283 posts in this topic

 I've just missed commenting on a discussion that has been closed a second time, and can't help but agree that it was probably the best course, but it brings up a recurring problem; and that is perhaps a need for the discussion on burner design as a general topic. I haven't seen any other topic that gets heated any where near this fast in the Gas Forges section. 

I don't no why egos get so quickly bruised on this subject; there are lots of other details that can ruin a forge build; perhaps it's because poor work on the others isn't so spectacularly obvious; be that as it may, burners seem to be the item that folks show the most willful ignorance about in starting out, and the most deep denial over, when ending up!

I have heard a plethora of good advise on the subject from others and have given lots of it to boot. But, the strongest impression the comments I've heard formed are anger at the very idea that some have at doing a little reading on the subject before the fact, and a determination to argue after the fact, in stead of fixing the mess. Perhaps the heart of the problem is too little attention paid about the WHY some detail insisted on is necessary?

why can't a fella stick his gas jet near a hole in the back of a pipe,   and just get on with the deal, huh; why not already?!?

Answer: You don't get the incoming air that gas stream is "sucking" in to swirl at the same time, so gas and air  doesn't  get adequately mixed together to properly burn; this is why linear burners are designed with a pipe reducer fitting or other funnel shaped part stuck on at its rear, and the gas jet gets mounted behind that.

What if I don't want that a big old fitting hanging on the end of my burner?

Answer: Then you have to makes some air openings in the side of the burner near its rear, and it becomes a jet-ejector style burner, instead of a linear burner. Most people use holes for the air openings in their first burner, because it's the easiest form to make, and possibly on the "more is better" assumption, they drill way too many holes of as large as they can over way to large an area in the pipe, and then crown this effort by mounting their gas jet near the rear of the whole mess, instead of near its forward area. Where did they go wrong so wrong?

It foundered on the  "more is better" assumption. You only need about 40% more surface area from all those air intakes put together than what is found in the cross section of the burner tube's pipe, so they never needed that mess of gopher holes to begin with; there is a lot more to say on even just this subject, but first lets see if we can even get through with the "knockdown drag out" over these statements. Let the feathers fly. 

rorge

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Oh no, I'm going to defer to the "ex-spurts" lol. As all I know about gas burners is from cuss'n my proforge and reading you and Jerry's posts on the subject. 

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I never thought  to say this, Charles, but buying is maybe the better path for many smiths; if they dislike putting out the effort to understand what they are doing before they begin their build than why not?  Especially with some of the low cost choices available today. Devil Forge brand is a good example; are they  a great product? Not hardly, but they will give more than someones money's worth, and bring beginners up to proper starting point where they can easily finish building a good forge, instead of a complete mess.

The problem is getting any of the customers to check back in with us, once they complete the process :angry:

Mikey 

 

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I will wade in on a gasser build some day and I expect you to be alive and cognient enugh to help me! That goes for Jerry as well ;-)

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When you do I'll try and get over my shock enough to answer any questions you have Charles.

I"m going to mostly lurk in this thread though, I'm far from finished sponging information on burners from Mike.

Frosty The Lucky.

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This thread could not have come at a better time as I've just spent the last 4 weeks pouring over different burner information and trying to wrap my head around all the info. I want to have as clear an idea as possible before I build my first forge. 

Thanks in advance for all the information. I'm now going to sit back and greedily absorbe all the upcoming knowledge!

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Darious,

And you are the vary sort of pupil I was hoping to give the advice to! First, I would advice you to obtain a copy of my old book "Gas Burners for Forges, Furnaces, & Kilns. No, this isn't a sales pitch; it has been pirated to the net for yes, so you can obtain a free copy. Because there has been a lot of water flow under the dam since publication, I can update you and others who read this. This is IMHO  your best pass, but far from your only one. We can speak  about burners from other designs; there are a number of worthy designs floating around; it makes no difference which one you want to go with. My first burner was a Ron Riel linear design, which was quickly  modified, and we where off to the races. With  the MIG tip modification and a step style modified combustion "flare" (burner nozzle) it is still one of the best burner out there, as is the Frosty "T" burner, for a lot less work and money invested then either mine or Ron's. Next we come to the Modified Side-arm burner, which has been around for many years; you can find a lot of knowledge about it on the Larry Zoeler Forge site, but he isn't available to give you personal input on the material, and my knowledge about it is a little weaker than is available than Jerry's and mine on the others burners.

