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Burners 101


Mikey98118

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I've been tinkering with the T burners and 3D printed vortex burners I've recently made and I'm getting more confused about reading and tuning flames, instead of less so!

I had my two 3/4" T burners with .035" mig tips running what I thought was slightly reducing (slight aqua/green tinge to the primary flame? Is this right for reducing/rich?) but more neutral as I increased the pressure (a more pure blue?) due to more induction of air. Follows my understanding of the induction curve they should follow.

But last night I did a comparison of that with my 3D printed 1/2" AFB version 30 copy with a .023 tip and I couldn't get that more pure blue colour regardless of where I put the tip. Does this suggest I should got to a slightly smaller tip so there is less fuel for the amount of air able to be induced?

On a similar but side note: I've been struggling with how to read flames and the thought occurred to me last night: Would kitchen stove burner flames make a good benchmark for comparison? Are they designed to be reducing so as not to damage steel pots and pans? Because they run at less pressure, it's easy to see the aqua/greenish blue primary flame and the blue secondary with flecks of yellow/orange.

Sorry for all the scattered questions in my long and rambling post!

Cheers,

Jono.

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 A slightly reducing flame starts when the flame softens from a hard primary flame to include a wisp of secondary flame. Thereafter, the only question left is how reducing you desire it. I don't consider any gas flame with a hint of green in it to be slightly reducing; by that point the question is how heavily reducing it is, to my mind. Others may feel differently, and maybe they're right, too; anyways, as right as me.

Some things don't have definite boundaries; just people insisting they know where those are :)

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Thanks Mikey. That's the other thing I'm still struggling to interpret, the parts of the flame. Can I ask you if I'm interpreting these pictures correctly? They were from beginning to tune my T burners. ( I've already posted them in the T burner thread for that purpose, but I post them here to learn how to read them myself)

This is the same burner, low, medium and then high pressure.

2024838332_51sttrimmedpressuresmall.jpg.a1b155a2316d1929be089d15779bc25d.jpg

1949168357_61sttrimhighishpressuresmall.jpg.8b9e8a56b152d9906257f02b85201e03.jpg

128973924_71sttrimjetroarsmall.jpg.5dde51a6047261f81e6218f09a553dd4.jpg

My interpretation is that the first one is still quite reducing, indicated by the green tint but also from the whitish secondary flame at the tip of the primary flame. The second one is less reducing with no whitish secondary flame but still a slight green tint. The third one is more neutral as more air is being entrained at the higher pressure.

Am I reading this correctly/looking at the correct parts of the flame?

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I'll let Mike tell you what he thinks of the flames but I know one of your problems, maybe the biggest. You are trying to make and tune two very different burners and it's confusing you. Tune ONE at a time, it'll be much easier.

A last note, any ejector type burner, even at the home made level should have a pretty flat induction curve across propane psi. range.

Frosty The Lucky.

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1 hour ago, Frosty said:

You are trying to make and tune two very different burners and it's confusing you. Tune ONE at a time, it'll be much easier.

This is worth saying repeatedly!!!

Furthermore, it is confusing for a beginner to use greatly different light levels, when judging a flame. After more than two decades it is merely distracting,

Your interpretation is dead on. In fact, the third flame photo would have been considered as showing a neutral flame, by anyone but a combustion expert, for a long time. Most smiths would still be perfectly content with it. Some of us are just pick, picky, picky :rolleyes:

No; I'm not trying to confuse you. The idea is to invite a certain nicety of judgement, because that third flame is a matter for personal preference. You could stop here, or keep refining the burner. Which path to choose, depends on whether or not you have a use for the difference... or are just picky :D

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Frosty and Mikey, I hear what you're both saying about tuning one burner at a time. Yes, the two different types of burners have quite different flames. My post was more about making sure I was reading flames correctly. I mentioned adjusting the 3D printed one because it is easily changed and I thought it might help me clarify my understanding. When it didn't, I came here :)

Frosty, is it the tuning that helps flatten the curve? The three images above are the same burner at three different pressures and it must be inducing at different ratios because it's becoming more neutral as pressure increases. I haven't taken much off this mig tip yet.

Cheers,

Jono.

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If it's properly tuned the curve is less noticeable. The real trick is getting a good balance between combustion air induction and propane in the device itself. The way I tune a burner is by adjusting the device, once I get it in range I don't need anything else. 

Frosty The Lucky.

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Dremel’s #409 (15/16”) cutting discs are the only old-style jeweler’s disc that are suitable for steel work; 15/16” are the smallest diameter resin-bonded cutoff discs available; none of them are fiberglass reinforced, but these are just adequate to the task, because they are thicker than the standard jeweler’s disc; those shatter in seconds.  Dremel’s #409 discs will stand up to light work, if treated with care; they are the safest method of cutting next to inside corners, cutting out really small air openings, and squaring end holes in slots, to make rectangular openings, in vary small burners.

