Dodge Posted March 22, 2009 Share Posted March 22, 2009 OK, I think I have read just about every article about gas forge burners, from A to Zoeller and I'm sure the are so mighty fine burners in between. The consensus among all the different designs is that a "properly tuned" 3/4 burner will heat to weld temp approximately 350 cubic inches of forge chamber that is constructed with the typical ceramic wool liner coated with an ITC 100-like product. My question is this: If one was to construct a "properly tuned 1" burner, what sized forge chamber could one heat to weld temperature? My proposed forge will be a cylinder 6" x 15" which calculates to roughly 424 cubic inches. Would the larger burner make up for the the additional 74 cubic inches? One might ask, "Why not just run two burners?" For simplicity, I would rather run just one. "Why 1 inch?" one might ask. That's just the way the coin landed. I think it was "heads!" Thanks for putting up with me Scott :D Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 22, 2009 Share Posted March 22, 2009 (edited) Yes but not evenly. A 1" burner is almost 2x the cross section of a 3/4" burner and puts out a bit more than 2x the heat. The problem is your forge is so long and narrow the heat would never distribute evenly. If even heat is important I'm afraid you'll need two 3/4"ers. Frosty Edited March 22, 2009 by Frosty Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 22, 2009 Share Posted March 22, 2009 Dodge- IMO, 15" long chamber should have two burners because you aren't going to get weld heat coverage for all the chamber. I think 250 C.I. coverage for a 3/4" burner is safer number. From your discription, sounds like you want to enter from one end and not a side? Personaly, I would realy reconsider the one burner and go with two. Are you making or buying your burners? My reasoning is that you can always run one burner for small stuff and then two for longer projects. My forge is bigger but has two burners and I run one most of the time, but boy, it sure is nice, when I want to heat something long to have both burners so I don't have cold spots on the work when forging. Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 22, 2009 Author Share Posted March 22, 2009 Dang it. You guy really knocked the wind out of my sails LOL. But I 'spose I am asking a little too much from the laws of physics Back to the drawing board... Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 22, 2009 Share Posted March 22, 2009 Drawing board? How do you draw with a board? What kind of wood is it and how do you keep it from catching fire? Frosty Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 22, 2009 Share Posted March 22, 2009 maybe he pounds it out... to draw it It always easier to erase a problem in pencil than in a finished product! Quote Link to comment Share on other sites More sharing options...
Judson Yaggy Posted March 22, 2009 Share Posted March 22, 2009 Two burners also gives you the opportunity to put a valve on each one and run them independently for shorter or localized heat which is sometimes useful. Quote Link to comment Share on other sites More sharing options...
saintjohnbarleycorn Posted March 22, 2009 Share Posted March 22, 2009 Just a thought here, I put a burner in an old burnt out gasser. What I found out was when I was using it and doing some bending and forming I wanted the gasser wider than taller. Lets say you make a scroll or an s shape, its thin and wide. I was doing tow or three at a time and saw that a wide front opening would be really handy. I was thinking of the tube type of gasser but actually using one I think a rectangle is better suited to forging. I know round is easier in a lot of ways, pre made even. I have a lot of things I could make a round one out of ready to go. but I think I will go to the trouble of making it squarish. Maybe the beehive style? Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 22, 2009 Share Posted March 22, 2009 Mailbox shaped is a happy compromise. Larger dia pipe split in half or less. The arch holds Kaowool without special hangers, directs the burner flame well and acts like a lense to focus the IR radiating from it towards the center of the chamber. You get a wide flat floor in the process. A flat roof can be a trick to keep in place. Frosty Quote Link to comment Share on other sites More sharing options...
Brian D Posted March 22, 2009 Share Posted March 22, 2009 I really like the idea of a mailbox shaped forge. It would really make the ceiling in the forge easier to manage. I used Duraboard in the flat ceiling of my forge and it does get a bit tricky to hold it in place without sagging. I will surely keep that in mind for the next one I build. Quote Link to comment Share on other sites More sharing options...
