Castable over Soft Brick?

[Robert Simmons]

I was thinking of a way I would put a castable roof for the variable volume forge I am adapting from Frosty's design and I was trying to think of a way that i could make a lighter weight roof than simply casting the whole thing. Frosty use Pleated kao wool but it doesn't seem that he would do it again from our conversations. So my idea was kind of simple.

Basically I would build a box the Size of the roof out of angle iron placed one on top of the other so that it makes a T or perhaps a piece of a small scrap i beam. The idea is that the angle iron would extend into the castable and help hold it in place giving it support. Then I would put the frame over a piece of hardboard coated with oil for release agent and fasten it down. I would then pour a 1" thick layer of castable. After that (and while still wet) I would place in firebricks separated by about 1/2 an inch channel between the bricks. Then I would fill up the channels and put another 1" of castable on top of the soft bricks and smooth off then let the whole thing harden.

So what do you think, would that possibly work or am I kind of nuts here? If so, then why?

Thanks in advance.

[Mainely,Bob]

I would look at how industrial furnaces are constructed and use some of the ideas there.

The quick story is that whatever anchor you use needs to stand up to heat and be buried in the refractory.
My experiences repairing foundry furnaces told me that you want to allow for expansion and distortion when heating and cooling take place.Rails and solid forms tended to rack and break things.Isolated single points and/or flexible mounts that moved independent of both the shell and the core lived longer.Many times we used simple stainless bolts with a nut and washer on the outside to hold the refractory.
The furnaces I worked with were also built up from soft brick sides with anchors embedded(hard brick over soft for the floors to take the abuse) and then coated.It was a given that the shell would fracture some where down the line so they used something that bonded well to the brick and even if it fell away in areas the brick remained in place till repairs could be made.
These furnaces ran 24/7 and were only shut down to load or for maintenance/repairs.

Hope this was of some help

[arftist]

Two thoughts, first, could you use a kiln shelf? They are strong, long lasting and reasonably priced. I have some that are about one square foot.

Second, yes you can cast your own top. I would build the frame simply from angle with the legs oriented in on the bottom, the make up a mesh of sorts of stainless steel rods (threaded rods would add some serious teeth), 3/16" or 1/4" diameter would be plenty, but space them close, perhaps create 2" squares in a grid. Weld the stainless rods to the inside of the angle frame, about halfway up.

As Bob said above, it will not last indefinitely, but it will work.

[kcrucible]

You could certainly do it (I did castable over wool... if it can work on wool, it can work on a nice solid brick!)


The big trick is going to be how to get it to adhere. Embedding screws or something MAY work in the short term, but exposing steel to near-welding heat is probably not going to work well in the long term.


One trick I can think of is similar to a trick I did to create a "hook" which is solidly affixed to a chunk of polished rock. You could use a drill to put a couple of holes in the surface of the brick and pivot it around to create a slightly larger cavity inside the brick than the neck. The deeper you make the hole the stronger it's going to be. Maybe a 1" drill bit, with a 1.75" hollow, or something. Put a side mould on the edges to allow you to put 1" - 1.5" of castable on "top" of the brick, where the castable will fill the hole. Allow a lot of time to set and solidify, then do a bake-out in your oven at 550 to strengthen it.

[Toreus]

I made a "button" out of soft firebrick, put a high-temp wire through it and coated the entire thing with high-temp cement (to prevent the wire from oxidizing away). That held my ceramic blanket in place really well until I got the forge hot enough to melt the retaining wires (and the work I had in it at the time).

If I was to do it again, I'd probably put chicken wire (or even better, a mesh of high-temp wire) between the first and second layers of blanket, attach that mesh to the shell, and hope that some more high-temp cement would be enough to glue the insulation to the mesh.

Same thing might work with castable- when it cracks, it might hold it together regardless, sorta like rebar with cement.

