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Rick Haibach

Propane Forge Question

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I have a scrap 8" x 24" air tank that I am planning on building into a propane forge with my brother in law this weekend to give to him for his birthday.  I have an adjustable propane regulator and the pipes/fittings to make one venturi style burner.  I was planning on lining the inside with 2 inches of kaowool and skinning with refractory cement then having a fire brick or two to set the metal on.  This would leave a 4" diameter hole in the center of the tank.  Here are the two options that I would like an opinion on though since for now I only want to do a single burner setup. 

Option 1:  Shorten the tank to 8 or 12" and run one burner in the center or offset towards the front.

Option 2:  Leave the tank at 24" and run one burner about 5" from the front but leave the option to add additional burners if he sticks with the hobby and wants to do longer items.  Will I have heat or combustion problems if I have such an offset burner and nothing behind it for the last 19 or 20"?  I don't care if the back of the forge doesn't get hot enough for now since he is just learning and probably playing around with smaller pieces of metal.  

Other question.  Is there any standard/formula for hole size in the front and back of the forge?   Should one be larger than the other?  I see a lot of guys putting a moveable plate on the front to hold some heat in.  

Any tips/feedback would be greatly appreciated!  This would be my first attempt at a forge and I am guessing some people on here have learned a lot of little tricks to improve things...  

IMG_20180227_180505.jpg

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There have been formulas for square inches per burner but given the ariety of burners and other factors I think of them as "rough guidelines".

I would say that your tank is a bit long for one venturi. But I would hate to give up the already attached feet.

Some debate exists about one vs two inches of wool. Given only a 4" chamber with your tank I might think about going to just 1" with coating. I think a bit more room for circulation would be better, also I am too clumsy to work in such a tight space with hot steel and tongs without perforating the lining. It takes a bit of room to get the heat to flow efficiently. There are some guys here who can probably eyeball your tank and burner design and dial in the best specs just shooting from the hip. With the varieties of forge builds possible I am prone to favoring an "intuitive" method rather than " formulaic"one.

 

I like your option #1. Remember you can only work on so much hot steel at a time. If someone moves to swords from knives there is a good chance they will need a second forge anyway.

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I am just a newb/rookie....but 8" seems a little small once ya get wool and refractory in there. I use and am a big fan of the muffle.....and doubt that would be an option in an area that small.

Edited by Kreg
grammar

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1 hour ago, Vern Wimmer said:

There have been formulas for square inches per burner but given the ariety of burners and other factors I think of them as "rough guidelines".

I would say that your tank is a bit long for one venturi. But I would hate to give up the already attached feet.

Some debate exists about one vs two inches of wool. Given only a 4" chamber with your tank I might think about going to just 1" with coating. I think a bit more room for circulation would be better, also I am too clumsy to work in such a tight space with hot steel and tongs without perforating the lining. It takes a bit of room to get the heat to flow efficiently. There are some guys here who can probably eyeball your tank and burner design and dial in the best specs just shooting from the hip. With the varieties of forge builds possible I am prone to favoring an "intuitive" method rather than " formulaic"one.

 

I like your option #1. Remember you can only work on so much hot steel at a time. If someone moves to swords from knives there is a good chance they will need a second forge anyway.

Thanks!  I definitely could go with one layer, of insulation which would give me 6" of workable diameter.  That might be a good start, then we can shrink it later if it is inefficient for some reason.  I am curious to hear some more responses.  

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1 hour ago, Kreg said:

I am just a newb/rookie....but 8" seems a little small once ya get wool and refractory in there. I use a big fan of the muffle.....and doubt that would be an option in an area that small.

Thanks!  What is the muffle option?  I have not heard of that before.  

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A muffle is a pipe that the workpiece fits in. It has one closed end. It is put in the forge, usually with a piece of wood or charcoal in it to keep it oxygen free.

They are used to reduce decarburization from the hot steel in an oxygen atmoshpere and also to provide a more uniform heat, usually during the heat treating and hardening process.sort of a high temp" mini-oven" in the forge.

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Check out the Build a Gas Forge attachment on the Forge Supplies page at www.WayneCoeArtistBlacksmith.com

Let me know if I can help you.  I prefer e-mails.

 

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Build mine from a 15# propane tank, cut a 4x4 hole in each end as doors, 3 layers of 1" wool, and like 1/4" layer of refractory. Single blown burner at a fair tangent about center of forge body. Inside is about 3.5"x15" ish cylinder. Honestly could have gone with 2 layers of wool and there'd still be plenty of fire for the size. As is, it'll hold a steady burn at around 2300. (It loves trying to get hotter, hence the idea that my internal chambet is a bit too small.) 

Pretty easy builf overall, considering I can barely construct a functional sandwich. Using the right tools is important though, trying to cut an angled 1" hole into the side of a round tank with a 4.5" angle grinder is... Let's just say it was a learning experience. Got the hole cut tho, and still have 10 fingers

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