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Understanding flames and atmospheres inside equipment

When looking at the flame from a really hot burner in a cold forge or furnace, It will appear much as it does out in the open air, but within moments it will lengthen and become smoother in outline, as the equipment starts to super-heat; it will also lighten in hue, becoming more transparent. There will be little to no secondary flame within the equipment, even while it is cold; lesser burners will make more complicated flame envelopes, but this is the ideal; these facts also hold as true for multi-flame ceramic burner heads as they do for single flame burners.

    You need to remember that there are at least two different flames going on within the average gas forge or furnace; the flame being input by the burner, and an internal atmosphere, which may extend to an output flame leaving the equipment via the exhaust opening. When blacksmiths discuss terms like dragon's breath it is such an exhaust flame they are speaking of; a very different animal than the burner flame. Not that both flames aren't equally important clues to burner performance, but they need to be treated separately for clarity. So, what amounts to a perfect exhaust flame? No flame at all.

    If we are speaking about the burner flame, straight blue from a single combustion envelope is the goal, but many older burner designs have a white inner flame ahead of a blue secondary flame, followed by a darker larger and less substantial appearing blue or purple tertiary flame from the combustion of secondary air. Buy or build a good enough burner to see no white in the flame, and then tune it well enough to have little or no secondary flame.

    The next question tends to be "how dark a blue?" Different fuels give off different hues, and lean flames are always a darker blue than neutral flames in any given fuel. In fact, a burner can be run so lean that the primary flame turns purple from the amount of red that excess superheated oxygen gives it. On the other hand, any slightest tinge of green in the flame is an unmistakable sign that it is way too fuel rich; such a reducing flame will also be pumping out lots of carbon monoxide.

    The simplest way to judge a neutral flame is that it’s blue is a lighter hue, and it has very little to no secondary flame; any darkening beyond that is from too much oxygen; it is called a lean flame as it is thought to be lean on fuel as compared to air input. In the end, you must tune a burner back and forth between rich and lean to educate yourself on what constitutes the best flame from your burner; you can do this out in the open air, or in the equipment while it is warming up.

    You can also get thin yellow and red streaks in a perfectly tuned burner's flame, due to breakdown products of oxidation from some alloys of stainless steel, mild steel, or cast iron in flame retention nozzles. Flame nozzles of #304 stainless can put on quite a show that way; it's harmless. #316 stainless nozzles make fewer streaks and last longer.

Fuel rich (AKA reducing) flames, range from the faintest tinge of green in a blue primary flame envelope (AKA flame front) to bluish green flames that are pushing so much unburned fuel into your shop's atmosphere that you feel like gagging. If the burner’s choke is completely closed the burner will make a lazy yellow flame like burning wood.

Neutral flames range from light to medium blue; they are neutral throughout this tint range for all practical purposes; what that means is, although their combustion chemistry is changing, you can't appreciate the difference without calibrated instruments.

    So how can you know when the blue leads the neutral range and inters oxidizing? The answer is that you can’t without a fair amount of practice. Eventually, you will learn to compare the flames from your burner at one time and another, so as to tune it perfectly.

Oxidizing (AKA lean) flames start just beyond medium blue, go through dark blue, and extend into purple, in the primary flame envelope. While learning to discern the boundary between neutral and oxidizing flames, it is helpful to use small pieces of fresh ground steel in the forge, how fast and how much it scales—in the forge—gives you a faithful comparison, as you self-educate about flames. 

    Flame color isn't the only sign of how well your burner is doing. The amount of secondary flame is also an important indicator; the less secondary flame the better. There is such a thing as perfect performance, which includes no secondary flame. Perfection is often the enemy of practicality. A small wisp of secondary flame is often better than no secondary flame at all; this is because air/fuel flames fluctuate more than oxy-fuel flames, so the "perfect" flame is likely to be slightly oxidizing part of the time. Since a wisp of secondary flame will burn up completely in the forge or furnace, it is better than scale added on work pieces during heating, or oxidative damage to super-heated crucibles. It should go without saying that tertiary flames indicate poor burner construction, or a very bad job of tuning.

    So what is the practical upper limit for secondary flame? Is there flame coming out of the exhaust opening? Then your burner is either tuned to rich, or its gas pressure is turned up to high.

    Even with the best possible flame (that you can detect visually), there will be some super-heated oxygen molecules that haven't had time to combine with fuel gas molecules before escaping the primary flame envelope; not enough that you can see secondary combustion going on. But, any superheated oxygen that impinges on super heated metal, will joyfully combine to rapidly create scale, and burn away some carbon content in ferrous metals. What this means is that a few inches distance between the visual end of the flame and your work pieces, or crucible, is highly desirable. Hot crucibles are inclined to suffer damage in the presence of superheated oxygen, leading to spalling, cracking, and early crucible failure.

