GradyS Posted January 5, 2019 Share Posted January 5, 2019 Hello everyone new member and getting into blacksmithing. My first forge was made out of an old propane tank and a naturally aspirated burner. It worked alright being lined with 2” of ceramic insulation sealed with Metrikote. The Metrikote didn’t seem to last very long and deteriorated quickly though unfortunately. The internal dimensions were far too large for what I was working with as well and it used a large amount of propane. This has led me to creating a version 2.0 learning from my first experience. Looking for any input/opinions on my new design. The burner is utilizing a small Dayton 75-ish cfm blower that seems to work excellent. Briefly tested inside the forge while I await an order of ITC-100 and Kast O Lite 30 before really trying it out. The forced air burner seems significantly more efficient on fuel requiring only 2-3 psi with the needle valve barely open while the naturally aspirated would require 5-10 and I was having problems with the flame running up the burner tube. Disregard the dot tube fitting for the propane supple it is temporary for testing. Should I consider adding a gate valve to regulate the blower? Should I perhaps reposition the blower to be below the forge itself? Ive done a ton of research but am at a point where I would like some personalized input on what I’ve been able to come up with given my limited budget using just what I’ve had on hand. Thanks everyone! V1.0 V2.0 Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 5, 2019 Share Posted January 5, 2019 2 hours ago, GradyS said: Should I consider adding a gate valve to regulate the blower? Should I perhaps reposition the blower to be below the forge itself? You should do both. Quote Link to comment Share on other sites More sharing options...
GradyS Posted January 6, 2019 Author Share Posted January 6, 2019 1 hour ago, Mikey98118 said: You should do both. Thanks for the advice. Quote Link to comment Share on other sites More sharing options...
Frosty Posted January 6, 2019 Share Posted January 6, 2019 Yes to both. Place the blower under the forge with the gas jet and use a couple elbows to bring it up and over. The elbows will help mix the propane and air more thoroughly. Propane doesn't mix with other gasses easily nor well and requires a little special attention in the form of: turbulence, cavitation, etc. to form a temporary mixture. How about showing us a couple pics, (NO videos please!) of your NA burner, one straight in the air intakes so I can get a look at the jet position and one of it burning before the forge gets hot. The difference in PSI between a NA and a gun burner has a lot to do with the motive force required to draw combustion air. In a Naturally Aspirated (that means inhales without help, Aspire means to "breath in" and usually means the breath of life eg. Expire usually means to die) Sorry for the digression. The only thing drawing combustion air into a NA burner is the propane stream. A gun burner on the other hand has combustion air provided by the blower so the only thing the gas jet does is introduce propane into the air flow. You see much lower gas psi in gun burners simply because the gas jet is larger so lower psi delivers equivalent propane. Being as the propane and air are NOT coupled in a gun burner, YES you need to be able to adjust both to control heat output. Does that make sense? Let us know if I muddied the waters too much. You don't really need to know theory or even the mechanics of burners if you just pick a set of plans and follow them closely. On the other hand, if you like to tinker it's hard to know too much about the subject. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 7, 2019 Share Posted January 7, 2019 We have all failed so far to mention that the box forge is doing well already (primarily the change in position is recommended for safety), and I think we all feel that your first forge could be made to run quite well with some minor changes Quote Link to comment Share on other sites More sharing options...
GradyS Posted January 7, 2019 Author Share Posted January 7, 2019 Thanks for the info! I got the blower rerouted to below the forge body and it seems to be mixing the oxygen and fuel better now. I am going to fabricate some king of manually sliding gate to regulate the airflow down at the blower in the next few days. I imagine in between that and the needle valve I will have the ability to really fine tune everything. Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted January 7, 2019 Share Posted January 7, 2019 You beat me to it. I was just about to post that if you are adding a couple of 90-degree bends and some extra pipe length to get the blower below the forge, do it in the larger bore pipe, not the smaller bore stuff. Looking at your blower, it seems to have about a 2" discharge. This reduces to 1" (maybe even 3/4") just downstream of the gas inlet. 1" pipe has 1/4 the area of 2" pipe and forcing air along 1" pipe takes much more pressure than forcing it along 2" pipe. Because of the way blower capacity tends to be quoted (maximum flow at zero pressure differential), you will have reduced your blower from a 75 CFM to a 19 CFM unit by reducing the area. This is not a problem since it is enough air to burn between 5.8 and 8.3 lb/hr of Propane: 5.8 lb/hr to Carbon Dioxide, 8.3 lb/hr to Carbon Monoxide. We tend to run rich (reducing) forge atmospheres with a mixture of CO2 and CO, so would burn somewhere reasonably near 7 lb/hr unless you have a way to reduce the air flow. The extra elbows and 1" pipe length will probably help to reduce gas flow and if that is 3/4" pipe you have used for the burner, you'll effectively have a 10.6 CFM blower able to burn between 3.2 and 4.7 lb/hr of Propane. It's still worth fitting either a globe valve or a sliding gate to bring the consumption down. If you can give it a threaded adjustment, you'll get much finer control than a simpler friction-held sliding gate. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted January 7, 2019 Share Posted January 7, 2019 Your box forge is definitely burning good and hot now. I will wait a while so guys who like fan-blown forges can tell you all they want, but we shouldn't allow your tunnel forge to grow dust in a corner; it can always bring a good price instead...once you fix it up. Quote Link to comment Share on other sites More sharing options...
GradyS Posted January 7, 2019 Author Share Posted January 7, 2019 The pipe coming out of the blower is 1.5” and then reduces down to 1” at the 90 where the fuel is being injected all the way into the forge. As mentioned I’m going to figure a system to regulate the blower. If I can scrounge up a gate valve I’ll use it, but most likely will be a simple piece of sliding sheet metal. I know as timgunn1962 said it won’t be perfect but it’ll be cheap. I’m already about $200 into it for everything after buying 20lbs of Kast O Lite 30, 1/4 pint of itc100, blower, and a few miscellaneous things. I really appreciate everyone’s input. Thank you. Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted January 7, 2019 Share Posted January 7, 2019 It doesn’t need to be expensive, or pretty, to make it finely-adjustable. A sliding gate will work and a couple of bent-up tabs of sheet metal on it can be enough to make things progressively adjustable with a long 1/4” screw. Quote Link to comment Share on other sites More sharing options...
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