite on the inside. Makes a fiber reinforced shell, packs down some, but works very well. No reason to put wool under the floor.

Castolite is rather slumpy and can't be molded like clay. More like working with concrete. It's a castable not a moldable. I've built small forges using a 10 - 12" pipe and a carpet tube for the inside and just cast the material.

Welcome back Robert!



Thanks.

Can I coat my forms with something so that they will release from the castolyte? That way I can make solid wood forms out of thin plywood and still get them out of the middle without burning them out or risking damaging the castolyte. Perhaps wax coated wood where I can melt the wax?

What kind of firebricks should I use on top of the 3" thick castolyte floor? Insulating, soft or hard?

Other suggestions?

Thanks a bunch.
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It seems koa wool is the common in forge lining. My forge is lined with it and I have no problems with it but would castolite or other refractories work on ther own.
I've been experimenting with making some refractories. There is a ceramic place near my shop and fire clay, alumina and all that stuff is fairly cheap in comparison to koa wool.

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It seems koa wool is the common in forge lining. My forge is lined with it and I have no problems with it but would castolite or other refractories work on ther own.
I've been experimenting with making some refractories. There is a ceramic place near my shop and fire clay, alumina and all that stuff is fairly cheap in comparison to koa wool.


Made a number of forges with just castolite, holds up very well. Heats up pretty quickly too, it's not a real dense castable. Should be about 2" thick in my experience.

Could just cast a loose slab of castolite for a floor.
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Made a number of forges with just castolite, holds up very well. Heats up pretty quickly too, it's not a real dense castable. Should be about 2" thick in my experience.

Could just cast a loose slab of castolite for a floor.


Wow! 2" of castable? Kast-O-Lite isn't very dense as castables go, but it's still about 10 times as dense as Kaowool! I think maybe you and I just operate on totally different scales, Grant. A little thermal mass isn't such a big deal if you're going to run all day.
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Well, Darryl Nelson has a number of them in his school made that way and they're ready to forge out of in 5 -10 minutes. It's also very insulating. Sorta like wood, you can have it glowing on one side and put your hand on the other side, right. Density isn't everything. My industrial forges were 6" of tightly packed accordian pleated wool. More thickness of whatever material you're using isn't worse.

I see a lot of people using heavy pipe for a shell. Do you think a thin layer of castable next to the highly conductive steel would be better than thick?

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Density isn't everything.


Right you are! (Although I admit that I have a little trouble getting my mind around that sometimes, especially when it comes to two versions of the same material.) Kast-O-Lite is ten times as dense as Kaowool (the 8#/ft^3 stuff), but only twice as thermally conductive at 2000 F. Which is pretty darned good for castable.

I see a lot of people using heavy pipe for a shell. Do you think a thin layer of castable next to the highly conductive steel would be better than thick?


Nope! I try to have enough insulation inside the shell that the conductivity of the shell itself is irrelevant.
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Great discussion. Now ya got me thinking, that often happens when I have to defend what I believe to be true. Sometimes I conclude that what I believe may not be true, it happens.

So, I'm thinking. I have one forge that is very tight, only one small opening. It often fascinates me (I'm easily entertained) when I toss a wad of flaming paper in to light it and adjust the mixture for a nice neutral to slightly reducing, that the wad of paper just sits there. I can still read it for five minutes or so! Well, there just is no extra oxygen to make it burn, it just "cooks" as the forge comes up to heat.

So what? Well, I'll bet I could build a forge out of wood that would work for a surprisingly long time (hours!) as long as there is not excess oxygen! I know: "Don't you have better things to do Grant"? And, yes I do.

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It's a tradition to cook over the bloomery maw when we smelt iron from ore.

Put the meat in the reducing zone of the flames and it *can't* burn but cooks amazingly fast---we generally count seconds to time it.

And yes I've had to fish meat "out of the fiery furnace" before when it exploded on the toasting fork...brushed off the charcoal and it was good to go.

Extreme heat with no free O2 is an interesting thing!

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So what? Well, I'll bet I could build a forge out of wood that would work for a surprisingly long time (hours!) as long as there is not excess oxygen! I know: "Don't you have better things to do Grant"? And, yes I do.


I bet you could! I suspect the dragon's breath would be pretty fierce as it offgassed (at least, until you adjusted for that). I've used wood inside a pipe -- closed at one end -- to create a reducing atmosphere for heat treating, and the flame was pretty impressive. I also wonder if the wood would crack and check a lot from the heat. But yeah, just holding a neutral or reducing torch flame on a piece of wood for a while kind of demonstrates the principle.
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Great discussion. Now ya got me thinking, that often happens when I have to defend what I believe to be true. Sometimes I conclude that what I believe may not be true, it happens.


If you mean my idea that the shell doesn't matter much if the interior is well insulated, my reasoning is just this. One thing I remember from back when I was a little smarter about sciency stuff is that the rate of heat transfer across a barrier is directly proportional to the temperature differential across the barrier. Big differential, relatively fast heat transfer. Small differential, relatively slow heat transfer.

Assume we have a forge with a wall consisting of 2" thick Kast-O-Lite, with the interior at 2300 F and the exterior at 150 F, with an ambient air temperature of 70 F. Now, add a steel shell to the exterior, in contact with the Kast-O-Lite -- the steel could be 20 gauge, or could be 0.25" thick. Initially, the interior of the steel shell is 150 F and the exterior is 70 F. Regardless of the thickness of the steel, the temperature differential across the steel (80 degrees F) is tiny compared to the differential across the Kast-O-Lite (2150 F) -- so the heat transfer per unit of time across the steel is relatively tiny. In other words, the shell doesn't make much difference. I think. :huh:

If you want to crunch numbers and such to see if I'm right, you could make a thermal resistance circuit.
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  • 9 years later...

Hi , can I use gypsum and silica sand 50/50 with lime and small amount of cement to make a 2inch insulation wall inside of a 9kg propane gas bottle as a forge to melt gold and would I need to paint the interior face with satanite or similar. A mixture breakdown would be appreciated or alternative Les 

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Welcome aboard Les, please read this  READ THIS FIRST   It will help you get the best out of the forum with tips like editing your profile to show your location because so many answers depend on knowing where in the world you are located. Other tips like how to do the most effective search (the forum search is not the best) and some will help in staying off the moderators radar.

Using cement is not recommended in a propane forge.

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Plaster of Paris and Sand?  NO! NO! NO!  Plaster of Paris, AKA gypsum, starts to degrade at around 232 degC. Gold melts at 1064 degC. See a problem?  Also that mix is not a good insulator so you would have to pump major amounts of heat in it to overcome the losses.  If you have enough gold to melt you should be able to afford a proper refractory to use.  If you don't have you searched on poor man's method of smelting gold ?

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