I searched around for a while and came up empty for this question so I apologize if I somehow missed it.

I decided to go wjth a 6" square steel tube as my shell for my forge and was thinking casting a refractory inside it would be my best bet.

My issue is, I have no way of knowing how much refractory to buy. I'm looking to keep the price as low as possible.

For a 6" x 9" square tube with a 3" tunnel down the center, how many lbs of casting material would I need?

I found this stuff on amazon that would work but it is only rated to 2000 degrees which may not be enough?

What did the manufacturer suggest when you contacted them?

you want to work out the volume of your tube, less the volume of your tunnel,( ?cubic inchs) then you need to find out how many lbs to fill ?many cubic inchs

it is only rated to 2000 degrees which may not be enough?

Think of it as ice, below freezing it remains ice, above freezing temperatures, the ice will melt. As long as you stay under 2000 degrees, the 2000 degree material should work.

 

Purchase material that us suitable for the job at hand.

Honestly couldn't find any info on the manufacturer to call them. Googling Kast o lite only results in vendors sold by the 5lb bag and up.

The volume I'm working with on paper should be a 225 cubic inches. That's after subtracting the area of the forging space down the middle.

Check out my tutorial on my web-site.  It will give you some idea for how much you will  need if you are building a forge out of a 20# Propane bottle or a Freon bottle.  You are going to use Inswool (ceramic insulating blanket) in addition to the casting, aren't you?

Honestly No I was not.

I was trying to copy the design of the "atlas mini forge" which appears to just be brick on the inside.

Would I be better off just dropping the casting and putting inswool on the inside with a brick floor? I'm only looking to heat treat but forging temperatures would be nice.

I suggest that you study the tutorial. 

You could just cast it, however, it would take a lot more Kast-0-Lite, be a lot heavier, take a lot longer to heat up and not be as efficient.

You could just use the Inswool but you would then have free floating fibers which are carcinogenetic and you do not want to breathing that.

You could use the Inswool and then paint over it with either Plistix or Metrikote, which would contain the fibers and reflect the infrared rays back into the forge and make the forge more efficient but there is no strength to either of them or ITC-100 and you would poke a hole through it almost every time you put a piece of metal into the forge or take it out.  

Honestly what I want to use is a stack of soft fire brick. Casting is way more unnecessary work.

My problem is that I cant find a local supply of soft fire brick on Long Island or NYC and shipping for the only place I've found is $17 for 3 bricks.

Soft Brick, high temperature fire brick, breaks up real easy. It has no support by itself. It is better to put them into some kind of container.  If you bump them, they will break.

Thanks for the advice. I changed my plan I decided to get a 5" steel tube that will perfectly fit the bricks and it will be cheaper.

So does it expand and contract at the same rate?   Did you check out any pottery supply places for soft firebrick?

 

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I buy all my refractory stuff at a local boiler repair place. There has to be a couple of those in your area.

 

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