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Flare Cone question??

Matt Watson

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I need some opinions. I have finished the shell of my new forge and will soon be starting to fill it with the insulation. I know its over kill but I'm using 2''Kao Wool with hardener to help support the 2'' ITC 100 HT. The outside dimensions are 14L x 13W x 13H. The final inside dimensions will be 14x5x5 350ci total for a 3/4'' single burner Ron Reil design (might change to a ''Mikey burner'' if I can get the time to go ta a buddy's machine shop to build it). I have been thinking of casting the flare cone into the refractory instead of a standard hole for it to fit down in. I'm thinking the mixing tube will be inserted through the top and 2'' of hardened Kao Wool then the end of the tube would come in contact with the start of the refractory and sit flush against it. The first 1/2'' - 1'' of the refractory would be cast at the 3/4 diameter of the tube then the last 1'' -1.5''  of refractory would be flared as the cone shape ( I thought I would just use a piece of plastic from a milk jug glued or tapped together as the mold to form the refractory around) . I'm thinking doing it this way would allow for me not to have to change flare cone periodically due to heat exposure and cycling. I've included a picture of the shell, material thickness is 1/8''. For those of Y'all that have more experience than me (probably everyone on here) would this work? Would you change anything? What length would you cast the flare cone 1'' or 1.5'' or would it matter?  I would just like to have some other people opinions / expert advice before I proceed any further. I can change the interior design if needed or something would work better. I also wondered if maybe an oval shaped interior would work better than rectangular?  Or maybe even Bowl shaped? The base is separate from the top so I can shape it any way that I want and for ease of maintenance. Thanks in advance!!


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If you use a Rile burner with a cross pipe with a hole in it, you have to use a tapered flame retention nozzle. But if you put a .023" MIG tip in the cross pipe, than you can use a stepped nozzle, making an end urn around all this awkwardness, while creating a much hotter burner. Go back to his burner pages and read up on my directions on how to do it. Don't forget to use the recommended 2" X 3/4" reducer, or it won't work.

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Hey Mikey thanks for the idea. I use a 1.5" with a 1/4 end plug drilled and tapped with a .25 MIG tip. That is centered with 4  1/4 ×20 bolts. The mixing tube is 8" and the flare cone when outside my current forge is a 3/4×1" reducer but the way I have it in my current forge it goes into the soft fire brick halfway and the last inch of it is ground to a taper  creating the cone. That's what gave me the idea for casting the new one. I'll have to look back and see the step design your referring to and see what to use and try it on my burner before I start this new one. A step would be alot easier to do and hotter is always better well maybe not anyways!

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No typo. From what I've seen most use just a thin coating due to the high cost of the material and high shipping cost. I purchased a pint which according to the label will cover a 5ft square area 1' thick. Which would give me enough to do what I'm wanting to do with a little left over. I figured instead of a thin layer that would be more susceptible to cracking, a thicker more solid foundation of the material would possibly last longer and be much stronger. I had thought of using a cheaper castible for the entire forge then using the ITC as a coating but most that I read about crack and break apart a lot quicker than those that had used a thicker amount of the ITC.  

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NO, one pint of anything won't cover 5sq. ft. 1" thick. 1lq.pt. US = 28.88 cu/in.

I sq.ft = 144 sq.in. x 5 = 720. 720 sq.in 1" thick most surely can't come out of ONE pint can.


Even if you went to the expense to buy enough ITC 100 to cover your forge 1" thick it wouldn't last. That isn't what  ITC 100 is designed for, its a release agent to prevent junk in furnaces from sticking, think glaze in a pottery kiln.

However, once you choose a proper castable refractory, (might I suggest Kastolite 30) casting the burner flare into the liner works well.

It's a good idea you just have the wrong material.

Frosty The Lucky.

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Frosty thanks for the reply. I looked back on their website and it says a pint covers 6.5-12.5 sugar feet. It doesn't specify a thickness on there. I'm not sure where I got that 1" from but i thought it was on their website. They have the 100 listed as a coating material and a castable and the 296 as a top coat but it doesnt really specify the difference between the 2. I sent them an email to inquire a little more details on the differences and as to weather the 100 is actually a bulk castable or just meaning it can be shaped. But now that you have pointed these things out and suggested the kastolite 30 as an alternative. I think I may just go that route and then use the 100 as a coating like you stated. Then I'll have plenty left over to coat a ribbon burn keg build that I'm thinking about. 

