Rossty Cage Posted June 3, 2013 Share Posted June 3, 2013 Hello all, Despite perusing the web, that a concise, general burner parameters--e.g. number of burners, orifice diameter, gas PSI, etc.--to chamber dimensions formula/ ratio for gas forges is absent bewilders me. Although finding orifice diameter to PSI to energy output (typically in BTUs) charts is easy, you would figure such a rule would be paramount and ubiquitous given metalsmiths' penchant for adapting and customizing their equipment. And the dimensional modularity of a firebrick gas forge (this problem is contingent and exigent for my plans to construct one) not only embodies those characteristics, but moreover greatly depends on this formula/ ratio with each rearrangement of the bricks. Plus, coal is becoming expensive and scarce while natural gas prices plummet. Thanks for your time and help, Steven Quote Link to comment Share on other sites More sharing options...
Glenn Posted June 3, 2013 Share Posted June 3, 2013 There is 35.97 cu ft per gallon of propane at 2546 BTU per cu ft giving a total of 91,600 BTU per gallon. Reference No matter what else you do, your only have 91,600 BTUs per gallon to work with. Quote Link to comment Share on other sites More sharing options...
Chinobi Posted June 3, 2013 Share Posted June 3, 2013 i think it comes up about every other thread in the gas forge section that one well tuned 3/4" burner will suffice for 300-350 cubic inches of interior forge volume, regardless of how you end up arranging your bricks to achieve said volume (within reason, no 350" long 1" cross sectional area tube etc) PSIg also comes up frequently, but my evening addled brain is remembering most prominently that everybody argues about what pressure to run their gauge at because nobody's gauge is the same and nobody can say if its actually calibrated, then it ultimately circles around to forget the numbers, tune the gauge and choke until you can actually see and hear that you have a proper flame. orifice geometry information is available here and elsewhere online, i haven't committed enough of it to memory to comment on it. google up zoeller forge for some solid guides for burner construction, youtube has a plethora as well. take a read through the gas forge section and you should be able to scare up enough information to produce a serviceable re-configurable firebrick forge. also, add your general location and there will probably be somebody within striking range that can perhaps shed some light on the local opportunities near you. good luck! Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 3, 2013 Share Posted June 3, 2013 Welcome aboard Steven, glad to have you. If you'll put your general location in the header you might be happy to find out how many IFI folk live within visiting distance. Correct me if I'm wrong please. From reading your post I take it you need some formula to design a forge? Or do you wonder why people practicing a craft of making, with skill and the general rule of thumb haven't produced a specific formula for something a person can adjust by the twist of a regulator or valve and judge accurately by eye and effect? I've been making naturally aspirated propane burners for probably 20 years now, easily capable of melting 3,000f. hard firebrick in a 350 cu/in chamber with one 3/4" ejector type burner running about 7-8 psi. Please let us know when you've developed your formula and what you do with it. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
Rossty Cage Posted June 8, 2013 Author Share Posted June 8, 2013 From reading your post I take it you need some formula to design a forge? Correct. Welcome aboard Steven, glad to have you. And I'm glad for such a responsive forum. Thank you. Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 9, 2013 Share Posted June 9, 2013 You're welcome. One of the reasons this forum is here is to exchange information, we all learn from each other. One of the defining characteristics of the blacksmith's craft as an art is everybody does it differently. Something that works a treat for one is a complete failure for another. Soooo they get together and swap techniques, now guy B can get IT to work but Guy A finds out that what Guy B did instead is a much better technique for him. The more information we trade the more everybody wins. Helping someone learn the craft yields as many or sometimes more benefits for the mentor. A good question is a gem to cherish, it makes us examine why we do things a way and more often than not the self examination helps the mentor do it better. It's a win win of epic proportions. About your formula, you don't need more than a basic understanding of how the things work and how to adjust based on observations. Trial and error is a core skill for blacksmithing. If you take a look/read through the gas forge section, you'll see some basic rules of thumb recurring. The overall rule of thumb is: one each 3/4" propane burner will bring 300-350 cu/in to welding heat. Correctly adjusted goes without saying and the construction must meet certain standards to achieve this. . . Of course. Does THIS rule of thumb mean you have to use a 3/4" burner? Nope, it's used as an example not a standard. Burner output is dependent on the output tube's cross sectional area and related ratios. I'll get to those in a bit. For instance, area is the square of the diameter so a 1" burner has 2x the output of a 3/4" burner and a 1/2" burner has 1/2 the output, a 1 1/2" burner has 4x the output. It's pretty straight forward, output is NOT a linear relation. This is exactly the same rule that governs Jet diameter but I'm not good at math to be able to calculate correct jet dia. so I just do it by trial and error and take notes. Heck, the entire thing is governed by Bernoulli's principles, it's all in books I don''t have the math to understand. The basic ratios for the naturally aspirated induction devices we use for burners are based on the throat diameter. The throat is the first narrow place in the device after the air intake ports. The tube length needs to be 8or9 x the throat diameter. The jet should be set back the throat radius from the throat. the last is the fuzziest and can be adjusted for discrepencies. The air intake ports need to at lest equal the throat diameter's area. Tha'ts it, the whole sheebang. Once you get one burning post pics and we'll help you tune it. Frosty The Lucky. Quote Link to comment Share on other sites More sharing options...
eseemann Posted June 10, 2013 Share Posted June 10, 2013 Guys, Take a look at this post, '?do=embed' frameborder='0' data-embedContent>> I have put up photos of my one brick Psychobilly forge. I have a 1/2 rod of 5160 in the photos that is glowing at or past non-magnetic. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted December 9, 2015 Share Posted December 9, 2015 Frosty states "This is exactly the same rule that governs Jet diameter but I'm not good at math to be able to calculate correct jet dia. so I just do it by trial and error and take notes." Trial and error with notes IS the best path to take with gas jet diameters, because, while how responsive a burner is to jet diameter in a given mixing tube size, jet diameter will make the difference. In some designs jet diameter is critical. Other designs are more forgiving, but the right size jet will prove itself best by and by. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted December 9, 2015 Share Posted December 9, 2015 Steven, Frosty gave you the common sense answer; to put it another way, there are so many variables that any concise formula you want to cook up is going to be so riddled with them as to be worthless. No one is going to all that trouble to present something unworkable, which is why you will never find a general formula. Even the few "rules of thumb" are only beginning points. Quote Link to comment Share on other sites More sharing options...
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