So a few years ago I posted an instructable about how made my metal casting foundry/forge using a mix of cement, perlite, and some other stuff that added up to a decent refractory concrete to line the forge. You can find the instructable here.
I figured that I could reach higher temperatures faster, so I did some research and decided that with some better insulation it would retain more heat and be overall more efficient. The problem with better insulation is that it's really pricey. I wanted to make the foundry better, but not spend too much more on the upgrade. I had preferred to use kaowool, but it's crazy expensive, so I found an alternative that's expensive, but manageable. You can find it here, just scroll down to the TaoFibre Blanket.
And for comparison kaowool.
Step 1: Materials
Things you'll need:
Foundry from my previous design (or a cut propane tank)
Kaowool or alternative
Chisel or thick flathead screwdriver
Exacto knife or box cutter
Tarp or something similar
Step 2: Breaking Out the Concrete
**If you are starting from scratch with an unprepared tank, see my old instructable on how to prep it, then go to step 3**
First off, put down the tarp. It'll help with cleaning up the debris from smashing out the concrete. Then just go to town with your hammer of choice to knock out as much concrete as you can, using the chisel when necessary.
Step 3: Measure and Cut Insulation
I bought a bulk roll of the blanket, so I needed to cut out what I needed from it. Note: when handling it, wear gloves and a respirator as the fibers are harmful if inhaled. Just place the tank on top of the blanket and cut out what you need to fit it. I used two layers of 1 inch material, so the thickness was two inches of insulation. Me and my dad used some complicated math to figure out what thickness we needed to keep the external temp down using the insulation and burner specs, which ended up being around 1.7ish inches. Because the sheets were 1 inch thick, I just did 2 inches because why not. The math sucks, so I recommend not doing that and just taking my word for it (it was a pain to figure out). If you do only 1 layer, you'll need 2 circles for the lid and bottom, and 1 rectangle for the inner circumference. If you do 2 layers, just double it.
Step 4: Put It in the Now Empty Tank
Now that you have the insulation cut and the tank emptied, you need to install the insulation. Start with one (or two) of the circles and press them into the bottom of the tank (it'll be a snug fit). Next do the same for the lid. Now put the long piece(s) into a roll slightly smaller than the tank and place it in. Then expand it so that it fits snugly around the insert diameter of the tank. If there are any gaps, just cut out a small piece of insulation and press it into place.
Step 5: Cut Out Holes
The foundry has 2 holes that need to by cut out of the insulation once it's in place: the burner hole and the exhaust hole. Just use an exacto knife or box cutter to do it. Don't make the burner hole too big or else the burner won't sit in place while the foundry is running.
Step 6: Add Firebrick and Hard Face
While I haven't actually done this yet, I'm planning on placing a firebrick in the bottom of the foundry to add support, and I was told in the comments that a hard face, such as kast-o-light 30, should be used to increase the working temperature, and to keep the fibers of the blanket in place.
Step 7: Done!
Congrats! With those few steps and a little bit of time and money, you just upgraded your foundry (or made a really nice one if you didn't have one before) that can get up to iron melting temperatures. Be careful, this is really really hot. Have fun!
PS: Be sure to vote for me in the Metal Contest, The Handtools Only Contest, and the Reclaimed Contest!