I'm curious though since you have experimented with alot of burners along with Mikey and yalls along with Ron's seem to be the top designs. Have you ever tried a single orafic with a y split at the burner end? The reason I ask is I put a t reducer 1"×3/4" at the end of my burner the other day just to see if it would work and it did. The flames weren't as stable as a single flame but they worked, I'm assuming because when the air and fuel mixture hit the end it created an eddy current like in the ribbon burner. Do you think it would be possible to do the y split with two steps or tapered flares roughly 3 inches apart? I thought maybe a design like this could reduce the case of cold spots in some forges or maybe even step the orifice diameter up and run it like a fuel burner? I may be completely off base though.

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Frosty also said the ITC100 won't last, in his post.  It is not designed for this and it flakes off quickly.  Wayne Coe sells Metrikote and Plistix and Larry Zoeller sells Plistix.  Both options are better options for the hot face.  

On the kastolite, it is recommended not to over kill it.  It is used to armor the walls against clumsy hands hitting the walls with the metal and to cover the fragile hazardous blanket from the flame.  Add enough to be protective but no more.  As you add more, the forge requires more fuel to heat, it takes longer to preheat/cool down, and it can reduce the maximum temperature it can reach.  I have seen recommendations between 1/4 - 1/2 thick layers.  I use 3/16 inch currently and it is tough enough for the occasional bump but I am careful when placing my iron in the forge.

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I am now starting to get a little confused with the refractory choices. I thought the ITC 100 HT was supposed to be the best stuff out there due to its insulating capabilities reflecting the heat back in and reducing the overall cost of fuel. This is the main reason I was wanting to overkill this forge I figured spend the money up front to build it right then it will save in the long run. From what I'm reading on both the Metrikote and the Plastix they are used as an insulator final coating like most have done with the ITC 100 HT. According to ITC website the 100HT can be used as a coating or a castable refractory. My interpretation of that is that you can mold a thick base etc. if you choose to do so. I did email them for clarification to be sure, but I haven't heard back as of yet. It also stated on their sight that a pint will cover 6.5-12.5 sguare feet but as Frosty pointed out a Pint wont cover but 28.88ci. So I don't have enough for what I had originally planned on doing. The 2'' Kaowool with the rigidizer will help insulate it but the castable material whatever I end up choosing will need to have an insulating property as well, and I will add a final layer 1/8'' thick of the ITC 100 HT for maximum insulation capabilities. The Kastolite 30 that Frosty recommended seems to be what I'm thinking I will go with since I have 1,008 ci to fill and according to Zoeller's site 1lb of it will cover 18 ci so I would need 56lbs to cover the area I'm wanting to do without the ITC or 55lbs with the 1/8'' coating. Or I could do 3'' of the Wool and just 1'' of the refractory. My main goal is fuel saving, then durability second. I have several of the K 26 soft bricks lying around and that's what I currently use but I was tired of replacing them.    

The Rigidizer I bought for the Kaowool doesn't have a name as far as brand but I got it from Clay Planet $11.95 a quart. I copied the properties of it from their site if you or anyone else is interested.

Physical Properties:
Color clear
Solid content, % silica (approx) 28 - 29
Weight per gallon, lb (kg) (approx) 10 (4.5)
Nominal density, (wet), pcf (kg/m3) (approx) 75 (1202)
Maximum temperature rating, °F (°C) 2300 (1260)
Freezing temperature, °F (°C) 28 (-2)
Viscosity, centipoises @ 25°C 4
Specific gravity @ 25°C 1.203
pH 9.7

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If your main goal is fuel savings, there a lots of ways to accomplish that.  Several have nothing to do with your insulating choices. 

The insulating properties of the kaowool win over all the castables and bricks for insulation value and lack of mass.  The downside is that it is fragile and when heated, breaks down and creates hazards you don't want to be breathing.  Usually 2 inches is recommended.  There has been recent discussion about 1 inch being enough and also some talking about trying 3 inches.  With 2 inches, I can hold my hand on the shell of my forge for a few seconds after it has run for hours.  Three inches might provide some savings but I wouldn't expect it to be much.

The reradiating coatings (like ITC) are used to increase internal temperatures inside the forge.  The coating absorbs energy, becomes very hot, and radiates that energy to heat your work.  ITC is a poor choice in that it breaks down quickly in the forge environment and is expensive.  People are happy with Metrikote and Plistix which serve a similar function.  A thin coat is better then a thick one.

You could put the coating directly on the rigidized blanket.  This would prevent the hazardous breathing situation and produce a forge which heats very quickly to highest temperatures.  The walls are fragile to bumps.  If you are clumsy with metal placing, it might break through and require patching.  

