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New Forge: Lining Questions


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Never posted before, but been reading.  I've been building forges and furnaces since the 1980's.  Here's one I designed and posted several decades ago: http://www.rotblattsculpture.com/Articles/buildingabronzec.html.  I've been using Reil burners and built Mikey burners as well.  Now I thought I'd build a ribbon burner (or multi burner?) with a gun type delivery.  I'll post some pics later.  Anywho....I've been reading on how you line forges.  I've done mine different.  In the old days, I just used ceramic wool.  When the dangers of the fibers and the wonders of the ITC stuff got publicized, I started to coat the fiber with a straight Zircon and Colloidal silica for shell casting.  This was back around 10 years ago and I was teaching Art Foundry Casting at Cal State University Long Beach and got a sample of Zircon from Remet (a foundry supplier).  It formed a good paper thin coating on the ceramic fiber.   Heated up instantly, and stabilized the wool.  

Specs on my new forge=> Size: 9-1/2" diameter party helium tank elongated to 13" inside length.  1" inswool with flat bottom.  That makes a 7-1/2" ID minus a little from the bottom.  

Question #1: Now what I see recommended is to first rigidize, then put on a 1/4-1/2" coat of refractory (like mizzou), then a coat of Zircon based wash.  That's a massive heat sink - and really heavy. I've done fine with the paper thin coat.  It lasts a long time, and if I need to I can just touch it up if it gets damaged.  My forge linings last quite awhile.

Question #2: Everybody is talking 2" of ceramic wool lining and seem to think that it's necessary for a welding heat.  I only use one inch.  The skin of the forge gets hot but I weld all the time.  I did some calculations, and if the skin of the forge gets up to 300 degrees over ambient temperature, that's still only a few hundred BTU's.  Even a Reil Burner puts out well over 100,000 BTU's, so the few hundred lost to the skin is minimal.  The only downside is the skin gets hot.

Question #3: this is for Frosty if he is around.  First, thank you for all your work over the years with burners and sharing so generously!  The ribbon burner I just made has 18 holes, so for kicks and giggles, I duct taped a 3/4" Mikey burner to the ribbon burner intake. It burned great!  So I duct taped a 1" Mikey burner and it burned great as well.  But each time I shut them down I got a huge backfire pop.  My theory is that since I attached the burner to a 2-1/2" intake pipe there was large volume of unburnt gas in the plenum chamber and intake pipe that burnt when the pressure dropped. Do NA ribbon burners always do that?  With a gun burner the gas is shut off with the air still pushing thus the gas will just go lean and die.  With NA, the gas and pressure drop at the same time leaving gas rich air in the burner assembly and pipe.

Last: Thank you Mike for your books and your generosity as well.  I think I must have purchased your book right about when it came out because I made a few of your burners and was using them while I was teaching foundry back in 2006.  


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32 minutes ago, D.Rotblatt said:

but been reading.

Welcome to IFI... Have you read this yet? READ THIS FIRST

It will help getting the best out of the forum.

As far as lining a forge, if what works for you stay with it. Some folks are harder on the insulation than others, that's why I recommend a hard face like Mizzou or Satanite for durability. Can't help with the ribbon burner but I bet others who have experience with them will be along shortly.

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Thanks Irondragon.  I did peruse the "Read This First."  Thanks.  Partly I wanted peoples thinking on why they do a thick lining and if there are other alternatives.

Here's some pics of the forge.  The liner is rigidized, but not coated.  I will put a bottom of some sort on it.  Maybe a half brick or some refractory like Mizzou or Greenlite coated with zircon.  Haven't decided yet.  

That's the first burn of the ribbon burner....puts out some heat!  The damper is open 1/4 and I'm running at 2.5psi with three .052 holes venting into the pipe and the needle valve not open all the way.  Cranked it up all the way for a moment and it will forge weld....


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The Zircon (zirconium silicate) and silica coating for ceramic fiber blanket sounds interesting; it should be easier to deal with than Zircon and bentonite, although not good for as high a temperature. Do you use fumed silica and mix the two as dry powders, and then add water? What proportions or thickness do you aim for? Any preferred technique for application? Can you just heat cure it in a few minutes? Inquiring minds will want to know the specifics.

I looked at your article; it reminded me of the online casting groups that are long gone; a pity that. Welcome to the group. Does the "D" stand for Dave or Dan?

You mentioned that a 1/2" thick layer of castable refractory constitutes a massive heat sink; compared with a thin coating of zircon it does. But how much of a heat sink depends on the refractory, and good or bad can be a point of fact, or just a point of view. Some people consider the armoring effect of a cast refractory layer to be important; others feel reasonable care should make it unnecessary. I'm part of that second group, but worked around gorillas for so many decades that I know my preferences are not practical for most. 

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Hey Mike!  Nice to virtually meet you!  