[Sweany]

just some ideas, the soft brick is easy to cut..

http://www.ozarkdreams.com/oven_chamber_top.htm

[tlreif]

Are you asking about this because you already have these materials? Because if it was me, I would use the refractory board. It is rigid enough to stand up to your design. In fact I would use 2 layers for better insulation factor. Just a thought.

[Robert Simmons]

Are you asking about this because you already have these materials? Because if it was me, I would use the refractory board. It is rigid enough to stand up to your design. In fact I would use 2 layers for better insulation factor. Just a thought.

The problem is that stuff is horribly expensive and has a quite low temp rating. I looked into that and decided I could pour a 2" layer with about 1/4 of he cash. I would like to get some more specialty stuff like high phosphate bonded ut I have no idea where to get that.

[tlreif]

You Must be going to get it really hot! I use it in my forges and have never had any issues with it. As for the expense 120 bucks for a 2 foot by 4 foot piece is not bad in my book. considering that will build a lot of forge. Good luck and keep us posted on your progress.

[Robert Simmons]

You Must be going to get it really hot! I use it in my forges and have never had any issues with it. As for the expense 120 bucks for a 2 foot by 4 foot piece is not bad in my book. considering that will build a lot of forge. Good luck and keep us posted on your progress.

I would like to get it to forge welding temps, perhaps use it also with a crucible for a melt of aluminum, brass, etc as well. So yeah, I want it hot.

As for the cost, clearly you are better in the area of finances than I.

[MattBower]

Robert, the large amounts of castable that you seem to want to use are going make your forge much, much slower to get up to temp. Even insulating castables tend to have only about half the insulating value of ceramic wool, and dense castables like Mizzou are closer to 1/4. Unless you tend to run the forge for long periods at a shot, that's really going to hurt your efficiency.

[Robert Simmons]

Robert, the large amounts of castable that you seem to want to use are going make your forge much, much slower to get up to temp. Even insulating castables tend to have only about half the insulating value of ceramic wool, and dense castables like Mizzou are closer to 1/4. Unless you tend to run the forge for long periods at a shot, that's really going to hurt your efficiency.

Perhaps but i am struggling on how to get a roof that is large enough to cover more than spanning over one brick. I need osme sort of solid roof and I am not sure how softw bricks could be made to do that with the burners going through the soft brick. If you have any ideas, I would love to hear them.

[arftist]

http://www.sheffield-pottery.com/Kiln-Shelves-s/110.htm

Cone 10 is almost 2400 degrees. I have been using these for many years. They can be easily drilled with a cheap carbide tile holesaw available in hardware stores.

[Robert Simmons]

I am now thinking of perhaps taking the KAO wool I have and coating it with something to turn it into a fire brick. I hear there are KAO wool rigidizers that make the KAO wool stiff so that it can hold its own weight. If that was the case I could coat it with a rigidizer, put another layer on and rigidizer and finally on the top I could put a thick coating of an ITC coating to make it more thermally efficient. It would be pretty easy to cut holes in the top and I could put in three to four inches of insulation without really buying much at all. I just have to figure out the right materials to essentially turn soft KAO Wool into a hug insulating brick.

Castable forge flares are also a thought. I wonder if anyone has done those.

[Dodge]

I am now thinking of perhaps taking the KAO wool I have and coating it with something to turn it into a fire brick. I hear there are KAO wool rigidizers that make the KAO wool stiff so that it can hold its own weight. If that was the case I could coat it with a rigidizer, put another layer on and rigidizer and finally on the top I could put a thick coating of an ITC coating to make it more thermally efficient. It would be pretty easy to cut holes in the top and I could put in three to four inches of insulation without really buying much at all. I just have to figure out the right materials to essentially turn soft KAO Wool into a hug insulating brick.

Castable forge flares are also a thought. I wonder if anyone has done those.

