Dueldor Posted January 21, 2022 Share Posted January 21, 2022 Hey folks tried searching google and here to see if I could find anything on what temperatures can “chimney” out the burner of a cooling gas forge but came up empty. Has anyone done any testing to see what kind of temps can backfeed? Looking at a couple components that have a max temp rating of like 250* and want to make sure I’m not going to melt or warp or ruin anything. Thanks folks! Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted January 21, 2022 Share Posted January 21, 2022 250 Kelvin you are in trouble; 250 C you are probably all right, 250 F and I'd worry; of course it depends a LOT on the type of burner, size and how it's arranged. I really dislike vertical placement of burners for several reasons with CO and the chimney issue having the greatest weight. Quote Link to comment Share on other sites More sharing options...
Dueldor Posted January 21, 2022 Author Share Posted January 21, 2022 Sorry 250f. Ribbon burner 6” long 3” wide horizontal placement at the top of the forge so that it enters on the round already to swirl. So is vertical placement the only time the chimney effect happens. I figured with having the burner horizontal but at the top it would create the same issue. Sorry if I’m not explaining myself well. Words are not always my strong suit lol. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted January 21, 2022 Share Posted January 21, 2022 The chimney effect is caused by hot air/gasses rising due to lower density. In a horizontal pipe not much room for that to take effect. Quote Link to comment Share on other sites More sharing options...
Buzzkill Posted January 21, 2022 Share Posted January 21, 2022 Is this a blown ribbon burner or naturally aspirated ribbon burner (NARB)? Is the mixing tube that feeds the burner horizontal or vertical? If the mixing tube is horizontal there shouldn't be much of an issue as TP said. The hot air has to have somewhere to go for it to be a problem. With a blown burner there are normally a few bends and turns in the air supply line so I wouldn't expect there to be any appreciable chimney effect. Most NARBs I've seen or built have the mixing tube perpendicular to the the flame face of the burner, so again not too much likelihood of a significant chimney effect. 250 degrees F is not much though in terms of forges, so if a component can be damaged at that relatively low heat you could have issues even without any chimney effect. What component(s) concerns you? Quote Link to comment Share on other sites More sharing options...
Dueldor Posted January 22, 2022 Author Share Posted January 22, 2022 This will be forced air ribbon burner. Thinking of installing an electric shutoff solenoid. For both safety and temp control. I’m considering wiring the solenoid to a pid/ssr setup to control temp as well as should power go out for whatever reason the gas is immediately shut off as well. It sounds as though I shouldn’t really have much to worry about though as far as burning the component. Quote Link to comment Share on other sites More sharing options...
Buzzkill Posted January 24, 2022 Share Posted January 24, 2022 A normally closed solenoid for the gas supply should be more than far enough away from high heat to avoid damage. If the blower and solenoid are tied together then the PID system should work ok after getting it tuned initially from a fuel to air ratio point of view. However, generally speaking you want to leave the blower on for a while after the gas is turned off to avoid the potential for explosion in the mixing portion of the system. If the blower is left running without any fuel to burn, that will cool the forge fairly rapidly. For my electric furnace the "on" cycles tend to be really short as the system approaches the desired temperature. I'm not sure how that will play out with a gas and blower system. You may be able to run an idle circuit though where there is always a minimal amount of fuel and air in the right ratio and then the PID controller runs a second fuel line and blower (or blower setting) for "full blast" forging. You'd need a second normally closed solenoid for safety before both of the circuits though. I considered doing something similar early in my forging experience, but ultimately concluded there wasn't enough advantage for me to make it worthwhile. For most of the things I forge, "eyeballing" the temperature is close enough. I did build the aforementioned electric heat treating furnace for alloys that require more precision though. Quote Link to comment Share on other sites More sharing options...
