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Burners 101


Mikey98118

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Or perhaps how small a ribbon burner...I was once using a large forge heated by a ribbon burner and accidentally had my 2.5" sq stock welded to some 3/4" round stock, the round stock owner re-positioned it in the forge and ran it up alongside of my piece and it welded---had to use a hand sledge to separate the two.  This was at about 7000' altitude too...I was impressed.

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The burner part most often left off

No matter how well you build your burners, you still need to limit air induction through the space between the burners and their burner ports, from being induced by the flame. In fact, the better the burner the greater the air entrainment will be, while the acceptable amount of secondary air intake will shrink. To check out how much secondary air your forge can use, stuff different amounts of leftover ceramic wool around the burners, temporarily. A simple permanent solution can be had with flat washers, which are held in place with nuts that are silver brazed onto the washers and thumbscrews to keep the washers at the right hight.  Why adjustable? Because how much secondary air is entrained/induced will depend on flame force. But some secondary air will be needed for most burners.

Excessive secondary air from burner portals can reduce forge temperatures as much as 10%, while greatly increasing scale on your work.

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Regulators at a glance

Many torch regulators can be used with LPG--but never old acetylene regulators; some new acetylene regulators have seals that won't be dissolved by LPG fuels. Unless you have a gas equipment EXPERT telling you that a newer acetylene regulator has the right kind of seals, don't use it; gas equipment fires are not fun.There are more multi-fuel shop regulators becoming available on torch sets; they are safe with LPG. 

The most useful regulator is a 0-30 PSI (pounds per square inch.) LPG (liquid petroleum gas) regulator. The cheaper 0-20 types are good enough for forge use if you're careful with them, but don't kid yourself that all you lose for half the money is some pressure range. the 0-30 regulators are much better quality IF you buy the main brands; there are lots of cheap import look alights being passed off on the careless! Careful use starts with always closing off the pressure on your regulator when you shut down the forge. Open the regulator slowly when you start up the forge; you don't want full cylinder pressure slamming against your regulator and pressure gauge parts. BTW, look-alike equipment is also flooding the market on torch regulators too; if you don't see a well-known brand name on the equipment, it is probably junk.

NOTHING prevents you from using any LPG regulator. It doesn't matter about matching up threaded fittings from different countries. Regulators can all be put together with any pipe fitting, using a short length of fuel hose, and barbed hose fittings.

There is no free lunch. If you think a proper regulator is too big an item in your forge budget, make cheap with something else; not the regulator. Just about everything in your forge and its burner can be upgraded later, but regulators are only going to go up in price.

 

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Liquid fuel burners

Kerosene, and then gasoline burners have been around for over a century, and both the original pump-up hand burners and the new oxy-gasoline torches are available today. The classic kerosene and gasoline hand torch makes a single flame envelope of neutral blue, which is nevertheless rated by so-called experts as burning at a lower temperature than propane; I do not believe their conclusions.

What made the old style gasoline burners dangerous were their leather seals. There are modern versions of such burners available from China, which use modern plastic seals, and steel flame nozzles, instead of brass, which can serve well enough in forges and casting furnaces, in places were gaseous fuels are scarce or expensive.

There are also safer English manufactured gasoline weed burners, which have a separate gas tank and flame head, for the cautious-minded.

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Mikey, thanks for the information.  I have 2 vintage blow lamps as they were called and wondered if they could be used to heat a forge.  I made new leather seal for one and tested it with 90% alcohol but never worked up the nerve to test with gas. The jet would make an alcohol flame but only with a pilot light as the torch was meant for gas. 

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Insulation

It only takes a moment's comparison between heat lost through an exhaust opening with heat lost through forge walls to make it clear that just insulating the forge, to lower heat loss is a waste of time. You are insulating the forge to superheat its internal surfaces into high levels of incandescence; at least into yellow, and hopefully into white-hot ranges. An efficient forge is a radiant oven. The burner flame is primarily used to create radiant heat transfer; not for heating stock directly; get that straight in your mind, or give up all hope of knowing what you're doing in forge design. Why? Because every choice you make about refractories, kiln shelves, and ceramic fiber products needs to reflect the need to superheat the forge interior without gutting those materials.

    Insulation in walls and under the floor have consisted of two one-inch thick layers of ceramic fiber blanket for many years inside curved forge walls, and one-inch layers of ceramic board, with a further one-inch layer of ceramic blanket between the board and forge shell, in box forges.