If you are concerned about cost, ITC will kill you trying to put it on "thick". Its really just designed for a reflective coating. I simply used refractory mortar thinned to a thick milk shake consistency and applied a couple layers with a rubber gloved hand over my ceramic wool to build up about 1/4" to 3/8". Its rated at 3000 degrees and is quite durable. I found that my single 1.25" blown burner will actually melt steel even at the lowest regulator setting. I wasn't trying to melt; Just not paying attention

Pic attached is at 3 psi

[Sweany]

Dodge, I like it! B)

[Frosty]

That's a seriously hot looking mailbox you got there Dodge. I hate getting bills too, wish I'd thought of that!

There are a few ways to take care of the breathing hazard Kaowool can cause.

Using a rigidizer or other stablizing coating is easy and pretty sure fire. I do something similar to what Dodge lines out. I have some Kaolin clay I've had for years, some is mixed as a thinish slip so it'll soak into the Kaowool. Once dry it fires HARD and makes the refractory less suseptible to flux. Kaolin being a high alumina clay.

Over that I'll apply ITC-100 for increased efficiency but ITC-100 alone will really reduce the airborne particles.

What I did some years ago was to make a double lined forge. The inner liner was Pyramid Super Air Set 3/4" thick. Surrounding the hard inner liner was the 1" 8oz. Kaowool insulating outer liner. Both were contained by a steel pipe shell so no Kaowool was exposed in open air.

Recently however a new and maybe superior solution has come on the market, soluable refractory wools. These refractory wool fibers simply disolve in your lungs if breathed so there's virtually zero chance of silicosis or mesothelioma. A web search of soluable refractory fibers should tell you more than you ever wanted to know.

Frosty the Lucky.

[MattBower]

Recently however a new and maybe superior solution has come on the market, soluable refractory wools. These refractory wool fibers simply disolve in your lungs if breathed so there's virtually zero chance of silicosis or mesothelioma. A web search of soluable refractory fibers should tell you more than you ever wanted to know.

I almost mentioned this, but the OP is concerned about asthma, and that may be a somewhat different set of problems than the typical issues with ceramic wool. Still, if it's any help, I know one place you can buy the "safe" stuff is from High Temp Inc., on eBay.

[maddog]

Thats a very nice setup you got there Dodge. Very straightforward and very effective. You have some serious hot in there! I like the way the grinder seems to be staring at the fire the way sunflowers track the sun .

Can you give some details about the square framed face with the mail box opening? I'm guessing wool with a coating of mortar or refractory slip?

Thanks.

[Robert Simmons]

If you are concerned about cost, ITC will kill you trying to put it on "thick". Its really just designed for a reflective coating. I simply used refractory mortar thinned to a thick milk shake consistency and applied a couple layers with a rubber gloved hand over my ceramic wool to build up about 1/4" to 3/8". Its rated at 3000 degrees and is quite durable. I found that my single 1.25" blown burner will actually melt steel even at the lowest regulator setting. I wasn't trying to melt; Just not paying attention

Pic attached is at 3 psi

What about that temp and what id did to the fiber? Any idea? I was wondering if I visited HiTemp on ebay and used 3200 degree mortar over2372 degree bio-safe fiber blanket with rigidizerand topped it all off with a thin coating of ITC-100. Would that hold up to forge welding temps? Would the mortar and ITC-100 shield some of the heat from the fiber and make it hold?

I am trying to build a flat top for a variable volume forge (based off frosty's design) and possibly even a bottom plate as well. The idea would be to lay out 4" thick of blanket in two layers into a frame made of 1/4" wall x 2" angle iron. The blankets would first be cut for the 5 burners in the 18" x 18" flat top forge and cut carefully so I have plugs to use when a burner hole is not in use. Then I would stack them up and ridigize them one at a time. Then I would put them in the frame and start to cover with mortar and build that up to say 3/8ths or even 1/2" thick. Finally all hot surfaces would be coated with ITC-100. The only things that make me worry is thermal cycling of the mortar and having it not crack and fall in the forge (at least not too quickly and finding a way to bond the mortar to the frame since the whole thing will be basically upside down with the frame on top. For the bottom, I wouldn't want the ceramic fiber to be crushed with items in the forge nor would I like it to be disolved by flux.

