castable refractory recipe question

[Noah Tasker]

I am wanting to make a new forge. I have used the wool blanket insulation and it has proved too fragile. And also the forge doesn't get hot enough to forge weld which I am dying to try! Anyway, my idea is to make a cast forge but I don't want to have to sell a kidney to have castable refractory shipped to me. I found a recipe online that was used for aluminum casting. It consists of four quarts perlite and one quart of 3000 degree furnace mortar. I planned to buy a small amount of mizzou castable refractory for a liner and to use the homemade stuff for a secondary layer. Any ideas?

[Geoff Keyes]

This has all been said before, but here we go.

 

If you can't weld in your forge as it is set up, then you probably won't be able to take the same setup, line it with castable, and weld in that.

 

Here is the issue. The wool blanket stuff has very little physical mass, and it's an insulator, so you only have to heat the surface of it to get the forge hot. The part behind the surface acts to keep the heat inside. The castable is not an insulator, it resists the temperature and retains heat. With a hard material making up the forge, you have to heat most of the mass to get the forge to start heating the interior. It take a lot more gas, and a lot more time.

 

I have 2 forges, one I weld in, one I can weld in, but don't. The non-welding forge is just Kaowool, with a layer of Satanite and ITC100 over that. The reason I don't weld in it is that nothing is protecting the floor of the forge and so hot flux will eat it up. The welding forge has a hood of Kaowool, Satanite and ITC100, and a floor of hard brick, which resists the flux. The difference is the non-welding forge comes to heat in about 90 seconds. The welding forge takes 20 minutes, all of which is time to heat the floor. These forges are about the same size and they use the same burner, same blower.

 

Lets look at your setup. What kind of burner are you using? How big is the forge? How much insulation are you using? Is it top-coated?

 

I understand your problem with durability, the wool blankets can be fragile, and they really need the top-coat to work at their best. Dave Lisch uses a single 1 inch Kaowool blanket, soaked in a slurry of mizzou. This gives you a hard, durable surface combined with some of the insulating qualities of the Kaowool. It takes longer that a straight Kaowool forge to heat (10-15 minutes for an 8" x 12" space to come to heat) but in a production shop they hold up well.

 

I think you would be better served by figuring out why your present forge won't do what you want, than spending your time on an experimental setup that may or may not work. Then, if you are still not happy, armed with more information, you can move on to something else.

 

Just my .02, YMMV,

 

Geoff

[Sean McGrath]

I agree that simply changing insulation isn't going to change your max temp.

 

I used Kaowool all the time at work, and naturally, we decided to play with it one day (messing with one of the apprentices). I held a piece of 2" on my bare hand, while one of the other guys blasted my hand with a rosebud on a oxy/acet torch. The surface of the kaowool started glowing red, but we got tired of playing with it before any heat ever reached my hand. That should give you an idea of how well kaowool works as an insulator, especially when you use two or more inches of it inside a forge...

 

 

 

Edit: I should put a disclaimer here saying never try this yourself. If you have any that has absorbed moisture, it could flash to steam and burn you badly.

Edited June 11, 2011 by Sean McGrath

[Noah Tasker]

I guess I should have been more specific in my question. My main question was to see if anyone had experience with using perlite as an insulator on a forge. I chicked online and found that it is only used for industrial purposes at temps up to 2000 degrees but I didn't know if the high temp mortar and the mizzou liner would make up for that. I am also planning to change the burner layout. My current forge is an atmospheric forge that I made based on the Zoeller forge plans. If I make this new one I plan to make it a forced air burner and to put in another burner as well as making the chamber longer so that I can forge longer blades. Sorry for being so vague, just wanted to get a feel for this refractory recipe.

[Greg H.]

I guess I should have been more specific in my question. My main question was to see if anyone had experience with using perlite as an insulator on a forge. I chicked online and found that it is only used for industrial purposes at temps up to 2000 degrees but I didn't know if the high temp mortar and the mizzou liner would make up for that. I am also planning to change the burner layout. My current forge is an atmospheric forge that I made based on the Zoeller forge plans. If I make this new one I plan to make it a forced air burner and to put in another burner as well as making the chamber longer so that I can forge longer blades. Sorry for being so vague, just wanted to get a feel for this refractory recipe.

 

It depends on how thick your high temp layer is - if it is only a skim coat, then it's not going to offer very much protection and damage can occur under the high temp layer and when that happens the skim coat of high temp refractory can flake off.

[Noah Tasker]

I was going to make the liner about an inch thick.

[Alan Longmire]

Industry uses the heavy castable because they keep those furnaces at heat for days or weeks at a time. In that setting, the retained heat makes up for the gas it takes to get the whole thing up to temp. They do insulate the outside with wool to keep the heat in. For home use, unless you're running a serious crucible furnace, it's really just a way to waste gas while it's heating up.

 

By all means slap a quarter-inch of Mizzou inside the wool, that will provide a hard shell to keep the wool intact and prevent loose fibers from floating around in the shop, a very real hazard.

 

If you're tearing up the wool, stop being so rough!

[B. Norris]

Noah,

 

I am about to make a very broad generalization, for which I apologize in advance. When smiths first start using propane forges they seem to want to make one forge that will do everything. Later, the same smith will have several, specialized, propane forges. What I'm trying to say is that while it is possible to make one forge that you can bladesmith in, weld in, and heat treat a sword in - you will pay a premium in fuel to be able to do so and it will do none of these things very well.