    K26 insulating firebricks have become a tougher alternative to a ceramic board in box forges and a better alternative to ceramic blanket under floors in round forges; they are available from eBay and other online sources.

     There are several kinds of refractories used for hard firebricks, but only one kind that used to be sold for insulating firebricks, until recently: that was the pinkish to yellowish bricks made by including a foaming agent in clay refractory to make the lightweight  bricks that are use rated to 2300 F, which you see used all too often in old gas forges, and electric pottery kilns. To call them friable is to completely understate their fragile nature; calling them future rubble is more to the point. Such bricks are better used as secondary insulation in things like Pizza ovens; equipment that tends to heat up and cool down slowly during very long thermal cycling; just the opposite of a forge.

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On ‎2017‎-‎11‎-‎30 at 2:55 PM, eseemann said:

Mikey, thanks for the information.  I have 2 vintage blow lamps as they were called and wondered if they could be used to heat a forge.  I made new leather seal for one and tested it with 90% alcohol but never worked up the nerve to test with gas. The jet would make an alcohol flame but only with a pilot light as the torch was meant for gas. 

For the correct mixture with air, you need about twice as much methanol as gasolene. The diffrence is not quite as big when using ethanol, but you still need way more than you would need gasolene. Bottom line, if something is designed to mix gasolene and air in the correct proportions to burn, there will be adjustments needed to increase the amount of fuel alot before it can burn alcohol well. Well known from people running engines on various fuels, a carburettor designed for gas might not even have large enough passages where the fuel enters the carburettor to let it keep up with how much fuel the engine needs running on alcohol - and that's before you even get to all the diffrent parts that makes sure the carb adds a specific amount of fuel to the air coming through it.

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I just read the entire thread, start to finish. Too bad it's so long I've probably forgotten the first half by the time I finished it... :P There's a huge amount of info here, alot of it easy to understand, some would benefit from a simple picture or something like that - english is my second language, so every once in a while something just doesn't translate.
 
I have a hand held torch using disposable gas cartriges (same as weed burners use), it works well for what it is but it is simply too small for many occasions. I do have a oxyacetylene welder I can use for those accasions, but it isn't easily portable so the goal is to build a bigger capacity handheld burner, still using the cheap disposable butane/isobutane gas cartriges. I am making the assumption butane/isobutane burns similar enough to propane, so a burner based on the information I've found here (and hopefully understood correctly) would be close enough to be tuneable to a good flame.
 
The torch "to beat" is a handheld Campingaz unit with a 5mm (just over 3/16") mixing tube. It can get small steel items hot enough for hardening, just barely hot enough for bronze brazing two M6 screws together. Alot of what I do is general mechanic jobs, like heating aluminium engine blocks/wheel hubs to release the old bearings and insert new ones. Nothing fancy really.
The temperature I can reach today is acceptable, but I want to be able to get bigger items that hot and/or reach that temperature quicker.  A logical solution seems to be a bigger capacity burner (and not made of brass) for any general heating use, and once I've got that perhaps a beancan forge or something like that. Would be nice to be able to start forging... but general heating is the main idea.
 
The basic plan is a linear burner, because I have read here they work well in small sizes.
I'd like to use a MIG tip for simplicity (assuming the gas canister can give off gas fast enough to feed that, worst case I'll have to put it in a water bath to maintain temperature), if I can get my hands on a more suitable jet in the 0.5-0.6mm range for a good price I'll might go with that instead. Either way, I'm aiming for somewhere around 3/8"-1/2" mixing tube. Mixing tube length rule of thumb says 9 times diameter, although I remember someone mentioning handheld small torches might benefit from longer tubes. I'm thinking 10-11 times diameter to begin with, shortening it is simple.
 
I'm thinking a stepped nozzle. Overhang slightly longer than mix tube ID. Not sure about nozzle ID, but that should be simple to experiment with.
 
For the other end of the burner, I'd like some input. If I understand correctly, linear burners likes to have some sort of "funnel" before the mixing tube, with a starting diameter of ~4x tube ID.
I can easily cut and roll a cone of sheet metal, and weld or braze it to the tube, would that be a sensible construction? Aerodynamically, it would seem way better than the pipe reducers others have used successfully... although sometimes you need a "less aerodynamic" design to cause some turbulence or for other reasons, so that might not be a good thing. Also, if such a cone seems like a good design, should I go with a short cone with steep walls (red in the picture), or a shallower, longer cone (green)? I'm guessing the shallower cone would flow more air (perhaps a good thing with a 1/2" tube and slightly too big MIG jet), but again, aerodynamic efficiency isn't always what you need.
I'm guessing I'd want some form of air choke. Right now I don't have a clear design for the gas jet/tubing or how it will be held in place, that depends on what I can get my hands on, but something like a washer sliding on the gas pipe should work for choking I think? (Orange on the picture.)

