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I Forge Iron

My new propane forge


Nghtmrknife

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Brick stinks for a forge floor it's too great a heat sink and will take more fuel to get hot than the rest of the forge put together. High alumina kiln shelf is far superior. Are you planning on kiln washing the ceramic blanket?

Have you looked at the propane forge section of Iforge? There are a LOT of good forge plans posted to help you do it right.

Frosty The Lucky.

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If you are going to use a hard fire brick for the floor, I'd suggest going with a brick "split" (half thickness) and supporting it from the forge casing with a backing of some type of insulation (I use compressed frax blanket with small steel standoffs welded to the casing).  If it is set inside the forge insulation layer it won't bleed as much heat as Frosty indicates, but will act as a bit of a thermal sink (i.e. will take longer to get up to temperature, but will transfer some of that heat back to the cold steel when it is put into the forge, or the door is opened for same).

I've only used AP Green high alumina fire bricks, as they are more resistant to flux contact, and I had some on hand from another project.  The high alumina kiln shelf Frosty recommends is likely the same type of material (use a wet diamond "tile saw" to cut one down to size).  If I had to source something new I'd certainly consider looking at bubble alumina fire bricks like these:  http://www.ktrefractories.com/Alumina-Bubble-Bricks.cfm.  Maybe they would send you one as a sample if you ask correctly...

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You don't have to kiln wash blanket but there are a number of good arguments in favor: Health, ceramic blanket sheds little whiskers of vitrified ceramic that can poke holes in your lungs where they shouldn't have thousands of itty bitty holes. Similar to but not the same as mesotheleoma risk caused by asbestos.

Another reason is durability, ceramic blanket isn't very tough, especially at heat, it will tear, and even sag and fall off at forging temps.

A propane flame is darned chemically active and will erode blanket both chemically and thermally.

Then there's the ever popular desire to weld in your forge, almost all fluxes are based on borax which is very caustic at welding temps, it dissolves ceramic blanket like hot water on cotton candy.

Lastly for the main reasons is IR reflectivity. There are kiln washes that contain zirconium, silicate or phosphate which is nearly diamond tough, laughs at temperatures you can NOT develop in a propane forge and is highly IR reflective. Or does it re-radiate it?

There is a lot of discussion about making tuning and using propane burners as well as forges in the propane forge section of Iforge. There are existing plans for forges similar to what you appear to want to make. Wayne Coe sells supplies in small enough quantities we can afford to line our forges with top notch materials. He also has plans posted.

Frosty The Lucky.

 

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Frosty,

It is good to see how thoroughly you've come to understand how undervalued high a alumina kiln shelf is as as a forge floor. It was undervalued by me as well; I only considered its mechanical virtues, until last year. It was during research for a crucible text that I discovered how excellence  high (purity) alumina products are at insulating; about seven times higher than fire brick; this is just enough to drop temperatures from hot to cold faces sufficiently  to keep the ceramic fiber insulation below the floor from being destroyed in short order:unsure:

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  • 2 weeks later...

Mike: Do you know the R value of kiln shelf? Even hard fire brick is better than lime stone but that's not saying much it'd still take probably 10" to equal R-1.  Just guessing but it sounds like a mere 2" of kiln shelf is approaching R-1?

Coolness indeed.

I don't know how thoroughly I understand high alumina kiln shelving is or even how underrated it is. I'm a simple guy, if it works enough better to be worth the money I like it. I know we talk like I know how to make high efficiency forges and maybe I do have a handle on it. What I'm using for a shop forge has more flaws than features. The New forge I built to replace it as my travel forge is worse, I didn't make the same old mistakes, oh no, I improved on them. The new mistakes are much worse, I didn't even take my own advice. <_<

Anyway, I'm looking to break the liner out completely except maybe the roof and try something else. I cast a thin inner shell from a high alumina castable then backed it with the same stuff cementing perlite together. Talk about a lousy insulator! I can just get it to high orange if I really restrict the volume. <sigh>

The latest plan is to insulate with Kaowool and make the contact layer from high alumina kiln shelf. Then kiln wash that with Zircopax HT bound with the Green Cast 94 high alumina castable sifted free of aggregate.

I've got the burners trouble shot and tuned but it's still NOT hot let alone HOT enough.

I'll let you know how underrated I think kiln shelf is in a while. ;)

Frosty The Lucky.

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  • 3 weeks later...

 

Frosty,

I'm sure that somewhere there is an exact number for the insulating value of high alumina kiln shelf, but since it isn't an issue for sales reps, who are busy talking about how much weight they can take at high temperatures (remember, they are kiln furniture), finding it could be quite a chore. Just using one in a forge will provide all the input you need. I was lucky, and never bothered with anything else, thanks to Ron Riel's input. My own forge design had much owed to him, which I freely acknowledged in the book. So for as I'm concerned, his little mini forge is still one of the best design around. It seems odd to me that he isn't writing on this group...

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So, where did I come up the the seven times the insulating value of regular hard fire bricks datum in the first place? From the only source that cares about it: crucible manufacturers, who don't use it for a talking point, but as a caution. This is why the best high alumina crucibles are quite thin (even the cheap ones are a long ways from thick). In fact the only crucible material that is more insulating is zirconium, which, do it its ability to re-radiate energy back toward its source, can be used as both crucible and furnace in one! If I wanted to try to improve on high alumina kiln shelves, it would be by adding a layer of zirconia over one of them.  I have already uses ITC-100 for this, and It worked fine; but knowing what I do now, I will use a thicker coating for the purpose next time.

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Thanks Mike that was more just curiosity than need. I was thinking of using kiln shelf for the whole hot face in a forge so protecting the Kaowool behind it is a factor.

Recently we've gotten enough info from members here who use Kast-O-Lite products I think the club is going to start using  Kast-O-Lite 30 rather than the $x3.5  (97.)

I can afford a bag for less than what I was going to spend for barely enough to line the forge so I can experiment a bit. I think I'll try adding a little Zircopax to the flame face directly and see what happens. ;)

Oh I discovered why my new forge wouldn't get hotter than mid orange. I was playing with my calculator figuring coverage for the more expensive refractory then was looking at placement for a ribbon burner. Yeah, I think about several things at the same time this next bit will show how well. I was looking at the quicky sketch on graph paper I was using to visualize a ribbon burner and it struck me. Half the forge floor is 12" x 12" and almost 5" deep! Criminy, that's more than 2X the volume a 3/4" burner will bring to welding temp!

So that's the truth Frosty's multi tasking ability, I'm fine so long as it doesn't involve simple arithmetic. :huh:

Frosty The Lucky.

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