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T Burner Illustrated Directions


Frosty

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By the mixing tube length I assume these are 1/2" burners, yes? Then yes, the flare should be much shorter, 3/4" to 1" should be about right. The flare is part of the mixing tube's total length.

I can't really evaluate the burn without a pic or two but it sounds like it's burning WAY too rich. a low velocity flame is a good thing but it has to have the right ratio to make good heat and be stable. 

Please enclose a couple pics and the parts list you used in your next post, we'll get it tuned up. I'm also not clear about the burner orientation, are the burners perpendicular to the forge or each other.

Frosty The Lucky.

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1/2 inch?  Crud, I must have missed something.  I used the .pdf linked in the very first post, it says 3/4 inch by 6 inch nipple?  Completely possible I misunderstood something there.  In any event, I'll get some pics tonight and monkey with the flare length, it sounds like it's too long anyway.  Easier to troubleshoot that than go buy a new regulator!

Thanks again Frosty, I'm always amazed at the collective knowledge on this site.

Be safe.

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OK got some pics.  I shortened the flare to about one inch past the end of the nipple, that seemed to help a bit.  I got a steadier flame, but still not quite consistent.  It looked stead enough I thought I'd try to get something hot, so I threw a 9-inch bolt I had lying around in there and it was just starting to get yellow when my flame started sputtering again, then backfired (?) back up into the tube and I had flames shooting out the sides of the T at the top!  So I shut everything down and moved on to something less potentially catastrophic - cold bending some steel rod!

 

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The sputtering is usually* caused by the flame speed through the mixture becoming faster than the flame speed along the burner tube.

It is usually a sign that you need more gas pressure. 

The flame speed is a function of several things: the air:fuel ratio, the temperature and the pressure are the 3 main ones. 

With the burner design you have, the tuning is what determines the air:fuel ratio and you have no real way to adjust that once the burner is running.

The pressure that affects the flame speed is the pressure of the mixture, not the feed pressure of the gas. It is not really something you have very much control over, as it'll be within one or two percent of atmospheric pressure whilst the forge is running normally. 

The temperature is the big variable.

As the forge heats up, the temperature increase causes the flame speed to increase. At some point, the flame speed through the mixture may become faster than the mixture speed along the burner tube and the flame will travel down the tube. As the flame-front moves down the tube, it radiates heat ahead of it, heating the mixture ahead of the flamefront and increasing the flame speed. The accelerating flamefront causes a pressure wave, which moves ahead of the flamefront. The mixture just ahead of the flamefront is now hot and at higher pressure, so the flamefront accelerates down your burner tube until it runs out of mixture to burn and goes out. At this point the burner tube is full of burnt gases. Some of the heat released as the flame ran down the tube will have been absorbed by the burner tube, so it is now a little warmer. The gas is still being fed, still drawing in air, mixing with it and moving along the burner tube. When the mixture reaches the hot forge, it ignites and the whole thing happens again. It may be quicker this time because the burner tube is hotter.

If the operator reacts quickly enough to turn up the gas feed pressure and thereby increase the mixture speed in the tube, the problem will usually go away. If the operator does not turn up the pressure before the burner tube has got hot enough to stabilize the flame at the inlet end of the burner tube, it's a case of shut down, let things cool and try again, preferably at higher gas pressure.  

Do you know what gas pressure you were running at the time? What is the range of your regulator?

The mixture speed is proportional to the speed of the gas through the jet. The gas speed through the jet is proportional to the square root of the gas pressure, up to "around" 30 PSI where the flow becomes choked (it reaches the local speed of sound). Above the choked pressure, increasing pressure still increases the gas flow, it just doesn't follow the same relationship.

If you have an idea of your gas pressure when the problem occurred, try again at higher pressure. I'd aim to double the pressure (which will give about 41% higher mixture speed) and if it works, maybe reduce the pressure in small steps with the forge at temperature until the problem starts to manifest itself again. That way you can establish the minimum running pressure for the hot forge.

You are quite likely to find it difficult to light a cold forge at high pressure. If so, light it at lower pressure and increase the pressure as the forge heats up.

 

* "Usually" is used here, essentially as a weasel word, to cover the possibility of your having done something really outlandish that I've not previously encountered.

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One thing he has done is to extend his flare into the forging chamber rather than just past the outer shell.  This makes it likely that over time the burner tube will get hot enough to ignite the fuel/air mixture inside the burner tube rather than at the end.  The longer that continues, the closer to the jet ignition can take place.

A couple other things that can cause those symptoms are a fuel tank that is nearly empty and a fuel tank that has cooled from the rapid use of the fuel so that the pressure has dropped too low to produce a stable flame at the end of the burner.

Yet another possibility is an obstruction in the fuel supply line or the jet itself.

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Tim: I don't think you have a handle on how these particular burners work. The "mixer" is the burner tube. The mig tip is the gas jet. In a simple ejector type induction system pressure IS what determines fuel air velocity. You can choke to reduce combustion air, that'll slow it down and make the mix a richer. Flared ends of the mixing tube can act as flame holders, the increase in area means the fuel air mix has to fill a larger volume so the velocity falls with the pressure.

None of these things are the problem with Chris's burner, the tip is extended into the chamber. :o 

Chris: Your burner is getting hot enough it's pre-igniting the fuel air mix. Combustion IN the mixing tube is causing enough back pressure the velocity is falling below the rate of propagation of a fire in air propane mix and you get flames shooting out the T. 

Pull it back so no more than about 1/4" of the TIP is in the shell and see how it works. The flame looks pretty good.

Post a couple pics next time you try it please.

Frosty The Lucky.

