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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

Hammer

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!

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## 12 Discussions

How hot have to you taken it up to? I have been contemplating building a furnace to do the typical aluminum melts, but honestly really would like to get into copper, brass, bronze and even cast iron. That way you can make really nice items that can be machined to make different projects that much stronger.

4 replies

Aluminium - 1200F, bronze - 1550F, Brass - 1650F, Copper - 2000F, Iron - 2300F

Brass and bronze are fairly doable, temperature wise, but I advise against working brass untill you are WELL VERSED in the safety necessary. Zinc poisoning is bad, m'kay? Copper, silver, and gold are pushing the edge of what a furnace like this can do, but they CAN be done.

The temperatures for iron and steel are only a few hundred degrees more, but those degrees bump you up into the next technology bracket. You need different furnace designs, different fuels systems, more and better safety equipment. If you really want to do iron, find a nearby university with a sculpture department, and see if they do iron pours. Even with brass, it may be better to go be a helper a few times, to get a feel for it first. These metals are a whole different beast vs aluminium.

Thanks for the additional info. I am not really new to metal melting. I melted lead for decades now and aluminum is the next step, sort to speak. But I eventually want to be melting cast iron for projects that need to be that much stronger them mere aluminum. You can be sure when the time comes for me to venture into the serious metal foundry issues, I will have read and watched more videos then I really want to see. But I also understand the seriousness of doing such things. No safety issues will ever be side-stepped with me. When I get into any new hobby, I get into it seriously but safely. Thanks again!

There are some alloys of zinc, aluminum and copper that are almost as strong a iron, but can be made at much lower temps.

Ironsmither is very right, the other metals are very different from aluminum, although I have been able to do iron pours with this design, I found that it's much more finicky and you'll probably need a helper.

Take a page from the blacksmiths that have been doing this for decades now.

Get some Kast-O-lite 30. Use it as a hardface for your fiber. Not only does it up the service temperature to 3000 (vs 1800-2600 depending on your ceramic blanket) But it will also lock in the fibers very neatly, AND get you up to temperature quicker than the blanket alone.While you are at it, I would seriously consider putting a refractory brick in the bottom. Just fit it in there, then mud over everything with the hardface.

If you switch to a higher temperature fuel (waste oil burner, for example), then even the 3000 degree stuff will begin to fail eventually, you can just knock off the bad stuff, fill the cracks, and add another coat.

2 replies

Yeah I was already planning on adding the firebrick into the bottom, I'll definitely be looking into the kast-o-light 30 though, it sounds like it'll help a lot.

Do you have some kind of plinth to set the crucible on? Without one, I would think that the crucible would, at best, compress the blanket and reduce it's insulative qualities. At worst, it would make the crucible tip over and spill molten metal all over your foundry.