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Gas forge refractories and where they go


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1)  The shell is the container that holds the blanket, etc that makes the forge. The propane tank will be the shell. Yes?

Next comes 2 layers of 1" 8lb. Ceramic wool refractory such as Inswool insulating blanket. Kaowool is another product but is becoming a term for the wool refractory. It's a high temperature insulating layer made from ceramic fibers.

Next the rigidizer both stiffens the ceramic wool refractory and contains the fibers so they don't break free and drift in your air. The stuff is a breathing hazard and can do permanent lung damage.  Ceramic Wool Insulation, Safety Alert

The hard refractory comes next and provide armor against both heat, flame and mechanical damage being poked and scraped by work going in and out. Kast-O-Lite 30 works well in around a 1/2" layer but some guys like 1/4" others more.

The last is a kiln wash painted on about like thick latex paint as a final bit of armor and IR re-reradiator. (meaning it gets really hot and radiates heat back into the forge).  IR reflective coatings are Plistix or Metrikote.

 

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  • 5 months later...

I made a small propane forge using 4 large white soft bricks. What type of brick or other insulating brick can be placed on the floor of the forge that will withstand Flux and not melt?                                            

 I place a hard 2200 deg F brick in the bottom. The flux didn't affect the brick but the brick melted! That was a clue to find something else to place on the forge floor. 

The white high temp brick on the top of the forge cracked and then melted like a candle and dripped down into green glass puddles.

Flux eating the firebrick is a great reason to use a coal forge.

 

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High alumina and/or zirconia castable refractory, or a precast high alumina split brick or kiln shelf.  Reportedly Kastolite 30 has some flux resistance, but I haven't tested it myself.

Oh and you should use 2600 rated insulating brick for a forge inner layer. You will melt 2200 even without flux at high forging temperatures,  not to mention the flame tip.

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  • 6 months later...
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  • 3 months later...

Where in the build would insulating k26 rated fire brick fall?

Following that simply because I'm a beginner, minus the fact that I am a vacuum furnace operator for a heat treatment facility.  

Does the kiln wash go on top of the refractory? 

If so, isn't that like 3 identical components on top of each other which considering their application of being refractories aren't they negated by the outer layer?

What I mean is you say the rigidizer to firm up the ceramic wool but rigidizer from my understanding is usually of silica and or kaolin clay as a base and most are in addition ones that contain high alumina and zirconium. So then what would be the purpose of adding another hard refractory layer on top of that that is as well high alumina and zirconium which If I understand that reflective refractive. But then you finish with the kiln wash for another layer of the same things.

 

There are a few , here's o be I saw.    Commercial link removed per TOS  That are pastes or like I assume you mean by the kiln wash..  why wouldn't a thick layer over the top of the ceramic insulation be sufficient for the forge. 

And do you ever combine ifb firebricks with the refractory and kiln wash section mentioned?

 

I just wanted to say after wasting hours and hours on YouTube watching pure ignorance on building burners that I only.got one to work after reading your book at the very least I wanted to say thank you because every moron spouting out terms like hotter and insisting on a reducing coupling to increase the pressure who then proceeded to define the reason that works never understood how he didn't catch the fact that what goes on is what comes out. I wanted to strangle so many people

 

 

Edited by Mod30
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Welcome aboard Sanpan, glad to have you. If you'll put your general location in the header you'll have better luck connecting with folk living within visiting distance. Much of the information is location specific so it really makes a difference.

You should maybe forget the nonsense you read other places online and do a little reading in the Forges 101 sub section here it contains the most current information and discussions.

I have to assume you aren't an American English speaker your questions are put together in an odd way to how we speak. I'll do my best though.

Kiln wash is the "flame contact" refractory and is the final armor between the flame and the insulating outer refractory layer.

No they are NOT 3 identical refractories. Starting with the Forge Shell, the metal container holding the refractory forge liner.