Pick your poison and let the questions begin. 

 

 

 

Sorry about all those typos; they'll be around for a while. Also I don't mean to imply that you cant start with whatever questions are already on your mind. Please begin.

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Thanks in advance for all the help. To start with I'm probably going to be a pain with all the questions. It's how I learn best so better get them all down as best I can. 

First things first: I don't have any materials yet as I want to have a concrete blueprint with research done on it before I purchase anything.

Second: the only blacksmithing I have ever done was twist an iron firepoker in a historic forge as a class field trip almost 16 years ago. 

All that being said I've been interested in doing my own work ever since and only just recently found that I have the ability and time and space to do it at last.

What I have my eyes on is a version of John Emmerlings ribbon burner. For a forge I would like to build a rectangle out of fire bricks. Then line the inside and outside with refractory cement and round it out inside while it's workable. In theory anyway. Feel free to tear apart the design concept and please hit me with the worst of it. If I know all the issues before I start then I may design something better.

I mainly want to do knifemaking once I practice and learn how. 

For starters I would like to know what connections am I going to need from the propane tank to the burner. What recommendations would you share for choosing a material to transport the propane? And most important what safety features can I add between the propane and the burner? The more the better. I don't care if it's overkill.

I'll have more after but right now it's 2am here in Calgary and I have to be awake again in 4 hours.

Thanks again everyone

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Do you have a copy of John's ribbon burner plans? Mike and I play mostly with Naturally Aspirated (NA) burners and a ribbon pretty much needs to be a gun (blown) burner. I'm sure a ribbon can be made to work with a NA air fuel supply but I haven't messed with one so I'd be speculating.

Your plan for a forge isn't very practical for a couple reasons. All that mud is a serious heat sink and backed by fire brick makes it worse. It's going to need a LOT of fuel just to warm up let alone keep hot. If you used light insulating fire brick the brick will start breaking up quickly due to thermal cycling. It doesn't like large temperature changes quickly, expansion and contraction needs to occur slowly, light brick i pretty darned fragile. It's never used as the fire contact surface in furnaces and kilns it's always used behind at least one layer of 3,000f hard fire brick. You surely don't intend to put 4-5" of refractory cement over it.

Plastering the outside with refractory is completely unnecessary and a waste of refractory. It's like painting the inside of the sheet rock.

Brick pile forges are a good first forge. They're not terribly efficient but they're easy to alter seeing as they're just stacked bricks. They let you experiment with shape and size before committing yourself to a permanent construction.

Give these some thought we'll get back. I've had a long day and am going to hit the rack.

Jerry

 

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So, going on about funnel shape fittings on the end of linear burners, and its effects:

Swirl isn't the only advantage that they can provide. If an impeller blade is attached at the large end of a funnel or pipe reducer at the burner's year end, a stronger vortex can be produced at the fitting's small end. The  impeller blade doesn't even need to move to get the effect, although a weak fan motor will work wonders.

It is a given that a fluid running through a round restriction will form a vortex, but usually so weak a one as to make no practical difference, so that the term swirl or  is more appropriate.

But, for every minor increase in power added to a vortex its swirl and other benefits are greatly magnified. What other benefits? Increase flow of incoming air simultaneously with a large drop in air pressure in that flow; a magic combination that can be found in no other way. And with that we can move on to jet-ejector burners and their air openings.

To begin with jet-ejectors induct more air into a naturally aspirated burner than can be found from a linear style with a rear funnel, unless it is equipped with a fan, and then it is no longer naturally aspirated, even if it is an impeller blade fan.

The way a jet-ejector's multiple air openings create swirl is from twisting into a small part of a turn, as air travels into the burner, just ahead of its mixing tube area; that my be found as part of a single tube shape (Mikey burner), or within a larger area built up in part from a reducer fitting and a larger diameter tube section (Hybrid burner). It can be made up as  two opening on a pipe fitting ("T" buner), or even from a single opening (Modified Side-arm burner); all are examples of jet-ejectors.