Woody Posted March 22, 2009 Share Posted March 22, 2009 Dodge why not make a movable piece that can be brought up toward the burner to cut down the chamber size when you need to go to welding temp. Just a piece of 1 inch thick ceramic insulation board is all you need. When you need to weld, put it in to block off the back portion of the forge chamber. Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 22, 2009 Author Share Posted March 22, 2009 OK, I'm resigned to the idea of needing two burners, but I haven't given up on doing it as cheaply as possible. I like the idea of a movable plug to reduce the chamber size, but how tight would it need to be to be affective? I ask because I was thinking if I could simply cut a plug out of my inswool scrap and coat it with the same refractory mortar I am lining the forge with (see Greenpatch 421 thread) I can still get away without having to buy any additional materials, but it wouldn't fit real tight. There would still be some leakage into the "unheated" side, even if I used forms to mold everything to shape. Would it matter? Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 22, 2009 Author Share Posted March 22, 2009 OK, I'm resigned to the idea of needing two burners, but I haven't given up on doing it as cheaply as possible. I like the idea of a movable plug to reduce the chamber size, but how tight would it need to be to be affective? I ask because I was thinking if I could simply cut a plug out of my inswool scrap and coat it with the same refractory mortar I am lining the forge with (see Greenpatch 421 thread) I can still get away without having to buy any additional materials, but it wouldn't fit real tight. There would still be some leakage into the "unheated" side, even if I used forms to mold everything to shape. Would it matter? Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 22, 2009 Share Posted March 22, 2009 That'll work fine Dodge. That'll work fine Dodge. Sorry, I'm just too lazy to answer your posts individually. Frosty Quote Link to comment Share on other sites More sharing options...
Dick L. Posted March 22, 2009 Share Posted March 22, 2009 Dodge, I don't mean to hijack your thread but I have a question regarding the shapes mentioned. If the shape is cylindrical, either half like a mailbox or whole tube is it an advantage to position the burner tangent to the arch? Heat sources I've seen glassblowers use are built that way. I've been told they do it to get a more efficient burn by superheating the rough texture of the interior coating as well as the swirl effect. Curious what the thoughts are here in metal use. Dick Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 23, 2009 Author Share Posted March 23, 2009 Frosty, I know, Right? oops!! how did that happen!?! Dick, No problem. whats a hijack? I hope others learn from my questions as I hope to learn from others' questions that I failed to ask:) As for the shape, I'm hoping to find that it was one of the mistakes I made on my first forge. It was half an octagon with a flat floor. With two burners, I could weld but it was a gas hog and I had two hot spots. The burners came in a 45 degree angles in hopes of creating a swirl but the flat sides cancelled that effect. I'm bringing the burners into my new shell at a tangent to the curve so it will swirl. I think, glass or metal, an even heat overall is certainly desirable. Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 23, 2009 Share Posted March 23, 2009 Yeah, there are two schools of thought about burner angle. One school says aim them straight down at the floor. The other is the tangential crowd who want even heat. Like so much of the craft it depends on what you want. For a lot of smithing, myself included a hot spot isn't a bad thing. For someone who needs even heat for heat treating and such then that's important. Were I making another pipe forge I'd place the burners a bit farther apart than normal spacing and aim them towards the center as well as tangential to the forge wall. This would not only produce a vortex it would tend to push the fire towards the center of the chamber and maybe keep it inside a smidge longer. Were I making a box forge I'd place one pair of burners at the top aiming at the far side and another pair on the opposite wall about an inch off the floor aimed at the far wall. This is how I recall the burner arrangement in the forge in my high school shop class and it developed a very uniform internal temp. I suppose it'd be easy enough to make a cardboard mock up and use a smoke generator to see how things are likely to flow. Hmmmm. Frosty Quote Link to comment Share on other sites More sharing options...
Woody Posted March 23, 2009 Share Posted March 23, 2009 Dodge it don't have to fit all that tight, there can be some leakage by and it won't matter. The material and treatment you have in mind will work just fine. Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 23, 2009 Author Share Posted March 23, 2009 Frosty, I also have given some though to aiming them slightly toward the center. My theory is that although, at a tangent to the curve of the cylinder, the flame would sort of "crash" into each other and created a largely spread hot spot in the middle of the forge. I did in deed feel the advantage of hot spots in my old forge. The pic shows the positioning of burners in my old forge Woody, I was hoping so My thought is to cast a loop or such in one side to use as a handle to ease in placement and removal Quote Link to comment Share on other sites More sharing options...
