Two burner propane forge

6

629hugo

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Feb 10, 2013
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What is the best placement for two burners in a double burner forge? Forge will be about 600 inch^3 and I am going to use two burners. I know with one it is best to run on an angle from back to front and tangent to the liner but what about two? Should they be symmetric about center of forge one on each side?
 
Install the two burners similarly to a single burner as far as angle and tangent go. Place one about 20% forward from the back and the other about 70% forward from the back.
 
OK next question...I am using an air tank as the body. I am going to cut the ends off for ease of adding insulation and refractory. Should I weld the ends back on? That seems like it will be hard to maintain the forge after that. Or should I add hinges to the ends so that it can hinge and latch closed. I think sealing that up will be a little bit of a pain but would make it really easy to maintain the inner.
 
You can either tack weld it on in several places or put on hinges. Both work. If you tack weld it, just grind the welds off when you need to re-line it. Make one port big enough to get your hand/arm in for finishing the forge and maintaining it. A good trick is to make the back port about 4"X4" and them screw a plate over that larger hole to close it up. Some folks just place a firebrick over half the hole. The 4X4 opening makes inside work easy.
If the forge is built well, it could be many years from now before you need to pull off an end.
 
After I cut the end of the tank off, I made 4 metal clips attached with screws to hold the end cap on. Worked well for me. See pics below:

clips.png
 
Stacy- does there need to be an opening at the back at all? If I attached a plate on the back should I still leave a hole in it some air will flow? Also does that plate need to be insulated/coated with refract?

NC Biker is that the final opening size of the front or do you have a plate to reduce that opening down?
 
Stacy- does there need to be an opening at the back at all? If I attached a plate on the back should I still leave a hole in it some air will flow? Also does that plate need to be insulated/coated with refract?

NC Biker is that the final opening size of the front or do you have a plate to reduce that opening down?
 
629hugo said:
NC Biker is that the final opening size of the front or do you have a plate to reduce that opening down?
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What you see is the total opening of my forge as there is no opening in the back. I sized the opening based on this info I received from Stacy:

bladsmth said:
Some small to mid size forges don't have a back port (opening/door). By having the burner at the back you get more even heating. On a front and back ported forge, it probably doesn't matter....unless you block the rear port for some reason.

BTW, just so people who plan on building a forge understand, you need a good size opening for the combustion gasses to escape or the forge will have back pressure...which you don't want. A close forge ( which I see people draw up regularly) wouldn't even work. Roughly, the ratio is the ports need to equal about 20 times the burner nozzle area. If the burner has 1sg.in. area, you need a port area of 20 sq.in. If you use 3X4" front and a 3X3" back port, that would just make it.
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NC Biker said:
What you see is the total opening of my forge as there is no opening in the back. I sized the opening based on this info I received from Stacy:
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I like the large opening for ease of reaching into it if needed, obviously not while it is hot. But why did you go with only front open and not back, with two smaller ports?
 
629hugo said:
I like the large opening for ease of reaching into it if needed, obviously not while it is hot. But why did you go with only front open and not back, with two smaller ports?
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I felt the one opening would be fine with the length of my heat chamber (16") and the size knives I planned on making. Also, like you say, the large port makes it easier getting knives in and out, not by hand, but with tongs.
 
If you only have a front opening, it needs to be larger, like NC Bikers. If you have a port on both ends, they can be smaller. If you put a plate on the back, it should have the smaller port cut in it.
 
On a forge with a chamber length to diameter ratio larger than 2, I feel two smaller ports makes for a more even gas flow out the forge and gets more even heat distribution. It also allows longer blades and bars to be worked.
I like two square or rectangular ports of about 5-6sq.in. each..... 2X3" works well. If the lower part of the port aligns with the forge floor, then a blade will slip in and out easily.

One port works fine on "fat" chamber forges, like the propane tank one shown.
 
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once my forge is lined and coated it will be more than 2:1 length to dia. So I will go port on each end. What is the proper mix for satanite to coat the ceramic blanket? Do you go thin at first then a few thicker layers?
 
629hugo said:
once my forge is lined and coated it will be more than 2:1 length to dia. So I will go port on each end. What is the proper mix for satanite to coat the ceramic blanket? Do you go thin at first then a few thicker layers?
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This is from High temperature tools and refractory's web site:

Mix the Satanite to a thick paste...just keep adding water slowly until you get a pasty consistency that you can paint on with a paintbrush....roughly the consistency of sour cream. Spray the ceramic fiber insulation down using water with a hand sprayer to wet it lightly. Next, apply the Satanite to the wool using a paintbrush, covering all exposed wool surfaces. To cure it, you want to dry it slowly. First, let the forge sit for a few hours minimum to air dry a little, then fire up the forge just briefly and shut it down. Do this several times, allowing it to cool down in between and increasing the on-time with each subsequent cycle. You'll see water vapor evaporating the first few times you do this. Finally, fire it up and bring it up to full temp to fully cure it. You will probably want to apply at least two coats of Satanite in this manner...it's a little time consuming (do it over a couple of day period) but makes for a more robust coating. a 1/4" layer is a good thickness to shoot for. If you are going to apply ITC-100 over top of the Satanite, be sure to fully cure the Satanite first.
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As I recall I applied in two coats about an 1/8" thick each. Curing fully in between coats and then applied a few thin coats of ITC-100.
 
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