One fact of life we have to address is DRAG, which is the arch enemy of mixture flow. Any opening through which air flows creates drag as it passes by the air opening's edges, by creating eddy currents. Curved edges create more eddy currents then straight edges; the stronger the curve the greater the eddy currents. Can you think of anything worse for creating drag than lots of little holes? Thus the advantage of just two larger holes in a "T" burner is far superior, and even the offside single hole of a Modified Side-arm burner trump them; this is despite the fact that both of the latter two burners have threaded openings that air must pass through, which threaded side holes don't! Do we begin to appreciate how powerful eddy currents are at creating drag?

Moving in the opposite direction, Rex Price, while still studying burner design with me, sent his version of what he thought he had learned of my ideas; his burner used slots for air openings, instead of my rows of holes, thus combining straight with curved edges; the improvement was remarkable. So I came back with rectangular air openings to remove all curves from their edges, and beveled forward and rear edges for good measure. Such a boost in performance was gained that a radical new step stye flame nozzle became possible.   

 

   

 

 

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First thanks for the advice in the forge Frosty. I will strip that idea and start from scratch again. I think I can get an old propane tank to cut down. I will look up some designs. My biggest concern is that it has to be portable and not too large as I'm renting and it is being stored in a shed when cool and not in use. Disconnected from everything of course.

The Emmerling blower plans can be found here: www.waynecoeartistblacksmith. com/uploads/Ribbon_Forge_Burner.pdf

Although if I'm understanding correctly I may not have to worry about going through the effort of making that anyway.

Mike do you have photos of your design with the beveled edges. It sounds very efficient on gas.

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Darious,

The book has over 100 drawings illustrating quite specific text  showing every step of construction on every burner size listed, along with the very type of forge you want to build. however, instead of a five gallon propane cylinder, you will want to use a two gallon cylinder from a helium cylinder for balloon filling, or a two gallon cylinder for Freon; both kinds are nonrefillable, so they can be had.

A coffee-can forge might be even more handy for your needs; there are some nice examples of them on the Larry Zoeller Forge site.

But, if you wanted the slickest knife maker's forge around, a very smart fella came up with a design for an oval shape forge from car mufflers. You can find his email ab out it (in including photos) on one of our older pages from about two months back.

I am a fan of ribbon burners, but as I state about my own designs as well, "no one shoe fits all" and no single burner design is best for everything. The point of ribbon burners is hang time. Fuel use is very efficient with them, because they put out multiple small high temperature flames, which are also low velocity for what they produce. BUT nothing comes without a price, and so far  that price is compactness; that wont fit well in your present situation. There are other was to come up with an efficient forge; I would suggest you look on the 3/8"  Mickey burner posting from four months back.

Some guy built a 1/2" "T" burner a few months back and posted it; that would make a dandy burner for a miniature forge. We need to corner Frosty and get him to come up with plans for one in that size.

Having given you my best advice about how to proceed, I encourage you to go right ahead and "follow your druthers." If you really want a ribbon burner running a knife makers forge, do it. Some guys or looking into using inflation pumps. I feel that a hair blower should work well (might be a bit noisy). There are always ways to proceed if you want something badly enough. One guy even found a way to run a 40,000 Btu ribbon nozzle on a naturally aspirated burner; that's low, but I believe it would work out okay in a coffee-can forge.

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Darious,

Gas Burners for Forges, Furnaces, & Kilns has chapters on all the background knowledge you need to run the equipment, including all the fittings and hoses.

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The same burner ratios used to build a 3/4" or 1" T burner apply to a 1/2". The tube length = 8 or 9 x dia. bump the run dia up one. so a 3/4" x 1/2" T. The mig contact tips that work well are 0.023" to 0.025". Bear in mind the dia. rating of a mig tip is NOT it's ID, its the dia. of the welding wire it's designed to pass.

Some guys us a flare some don't, I use thread protectors I'm generously allowed to scrounge from the local HVAC plumbing service supply company up the road from me.

If you download the "Illustrated T burner plans" I posted a while back it lines out an easy way to build the things.

Teenylittlemetalguy is an Alaskan Association member and I've used his 2 brick 1/2" T fired blade forge. You have to keep an eye on your work or it'll melt it. He makes various welds with it often. His big forge is around 350cu/in fired by a 3/4" T burner, his BIG forge.