Next after the shell is the insulating refractory, whether 8lb. ceramic wool refractory or K-26 insulating fire brick. It's purpose is to slow heat loss through the liner and forge walls and doesn't withstand direct exposure to propane flame very well. Rigidizer is to stiffen ceramic wool refractories by fusing the fibers where they cross each other making it more structurally strong AND significantly reduces vitrified fiber particles detaching and floating in your breathable air.

Next after rigidized ceramic wool or IFB is a water setting, high alumina, castable refractory, the current favorite in the USA is Kastolite-30 li as it contains as part of the aggregate, evacuated silica spheres which not only make it weigh less it increases it's insulating properties. The purpose of a hard refractory inner liner is to provide armor against: mechanical damage, thermal damage to the insulating layer, and chemical damage from the propane flame and borax based forge welding fluxes.

Lastly the kiln wash is a final layer of armor even more proof against: mechanical, thermal and chemical damage. 

And NO, applying a thick layer of kiln wash doesn't work very well unless you wish to spend a lot of time and effort applying many THIN coats. Applying kiln washes much thicker than a layer of interior house paint will make it likely to flake off when heated to forge temperature. 

Lastly is an IR re-emissive  layer. This can be a kiln wash or an additive. It is a material with very low thermal conductivity and absorbs much more energy from the flame than regular refractories. It radiates thermal energy at a much higher rate than it conducts it. Zirconium silicate is highly effective as a re-emissive material though most commercial kiln washes don't contain it. There have been some encouraging experiments using a mixture of 95% zirconium silicate flour and 5% bentonite clay.

Hope this clarifies forge liners  little for you.

Frosty The Lucky.

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  • 7 months later...

Frosty, a point of clarification, if you will:

You (and others, like the sticky on the dangers of ceramic "wool") mention rigidizing that wool refractory, but I haven't seen any mention of methods or products to accomplish that goal. 

Is it assumed that you will encapsulate your wool in the castable layer?

Or is there some product or product class that specifically serves to rigidize the wool independent of castable?

Or do most available ceramic wool refractories come pre-rigidized?

My apologies for the newbie-ish questions - I have only ever forged with coal these las 5 years, but am looking into building a gas forge and want to make sure I do it correctly and safely. 

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Okay, I will.:)

Rigidizing refractory blanket has been discussed though I don't have a link at hand and it's much easier to describe it again than search out a link. I do NOT recommend you buy one of the commercial rigidizers, they're expensive, have a short shelf life ad don't work that much better than home brew rigidizer.

The current popular stuff is Fumed Silica or Colloidal Silica. Fumed is smaller particles and may be the only stuff available. Doesn't really matter so long as it's colloidal. Colloidal means the particles are so fine they won't settle out when mixed with water.

I get it for really inexpensive, about $12/ 8oz can at a local plastics supply/fab shop. It's commonly used to thicken two part resins so they can be applied without running off surfaces or whatever. 

This is NOT the recipe, I mixed a scant 1/4c in a large spritzer bottle with a couple drops of food coloring. The food coloring allows you to see where and how much you've applied the rigidizer It burns right out so you won't have to explain a pink or baby blue forge to the guys. ;)

You NEED to butter the blanket before applying the rigidizer. Buttering is a mason's term meaning wet it before applying mortar, you see masons dipping bricks in a bucket of water before laying them on the mortar. It's really important, if you apply mortar or rigidizer to a dry surface the surface will flash dry the applied stuff in contact so mortar doesn't penetrate nor "set" at the contact layer so it can't bond fully. Rigidizer suffers a similar fate if the fibers are wet the rigidizer is diluted and by capillarity draw into the blanket until it has diluted out. If the blanket is dry it flash dries on the surface and there is no capillarity at work so it just stops and it lays on the surface of the fibers for a lesser bond.

