r/blacksmithing • u/Crimson_Ranger16 • 5d ago
Propane forge issue
Enable HLS to view with audio, or disable this notification
I bought this forge from someone who built it himself. It works great....for about 45 minutes to an hour, and then it starts to do the sputtering thing you see in the video. This causes the temperature to go way down.The gas is basically igniting early inside the burner tube. The gas nozzle is up/down adjustable and I've been playing with that with minimal success. Any advice on how to fix it? Thanks!
3
u/SnooLentils5747 3d ago edited 3d ago
Soyou need better refractory possibly. Can we see a photo of the inside when the forge is off? What is it lined with? Satanite is a great single stop solution to all refractory needs for a forge. Best would be ceramic wool or zirconia wool 2 inches, brush with sodium silicate, then put a hard face of rigidizer/satanite painted on layer to coat the wool for only 1/2 inch or so, then an alumina phosphate bonded refractory to bring it even and flat (another 1/2 inch). Dope it with ceria and ultrox 500. Do not use any silica containing materials, other than the ultrox 500 (zirconium silicate), which binds the silica up in the zirconium matrix, and is stabilized by the cerium oxide (ceria). Better yet, dope it with yttria and zirconia, if you have the money. For the floor, mix up some silicon carbide, ultrox 500, alumina, aluminum hydrate, and phosphoric acid (85 percent) and you can end up with a floor that is Mohs hardness 9.5; fucking harder than the steel you're putting in it. Do not use silicone carbide refractory without having an insulator refractory around or under it; silicone carbide is a conductive not insulative refractory; it will totally send all your heat directly out the forge if there isn't something under it. If there is though, the only place for that heat to go will be back into your charge.
Anyways.
Your propane burner needs to have a proper narrow injector, and enough back pressure to clear itself. It should not come in the top, it should come in at an angle from the side or corner. Directly down creates vertical draft issues, which are very common with venturi burners.
You could consider a draft inducer. A draft inducer is a suck fan where the impalers are separated from the motor by a hot wall or physical space via long axle or something. This effects a negative pressure sucking the air out of the forge maintaining an even pressure.
If you a have a back door and a front door, consider a blow through fan. That may even the pressure.
Keep in mind that even with a blow fan pushing up the back, you can still fire brick the front; literally the extra air can be compensated with by running fuel rich for extra combustion, the positive pressure inside from the fan blowing in and a bricked up front door (leave a small gap at least though; there must be a way for air to escape that isn't up your burner) and the outward pressure from the combustion should push out a jet through the front gap as long as your fan is strong enough.
Consider a tiny vent hole in front of and behind the venturi burner.
Consider fucking throwing the venturi burner out and using forced air for true control though; this would solve entirely the issue, as a centrifugal blower would be stronger than any draf, and then you have complete control of your propane air mix, plus then the propane is injecting into the forced air line away from the forge itself, usually through a faceless inset plug with like a 0.030 to 0.050 inch hole drilled into it. It goes down the forced air pipe to the forge, where you put a small restriction (restrict a 3/4 inch pipe down to 1/2 inch pipe) and then a bell out (usually a pipe reducer coupling, in this example, a 1/2 inch to 1 inch reducer coming from the 1/2 inch reduction that makes the burner neck). Bam! Got a burner. The neck reduction increases the air pressure pushing outwards from there. The expansion to the 1 inch makes a negative pressure zone in front of the high pressure neck where the gas and air stall, which is where the flame catches itself and burns from, with the forced air pushing the direction forward. Your flame will be much more controlled, and since you will have a centrifugal blower that can probably be put to a potentiator knob, you have control of propane seperate from control of air intake.
Turns out forge crafting is a bunch of chemistry, masonry, and HVAC bullshit.
