mattjayne9090

Mizzou Castable Refractory

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I don't remember what brand I used but it had a 2600 degree rating. Hard as concrete. If this is what you have I don't recommend casting it too thick. The walls in mine are 3" thick and I think this acts as a heat sink. It takes a long time to heat up (15 - 20 min). I can weld in it but it takes a lot of gas to do it. Just MHO

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Well Matt it totally depends on how you are going to use your forge---something you forgot to mention to us.

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I'm building a new forge, I'll share what i've found out. Mizzou is dense and tough, but not the best insulator. Its themal conductivity is 7.4 BTU-inftsquared hr degree F At 2000 degrees F(whatever that means).
Kast-O-Lite 30 LI has a thermal conductivity of 4.4 which makes it a better insulator, but the guy at the boiler place said it's not as durable as Mizzou.
So in the interest of fuel economy, it might be better to make the floor from Mizzou, or simple boiler bricks, and the walls from Kast-O-Lite 30 LI.
Both of these products have a shelf life of six months or so, I put my bags right into gasketed ammo boxes to keep ambient humididty away.

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It'll be great to know how it works out. Keep us posted :)

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You can mix in very fine styrofoam or fine saw dust, mix it to the point it where it still sticks together, I don't know about mizzou but some of the commercial castables are specific about the amount of water you add, so be sure you still follow their mixing directions but add the foam or sawdust to that, make it 1"-1 1/2" thick, then make a hot face of straight mizzou about 3/8" thick, when you fire it the foam or sawdust will burn out leaving little air spaces which will act as insulation.
Or the best way to go is to get some kaowool and the put 1/2" of mizzou over that.
Good luck.

welder19

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Harbison-Walker makes a Kast-o-Lite that is rated at 3000 F. Kast-O-Lite is an insulating castable that is almost as good as a soft brick but not as good as fiber. I used it to build forges and I think it's great. It insulates and doesn't present the problems associated with breathing the fibers from insulating blanket. If your concerned about the heat up time you can apply ITC. That stuff works very well. Just make sure your design is well thought-out because Kast-O-Lite is about $55/55lb bag. That's if you pick it up yourself.

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Will you be forgewelding in it?

For just knives, no forgewelding and if it's done on the side rather than fulltime I'd go with kaowool as you save so much time on it coming up to temp. It's much lighter to move around and it cools off faster---you go to a demo you don't want to wait several hours to load it afterwards! (Faster warm up saves on Propane too).

If it's going to see rough use on a low industrial scale then a tougher heavier system is indicated, go with castable.

Note; don't assume this will end up being your only forge; most folks end up with several to cover different use cases.

As for problems associated with breathing the fibers from insulating blanket: SOFA actually had a test run with both a new forge and an old forge and with a whole day of use neither one ever exceded the OSHA limits for such materials.

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Yes perlite works also but it doesn't burn out it just acts as an insulator, which is ok but it has a relativly low melting point at which it becomes a flux and will damage your refractory, but if your not going to be doing much forge welding it would be fine.

welder19

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relativly low melting point


well that just set me off on a two hour odyssey :P


seems the melting point ranges with the particular perlite employed in the refractory from 890C (1634 F) to 1600C (2912 F) depending on the source

I didnt realize it wasnt rated for high temperature refractories (largely because its so widely employed in DIY foundry furnaces) :P

High Temperature Applications for Perlite in the Steel and Foundry Industries---SCHUNDLER PRODUCT GUIDE
Perlite is used in the manufacture of refractories where the average temperature does not exceed approximately 2000�F (1 100�C). Because of its excellent insulating properties, there is substantial usage of perlite in refractory castables, bricks and blocks. In higher temperature applications, perlite refractories are often used as back-up insulating layers for higher duty refractories.


PERLITE/SILICATE COMPOSITES FOR HIGH TEMPERATURE INSULATION AND FORMED SHAPES---A SCHUNDLER PRODUCT GUIDE
Perlite/Silicate Composits
TABLE - Typical Properties of Perlite/Sodium Silicate Composites (note the thermal limit here has an extra set of zeros :P even though its sited as the same source above :rolleyes:)
testing of perlite and vermiculite samples from British Columbia pdf




step by step guide to building a gas fired furnace
which employs perlite as a backing insulation and a castable 1700C (3092F) refractory)

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I wonder what the temp limit is for the perlite mine here in Socorro is? I know a fellow who has a dumptruck load they gave him when it was rained on before it could be shipped.

There is a bentonite pit locally too, but you have to buy a permit to load up---something like US$5 for a pickup load for non-commercial use...

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