Dueldor Posted June 5, 2022 Author Share Posted June 5, 2022 Wow so was totally not getting my notifications that there were replies lol. That spam folder is a black hole just sucks in whatever it wants. Yea I’m not going to hook the pid to the blower as well. I thought about it cooling the forge, but at those temps I’m not thinking the air is going to have enough cooling effect to really hurt it as well as it’s going to warm coming into the forge right? Also it seemed to me that keeping the air moving inside the forge would be advantageous as well. Would be nice if I could work it to have the gas solenoid shut off and then a delay of a few seconds and then the blower shut off as well, but unless someone can help me design a pid capable of such and help me understand how to make it go I don’t see that happening lol. Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 5, 2022 Share Posted June 5, 2022 It's not your spam filters, we just like messing with people in Colorado. What I don't get Buzz is exactly what the purpose is here, No I'm not going to read the whole thread so you can ignore me if you wish I won't mind. Anyway if the idea is to maintain a consistent temperature in the furnace then keeping the blower running without gas is going to cool the furnace. Then because it's chilled faster it has to restart sooner. I assume muffling the thermal cycles is the job of the forge liner. No? This makes me think I'd rather use an electric kiln. If leaving the blower on longer than the gas after shut down to prevent it firing back into the mixing tube won't you have to start the blower sooner to prevent it happening on start up? It'll take a little time for the flow velocity to build past the rate of combustion won't it? Bearing in mind I don't really know about this stuff and would talk to my buddies at the HVAC shop up the road, how does this sound. Won't the blower impeller free wheeling to a stop clear the mixing tube after gas shut down if they're on the same switch? On start up let the gas valve switch supply a second pressure check valve so there's a hesitation while pressure builds for the blower to get the flow rate up. That's just a WAG but if you're not going to buy the right components or learn to make them properly. . . Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Dueldor Posted June 5, 2022 Author Share Posted June 5, 2022 (edited) LOL! Had not even thought about startup. Maybe just sticking with a thermocouple and playing with gas/air flow rates to increase or maintain temps? Or this could all just be a concept that winds up in the round file receptacle. Was thinking it would be nice if I got into forge welding to be able to set the max temp and not overheat the metal and wind up with a useless puddle or a sparkler display lol! I do plan to build a heat treat oven eventually as well anyways so maybe the temp controlled forge is a moot point. Things to consider, thanks Frosty! Edited June 5, 2022 by Mod30 Excessive quoting Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 5, 2022 Share Posted June 5, 2022 You're just making a forge? Oh no you don't need thermostat heat control unless you have a commercial forging operation! Without reading the whole thread I was thinking you were heat treating. I light mine at the beginning of a session and shut it off for long breaks say lunch or when I'm finished and my forge isn't small. Not small enough in fact but I've talked about that many times already. Over thinking or adding bells and whistles just because is a very blacksmitherly thing to do. Welcome to the club. And what the hey, once in a while they pay off. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Dueldor Posted June 6, 2022 Author Share Posted June 6, 2022 Well that’s good because I am forever tinkering and designing. Can’t wait to start learning and making! Quote Link to comment Share on other sites More sharing options...
Buzzkill Posted June 6, 2022 Share Posted June 6, 2022 19 hours ago, Frosty said: What I don't get Buzz is exactly what the purpose is here, I assumed, perhaps in correctly, that he wanted to be able to essentially set a desired temperature and have the PID take care of keeping it constant. I thought about doing this some years ago shortly after I started smithing. If you set up an idle circuit that always provides the minimum amount of fuel and air required to keep the flame lit and then a separate controlled circuit can add fuel and air in the correct ratio as an "on/off" option then in theory it can be accomplished. However, after gaining a little experience I decided it was not work the time and effort to try to set up something like that for general forging. Most of the alloys we use don't require that level of precision for forging temperatures, and I think it is valuable to learn to judge temperatures by eye anyway. Of course moving from a dimly lit building into direct sunlight can throw our color perceptions off by a wide margin, but that's about the only scenario I can see where being able to "dial a temperature" might be worth the hassle. On the other hand, controlling the temperature more accurately for heat treating purposes is more valuable. My personal determination there was that an electric oven was much better suited to the task than a propane fired system. Although it takes my 110v heat treating oven about 3 hours to reach close to 2000 degrees F, I can control the heat within a few degrees accurately and consistently from room temperature all the way up to the max temp. So far I've used it mainly for tempering, but I do have some AEB-L that I plan to attempt to heat treat soon. The bottom line is the tinkerer in me loves the idea of the "dial a temp" propane forge, but the limited experience I've had and the practical side of me says it's not worth the effort for general forging. If a propane forge is setup up for general forging temps it's also fairly difficult to bring the temps down low enough for tempering, so I can't recommend it for that purpose either. It's one of those ideas that sounds a lot better and more practical than it really is imho. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted June 6, 2022 Share Posted June 6, 2022 So long as the heating chamber is exposed to direct flame impingement, temperature control is always going to be clumsy. However, I think it was Don Fogg who asked what I thought about a double chamber forge, with the lower chamber heated with an oil flame, and separated from the upper chamber with a high alumina kiln shelf that didn't extend all the way to the rear wall of the forge. I discouraged the idea, as I had already spent two years investigating oil burners, and concluded that they just weren't worth the hassle. However, if you used this arrangement with a gas fired ribbon burner in the lower chamber... Just in case you're getting too much sleep Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 6, 2022 Share Posted June 6, 2022 NARB is stable stop to stop on my old 0-20lb. regulator so they MIGHT work for a heat treat furnace but I've never done that kind of tinkering. I have a friend with an electric kiln he's upgraded the temp controls and gauges for heat treating. I'd drive to Anchorage and kick a $20 for the electric bill and give him the temps, times, ramps, etc. I needed and let him at it. If it was tricky stock I'd sent it out for heat treatment. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted June 7, 2022 Share Posted June 7, 2022 Muffle Furnace? Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted August 4, 2022 Share Posted August 4, 2022 On 1/21/2022 at 10:30 AM, ThomasPowers said: 250 Kelvin you are in trouble; 250 C you are probably all right, 250 F and I'd worry; of course it depends a LOT on the type of burner, size and how it's arranged. I really dislike vertical placement of burners for several reasons with CO and the chimney issue having the greatest weight. In the past I would have argued with your viewpoint. Today's materials make down facing burners that are aimed at a forge's floor no advantage. Therefore, I completely agree with your viewpoint. All things change. Quote Link to comment Share on other sites More sharing options...
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