Repost about 'rigidizer'

. . . sorry the first post didn't appear. I'm just finishing my first propane forge made from a 5 gallon can. I modified it slightly so it is no longer a cylinder, but is now a vaulted
arch. The floor consists of two -1" layers of kaolin with a 1.25" firebricks on the top of this. 3.25 total inches. The arches are 2-1" kaolin layers. The vaulted roof chamber (8" span, 4" high) seems to be very stable. Will it stay this way with heat. I already have the 'rigidizer' so now all I have to do is apply it and dry it. But I really don't understand the reason for it. It is said that it reduces the insulation value slightly. I take it for granted I would be safer to go ahead and apply the rigidizer, just for drill, if nothing else. Any input appreciated. .. ..in advance, thanks.
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I replied to it :-(
<snip> Hi theChas,
I have found that Kaowool will literally evaporate when directly exposed to an oxyacetylene torch, however Kaowool treated with Kaowool Rigidizer wont even go black.
I did an experiment with a piece of Kaowool I treated one half with Rigidizer and the other half without, and ran an oxyacetylene torch back and forth over the Kaowool. The untreated half disintegrated, the treated half was untouched.
If the wool doesn't come into direct contact with an extremely hot flame I'm sure it will be okay.
This is what I have found, others might have a different experience.
<snip>
theChas. wrote:

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I've had my torch in direct contact with the wool stuff that I've been using (aftermarket stuff) and never seen it vaporize but I do know if you get it hot enough it will get brittle and then it floats away in bits and pieces. Even if it's not in direct contact, once you start hitting it's temperture limit it gets brittle and begins to crumble. The stabilizer will prevent that. 1. It helps to keep your liner intact and 2. it keeps you from breathing the dust flaking off of it. This second point is probably the most important. I run on the assumption that breathing it is a very bad thing. I use a coat of satanite as a stabilizer. Cheap and lasts a while. When it starts getting beat up you can slap another coat on it. ITC-100 (I think) will increase the heat reflective properties and make it even better. I do two one inch layers of wool and the Satanite and never really needed anything else. I just built a new forge with a larger interior and my one 3/4" torch is still enough to get close to 2000F. Interior is 12 x 24 inch cylider minus the wool. Not sure of the math here. I'm planning to put a layer of Mizzou on the bottom to protect it from flux.
GA
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Kyle J. wrote:

Just use a hard fire brick, and replace it when it gets eaten, it's a cheaper solution.
Regards Charles
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Just to add a little to this, I've used soft and hard firebrick, and castable refractory. The hard firebrick takes a long time to get up to heat... In my old forge it would get good and hot in about 15--30 minutes with soft brick, and take 60+ minutes with hard. The problem with soft brick is that flux eats it away pretty fast, so you can expect to replace them fairly often. The hard brick lasts a long time, but takes forever to get really hot. The best solution I've found so far is to use soft brick and put down a layer of "hard" castable refractory cement on top, maybe 3/4" thick. I think if I was really motivated I'd cut some hard brick to 1/2" thick on a tile saw and use those as "pavers".
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snipped-for-privacy@rgs.uci.edu wrote:

That's a good way of doing it. In general castable refractory like "Forseco 165 arc" take a long time to heat up, but can withstand high temperatures. As a cover to high temperature products like K26 fire bricks or hi-duty Kaowool it's a good solution, and provides a stable work place. I would still recommend a removable hard fire brick at the base of your forge in case you want to do forge welding, and to increase the temperature of the fire box by reducing it's volume.
Please remember that your burner has to be suited (or of a greater capacity) for the size of your firebox. If you're trying to heat up a large area you're going to need a large capacity burner.
I'm making a forge out of a tool box at the moment, imagine a very small "Whisper Momma"... just because I want to. The lining is going to be hi-duty kaowool, rigidized naturally, and is going to have a loose hard fire brick as the forge base.
I intend to power it with a JTH-7. This is a really useful torch and powerful for a one-brick-forge, or a small coffee can furnace. I might be stretching it a bit in this new forge, but if getting to temperature is an issue I'll coat the kaowool with some ir reflecting paint.
The hard bricks are the best for the floor as they are hard, and don't crumble, and if you put enough heat on them they heat up quick enough ;-)
Oh, forgot to mention, steer clear of kiln shelving, it gets chewed up real fast.
Regards Charles
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The Mizzou is supposed to be pretty flux resistant and I can cast it to form. Since I'm planning to put it on top of the wool on the floor, it will be easy enough to change out and won't sink any more heat than required to bring it up to temp. It's about a dollar per pound dry weight and I don't figure on using more than a couple of pounds of it for a floor plate. My old forge has a ceramic plate that I fired out of high temp clay. It warped up on one end in the first firing but has been totally stable since then. I'd use that stuff if I could figure out how to fire it without the warpage. I think it just needs to be evenly heated the first time but at almost two feet long that is asking a bit much.

I think that is relative to the insulative properties of your forge. The less heat you soak out through the walls, the more you have left for the interior and the work piece. My new forge has a pretty big interior and I can still get it up to temp pretty easily with two inches of wool all the way around. If I was interested in doing much more than 2000F I'd be tempted to add a second torch but then I'd start exceeding the capacity of the wool liner. Recommended forging temperture for the tool steels that I play with is around 1700-1900F so I figure I'm golden. You can weld at 2000F if the atmosphere is right.

Doesn't sound like the bricks I can get around here. I'd have to order on line for the good stuff and there goes your savings in the shipping costs.

I'm betting it's not real flux resitant either...
GA
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snipped-for-privacy@rgs.uci.edu wrote:

Just buy them. They are called "half splits" if the guy I bought mine from was using the correct term. A little thicker than 1/2 inch, but suitable.
Cheers Trevor Jones
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I've gotten fed up with all the crumbled pieces of hard fire brick I've got laying around. The don't stand up to high temperture very well. They are heavy too. I'm looking for a rigid bottom that is insulative and lighter. Don't know if Mizzou has any less mass but I can form it thinner and custom fit it.
GA
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Kyle J. wrote:

I think the hard fire bricks you are talking about are slightly different to the hard fire bricks I get, let me explain.
The K23 is sometimes considered a hard fire brick, and as opposed to the K26 and K28 it is harder, but it is not what I consider a hard fire brick, as I can shape these with a spoon. All of these bricks crumble eventually.
I use the fire bricks you can get at the BBQ store, and these bricks are a little over 1/2" thick and you would need a brick bolster or diamond saw to cut them. They are usually a tan colour, dense and non-porus. You will not be able to crumble these bricks when operating at forge temperatures. They will crack if you direct a really hot flame directly at them, but it takes a few goes to do this.
However borax will eventually melt a hole through this kind of brick, I've almost managed it, but I think it will take another 3 years for me to do with my current work schedule.
Regards Charles
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Well, I was beginning to think you were talking about some higher quality material purchased on the internet or from a refractory supplier. Now that you have clarified that I'd have to say that you are probably talking about the same ones I am. :-)
I can get these from one of the local hardware/lumber yards and have been told you can find them at a barbique store. My very first forge attempt was a stack of these things. You can probably guess how that went. It's been my experience that they crack under a couple of heats - or less - and continue to crack over time. Don't much like them myself and don't use them as anything but temporary work structures now. You can build more heat resistant but less flux resistant bricks from perlite and and fire clay... Fire clay mixed with sand is supposed to make a pretty flux resistant material. Haven't tried this but I probably should.
GA
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For what it's worth, my forge floor is a chunk of alumina kiln shelf from a pottery supplier. It's stood up well to all the abuse I've subjected it to, including various kinds of molten-metal spill and a bit of flux.
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