Obrown101 Posted March 19, 2022 Share Posted March 19, 2022 So...I just finished building a large (too large, I’ve got my father’s habit of over-engineering) propane forge. I put 2in layer of ceramic fiber wool from CeraMaterials. I have firebrick on the bottom (on top of the wool). I have put a decent amount of a rigidizer coating on the wool. I’m not a safety freak, but I‘m also young and don’t want to die from lung cancer later on in life. Is rigidizer enough? Should I put another layer of some sort of refractory cement or something? I’m new to the community and blacksmithing and don’t know how to layer coatings inside a gas forge nor what is durable or not. Any suggestions? Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted March 19, 2022 Share Posted March 19, 2022 How large is "large"? I have a friend who works at a forge where they consider 1 foot square stock "small" and many friends who consider 1 inch square stock large. Dimensions! Quote Link to comment Share on other sites More sharing options...
Obrown101 Posted March 19, 2022 Author Share Posted March 19, 2022 It's an old air-tank with rounded ends (obviously) but is 25" from end to end and 16" in diameter. That's before I put the insulation in. Quote Link to comment Share on other sites More sharing options...
Latticino Posted March 19, 2022 Share Posted March 19, 2022 Yes your forge is likely on the order of twice the size you need right now. I'm a fan of putting a rather healthy layer (3/4" thick minimum) of high alumina castable refractory insulation (like the Kastolite 30 that Glen sells in the IFI store) as an internal protective wall in my forges, but I have some significant lung scarring from exposure to untreated ceramic blanket during my years as a glassblower. Rigidizer will keep down the bulk of the fibers, but it is an extremely thin topcoat layer, if applied correctly, and can be easily damaged (not to mention dissolved by flux). The castable refractory adds some thermal mass, so your forge will heat slower, but also acts as a bit of a "thermal battery" when you put a mass of cold steel into the forge (like a hammer head blank). Mixed and applied correctly it is a very durable surface and will also resist molten flux to a great degree. Quote Link to comment Share on other sites More sharing options...
JHCC Posted March 19, 2022 Share Posted March 19, 2022 What Latticino said. As usual. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted March 20, 2022 Share Posted March 20, 2022 My basic analogy is: would you buy a dump truck as your daily driver because you plan to get a load or two of gravel sometime in the future? Also many overly large forges are built because smiths want to forge swords! They haven't done enough research on forging swords to realize you only want to heat up as much steel as you can work before it goes cold, (say 1000 degF). Heating steel encourages grain growth, decarburization and scale losses ; so instead of making a weaker, lower carbon sword that is smaller than wanted why not do it like Medieval people did and work it in a fairly small hot spot---some Viking era blades were forged in forges with a 6" to 8" hot spot and there were done by professionals with strikers! Sword forgers need a fairly short forge with a passthrough in the back. Large forges are often handy for 3D ornamental work; but you pay for all that heated space! Blacksmiths often end up with several forges of different sizes and use the one that is most economical for the task at hand. Quote Link to comment Share on other sites More sharing options...
Obrown101 Posted March 20, 2022 Author Share Posted March 20, 2022 Thanks for the information on the castable refractory. I think I'll probably invest in some of it, just so I can feel a little bit safer about the fiberglass particles. I realize my forge is way too big. I didn't know what I was doing as a beginner and scaled it a bit too large. Problem is I've already spent the money on putting it all together so now I'm kinda stuck with it. I might build a small "insert" of sorts out of some scrap metal and the extra wool I have left. A smaller insert I can just slide into this one when I want to conserve fuel and do small work. I attached a photo of my setup (this pic was before I cut the hole in the front door). I still have things I'm going to change about it as I go along. Slow beginnings... Quote Link to comment Share on other sites More sharing options...