8 hours ago, Mikey98118 said:

Do you use fumed silica and mix the two as dry powders, and then add water? What proportions or thickness do you aim for? Any preferred technique for application? Can you just heat cure it in a few minutes? Inquiring minds will want to know the specifics.

I used to do a lot of shell mold casting.  The colloidal silica is the binder that is used for building the layers.  In shell casting, silica flour is mixed with the colloidal silica.  The mold is dipped in the slurry then sprinkled with crushed silica - first layers with fine, then medium, then course.  If you are casting iron, steel or a higher temperature material then bronze (I did bronze), then you use zircon flour instead of silica flour so it will take the heat.  The colloidal silica is a premix that comes in 5 gallon containers.  It looks like a milky water, a little thicker than water (could just be fumed silica in water, but I have no idea).  The type I use is called Adbond II, and I got it from Remet.  What I used to do is dab it onto wet ceramic wool with a disposable brush then just heat cure (never had the patience to just let it dry).  Thickness and feel is like an eggshell (just not so smooth).  One or two layers was all I use, basically to bind the outer layers so I won't be breathing in ceramic wool particles and I thought it would reflect (though now I find it's emitive...which I just found out by reading on this forum, thank you very much!).  I figured since it was reflecting, a thin layer was all I needed.  Seemed to work well, surface got brighter, wool was stabilized, formed a hard eggshell layer.  

I value a forge that heats up quick, and cools down quick.  The only advantage I see of a slow cooling forge is for annealing, but if I want to do that I have an oven.  A thicker heat sink liner is stronger so it holds up to more abuse, but will take a longer time to get to heat (thus use more gas).  I imagine it would also act as a storage for the heat, so if a cool piece of metal is put against it it would transfer some of it's energy to the metal (but that's an argument for a denser floor rather than a dense layer of liner).  The way I used to explain the advantages and disadvantages of ceramic wool vs a cast liner for furnaces is that if you are doing only one pour at a time, ceramic fiber is more efficient since it heats up quickly, but if you are doing a number of pours in a row, a cast liner is better as it holds the heat and you don't have to heat it up as much.  As you say, it's really just a matter of opinion.

But I think I'm starting to babble....I'll leave it at that for now.

BTW: First name is Dan, my son is Dave - right on both counts!


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Would you please consider transferring this, and what you previously wrote about using a zircon/silica hot-face thin coat for ceramic fiber insulation to the Forges 101 thread so that people will be able to read it at will, rather than just for a month? We are always looking for alternative hot-face coatings for forge interiors.


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Welcome aboard Dan, glad to have you. If you put your general location in the header you might be surprised how many of the gang live within visiting distance. 

#3, The plenum is filled with a flammable mixture and the flow exiting the outlets faster than it's rate of propagation is what keeps it from back firing. When You turn off the inducer: Reil, Mikey, or T there is no flow so it back fires. Guns shut down gas first then blower so the flammables are flushed before the flow stops.

I've made forges by rolling Kaowool and wrapping it in screen but I have a number of beginners want to use my forges so they NEED armoring. I was turned onto, "Kast-O-Lite 30 li," by the good fellows at Distribution International, the HVAC service and supply company in Anchorage. Great guys who ALL seem to like controlled fire and talking about it. It's a castable, water setting, high alumina, bubble refractory with a max sustained working temp of 3,000 f.

It isn't as good an insulator as K 26 light fire brick (ceramic tile) or the old light insulating fire brick but it's tougher and shurgs off welding temp flux. K 26 doesn't seem to mind flux either but I haven't been using it as long.

What you say about heat time and fuel cost is true but there are trade offs, durability is the main one for me. I'm easy on my equipment but there are times I've forged up some odd shapes that are really hard to get in or out of a forge without touching the liner and 2,600 f.+ kaowool is about as tough as cotton candy. 

1/2" of Kastolite 30 to a 300 cu/in cylindrical forge liner adds about as much weight as using split brick to make a flat floor but is well less than 1/2 the heat sink and isn't effected by flux.

I'll ask Admin to move this to the Forges 101 thread, it's easy. Just select "report post" and ask in the message window that appears. The "Report Post" button brings it to the attention of one of the mods immediately and can get results quickly, minutes sometimes. 

Frosty The Lucky.

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Thank you Frosty! I've been using Reil burners for decades, and never had them backfire when shutting off.  Nor do my Mikey burners.  

I too have some burnout kilns where the outside shell is just 1/4" hardware cloth with 1" of kaowool.  Used them for burning out ceramic shells, and have repurposed them as upright heat treat forges for hardening swords.

The Zircon/Colloidal silica binder shell is fine for being just bumped.  Even if it does crack or is punctured, it's easy to paint a patch on...only a few minutes, no drying time, but paint it on cool and fire the puppy up!

****I've moved the conversation to the Forges 101.  Glen just told me to cut and paste it.  We can move all this over there.

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