Frosty Posted March 23, 2009 Share Posted March 23, 2009 Hmmmm. I'm having trouble visualizing how the flame would move with that set up. Is that the one with the really thick refractory? The burners look to be burning nicely, just a little under gunned. Frosty Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted March 23, 2009 Share Posted March 23, 2009 A friend of mine has an old ferriers forge with a trashed liner and 3/4 to1" chunks of high temp fire brick and pieces of kaowool spread all over the bottom. It definatly gets hot. Haven't tried to forge weld in it but it is hot enough. Seriuosly, the only cold spot is the steel that gets put in it!! It is yellow hot in the top back corners!!! It sucks the gas though. His theory is the brick and kaowool bits bounce the heat all over the place....seams true. personally, I like hot spots as long as they are big enough! Quote Link to comment Share on other sites More sharing options...
saintjohnbarleycorn Posted March 23, 2009 Share Posted March 23, 2009 thanks, the mailbox idea is a good one, and not to hard to make I have some thin steel thats thick enough to weld. Ok so if I want two 3/4" burners what dimensions would you suggest that I make the mailbox? thanks for the info I have been on the doorstep of making one for the last two months now and I think this last part of the puzzle will do the trick! Looking forward to trying some forge welding when it is up and running. Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 23, 2009 Author Share Posted March 23, 2009 (edited) Hmmmm. I'm having trouble visualizing how the flame would move with that set up. Is that the one with the really thick refractory? The burners look to be burning nicely, just a little under gunned. Frosty Frosty, That was the problem. The flame didn't move. just hit the floor and I had two individual hot spots. Yeah thats the 3" thick "heat sink". They seem weak as they were just at an idle. I think mabe 5 psi or less. Just enough to light them and get the pic. After I installed inswool to the outside, I couldn't prop up to light anymore but it did help hold the heat in. It just still took a good 20 minutes at 10 - 12 psi to get to forging heat. Here it is at "full race" mode. My original intention was to replace the chicken wire with a permanent metal shell. interesintly, this chamber is aproximately 347 cubic inches. Two 3/4" burners should have been more than enough, but I believe the combination of the faceted walls, wall thickness and perhaps (?) burner overkill (?) played a roll in its inefficiency. One burner would by no means, heat the forge, even to a decent forge heat. These burners really performed well. I just don't believe I put them in the right environment. Edited March 23, 2009 by Dodge Quote Link to comment Share on other sites More sharing options...
courtiron Posted March 24, 2009 Share Posted March 24, 2009 Hi Dodge, I had a few thoughts for your design consideration, but wanted to find the reference for furnace temperature versus input BTU that I remembered. Went digging through the library and found the reference that I wanted in "Fuels, Combustion and Furnaces' by Griswald. .. an older book but fire hasn't changed that much in 60 years... Some notes on furnace temperatures Furnace Temp F desired needs BTU input/CF volume of furnace/hr 600-1,500 use 1,000-15,000 BTU 1,500 -1,800 use 15,000-22,000 BTU 1,800-2,000 use 22,000-35,000 BTU 2,000-3,000 use 35,000-150,000 BTU When you talk about blown burners you can't separate the CFM from the pipe size connected to it. I doubt that decreasing the outlet pipe size on a blower would maintain its rated CFM output. Since the BTU and gas flow are based on the CFM air flow, reducing the pipe size would be counterproductive. Regardless of the pipe size the and the fuel ratios, or more correctly because of the ratios the BTU output would be lower if smaller pipe sizes reduced the air flow. Increasing the pipe size would reduce the velocity of the gas column. If the gas flow slows down to much the flame front will move into the pipe instead of the firebox. For any given air flow there will be only one gas flow rate for maximum output. Lean mixtures produce hotter combustion gases than does a stoichiometric mixture, but run it to lean and you oxidize the furnace atmosphere... scale bad. That 60 CFM blower is around 530,000 BTU. 1 lb of Propane ~=22000 Btu's so the example of 530,000 BTU would require about 24 lbs per hour. At 100 lbs for 50 hours of burn time or 2 lbs per hour = about 44,000 BTU. So the 60 CFM blowers are not able to induce 60 CFM thru the 3/4" pipes. Most commercial burner nozzles are rated at an input pressure range of 3" of water column to 24" water column. This is far more than the typical blower that we are able to get our hands on. The blowers from hi-efficiency furnaces are probably the best bet for scroungers... curb side parts depot... Those same commercial nozzles are usually designed to use around 20% secondary combustion air. That means the nozzle is located a small distance away from the furnace wall and some (secondary) combustion air is drawn in with the gas exiting the nozzle on it's way into the furnace. Check out ordanthermal.com look for bulletin 3102 and bulletin 5760 Smilies Quote Link to comment Share on other sites More sharing options...
Dodge Posted March 24, 2009 Author Share Posted March 24, 2009 Courtiron, You lost me after 2000 Quote Link to comment Share on other sites More sharing options...
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