What do ya think?

[Dodge]

What about that temp and what id did to the fiber? Any idea? I was wondering if I visited HiTemp on ebay and used 3200 degree mortar over2372 degree bio-safe fiber blanket with rigidizerand topped it all off with a thin coating of ITC-100. Would that hold up to forge welding temps? Would the mortar and ITC-100 shield some of the heat from the fiber and make it hold?

I am trying to build a flat top for a variable volume forge (based off frosty's design) and possibly even a bottom plate as well. The idea would be to lay out 4" thick of blanket in two layers into a frame made of 1/4" wall x 2" angle iron. The blankets would first be cut for the 5 burners in the 18" x 18" flat top forge and cut carefully so I have plugs to use when a burner hole is not in use. Then I would stack them up and ridigize them one at a time. Then I would put them in the frame and start to cover with mortar and build that up to say 3/8ths or even 1/2" thick. Finally all hot surfaces would be coated with ITC-100. The only things that make me worry is thermal cycling of the mortar and having it not crack and fall in the forge (at least not too quickly and finding a way to bond the mortar to the frame since the whole thing will be basically upside down with the frame on top. For the bottom, I wouldn't want the ceramic fiber to be crushed with items in the forge nor would I like it to be disolved by flux.

What do ya think?

I personally, wouldn't used wool, even coated with mortar for a forge floor. However, once the mortar (I used AP Geenpatch421) has saturated the wool, it won't fall off in normal use. It may crack (most likely will crack as the first couple coats dry) but thats easily fixed by smearing more mortar over it. Thin multi layers letting each dry before the next works better than on big thick layer. As long as I don't poke the walls with materials, it holds up well. If I poke a hole, big deal! patch it with more mortar. One hole is not going to cause a melt down the first run. Which , BTW hasn't happened with it getting so hot as you asked. The Greenpatch is rated for up to 3000 degrees.

[Dodge]

Dodge, I like it!

Thnks

That's a seriously hot looking mailbox you got there Dodge. I hate getting bills too, wish I'd thought of that!

Frosty the Lucky.

Yup Frosty. Keeps those pesky rascules at bay
I think I have figured out why the forge won't get that hot at higher gas pressure. I believe my blower is under powered and the flame gets too rich to get much hotter at higher pressure. This hasn't always been the case however. I wonder if my fan is starting to fail. OTOH, Imagine how hot it might get if I put a stronger blower on. Can you say "China Syndrome?"

Thats a very nice setup you got there Dodge. Very straightforward and very effective. You have some serious hot in there! I like the way the grinder seems to be staring at the fire the way sunflowers track the sun .

Can you give some details about the square framed face with the mail box opening? I'm guessing wool with a coating of mortar or refractory slip?

Thanks.

Thanks MD. Yes, the door(s) are just as you guessed. The inside of the forge is basically round. I just chose the "mail box" shape so I had a flat surface for stock to sit on.

[pkrankow]

Just a thought, but kiln shelves are available in up to 24 inch widths.

http://columbusclay....m#Kiln_Shelves_

Phil

[stretch]

I have always had 1 burner in my forges and the last one I built I put 2 burners in. The refractory didn't last at all. It got way hotter than normal and something I had never heard of "Thermal Shock" was killing the refractory. The forge or oven mentioned earlier lasted longer because it ran 24/7. No thermal shock because it never shut down. I talked to a friend that had worked at brick making when he was younger and he said they never shut them down and when they did they shut down over a week. Now I have learned about thermal shock I have turned my forge down and it is lasting a lot longer. If I do turn it up to heat something real fast I turn it down and run it cooler before I shut it down. Works so far. Experiment still in progress so will know more later. From what I have learned thermal shock is the killer of refractory, not the high heat, if you use 3000 degree refractory or close. I tried soft brick one time and went very quickly back to insulating castable which I still use.
I hope this is clearer than mud.