    It is an advantage to build a tunnel, oval, or “D” forge with the flame angled away from heating stocks (and between the crucible and wall in furnaces), or with the ceiling at least far enough from the work in box shaped equipment, to keep the flame from impinging on heating stocks and crucibles; increased room for the flame is one of the reasons for including a plinth in your casting furnace. Since different burner designs create different flame lengths, and since they also vary by how far the burner is turned up, there can be no pat answer on the height of a box forge or the thickness of a plinth in your casting furnace; these are judgement calls on the builder's part.

    Most people find little reason to turn a burner on full blast, so the flame can be measured for length at a maximum of 20 PSI, and that can be used for a good height measurement in box forges. You want the length to be at two-inches beyond secondary flame tips. No practical forge can include further length for tertiary flames, so construct and tune your burner well enough to avoid making them. Crucibles are tapered at their bottoms and should be raised on plinths to help keep the flame from impinging on them, since most casting furnaces are round and have a burner placed low on its vertical wall, and aimed horizontally at a tangent between furnace wall and crucible walls.

    However, flame length is most important if your burners are top mounted and facing toward the equipment’s floor. Some people mount their burners high up on sidewalls facing horizontally across a box forge or furnace, to get around early flame impingement altogether; this saves heating stock, and also lowers thermal damage on walls (which can be further away the work, for the same cubic inches when ceilings are lowered; a win-win use of space).

    Is an exhaust flame just the tail end of the burner's flame? It can be just that in equipment that is loping along, with interior surfaces that are only at red or orange heat. But in a forge or furnace that is turned up into yellow to white heat ranges—no. In fact, the goal is zero output flame; just clear super-heated exhaust gases. When your forge or furnace is capable of radiant-oven performance, then everything about the exhaust discharge changes.

    With the average forge or furnace, a small amount of blue exhaust flame has been considered normal--in the past. But in really hot equipment, should you keep turning up the input flame beyond its ability to completely burn internally, you still won't get blue exhaust flames; some of the yellow-white “atmosphere” will overflow out of the exhaust, and complete combustion within a few short inches, but without a trace of blue or purple flame (which indicates a probable buildup of carbon monoxide).

    What is different? The forge or furnace itself is changing the combustion equation by super-heating any byproducts of the primary combustion envelope. How is this possible, since immediately after combustion, exhaust gas temperatures naturally decline? Intense radiant energy from incandescent surfaces is being bounced back and forth through those gases. All of the interior becomes an ignition point; not just refractory surfaces. Thus, secondary combustion is speeded up, ensuring left over products of the primary flame envelope have the time to completely burn off.

    If the equipment is red-hot, you should consider heat losses in combustion byproducts to be multiplying faster than radiant energy is being added. In pale-yellow to white-hot forges, combustion losses are being subtracted while radiant energy is multiplying temperature gains. It isn't possible to understand internal combustion processes in a modern forge or furnace as just a chemical process, because of heat gain from highly radiating surfaces; such equipment is as much radiant oven as flame appliance.

     So, exhaust flames from your forge can simply be the result of fuel that hasn't combusted, as in the case of fuel gas pressure being turned up way too high. The more common cause of yellow exhaust flames is a large secondary flame (from a poorly designed, constructed, or tuned burner), which cannot be completely combusted within the forge interior.

    I have noticed that fairly opaque looking yellow to orange flame can be made from some kinds refractory that is "cooking off" calcium from its binding agent; these flames will not abate until the process is complete. As the flame turns from yellow to orange, it becomes more transparent, and may even seem to sparkle in a manner reminiscent of fireworks, if the forge is running hot enough at the time.

    This doesn't preclude other colored flames, such as purple and blue from being present in the orange exhaust, but they are an indication of poor combustion, and must be ignored until the refractory finishes out-gassing. It is best to address one problem at a time.

Caution: Blue exhaust flames are a sign of a reducing forge atmosphere, which even a perfect burner will give off, if its air intakes are choked enough. Be aware that blue exhaust flames will be accompanied by carbon monoxide production.

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2 hours ago, Mikey98118 said:

In fact, a burner can be run so lean that the primary flame turns purple from the amount of red that excess superheated oxygen gives it.

Mike: I believe you are using "oxygen" by mistake in this sentence. It's the 70% atmospheric "Nitrogen" that superheats in the flame. The oxy is consumed and becomes part of a superheated compound (exhaust gas).

Or am I misunderstanding? 

It's a great series of articles Mike they're making me look at things differently but I can't NOT see little things like this. One picky butt to another.:ph34r:

Frosty The Lucky.