Irondragon Forge ClayWorks Posted March 20, 2022 Share Posted March 20, 2022 I think you will need more than one burner to reach welding heat and really need a bigger propane tank. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted March 21, 2022 Share Posted March 21, 2022 When I see folks mention sunk money I always wonder why it's cheaper to spend many times the extra money in fuel costs than a smaller forge would cost to build. Which is cheaper: a free car that gets 8mpg or one that costs US$1000 that gets 34mpg? Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 21, 2022 Share Posted March 21, 2022 When asked about the size of your forge, the INTERNAL volume is THE important number that determines how much burner is required to bring it to a specific temperature. Telling us it's 25" x 16" BEFORE installing however much liner you used isn't very valuable. The best I can realistically do is guestimate volume from your description as around 2,300 cu/in requiring SEVEN 3/4" T burners to reliably reach welding temperature. Length and width are a function of the shape work you wish to do and only count towards burners if the interior is long and narrow. So, what's keeping you from taking the ceramic blanket out of that shell and building a couple more practical forges? Let's talk costs a bit. I have a 2 burner forge as my every day user. It uses two 3/4" Ts as inducers to run the NARBs, I can run it hard for about 6 hrs. before it starts slushing a 40lb. propane tank. Which is why I run it off a 100lb. tank except at demos where I take two 40lb. tanks and switch off during breaks. So, how long would a 40lb. tank last running SEVEN 3/4" T burners? My experience says it will start slushing up in 45 mins. maybe 1 hr. My 4 burner way too large shop forge slushes up a 40lb.er in about 2 hrs. NOT the 3 hrs. a straight accounting would suggest. So, how about we help you build a more practical forge, we're good at that sort of thing. We REALLY do want you to be successfully addicted to the craft. Happiness is playing with fire and hitting things with hammers! Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Obrown101 Posted March 21, 2022 Author Share Posted March 21, 2022 You all make some very good points. I think I will make a new one with the insulation and burner I have. What size would you recommend for a beginner who wants to make some knives, axes, and such projects? Also, how did you figure how many burners for a certain length/width forge? What’s that formula look like? I appreciate everyone’s help getting me set on the right path. Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 21, 2022 Share Posted March 21, 2022 I usually suggest a brick pile forge to folks who don't really know what they want or need. I keep a case of Morgan Ceramics K-26 insulating firebrick handy to experiment with forge shape and burner placement before committing to building a permanent forge. Even so, I've never gotten it "right" every darned forge needs improvement. The basic ratio is one well tuned 3/4" naturally aspirated burner to every 300-350 cu/in volume. Ideally this applies to a monodimesional chamber, cube or sphere. That isn't too important so long as it's not too long and skinny or weird shaped. A good place to start is around 150-175 cu/in and a 1/2" NA burner. Below is a pic of a clamped together K-26 insulating fire brick forge, powered with a 1/2" T burner. Our club put together IIRC 17 or 18 of these in a two day clinic, the first day we built the burners the second we built the forges. This pic is about 4 minutes after lighting for the first time. The chamber is 4.5" x 4.5" x 9" for 182 cu/in. The only hard firebrick are the doors. Believe it or not the K-26 IFB (Insulating Fire Bricks) cost less than the hard split brick our supplier didn't have any split K-26 at the time. They all got a kiln wash of Plistex-900 which made them much more flux and abrasion resistant. We bought all the materials in bulk so a one off version will cost more than the $100 and change it cost club members. I wasn't in on the fine details of the design or I would've added an extending porch at both ends. All in all they came out very well. Some of the pro bladesmiths in the club bought one in support but ended up using them as their main knife forges. They'll get TOO HOT so you aren't running at max psi hoping to get enough heat and they sip fuel on the order of 16hrs on a 40lb tank and the draw is slow enough they don't slush up unless it's a COLD day. I'm not suggesting you build one of these even if they're a proven design both effective and economical. I'm posting this as an example of a good size forge, especially for someone learning the craft and wants to make blades. That a couple of our guys have stopped using the commercially made propane forges they used before says a lot to me. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Obrown101 Posted March 23, 2022 Author Share Posted March 23, 2022 I really appreciate this information Frosty. All I’ve got to do now is get to the scrap yard to get some more materials. Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 23, 2022 Share Posted March 23, 2022 You're welcome, it's my pleasure. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
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