Any input is appreciated!

burner.jpg

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On 11/15/2017 at 2:33 PM, Mikey98118 said:

This is one of those factors, that isn't necessarily a problem. But something that needs to be understood; not just excepted on the one hand, nor worried about on the other. Dragon's breath will produce more heat in your shop, and increase pollution in its air, increasing the need to blow out old air and replace it with new air. A CO monitor becomes critical. Also, all of that dragon's breath is wasted fuel.

One thing I have often wondered, and have not really been able to research a good answer for:  Purposefully having a more reducing flame; I understand there is wasted fuel, not used for heating the forge itself, I understand the CO byproduct from less than complete combustion... However, is there any determent to the steel in the forge? What steel, if it matters on this subject? Mainly high carbon knife type steels, damascus steels, 1080-95, 15n20, W2, 5160, 52100, and the like... My thoughts on the matter are: in forge/pattern welding, oxygen can be one of many enemies to good welds, so therefore an oxidizing, O2 rich, flame is not desirable. We shoot for neutral to slightly reducing to avoid O2. To be absolutely sure, can you tune the O2 way down? Can fuel rich, lots of dragons breath, flames be detrimental to the steel, or the welding process as long as the desirable forge &/or steel temperature is reached ? Do the un-combusted, or partially burned, gas particles interact with high temp steel to form impurities, or something else I have not thought of?

 

Any metallurgical philosophically oriented minds care to weigh in?

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I thought this would be a better place to discuss this rather than my newbie thread.  If not please move it back.  

the dragon's breath was so reducing that it was blue.  as an experiment, I replaced the pipe with the jet orifice from a size 57 (the largest the plans called for) to a size 60 (the smallest the plans call for).  

I noticed immediately that there was almost no dragons breath  with what was there being orangeish with the occasional blue tongue poking out.  I also noted that it would not run at 2 psi where the size 57 seemed perfectly content.  it seemed to initially be happy around 5 to 8 psi.  I had  a choke on the original, but with it being so rich, it only made things worse, so I removed it.

after running for about 15 min.  I noticed it intermittently cutting out.  I initially thought I was running out of fuel.  but there was at least a few pounds remaining in the tank.  it was about 40°F where the forge was.  I'll put a fresh tank on it tomorrow and see if that cures it, but wouldn't mind any thoughts.    

before this the only experience I had with propane was in  a grill and a garage heater.

thanks in advance.

Mike 

 

forge17.jpg

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On 11/20/2017 at 6:45 PM, ThomasPowers said:

Or perhaps how small a ribbon burner...I was once using a large forge heated by a ribbon burner and accidentally had my 2.5" sq stock welded to some 3/4" round stock, the round stock owner re-positioned it in the forge and ran it up alongside of my piece and it welded---had to use a hand sledge to separate the two.  This was at about 7000' altitude too...I was impressed.

I'll bet it was a gun burner, we've seen pics of ribbon burner forges with 4' of flame blasting out of them. The whole darned dragon not just it's breath!

The ones I made are naturally aspirated and I put them in a forge that doesn't make good use of the flame shape do I can't say. My shop's unheated so I'm not casting up forges for a few months. I'm still kicking around ideas for the shape, I"ll let you  know.

However I don't see why the old rule of thumb shouldn't still hold close, if you figure one 3/4" burner per 300 cu/in volume you should be close enough. Don't hold me to that though I haven't tested it out so I could be wrong.

Moto Mike I'd say your burner is intaking exhaust gasses from your forge making it sputter. It's another good reason to mount the burner at an angle, it keeps the intake port farther from the doors. It also invokes a flame vortex in the chamber.

Frosty The Lucky.

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14 hours ago, Jclonts82 said:

Do the un-combusted, or partially burned, gas particles interact with high temp steel to form impurities, or something else I have not thought of?

Any metallurgical philosophically oriented minds care to weigh in?

I don't know about the effect in a forge, or using propane, but...

If you use oxygen/acetylene welding for hardfacing (applying a layer of very hard and wear resistant metal, often to protect a cheaper base metal) you use a acetylene rich flame. The excess carbon increases the carbon content in the surface of the steel, lowering the melting point so the thin surface melts enough for the hardfacing to stick - in my handbooks in swedish they say you want the surface to "sweat", but not melt. You want to avoid a normal weld with deeper penetration, as that brings more of the soft base metal into the hardfacing, reducing its properties.