This is where kastolite comes into play.  It is tough at high temperatures.  It is somewhat insulative but it is also mass.  This is added to toughen the walls at a cost of fuel efficiency, heat up time, and maximum temperature.  The thinner you can get away with, and still armor properly, the better.

There is one caveat though, these rules of thumb are if you are a typical hobbyist user.  If this forge is to be heavy used, with lots of metal through it quickly, and it is not shut off often, more mass can be helpful in stabilizing temperatures.

A general recommendation which several have reported happy results with:

  • 2 inches of rigidized kaowool
  • 1/4 - 1/2 inch of kastolite 30
  • thin coating of Metrikote or Plistix

Your shell is very large, you could fill in the extra volume with rigidized perlite.  Mikey had recently talked about it in Forges 101.  I have never tried it though.

Other ways to save fuel:

  • Better burner design (Ron doesn't use Reil Burners anymore)
  • Proper baffle walls
  • An idle circuit (big savings for me)

As to forge shape, I have never built a forge with square corners but Mikey is usually advising against them.  He tends to uptalk the oval shape quite often.  Square corners do bad things to flow dynamics.  With your current shell, if you suspended the blanket with perlite, you could roll the blanket to create a more rounded interior.  The next big question you should be asking is how are you mounting the burner in what position.  Square forges tend to have the TDC mounted burners which Mikey also advises against.  

This is not intended to be discouraging at all.  Hopefully any of it is helpful in getting you to a hotter forge.  


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Matt: You're making a common mistake we've all (or most of us anyway) have made. A forge, especially a propane forge is a wear item. A propane flame at forge burner temperatures is VERY chemically  aggressive. It WILL wear out so trying to make one that'll last more than a couple few years get's expensive on a geometric scale and proves futile.

ITC-100 and other kiln washes are NOT insulators. ITC 100 is a release agent designed to keep stuff from fusing itself to furnace walls. It's approximately: 70% zirconium silicate and 30% kaolin clay. For some reason the kaolin won't fuse solid so ITC 100 stays like a layer of chalk and flakes&rubs off.

Matrikote and Plistex are also kiln washes but are not release agents, they're made to be flame faces and armor furnace liners. Again they are NOT really insulators though they conduct heat more slowly than some things. They aren't subject to the high temp chemistry erosion of propane and welding fluxes and they're HARD at welding temp.

That's what these particular kiln washes do. ITC 100 keeps stuff from fusing to your forge and does protect it from welding fluxes but does NOT provide mechanical armor. 

Matrikote and Plistex are not release agents, molten stuff WILL stick to them but they're tough, chemically fairly inert to what we're LIKELY to put in a forge. They provide  mechanical and to a lesser degree chemical armor.

Yes, you can kiln wash Kaowool or other ceramic blanket refractories, In fact my crazy silly too large shop forge has a roof of pleated Kaowool kiln washed with ITC-100 and has held up to all but getting poked and scraped for better than 10 years now. 

A number of us have been experimenting with home brew kiln washes and hard refractory liner recipes. As it stands it looks like 2-3% Bentone or Bentonite and 97-98%  zircopax fires to a HARD ceramic that is chemically and mechanically robust. The mix in various %s is in common use for high temp crucibles. 

Zirconia in one of it's various useful to us forms conducts heat slowly so it gets HOT and holds it. I think of it like a HEAT BATTERY and use that idea as a working handle. It sheds heat though slowly, spherically. If it's in a 2D layer as a kiln wash over another refractory, it's ability to shed heat is restricted. First by the equally HOT zirconia next to it in the plane, it can NOT shed heat that direction. Being bonded to a refractory behind it gives it a potential direction to shed heat but if it's a high efficiency insulator it runs into a hard push to shed heat. 

So, the easiest path to shed energy and energy ALWAYS takes the path of least resistance is to re-radiate it back into the open space of the forge.

ITC 100 would work very well as a forge kiln wash IF it was a hard finish but it isn't.

I don't have Matrikote or Plistex to play with or I'd see just how little I can get away with in a mix with zircopax and still get a HARD kiln wash. 

I have plans for a new forge specifically for the ribbon burners and am planning on making a flame face of 4 pts zircopax to 1 pt. Kastolite. and back that with 1/2" of Kastolite 30. 3 pts. zircopax to 1 pt kastolite with the aggregate sifted out has worked nicely for the flame face in my last forge. 

