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Propane forge troubleshooting


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Howdy, my name is Mark. I built a propane forge about a year ago. The chamber does not heat properly. It has cold spots and doesn't get the metal as hot as it should. I need to remeasure it, but I'm pretty sure the mouth is 6"x6" with a depth/length of 18". 6" from burner to burner. I used the common ez burner style. 1.25"x.75" reducer. 8" 3/4" pipe with a flared end. For insulation I used 2" soft firebrick. And then it's kiln shelfing on the bottom (3/4" thick) and sides (1/2-5/8" thick). 

The propane is a high pressure 10psi regulator

When I thought the problem was that too much heat escaped, I closed up one end and it did not help. I also tried raising up the floor, but this just made smaller hot zones and larger cold zones with no improvement. 

I can't really raise the burners higher or lower the floor without cutting welds out. I made a steel box all around it out of angle iron and plate 1/8". Before trying something like that I was hoping to get some advice from you folks. I remembered reading a lot of forums here when I was making plans and constructing this. 

Thanks in advance for the help. Please let me know if there is any more information I can add that'll be useful, and if you want me to post pics of attempts of changes.

Thanks again,

-Mark

 

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Welcome  board!". try the "burner placement" thread. It answers almost all of your questions. It's a relatively new thread with lots of info.

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Volume of the interior of forge seems large to me, and the burners too small; reducing the interior size or increasing the bore of the burner tubes should help. The size of the reducers seems a bit small and may be reducing the amount of air mixing with the fuel. Closing up the door opening some should help as well. I would try to get the gas arrangement centered to keep the gas flow as equal as possible going to each burner. What is your orifice size?

Edited by SteveShimanek
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The orifice size is #57 bit. 

This is a tutorial online I found for the burners. https://docs.google.com/document/d/1Qu6X5qjb_TRH0V9OLoXjxqM_PCux4yir7ZhaNfuZNQI/edit?usp=drivesdk

 

That inline where it connects to the 3 1/8" fuel lines to the burners is 1". They have plenty of fuel going to them. Originally it was smaller and I had to make it larger because it wasn't getting gas quick enough to get the burners going

Edited by Farmer Mark
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Just looking at the pictures and you will see how the three burners coming right down on the floor of the forge creates hot spots and, as has been said before, the volume of the forge is huge.

Another thing that I noticed that scares me a bit is how close you are running that forge to a combustible surface.  You start getting a dragon's breath coming out of the back of that forge and you could ignite the wall.

Doug

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You can obviously see the hotspots created by the design. This is typical of the "farrier's forge" type of design.

I would tend to think that Steve has the best idea by sealing up the huge front opening you can't help but keep more heat in. 

If you absolutely HAVE to use 3 burners in a forge of that length for bladesmithingit means the design of the forge is less than optimal and, sorry to say, problematic.

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3 minutes ago, Kreg said:

Just thinking out loud......maybe he could toss some wool and refractory cement in there.

That would help his volume issue a bit and make it more efficient....and then a muffle.

Good idea. Some insulation and refractory, with reliefs for the burners wouldn't hurt a bit.

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30 minutes ago, Doug Lester said:

Just looking at the pictures and you will see how the three burners coming right down on the floor of the forge creates hot spots and, as has been said before, the volume of the forge is huge.

Another thing that I noticed that scares me a bit is how close you are running that forge to a combustible surface.  You start getting a dragon's breath coming out of the back of that forge and you could ignite the wall.

Doug

Too add a bit to your concerns I'd like to see that manifold away from the forge body

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That side is always cold, however moving it farther away probably wouldn't be a bad idea. It's about 20" away from that wall and I have the back side kind of covered or the heat more dispersed. I also have a fire extinguisher right behind me.

Confirming those measurements from earlier 7.5" wide by 8" tall by 18" deep. 5.75" between each burner. 

Before when I tried raising the bed up it didn't seem to help heat the space more as of make more concentrated hot spots. I did take a look at that linked forum. It would be nice to get this one to work and not have to make a new round one. 

 

The building I am in is only 8'x10'

 

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I'm not much of an expert on burner or forge design.  So take this with a grain of salt, but 10psi seems pretty low for a 0.043" orifice.  I hit 25PSI to get to welding heat with a single 0.035" orifice.

I agree with the others that you have a huge volume you are trying to heat up.  

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59 minutes ago, Farmer Mark said:

 

Before when I tried raising the bed up it didn't seem to help heat the space more as of make more concentrated hot spots. I did take a look at that linked forum. It would be nice to get this one to work and not have to make a new round one. 

 

 

 

 

 

With that placement, the square interior, and that insulation hot spots will be a way of life. You do have enough room in there to "cylinderize" ( I think I invented a word) the interior with insulating "wool" and refractory coating, maybe using something of appropriate size as a "form", and that would help a whole lot even with that burner placement. With the right size interior you could, most likely, run just two burners and never miss the third one. If you also wanted to re-angle the burners (should be pretty easy on a square box with cylindrical interior) it would be about as good as a cylindrical body model as far as I can see.

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Increase your air intake adapters and orifice size to .035, close off front and back openings somewhat, and the forge should start to put out some radiant heat from the lining, not just from the burners.

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