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Christopher Price

Building a forced-air gas forge

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I posted this in the tools section, and if the cross-post is verbotten please feel free to take one down or the other, I don't much care which.

However, for the general benefit of beginners and people wanting to build a forge, I went to the trouble of filming myself and sharing some thoughts on how to go about putting one together. I hope people find it useful, and I appreciate feedback... I'd like to do more videos, and constructive suggestions of "more of this" or "less of that" would be helpful to me. Thanks.

 

 

Edited by Christopher Price

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Nice job! Of course sound is always an issue doing shop videos so if you could find a way to keep it more consistent that would be a plus.
However, that is my only critique. I'd love to see more about the ribbon burner design, I really like the flame it puts out.

 

Jared

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Always enjoy these vids , thanks for sharing Chris ,

you have me thinking ribbon burner now before I re and re my forge !!

Edited by BCROB

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Guest guest T

I have been wanting to build a venturi burner but I may go with this instead! thanks for sharing the video it was very informative.

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Thanks Chris! I picked up a some materials and plans from Wayne at Quad State, and have an old fork lift propane tank that will become a new ribbon burner forge soon. Your video answered quite a few questions.

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I'm glad people are finding it useful.

 

My impressions using it this week are, it is a much more stable heat than the old 1" pipe inlet. The entire forge gets to a nice even yellow glow once it warms up, and a bar laid in heats evenly across 6 or 7 inches before tapering off, with no overheated points along the bar. This is excellent for twisting, normalizing, or prepping for heat-treating.

I have not yet tried to weld in it, that will be the real test. Just looking at the character and colors inside while it's running, I don't anticipate any problems, but I can't certify it until I've done it successfully, and I need to get a couple pieces welded up this weekend before F&B next weekend. Otherwise I'm very happy. It's even a little less loud than the original plumbing. There's no quieting down that blower, but the flame noise is reduced, the "roar" is very soft and subtle compared to the "ripping" noise the old flame had.

 

The last serious benefit, is that the new lining is insulating so much better than the old - fresh wool and the Mizzou shell seems to hold the heat a lot longer, and better, than the old satanite-coated wool. I can't imagine kaowool losing its insulation properties through regular use, assuming it's sealed up pretty well and nothing weird is getting in there - but there is a distinct improvement in the hang-time of heat once I shut it down. This is excellent for annealing, and speaks to the increased efficiency of the unit.

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So now you have me building a ribbon burner :)

 

Is your inlet a 1" pipe with no geometry change between the air and gas inlet? Is there no need for a reducing bushing since the mixing happens in the space between the castable and the inlet? Thanks!

 

Jared

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Chris, I am anxious to see the weld results. I am rebuilding a forge similar in size and condering the ribbon

Gary t

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So now you have me building a ribbon burner :)

 

Is your inlet a 1" pipe with no geometry change between the air and gas inlet? Is there no need for a reducing bushing since the mixing happens in the space between the castable and the inlet? Thanks!

 

Jared

 

Correct, 1" pipe from the tomato can reducer, all along the various fittings, into the manifold which is cast into the burner. Air geometry changes from 1" round to the 3x6" space behind the castable in the manifold, out the little holes, and combustion happens in the forge itself. It seems plenty well mixed by the time it hits the chamber, and that's only after 6 or 8 inches from where the gas is injected into the forced air stream.

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Awesome. Last question, if I may: what are te approximate dimensions of the metal box before the castable was added and the thickness of cast able that you used? I'm trying to use the scrap around the shop but I'm not sure I have anything deep enough for the metal box.

 

Thank you very much for answering my questions!

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I think my box was made from 2" c-channel, the kind from home depot that just has short lips on each end. Cut a 6" length, cut another and then zipped the second in half lengthwise - welded the cut ends of those to the lips of the first, with the new lips facing "in", then found some scrap to close off the sides with. blew a 1" hole in the back of it and welded on my 1" pipe (5" nipple, welded directly to the body of the forge as seen in the video).

 

There's probably 1/4" of castable around the outside of the box, 1/2" under the lips (forge-facing side) and maybe 1/2" space inside the manifold - most of it should fill up, but enough space for air to move behind the brick you're making. I may have to make another, and film it, to really get the finer points across.

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That description coupled with the images here http://blacksmith.org/forum/tutorials/ribbon-forge-burner/ make perfect sense. Thank you for taking the time to detail the process, it is very much appreciated!

 

Jared

 

Exactly, except I don't use a baffle - I see no need for it, as all it does is add backpressure to your air system, and the small holes of the burner do a plenty good enough job of that already. Mine's not as pretty as that, but once you understand the principle, the details matter less - important parts are, weld the manifold tight so you're not blowing fuel-air out where you don't want it, and use enough castable to get a good brick. The rest is entirely style and personal taste. You could make a 12" long burner if you had a really long forge, and I'm considering just such a thing for a sword-length heat treating furnace - 55 gallon barrel, run the fuel-air pipe out the bung with an inch of wool inside, and small holes front and back... and a long burner I can run on low to get a really nice even non-aggressive heat with.

 

The glass guys just replace every 2nd or 3rd brick in the wall of their furnace with these, and get amazing heat with no drama.

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I am inspired to see that your arc-welding skills are on a par with mine, yet it works! :lol::P

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That was a messy joint, and I'm out of regular electrodes, so I was using 7018's, really inappropriate to the work, and I hadn't dried them. Sue me. :):P

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Chris, I am dying to know how well and tweaking had to done, if any, to weld and what did you use to weld?

 

Thank you gary

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No tweaking required. I had to get used to a slightly different mixture for lighting it, but that's all - a little more air and gas than I'd used with the straight pipe, but otherwise it runs perfectly. I get a very nice, even, heat after just a few minutes running. A length of 1" square bar will have a nice and perfectly even heat over 6 or 7 inches of length, perfect for twisting.

 

My shoddy welding was just using a regular stick electrode welder, to get the metal parts put together and sealed up as best as I could get them. Nothing special.

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Sorry it's taken me a while to answer, haven't had a chance to work in the shop for the last few weekends - but tonight, I did go out and weld up 3 different stacks - some steel cable, half inch - welded up nice and solid. Also welded a large 2x2x8 stack of 1084 and 15n20 (15 layer), and a 9-layer lump of wrought iron, and phosphoric wrought iron. Welding temps reached easily on all three projects, very happy with the performance. Hopefully I'll have pics of some finished work before long, and maybe more instructables on video in the coming weeks.

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I love my coal forge for most things, especially making axes and thicker stock, as well as blades, but forge welding and heat treating are a bit of a pain for me. I will have to do something like this, I think I have almost everything to build one.

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So you casted the brick, and then basically adhered the steel plate/boxish mixing area with more castable? Or is the C-channel in the original casting when it was wet?

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The manifold is like a 3-sided box with lips facing inward on the 4th (hot) side, and it is placed in the wet castable so that those lips provide a ledge that holds everything together. In the video, I had to add a little more because my first mix was too watery, and cracked as it dried, so I spackled the outside with mizzou to give it a little more integrity, but the initial casting done well shouldn't need that.

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Built two manifold boxes today. One for me and one for a good friend. These are made the same way from the same material you described Chris, except these are 9" long.

20150611_212454.jpg

20150611_212503.jpg

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