 

Don Fogg uses the same "Fogg" style forge (an upright piece of pipe with two "doors" cut in opposite one another and run on a forced air burner) built from 8" diameter pipe to forge knives and swords in. You do not have to heat the entire length of your sword to forge it and, in fact, taking such a long heat will cause problems. With a long section, at temperature, it will move and bend where it is hot even when you hit it somewhere else. A shorter heat allows you to move the metal only where you want to. Heat treating is a different story and you have to get the entirety of the blade to the same temperature. Why waste the fuel and cause yourself more hassle when you can burn less fuel and have fewer bends, waves, and twists to correct?

 

If you want to weld, forge swords and heat treat swords you would be much better served by three forges - one for each purpose.

 

~Bruce~

 

P.S. I am trying to save you money and hassle, not dump on you! Besides which, I already tried to make one forge that would do it all... Now, well, I've built two and am working towards the welding one!

[Doug Lester]

Reguarding your home brewed castable refractory of pearlite held together with a mortor, most of these home brewed products don't work nearly as well as commercially available products. For right now I suggest that you go with the Mizzou over a Kaowool/Inswool lining. That's what I have for my large forge and I can get it up to welding temperature with one blown burner. As far as the expence of shipping goes-if you don't have the money to do it right, when will you have the money to do it over?

 

I also built a small horizontal forge, the fire chamber is about 7" deep and 3" in diameter, from Cast-O-Lite. It is also powered by a blown burner. I've never measured how hot it gets but I think that it could come up to welding temperatures also. It's lined on the outside with insulting bricks. If you really want to make a cast body, I would keep the minimum thickness of the walls to about 2". Mine had a minimum thickness of 1" on the sides and it cracked across that thickness on both sides from the stress caused by the weight of the burner assembly. I patched it with furnice patch and wired it toghether with bailing wire. I also wired the burner to the metal frame to support it, which I should have done in the first place. The doors are made from Insboard which is held on by the angle iron of the frame.

 

 

 

Doug

[Mick Maxen]

Mizzou has been mentioned a couple of times. Is it a brand name for something, or a mix of "stuff". Its not something I have heard of in the UK.

 

Mick.

[Matt Bower]

I have tried the homemade stuff and I will never go back to it. Don't waste your time.

 

Perlite contains a lot of fluxes. At welding temps it'll actually lower the melting point of the Mizzou or other matrix.

[Geoff Keyes]

It looks like it's a brand name

 

The forums here might help you as well.

 

Just to expand on what was said earlier, we all like to build it ourselves, build it on the cheap, build it out of dirt . I do this myself, but there is a time and place for it. Sometimes it pays now and in the future to use proven tech. I think this is one of those cases. As above, a forge for welding, a forge for forging, a forge for HT, seems like a big expense. I don't think I've spent more than $100 on any of my forges (maybe just a bit more than that, but not much). The advantage is that I only burn gas when I need to, and I don't burn the tips off of blades. This happens when you're heating all of a blade just so you can work on a 2 inch spot in the middle. My vertical forge runs on less than 1 psi of line pressure and heats a zone about 4-5 inches long, anywhere on the bar. I can weld in it, so long as the weld faces are not longer than 4 inches or so.

 

My welding forge runs on 4-6 psi, takes 20 minutes to heat up, but will heat a weld face 12 inches long and will take a 7 inch tall billet, more than I want to carry around, really.

 

My HT forge runs on 4-6 psi line pressure, stepped down to about 1/2 psi. I find that I need higher psi to make the burners run at 1500-1600 degrees without sputtering.

 

I'm not trying to beat up on you either, I'm just trying to give you the benefit of having built 20 forges, and seen several hundred. Take it for what it's worth.

 

Geoff

[Sean McGrath]

Mizzou has been mentioned a couple of times.

 

It's made under the A.P. Green name, and "Mizzou" is a slang term for "Missouri". A.P. Green's main headquarters were in Mexico, Missouri, but the company got bought out several years ago. Don't know who owns it now, but they still use the brand name actively, and still make many of Green's products.

 

We still have an operating A.P. Green Firebrick plant here in Fulton, and along with regular Firebrick, they supposedly make the brick that lines the launch pads for NASA. Unfortunately, the plant here in town doesn't make the castable refractory (because I have a couple of friends who work there ).

 

I have played with the pulverized mixture they use to make the firebricks with, a friend brought me a gallon bucket of it. I mixed it with water and attempted to line the firepot in my forge with it. It lasted about a week, then gradually started cracking and falling apart.

[Wayne Coe]

I sell Kast-0-Lite 3000 and Kast-0-Lite 2600 castable refectories. Kast-0-Lite is a light weight insulating castable. It is not as good an insulator as Inswool but is better than other castables. I usually use 1 inch of Inswool and about 1//2 inch of Kast-0-Lite in order to build a good tuff forge. I also sell Plistix which is an Infrared Reflective product and which helps keep the heat in the forge and reflected back into the metal.

Kast-0-Lite 3000 is $15.00 for a 6# bag.

Kast-0-Lite 2600 is $12.00 for a 6# bag.

Plistix is $10.00 for a 1 pint bag.

Inswool is $8.00 per 2 foot wide running foot.

 

Let me know if I can help you.

[Noah Tasker]

Thank you all for the feed back. I think that instead of trying to build a new forge I will revamp my current forge. I'll put a liner in and change the burner to forced air, and for forging swords I'll put a door in the back. Thanks again for the help.