I recommend cutting blanket a little too large so you have to compress it to fit, this will hold it in place until it's rigidized and later held in place by the hard refractory. Once in place spritz it generously (don't get silly though) with water and spritz it with your rigidizer solution until the entire surface is coated. If it soaks in and disappears do it more, this is a good thing.B)

Mike recommends drilling a drain hole or two in the bottom of the forge shell to let excess water drain so it won't have to steam out as part of the curing process. I give that a hearty thumbs up. Once it's reasonably dry you want to fire the rigidizer, a butane torch works or you can just fire up your burner for a minute or so. Just until the liner reaches low red heat is good, fumed silica vitrifies at about 2,000f and being so fine it reaches vitrification conditions WAY before the things around it. Now the fibers in the blanket are pretty well welded together by fired silica.

This not only encapsulates the fibers it makes it a lot stiffer and more structurally sound. Your hard refractory liner will last longer if the surface it's resting on doesn't flex under it. Try laying a froze Hershy bar on the table top and pressing on it with a finger, nothing, yes? Now try laying one on a sponge and pressing, broken pieces yes?

Remember to butter the blanket when you apply the hard refractory for the same reasons as above. Hopefully a water setting hard refractory. Once it sets it needs cure time, just like a concrete sidewalk. It needs 100% humidity for a day or seven to reach full strength and heat rating. I've been perfectly happy leaving it sealed in a plastic trash bag with a gallon of water or so for a day and a half.

Let it dry and fire it up. If you use Kastolite 30 you don't have to DRY it, just not damp is fine and if you fire it to dull red and let it cool it's good to put to work. Commercially Kastolite products are gunnited on HOT furnace walls by guys wearing aluminized fire suits and the furnace fired right back up when the repair is made. 

The above recommendations regarding hard refractory application and cure is specifically for Kastolite 30 and applies to some other water SETTING refractories. There are refractories that have to dry and be fired like pottery, I do NOT recommend them.

Once the hard refractory is set applying a good kiln wash like Plistex is the frosting on the cake. It fires to a non-porous ceramic coating. It's high alumina so impervious to molten caustics like borax based flux and the high temp chemistry propane flame is famous for. It's hard as a Navy coffee mug so you don't have to worry about gouging it with a piece of cold steel. 

ITC-100 is great for what it was formulated for but it wasn't intended as a forge kiln wash, it stays friable and eventually rubs off.

I hope this is more clear.

Frosty The Lucky.

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Thanks, gents. 

Thomas: Point taken, and I have no doubt some of those 633 do answer the question, but after my first dozen or so mentions of it with no explanation, I decided to save myself from reading potentially 621 more that may or may not. Like I said in my post, lots of mentions (like Glenn's at the top of this post), but very few (none that I had found) explanations with enough detail to be useful. YMMV. 

Cheers,

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  • 9 months later...

I am building a forge at the moment (box shape, not round), and have a question relating to this...

- I have ceramic wool

- I have castable refractory (Vitcas 1700 deg C)

- I have some wash to go over the top

HOWEVER I DON'T HAVE RIGIDISER!

Could I just line the forge with the wool (hoping friction will hold it in place!) and then coat with the castable? Or line the bottom & sides of the forge with wool and then coat with castable, wait for it to dry some, before turning upside down to line the top part of the forge?


Cheers :)

 

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The flat roof of a box forge are more problematical though there are some tricks. You can run screws in from outside partway into the ceramic blanket to hold it in place. Not too far or they'll conduct excess heat through to the shell, annoying ore than a real problem though. 

You can find fumed silica at plastics and fiberglass supply stores, it's used to thicken resin for various reasons. There are two types be sure to get the hycrophilic type so you can mix it with clean water easily. 

Lacking that your last plan works well enough just don't try to rush the curing process or it will sag. 

A good kiln wash as a final layer of armor is always a good idea, you want a high alumina wash that fires hard like ceramics. 

This is just a thought, I've never tried it but if you buy a kiln wash you need to mix with water you might be able to mix it very thin and use it like a rigidizer directly on the blanket before applying the hard refractory. Remember to "butter" the blanket before applying rigidizer or refractory. Buttering means wetting it say with a spritzer so the next layer can bond properly. Applying any mortar to a dry surface causes it to flash dry rather than bond and set properly. This leaves a thin layer of dry cement, mortar, etc. between layers so they are more likely to flake or spall. 

Frosty The Lucky.

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