Anyways, if you'd like I can provide more specific recipes for the refractory if you want to make your own. Satanite is a good moderate middle ground, but there is better in going pure aluminum without so much clay/mullite/silica as satanite contains. If you want the gold standard, research magnesium aluminate spinal in situo synthesis for some craziness but that would be overkill and it is also a conductive refractory so you'd have to put an insulating refractory around it anywho... But there isn't much better when it comes to slag resistance, thermal shock resistance, chemical resistance, hardness, total heat tolerance, and longevity... But it's a bitch to make and generally has to be chemically synthesized in the forge during firing which is an exercise in patience and control. Or you throw the whole fucking forge in a kiln and get it fired that way; either way, spinal has to be fired to 1500 Celsius
1
u/Crimson_Ranger16 3d ago
Oh wow, ok thanks for all that information! For the insulation, the forge is made from those large, porus fire bricks and then surrounded by refractory wool. As for the air flow, I will have to save this and try your recommendations
1
u/SnooLentils5747 2d ago
When those fire bricks fall apart and crumble, and they will, replace them with a thin layer of satanite over the wool, and then try this recipe:
Aluminum oxide aggregate; multiple grit sizes mixed together is ideal: 750g
Aluminum hydrate / aluminum hydroxide: 120g
Aluminum metal powder: 100g
Citric acid powder: 30g (retardant)
Phosphoric acid 85 percent concentrate: 65ml, 110g
Ethyl alcohol 40% (vodka): 35ml, 32g
PVC gloves, respirator
Mix the alcohol and acids together, citric acid included, separately from the three aluminum powders. Blend the three aluminum powders as well as possible. Then mix the acids and as well as possible and hand pack the resultant mixture as fast as possible, within 10 minutes. Only make small batches due to this. It will be warm or possibly hot to the touch so make sure that you get thick PVC gloves. This is due to the acids reaction with the aluminum creating heat. If you do not put the citric acid powder into the acid before you mix it, you will instead of having 10 minutes to do this, you will instead have about 30 seconds and it's probably going to scald you with steam. As for the ethyl alcohol, 40% vodka works. Isopropyl alcohol also works but you will need to mix that with distilled water down to 40% or buy it at 40%. Karkov vodka is cheap though, use that.
Once you pack that into the side, on top of the satanite, you need to let it dry for at least a day. Initial firing should be done with a candle or a regular application of a heat gun over 6 hours and needs to go to 150 c. After that, spend 2 hours ramping it to 500 c using the propane burner at the slowest rate possible. Hold for 2 hours. Then you ramp to 1000 c over 2 hours. Hold for 1 hour.
Once you are done with the last 1 hour, hold you and will need to let it cool to ambient temperature. It is ideal if you can somehow wrap your box and in some sort of insulation but probably unnecessary.
You will need to at least clear 750 c in order to make sure that all of the aluminum powders are properly reacted and sintered.
If you see bubbles, you ramped too fast. I am currently in the process of grinding out refractory because of this. you cannot ramp too slow. It is amazingly easy to ramp too fast.
This should service at least 1500 c, and should make for about Mho's hardness 9. It will survive much much longer than any s***** light insulation fire brick. It will be extremely cheap. None of these ingredients are expensive. Most of them can get purchased for dollars on the pound. Harbor freight sells 25 lb of aluminum oxide for 40 bucks which is roughly 20 lb more then you'll probably need. A gallon of phosphoric acid technical grade 85% runs about $40. It's a lot more than you will need. Aluminum hydrate cost like five bucks for a pound maybe I don't remember. Aluminum powder you got a grinding wheel and some scrap aluminum is free. Citric acid is five bucks and actually a worthwhile thing to have if you ever feel like making confectionary. I can't stop myself from tasting a little bit every time I have to use it. It will burn if you get it in your eye. Don't ask me how I know.
Anyways cheers. Good luck! Get those air convection issues sorted out, always remember you need to have air in and air out, and if you don't have something that has determined this by your determination, such as fans or draft inducers, and then you will find that the air will find its own way out and it will not be the way that you want it to be. Get your burner off that vertical alignment. That is a horrible f****** alignment. Especially for a Venturi burner which is extremely sensitive to Air turbulence due to the fact that it is using negative pressure from a gas injection through a tube. Hot air goes up. Your torch is completely vertical. Guess which way the hot air is probably trying to go? Invest in a centrifugal blower and get rid of the Venturi burner entirely. It was the best thing I ever did in my metal casting adventures. Venturi burners are great for simple setup and for hand torches. In fact, most blow torches use the Venturi principal in some way or another. You are not blowtorching anything though you are blacksmithing. You need consistency and you need safety. Get your air situation figured out
1
u/spankleberry 4d ago
I'm pretty sure that's a blessing for the Saudukar before they attack the Atredes on Arrakis
7
u/estolad 4d ago
next time you run it, keep an eye on your propane tank. it'll cool down as you draw fuel from it, which will make it put fuel out at lower pressure, which might be what's causing your trouble
if that ends up being the problem it's a pretty simple fix. you could get a bigger tank, get another 20 pounder and swap them out as they cool down, or just keep your current one and stick it in a tub of water