I'm not suggesting you experiment, there are proven forge designs on Iforge in the "Forges 101" subsection of the "gas forge section" of Iforge. I can't help redesigning things, it's how my mind works I redesign EVERYTHING I see, use or hear. I think some ideas are good and should be law. Say I think every inside door release in vehicles sold should be identical. Same for seat belt releases. If you've ever struggled to find the door latch and seat belt release in a burning car you'd know exactly what I mean. I carry a SHARP pocket knife everywhere and am darned jumpy on airline flights because it's checked. 

Sorry about the side track, I can't help that either. The point is, don't experiment or try and mix and match designs till you have a GOOD handle on how they thing work and know what you need. Yes?

Splitting the output of a home made naturally aspirated burner. Uh HUH, no luck here, I couldn't even get a fan nozzle to work and the last one I tried before giving it up as a game of silly buggers, was only slightly fanned. A "normal" flare flattened about 1/4" and widened to  make up for the volume change so it still had the same 12% increase in volume. Pfffft, poor performance and no worthwhile modification of the flame in the forge.

It's why I started messing with the ribbon burner. 

I know I probably made this more confusing, I hope not but the take away in short is: keep it simple and use a proven forge & burner design WITHOUT trying to mix and match. When you're beginning you just have to take people's words for some things. Just be careful of who's word you take. Youtube is NOT the place to learn unless you already know what to believe.

We'll help.

Frosty The Lucky.

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Hello Frosty, I understand completely about your thoughts on the car handles, seatbelt latches and knives. Being a police officer the past 12 years I've seen a few that couldn't make it out of a burning car and burned myself in the process of getting a guy out once. But back to the topic. So the best insulating material for forges is Kaowool but you need a hardener for longevity, and the ITC 100 isn't useful except for its radiant abilities so only a thin layer would be useful. I want to be able to keep the heat in the forge as much as possible just as everyone else. That's why I was thinking 4" of thickness. I was thinking doing that it would also keep the body of the forge cool to the touch. Doing a little more digging talking with you and others. I'm now thinking I will use the wool with rigidizer and then about 1/2" - 1" of castable and coat the lining with 1/16"- 1/8" of the ITC. But also go away from square to oval shaped. Should be interesting trying to get an oval inside a square but I may just start all over an turn that body into a wood stove to heat the shop. 

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Keep in mind that the thicker your castable refractory "armor" is, the longer it will take to bring your forge up to temperature and the longer it will take to cool down afterwards.  If you plan for all your forging sessions to be a minimum of several hours long then you may want to go that thick, but if you want to fire up the forge and be banging on hot steel in 20 minutes you may want to keep it on the low side of a half inch. You might want to go a little thicker on the floor than elsewhere though.

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I've been first on the scene of burning vehicles three times, the worst was a roll over that crushed the door down enough we couldn't open it the driver was hanging upside down from the belts when it started burning. I can't tell you how glad I was we were in a ditch where I could soak my shirt sleeves and cotton monkeygrip gloves so I could reach into the flames long enough to cut the belts. Fortunately rolling down the ditch a couple times had soaked him in mud and water so the few seconds he was in the fire didn't burn him . . . apparently. He was breathing on his own when we got him up on the shoulder so he maybe didn't breath flames.

Anyway. If you already have the ITC, use it, there's better but if you have it. . . Yes? If not, the money can be better spent.

Two 1" layers of ceramic blanket keeps the outside of my forges from burning you if you touch them and that's good enough for me. More insulation might be better but I don't think it's significantly better. Rigidize it for sure both for durability but more so to ameliorate the breathing hazard. When I cut Kaowool I just wet it down so loose fibers can't drift and I wet it before rigidizing or covering with Kastolite. Masons call it buttering and it makes a real difference.

1/2" hard refractory seems to stand up to the ham handed in my forge and we have a few in the club. A little more or less. . . Why not? Real thick, say 1" and more would be appropriate if a person were moving a lot of stock through the forge as the extra thermal mass acquires and holds more energy. Longer to heat and cool just is in that case and you'd be running it all day anywho.

I usually recommend ITC and other kiln washes be applied (brushed on) at the consistency of thick latex paint. Make it thicker in thin coats and allow it to dry between them. Thick coats at once tend to check and flake. It's like painting a car, lots of thin coats = nice:), one thick coat = runs drips wrinkles and flakes. :angry:

Do the burner ports the same way, make the hole in the blanket about 1" wider than the end of the burner, rigidize, plaster with hard refractory and kiln wash. It can be most any shape you like though I couldn't get a wide flat flare like you get in a bernzomatic kit, to work worth didly.

Frosty The Lucky.

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