Frosty The Lucky.

 

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Thank you guys so much for all the advice. I downloaded the book and am settling down for a good read. I'm gonna have to see about getting a hard copy of it though as nothing beats the feeling of running the pages in in your hands. I will update you guys with the plans as I go along and post pictures as I start building.

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Frosty,

Thanks for that needed information for guys looking to make smaller "T" Burners; I think they are important for knife makers who don't want to be stuck building a Mikey burner:)

Darious,

Whichever burner. and the forge you decide to place it in after looking through the various material recommended for you to look at;  one part of the book that is outdated is the advice to employ a 4-/2"  angle grinder as your primary construction  tool. At the time that book was written, small angle grinders were a better deal for the money than small electric die grinders were;  this is no longer true. On top of that eBay features even better deals on Dremel tools. Both the rotary tools and their accessories  are now  so improved that they are the only way to go for cutting and shaping the sheet metal for  small forges. 

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 Mixing Tubes

So moving beyond the  air entrances on a burner body,  we find the area called the mixing tube. The rule of thumb for figuring out where to begin looking for the optimal length for  the mixing tube area on most burners is called "the rule of nine." You normally use nine times the inside diameter of the tube body to measure the length of the mixing tube, from where it begins beyond the air entrances, and where the tube body ends; this does not include the area of overhang of the flame nozzle ('AKA flare), which is additional to it.

A rule of thumb makes a nice starting paint for the perfectionist and a good enough ending point for the generalist. On a Mikey burner I would shave that to eight times the length to come up with the hottest burner, and as much as ten diameters for the smoothest burner for hand torch work out in the open air.

Further more, a Vortex burner would average fourteen diameters to make a smooth flame in ambient air.

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The nice thing about a rule of thumb is that it presents an implicit warning that it can't be considered the end of the matter. Where as a general formula can end up so full of exceptions in the real world as to be useless; as would be the case here because of all the variants presented by flow velocity and pressure in later burner designs. 

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                                            Flame Nozzles

We are getting close to the heart of the matter now. Not flame nozzles of course, but control of the flame, which flame nozzles are all about; every part on  a burner exists  to encourage and control the flame. The real difference between a forge and a forest fire is flame control.

So, lets begin by crushing the fiction that you can freely do without flame nozzles; yes you can often do without them, but it isn't free; in most cases it simply allows more of the flame to disperse into the general confines of the forge chamber, will a flame nozzle will help confine more of it to a smaller, and therefore hotter, area near the burner opening

There are apparent exceptions to this, found among devotee of brick pile forges; but a closer look shows the way the burner is placed in the brick forms a working burner block; a very power deign of flame nozzle. Such installations are not to be dismissed as inconsequential; there is a rich chunk of research awaiting here. 

 

 

 

 

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So, getting on with some background about flame nozzles: The most usual nozzle material is #316 stainless steel pipe or tube, followed by #304 stainless; these two alloys are not the very best material available, but they are the best the average guy can find and afford. Next comes cast iron, followed by mild steel.

These nozzles allow the flame to be fine tuned by varying the amount of overhang it is set beyond the end of the mixing tube. Both flared and stepped designs will help tune the flame, but stepped nozzles do it with more range: this is because one-half of its enlarged area is is formed by the flare on its end, so that it does not change the the length to diameter ratio now matter where it's placed. The ratio is only effected by the length of tube it is part of because of the thickness of the mixing tube, which forms a small step.

Step nozzles replace the flared area, and use a spacer ring on the rear end of a larger tube to create a larger step (shoulder) between the mixing tube and the nozzle area; both kinds of nozzle designs are needed, depending on how fast the fuel and air mixture flows down the burner.

The usual length of overhang for a step nozzle will end up between 1/8" and1/4" longer than the inside diameter of the the mixing tube. Just as mixing tube length can be used to soften the flame for brazing and other hand torch work, nozzle overhang can be used to tune a burner for special flame effects.

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You will notice that my remarks are long on why-for and short on specifics. There isn't space here to write another book. The aim of this discussion is to get guys who are looking to "throw together just any old burner" why some of the ideas floating around are just plain wrong, so that they will hopefully not end up with a joke burner or a bomb.