O/A welding is not all that common any more due to being slow and expensive, but compared to MMA/MIG/TIG it still puts down the cleanest hardfacing layers thanks to the ability to use a acetylene rich flame to just barely melt the surface - the electric welding methods all cause deeper penetration (at least in this case when you want to avoid penetration).

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For blade smithing a reducing atmosphere helps *prevent* decarburization and *lowers* scaling as the blade only scales outside of the forge; so if you can get the required temps and have proper ventilation for CO it's a GOOD thing.  My smithy has open gables and two 10'x10' roll up doors, one mounted opposite to the other along the general wind direction as I have a great respect for CO and like to make blades.

 

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My forge area has a roof, and 1 wall (40' shipping container). More of a cobbled together lean-to made from purely salvaged corrugated tin roofing, purlins, and galvanized rectangular tubing for legs... LOL, all it cost me was 8 bags of quickcrete to set the 4 poles in and about 3lbs 7018. So mainly open air for me!

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17 hours ago, Frosty said:

 

Moto Mike I'd say your burner is intaking exhaust gasses from your forge making it sputter. It's another good reason to mount the burner at an angle, it keeps the intake port farther from the doors. It also invokes a flame vortex in the chamber.

Frosty The Lucky.

Thanks Frosty, I'll see if I can create a steady air current to take it away.  

 

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42 minutes ago, Mikey98118 said:

I believe that that carbon monoxide has no ill effects on heating steel; the same can't be said about your lungs.

Right you are Mike but CO is hard on your hemoglobin's ability to carry O2. And the O2 depleted exhuast coming out the forge doors chokes out the burners. So efficiency or not it's worth avoiding CO production as much as possible. THAT'S from a guy who tunes his burners to run slightly rich. My shop's over ventilated but I still notice the effects after a few hours so I don't run too long. The new ribbons are more neutral and being much slower flame velocity they don't draw very much outside air in through the door making it much easier to get a non scaling forge atmosphere.

Frosty The Lucky.

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On 12/8/2017 at 7:14 AM, G-son said:

If you use oxygen/acetylene welding for hardfacing (applying a layer of very hard and wear resistant metal, often to protect a cheaper base metal) you use a acetylene rich flame. The excess carbon increases the carbon content in the surface of the steel, lowering the melting point so the thin surface melts enough for the hardfacing to stick - in my handbooks in swedish they say you want the surface to "sweat", but not melt. You want to avoid a normal weld with deeper penetration, as that brings more of the soft base metal into the hardfacing, reducing its properties.

True; a neutral oxyacetylene flame will leave some additional carbon in a weld bead; this is why the process used to be used for ribbed spring steel engine tubing.

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G-son states
"The basic plan is a linear burner, because I have read here they work well in small sizes.
I'd like to use a MIG tip for simplicity (assuming the gas canister can give off gas fast enough to feed that, worst case I'll have to put it in a water bath to maintain temperature), if I can get my hands on a more suitable jet in the 0.5-0.6mm range for a good price I'll might go with that instead. Either way, I'm aiming for somewhere around 3/8"-1/2" mixing tube. Mixing tube length rule of thumb says 9 times diameter, although I remember someone mentioning handheld small torches might benefit from longer tubes. I'm thinking 10-11 times diameter to begin with, shortening it is simple.
 
Sorry for the slow reply; it is the flu season in my house.
 
The smaller a burner is below 1/2" size the trickier it is to tune. The smallest Mikey burners I have built are 1/4" size; while I can make them run with perfect flames, they have a very short turn-down range, which means that I can build hotter linear burner because their lower quality flames can be turned up much stronger. Smart is as smart does.
 
I'm thinking a stepped nozzle. Overhang slightly longer than mix tube ID. Not sure about nozzle ID, but that should be simple to experiment with.
 
I went through a phase were flame nozzles were kept as short as practical; this is a mistake with smaller burners, because axial alignment becomes much more important in every part of them. 2-1/2 times the mixing tube diameters work out best. About 3/32" to 1/8" thick spacer rings in step nozzles generally work out best. 
 
For the other end of the burner, I'd like some input. If I understand correctly, linear burners likes to have some sort of "funnel" before the mixing tube, with a starting diameter of ~4x tube ID.
 
No; a three to one ratio of air opening to mixing tube inside diameter is what I recommend for Vortex burners, and the minimum ratio I would recommend on for linear burners without superchargers.

