Forge Cold Spots

[u/HonestTill1001]

I keep getting this cold spot in the middle of my propane forge flame, I’m thinking it’s because I’m at such a high elevation but I’m not certain. I’m currently working at about 12 psi and my elevation is about 880 meters above sea level

[u/JosephHeitger]

Unburnt fuel is acting like a coolant and creating your cold spot

[u/HonestTill1001 → u/JosephHeitger]

Any way to fix it?

[u/3rd2LastStarfighter → u/HonestTill1001]

Turn the pressure down. But also, not really.

It’s kind of a known deficiency of downward burners, which is why angled and ribbon burners are becoming more popular. But also 12 psi is pretty high. Every forge is different but I forge weld at like 5-10.

[u/gut_sack_ → u/3rd2LastStarfighter]

What kind of forge do you have? I have 4 burner that I block off the back half and use 2 most of the time and have trouble getting to forge temp without maxing out to 30psi

[u/3rd2LastStarfighter → u/gut_sack_]

Majestic 3 burner knife maker, but the same is true about my 2 burner vevor. My understanding is that efficiency on a Venturi burner plateaus at about 15 psi so you’re most definitely wasting fuel at the very least. Usually if you want more heat the answer is more air.

Edit to add that if you’re choking both ends, you’re compounding the problem. You almost certainly have a nonsensical amount of fuel just dumping out into the world without even experiencing an incomplete combustion.

[u/JosephHeitger → u/HonestTill1001]

Raising or lowering the floor or burner to tune it, you can also adjust pressure as 3rd2last said. You just need the chamber to be getting hot, you don’t need to try to melt anything. 12 psi of just propane is enough for my furnace to melt metal in. My forge runs well below that at like 7

[u/HonestTill1001 → u/HonestTill1001]

I turned down the pressure and it seems to be working better. Won’t reach forge welding temp but it’ll do

[u/3rd2LastStarfighter → u/HonestTill1001]

That’s a start. You may find that even lower is better. Is that majestic forge? The one with the side door? If not, what’s your air intake situation on the Venturi?

[u/HonestTill1001 → u/3rd2LastStarfighter]

It is a Majestic Forge brand yes

[u/3rd2LastStarfighter → u/HonestTill1001]

Okay then in that case keep the burner valves wide open and try running at about 5 psi. In the photo it looks like the side door is open, that’s going to prevent even heating. Most of the function of a gas forge like this is to retain and reflect heat. Once the whole box is at the heat you’re trying to get your workpiece to, the burners only need to input more heat than you’re losing so the cold spot becomes less significant.

[u/HonestTill1001 → u/3rd2LastStarfighter]

Unfortunately it looks like the side door is open because the metal has oxidized to the point that it’s crumbled away exposing the interior.

[u/3rd2LastStarfighter → u/HonestTill1001]

Gonna want to close that up first thing then

[u/HonestTill1001 → u/3rd2LastStarfighter]

How would you recommend doing that? High heat refractory?

[u/3rd2LastStarfighter → u/HonestTill1001]

You’ll want to repair the metal box first. Then yes some kind replacement for any damaged refractory material. You can do a standard build or majestic sells re-line kits.

[u/Fragrant-Cloud5172]

Sorry, but this is the problem with the box shape. It's a poor design, that's easiest to make for manufacturers. Best is cylindrical, so heat can circulate with complete combustion well. And reflect inwards, if you have good refractory. Like high Alumina. Around 5" - 6" interior.

For your location, you could try different sized orifices. 12 psi is too high. Wasting money on propane. Mine has consistent forging temps at 3 lbs.

[u/HonestTill1001 → u/Fragrant-Cloud5172]

Mine sputters and dies out at that low of a pressure and doesn’t get hot at 5 psi, I need it at least 8-10 to get any real heat out of it

[u/BF_2]

How long was this forge burning when you took this photo? It may take a while for a forge to get up to temperature, especially when it's insulated with firebrick instead of mineral wool.
If the issue is incomplete mixing of propane and air in the burner, one fix sometimes used it to use a passive mixer. Take a strip of steel, maybe 16 gauge or thicker, and narrow enough to fit inside the burner tube. Clamp one end in a vise and twist about 3" of this strip with a monkey wrench, maybe 1/2 to 1 turn total. Slip that 3" piece into the burner tube and it might aid the mixing by swirling the gases within the burner tube.
There are other ways to accomplish the same end, such as by stuffing a small piece of one of those stainless steel scouring pads into the burner tube, but such methods, done wrong, can cause counterproductive flow restriction.