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Mike how about explaining exactly what the dia. increase the nozzle or flare makes works. I don't mean what it's use is, eg. controlling the flame, but the physics of what and how it does it.

Were you reading my mind again? I was almost ready to sign and submit this one and yours showed up. I'm going to let the question stand though. You can explain the basic physics without even writing a full page let alone a book. :P

Frosty The Lucky.

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Frosty,

Don't hesitate to go ahead on with your own writing, and even questions mine; both our views will only add to what people can can come away from what they read, because details of construction depend so much on how fast and and how low pressure the flow of fuel gas and air down the mixing tube is into the flame chamber made by the nozzle; and these factors are dependent on the overall design of a burner.

There are two functions of flame nozzles; the lesser (but still important) of them is to provide a low pressure area barrier before the mixing tube; thus providing a safety factor by reducing the ability of flame to burn-back down the tube into the burner; resulting in increase stability.

The greater function is, by reducing pressure in the nozzle it helps "glue" the flame in place. Expanding gases from combustion creates pressure, which can blow the flame away from the end of the burner, blowing it out: all there is to stop that is the counter pressure of ambient air beyond the flame envelope (AKA pressure front). What air pressure? Only the difference between surrounding air and the lowered pressure of a partial vacuum formed by the drop in mixture pressure made by the the increased internal diameter in the nozzle area.This can also be added to the partial vacuum formed in a vortex in newer burner designs.

There is an additional factor gained by flame nozzles; the ability to partially "suck" the flame back into the the nozzle area, super-heating the nozzle into incandescent temperature; thus creating a large second ignition surface to add to the the flame front that ignition normally tends to burn back into the gas pocket from.

Finally, there is a synergistic motor affect created through the ability of flame nozzles to allow combustion rates to be greatly increased. Just as we are aware that the gas stream at the burners other end entrains air into the mixing tube by induction (Bernoulli's Principle), the flame itself can become, in effect, a second induction motor, speeding up mixture flow even more within the burner.

But, the flame also becomes a powerful induction motor on the outside of the burner, cuasing a lot of secondary air flow passed an entrance way, which should therefore be partially or fully closed (depending on burner design), in order to stop or at least slow secondary air, as needed.

 

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So, what kind of increase am I dealing with all told for the diameter of the nozzle areas? Originally I used schedule #40 water pipe, which meant that the wall thickness for every mixing tube, and spacer ring from which diameters came, increased approximately forty-thousand of an inch over the previous burner size (mixing tube wall and another additional forty-thousandths over each previous pipe wall thickness for each spacer ring; all those walls thicknesses put together also became doubled in the process, because thre are two shoulders encountered for every pipe wall. So, the answer to your question would require a chart.

Suffice it to say that the question doesn't need an answer, so long as schedule #40 pipe is used, or a a pipe chart is looked at before tubing is substitute for it. I did occasionally try departing from these wall thickness, only to find that very little variation would ruin burner performance, and so became satisfied that I wasn't missing any bets with it.

While pretty much finding these tolerance "written in stone" for that burner seines, it doesn't follow that they will work with others. Every burner design ends up with very different gas/air mixture flows, and that changes all the rules for it.

Vortex burners are so different that they can run with two to three different nozzle diameter, and ribbon burners are so different they need a completely different write up!

I have seen threaded unions being happily run on other burners that would ruin a Mikey burner's performance...is there an end to it? I don't think so.

 

 

 

 

 

 

 

 

 

340

 

 

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                                                      Gas jets

In one form or another, capillary tubes have been used all over the world in recent years for gas jets on burners, for the vary good reason that they work much better than holes drilled into the sides of  pipes, are the somewhat longer drilled out brass forms used as jets on gas and oil home air heaters.

MIG wire contact tips was the most convenient source for such jets for most burner sizes desired for years. But the variety of hole sized available from this source has become a problem as miniature burners became more popular; this is because the smaller a burner's diameter the more critical it is to match up the jet diameter properly to the burner body's diameter.

So, blunt tip dispenser needles have now joined MIG tips as gas jets of choice; they can be purchased from various online sources with convenient base configurations to make  them easy to assemble with other burner parts.

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