 

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I could be mistaken about which molecule is causing this color. My thinking is that oxygen molecules are combing with with fuel molecules as usual. Nitrogen content is not raised in percentage over any other kind of flame, and fuel molecules are busy combining with oxygen. The only excess with a very lean from are fee oxygen molecules. And so I have assumed that their presence is what is creating this color. However, we all know what assuming leaves to, So, I could be embarrassingly mistaken :rolleyes:

But, I don't think so.

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Okay, I see your logic, makes sense. I was thinking of colors emitted by different superheated gases. But you're right, the ratio of nitrogen is unchanged, that idea is 86ed. 

From rich to neutral goes through phases of blue and clarity. Roger that.

That pretty much leaves unburned oxy as the culprit. 

I agree, it's probably the excess oxy. As far as my non-chemist Sherlock thinking goes. 

Frosty The Lucky.

 

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MIG tip update

I have been advising people to buy their MIG contact tips online for years, because they had so many bad experiences when trying to buy them from regular welding supply stores. When you ask a sales clerk for a single MIG tip (as so many people did), they will usually just lie about them being available, to get rid of you as fast as possible.

 

    Everything changes in the marketplace. Today, most of these stores have packages of MIG tips on display. You can buy five tips at a reasonable price, making an end-run around the usual awkward scene with a sales clerk. In the meantime, online sources now mostly sell imported tips, and these can very wildly in quality.

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Let me see if I have this straight. I point out something I THINK is a mistake. You reply with a cogent logical explanation I believe understand and agree with. At least till someone who actually knows gives us straight information. 

In response to me agreeing with you you offer an official waffle leaving me flapping in my own exhaust.

Thanks Mike. I still don't get it but thanks, you're a pal.

Frosty The Lucky.

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Frosty and Mikey the two of you sent me down the rabbit hole with this conversation yesterday and I am still there today.  To say that the gases are superheated is maybe a misnomer.  What I read yesterday is that superheated refers to any  temperature above the state transformation from liquid to gas, whether it be 1 degree or two thousand.  I looked into incandescence/incandescent and found some interesting pages.  Here is the first page:

http://www.webexhibits.org/causesofcolor/3.html

And wikipedia, of course:

https://en.wikipedia.org/wiki/Incandescence

I kind of like this site:

http://www.webexhibits.org/causesofcolor/3BA.html

And the Oxygen vs. the Nitrogen causing the colors you see--could be both judging by the color spectrum of those elements.

http://www.astronomy.ohio-state.edu/~pogge/Ast350/Labs/Lamps/index.html

Oxygen has more in the blue spectrum but there is more Nitrogen.  I did not go so far as to see what colors are presented by Carbon Monoxide/Dioxide, water vapor or other combustion byproducts.  Google can drive you mad with too much unrelated information just because one word of your search term matched.  Sometimes like a not too bright overachiever.

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Granted superheated is the wrong term but it sounds better than super hot doesn't it? It can also refer to a gas hotter than the transition temp to plasma. 

Water is dangerous stuff where super heated or chilled is concerned, it can do unpleasant things. Ever read about the old steam engine days? Scary stories, especially the river boats. 

Without looking things up I'd suspect hydrogen being a culprit for red IF a forge is hot enough to cause chemicals to fluoresce in their spectra. (I worded that badly but I'm not looking things up at the moment and will happily accept corrections.)

I have to tentatively stick with Mikes logic to a point. A lean flame is pretty transparent. The "purple" tinge to the envelope is the interesting noodling we as nonledgeable participants are enjoying speculating about. 

Here's a relay from the voices. Perhaps the purple tinge isn't due to radiance. Perhaps it's due to filtering. We know the flame envelope is emitting light or we wouldn't be talking about it's color. So perhaps instead of emitting slightly More red, it's actually filtering / blocking LESS red.

Hmmmm? 

Does anybody else have something they'd like me to toss a monkey wrench or klumpen into?

Frosty The Lucky.

 

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22 hours ago, Frosty said:

In response to me agreeing with you you offer an official waffle leaving me flapping in my own exhaust. Thanks Mike. I still don't get it but thanks, you're a pal.

Frosty,

Sorry for the late reply. This time Kathy was in the hands of the doctor gods (and people actually think old age is boring).

Waffling? No; people do that to cover their six; not to risk it. I stated something as fact in my book notes, that I don't KNOW to be fact. That bugs me, big time!

As for leaving you feeling like you were swinging in the breeze, I apologize. I am genuinely sorry for that.

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Give Kathy my best please! 

I was funning you about swinging in the breeze, it's a comfortable state for me. 

I get regretting stating as fact something you don't know. It bugs me too, unfortunately I get carried away and so it without noticing.

The waffling statement was uncalled for. Once again I say something I think is funny that isn't. My bad.

Frosty The Lucky.

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