I can easily cut and roll a cone of sheet metal, and weld or braze it to the tube, would that be a sensible construction? Aerodynamically, it would seem way better than the pipe reducers others have used successfully... although sometimes you need a "less aerodynamic" design to cause some turbulence or for other reasons, so that might not be a good thing. Also, if such a cone seems like a good design, should I go with a short cone with steep walls (red in the picture), or a shallower, longer cone (green)? I'm guessing the shallower cone would flow more air (perhaps a good thing with a 1/2" tube and slightly too big MIG jet), but again, aerodynamic efficiency isn't always what you need.
I'm guessing I'd want some form of air choke. Right now I don't have a clear design for the gas jet/tubing or how it will be held in place, that depends on what I can get my hands on, but something like a washer sliding on the gas pipe should work for choking I think? (Orange on the picture.)
 
If you can easily create your own sheet metal cones, then you have a great advantage, because you can choose to use longer cones; here is a fine place to go with four to one length to diameter.
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"Sorry for the slow reply; it is the flu season in my house.

The smaller a burner is below 1/2" size the trickier it is to tune. The smallest Mikey burners I have built are 1/4" size; while I can make them run with perfect flames, they have a very short turn-down range, which means that I can build hotter linear burner because their lower quality flames can be turned up much stronger. Smart is as smart does.."

No rush. It's a project for this spring probably, so I've got plenty of time to do research and try to find materials.

Allright! I'll probably go for ½" first and hope I can get enough gas to feed it - if I can't get it to work on a handheld burner I can still keep it until I buy a bigger propane tank, and move on to a smaller burner build for the handheld. 
 
"I went through a phase were flame nozzles were kept as short as practical; this is a mistake with smaller burners, because axial alignment becomes much more important in every part of them. 2-1/2 times the mixing tube diameters work out best. About 3/32" to 1/8" thick spacer rings in step nozzles generally work out best. "

Great info, thanks! The smallest burners certainly seem to abide by a diffrent set of rules. 

"No; a three to one ratio of air opening to mixing tube inside diameter is what I recommend for Vortex burners, and the minimum ratio I would recommend on for linear burners without superchargers."
"If you can easily create your own sheet metal cones, then you have a great advantage, because you can choose to use longer cones; here is a fine place to go with four to one length to diameter."

Okay! To be clear, the 4:1 length to diameter of the cone, that's relative to the mixing tube (and cones small end) diameter? Lots of diffrent diameters everywhere, and english is just my second language - easy to get confused...

If I got this right... Let's go through the numbers for the cone using a ½" mixing tube.
Air opening with the 3:1 ratio would be 1½" diameter.
Cone length with 4:1 ratio makes the cone 2" long.

It does sound like a fairly steep angle, but perhaps that's the way it's supposed to be. Dimensions doesn't sound completely crazy, so I'm guessing I haven't made a mistake in the calculations.

I think most people can make their own cones out of thin sheet metal. The original reason I bought my welder was to make tuned exhausts for twostroke engines, and those are made up mostly of a series of sheet metal cones welded together. There are ways to calculate and draw a template that rolls into a cone of any desired size, but today most of us are lazy and lazy means someone has made a computer program for it. Just put in the desired dimensions, hit print, and you get a template to cut the sheet metal after. Once the metal is cut out, it "only" has to be rolled into a cone - a bit of a challenge if you use too thick metal but a piece of round bar or pipe with appropriate diameter and a mallet usually makes that job resonably easy. Weld or braze the seam (maybe even soft soldering works at the back end of a burner?) and you've got your very own cone, any size you like it. 


 
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10 hours ago, G-son said:

I think most people can make their own cones out of thin sheet metal. The original reason I bought my welder was to make tuned exhausts for twostroke engines, and those are made up mostly of a series of sheet metal cones welded together. There are ways to calculate and draw a template that rolls into a cone of any desired size, but today most of us are lazy and lazy means someone has made a computer program for it. Just put in the desired dimensions, hit print, and you get a template to cut the sheet metal after. Once the metal is cut out, it "only" has to be rolled into a cone - a bit of a challenge if you use too thick metal but a piece of round bar or pipe with appropriate diameter and a mallet usually makes that job resonably easy. Weld or braze the seam (maybe even soft soldering works at the back end of a burner?) and you've got your very own cone, any size you like it. 

Post a how-to on this subject here, sharing your knowledge with others, and I will go out of my way to help you all the way through your burner builds, step by step and till they are done.

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