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I Forge Iron

Right burner size


jacobd

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Hi guys, the shop I share has a regular coal forge, but I want to build a smallish propane forge for working on knives as in the past I've ruined knives due to improper heat control (burning them and yelling bad things). I just want to use 8-10" diameter piece of nongalvanized lightweight stove pipe, line it with Inswool, and use a couple firebricks along the floor, maybe add some ITC later. I plan only on it being 12-16" long, and with 2 inches of wool lining it. Recommendations on a burner to buy or build to suit that size? I don't plan on welding in it. Also, I've been looking on hightemptools but while I do have some disposable income I am on a college budget, so recommendations for where to buy and what to buy would be awesome. I could probably build it but I have no experience with gas forges and am sure you guys could help. If you wanted to build a forge that size on a budget how would yall go about it? Or should I just buy the smaller devil forge on ebay. I was hoping to get out cheaper than $180. Not including bottle and reg. My main question is about the burner but I'm all ears to anything you guys have to say. 

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The main determining factors for forge burner are: Volume and shape, desired temperature, type of liner.

If you go with a 10" shell and 2" of ceramic wool it will have an ID of 6", not counting any little oddnesses caused by the floor. figuring area the of the ID in sq." you get 28.28 sq". Multiply by the chamber's length. x12= 339 cu"  and x16"= 452 cu".

By the volume a 3/4" burner will bring 300-350 cu" to welding heat so your 12 chamber is middle of range. The 16" needs more burner.

Now we get to shape just using volume only works for a chamber that's roughly equal size in all 3 dimensions. 6" Id x 12" L is pushing it for equality but close enough for most folk. The 16" L is too long and narrow for even close to consistent heat. It's too much volume for a single 3/4" burner anyway so mount 3ea. 1/2" burners on an even spread and it's golden.

Just because you have enough burner to bring it to welding temp doesn't mean you need to turn it up that hot. It's better to have it and not need it than need it and not have it.

Any of the high temp refractory ceramic are about the same performance ways so if I forget and type Kaowool it's only because that's what I use and I can remember the name. I'm basically lazy and don't want to keep going back to see what you're using. They're equivalent so it's just me being lazy.

Anyway, I HIGHLY recommend you use a kiln wash for a couple GOOD reasons. Even if you don't care about replacing it frequently the fibers are BAD things to get in your lungs. Heavy exposures can result in silicosis. Encapsulating the blanket with a kiln wash is a serious safety precaution. The other main reason is durability, ceramic blanket especially at forging temps is VERY fragile, it tears, gouges and generally just melts a fiber at a time till it's gone.

Mike Porter and some of us have been discussing kiln washes from rigidizers to IR reflective wash layers, ITC-100 is an IR reflective kiln wash. If my memory were better I'd link those threads but you'll need to look them up, they're ongoing. Use a kiln wash, you won't regret it.

Don't use fire brick as the floor, soft insulating fire brick doesn't like thermal cycling so just firing the forge up and letting it cool a couple few times will have it crumbling and if you do decide to do a little welding the flux will eat it like hot water on a sugar cube. Of course hot flux goes through Kaowool, etc. like hot water through cotton candy. Kiln wash!

Hard fire brick is a major heat sink and will increase fuel use and forge warm up time significantly. It's more resistant to fluxes but still dissolves in a hot caustic environment. Use kiln shelf instead. It's thin enough to lay ON the Kaowool insulating liner so it hardly causes increased fuel use at all. It's lighter, more heat resistant and is more flux resistant, kiln wash it and it's darned durable.

I really like stove pipe for pipe forge shells, it's plenty strong enough to support darned heavy loads without trouble. My personal favorite is stainless steel stove pipe, it's more expensive but is a good IR reflector more heat resistant so it lasts longer and is shiny. Ooooh SHINY! :wub:  Seriously, stove pipe doesn't require much for tools, a hand drill and bits, tin snips and either pop rivet tool or sheet metal screws. You can buy parts off the shelf, the wall hangers make perfect legs and they're way strong enough. You can get busing reducers to help encapsulate the kaowool on the ends.

In the last day or so a fellow posted a VERY good set of plans for building a Vault (mail box shaped) forge. If you substitute stove pipe where he used sheet steel and tack it to cut plywood for the bottom you can cast the hard refractory liner easy greasy. If you decide to go this way and have questions give a shout.

I think that about covers the basics of your questions in the typically LONG winded Frosty way but I think it'll give you some things to think about.

Frosty The Lucky.

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Thanks! I appreciate the advice. I'm not very experienced yet but I've generated a respectable amount of scale this far. If that's a decent measure of experience. I'm having trouble getting even heat on a blade that's a little longer than the hotspot in the coal forge, and figured I would do better in a gas forge, atleast in respect to heat control. I ended up burning a very small spot on a blade I have 8 or so hours in, and decided for knives at least I want a little bit better control. 

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That depends on where you're generating the scale doesn't it? You have to keep the blade moving through the fire to keep the heat even. Even if you change the shape of the fire it's not going to really be even, keep it moving. That's true in a gas forge as well just less so.

Frosty The Lucky.

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Frosty's advice is golden, and I will just add a few of details to it. Since you're working on a limited budget:

(1) The more homemade materials you use the better off you'll be, so long as you pay close attention not to use them as primary insulation, nor as hot-face surfaces (with the exception of kiln wash).

(2) Using Perlite from the garden section of your local large hardware store, mixed with sodium silicate or rigidizer poured through the Perlite between stove pipe and whatever you choose for a removable i,inner form, create a rigid low cost outer insulating layer. There is a good video on YouTube of a small forge packed with a homemade mixture Perlite and a good "glue" that is perfect for this outer insulation layer ONLY: after packing this very practical and strong secondary insulating layer in place, and heat curing it with the burner flame, use the ceramic blanket for the inner insulating layer.

(3) Before brushing on the kiln wash sealing coat, soak the ceramic fiber layer(s) in rigidizer (fumed silica in water; use a spritzer to apply, a day to dry, and then slowly and periodically apply flame heat until the fiber is quite rigid and all steam is exhausted).

(4) After doing some research on this site for the preferred kiln washes, coat your chosen mixture over the whole interior; both rigidized ceramic blanket and high alumina kiln shelf floor.

 

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