 

 

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Ah ha!  I had read about the tip being just inside the shell, and thought that meant the ENTIRE forge - e.g. INSIDE the forge.  If I'm reading this correctly this time, the tip being just inside the shell refers to the steel tank shell, it should NOT protrude into the forge chamber proper. 

I'm currently using a 20 pound tank, it's full.  I know the regulator is high pressure, I believe 0-30 psi but I bought it a few years ago.  Before this last fire up I broke everything down and blew through the hose and regulator to see if anything was blocked.  Sounds like adjusting the depth of the tube into the forge is a good place to start next.

If the rain holds off, I'll be trying it again tonight. 

Thank you so much, gentlemen!

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When you fire it up again, if it starts out ok, but then goes back to sputtering it's not likely to be an obstruction.  If it sputters immediately again and won't burn at the end it could be.  Even though you cleared it out, if a small particle came loose and lodged in the jet you could get those results. Most likely though it does have to do with the flare being down inside the forge.

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OK - pulled the flare back to just inside the steel shell.  There is now about 1 1/2 inches of wool/cement between the end of the flare and the forge chamber.  That seemed to help quite a bit (imagine that!).  Still a moderate amount of sputtering.  No backfires back into the T this time, but it kind of felt like it wanted to.  Right now I'm just trying to get one burner tuned properly before installing the second; just occurred to me, it might make a difference having both burners going at the same time?  Am I wasting time tuning one then the other?  Here are some pics:

 

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Is the sputtering happening only at low pressure, high pressure, or throughout the operating range?  Is there any chance a breeze (from any source, even a fan) can reach the air intakes?  It doesn't look likely that you have an issue with recycled exhaust gases, but that is a possibility.

If you have the 2nd burner built already you may want to try it to see if the symptoms persist.  That may help narrow down the possibilities.

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Could be a breeze, I'm working on it outside.  Shop is kind of cluttered right now.  Not set up to supply gas to both at once yet, probably work on that this weekend.  Sputtering is more prevalent at low pressures, but at higher pressures it kind of acts like it's TOO high a pressure, if that makes any sense, like it wants to blow itself out.  That makes me think I need to trim the mig tip back some more to get more air mixed in with the gas.  I'm closing in on 'er, though!

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Don't get too concerned about the flame wanting to blow itself out - as long as your burner is tuned well.  Once the inside of the forge is glowing hot the flame pretty much cannot blow itself out any more.  I generally let mine run about 5 minutes or so on fairly low/stable pressure before turning it up.  Once it's glowing hot inside I can go to max pressure with no problems.  If I did that when I first light the burner it would definitely blow the flame off the end of the burner.  You may need to trim the tip a little. Your flame looks to be on the rich side to me, but I don't consider myself to be an expert in burners or interpreting photographs of their flames.

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We have a different understanding then.  My understanding and limited experience is it works better to place the end of the burner or flare about a half inch inside the the shell, give or take a little, which puts it about 2 inches from the forge interior if you are using 2 inches of blanket and a half inch hot face material.  I usually cast the burner ports with refractory material though, so there is refractory from the shell to the forge interior in that one spot.

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I just want to say that I was intimidated by building a burner/forge, but this was ridiculously easy. I couldn't find a tap-wrench to fit the 1/8" pipe tap(they were sold out unless I wanted to buy a $60 tap wrench/bit kit.) and I was stupid and wanted to look down my drill hole before using the tap, so my first attempt was not quite perfectly vertical, but the 2nd time I did it exactly according to directions, and it looks great.

My flame keeps blowing itself out, or "wooshing" at low pressure, but I am pretty sure it is just rich, and and I need to trim the mig tip down more. Just waiting to get a forge before I final-tune it.

Is there a "minimal viable size" for a forge with this burner? I have a bunch of fire brick left over from a pizza oven I built, and want to mess around with while I await my kao-wool, and was going to build a small brick-pile forge for a small knife I'm working on, so I don't need much space at all.

Also, just out of curiosity, what effect would it have if I used my off-skelter original T, so the injector wasn't spraying strait down the pipe?

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What size is "This size burner" to which you refer? The volume to burner dia. ratio is based on the cross section area of the burner at the throat. NOT the flare, intake, etc. the narrowest part of the mixing tube. The burner to furnace volume ratio is pretty straight curve. 2x burner sq/" = 2x forge volume. This is not an exact ratio, nothing about the T burner is exact, it's a good enough to work well for minimum investment in materials, tools and skills design.

It is however easier to turn one down below max than it is to turn it up higher than max.

Frosty The Lucky.

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So my firebrick forge interior is going to be 9"x4.5"x4", so 162 cu inches. I was just worried that that small of an area would be too small and negatively affect the burner, or the flame would be too close to fire-brick surface.

Also with a t-burner, does horizontally vs vertically mounted make any difference?

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On 10/6/2017 at 8:10 PM, Danjmath said:

Here is a video of my 3/4" T-burner inside my temporary fire-brick forge.

I don't have a gauge, but I start off at about 3-5 psi, the lowest I can keep the flame going, then about 20-25 seconds I get up to what I guess is about 15 PSI (about half way to maximum on my 0-30 regulator). I am having a hard time dialing in the burner since it is only 4" from the forge floor. Do I need to make the forge a little higher, or trim my MIG tip any more? Thanks,

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Well I got the sputtering problem licked - turns out one of my jets was not quite lined up as well as it could have been. Drilled and tapped a new T and all seems well now.  It doesn't seem to be getting as hot as I think t should be - I can forge with it, but it doesn't seem to be getting welding hot, and there is a lot of dragon breath.  Can I close off the back a bit with some brick, would that help? 

 

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Cast 1, was able to pull all the glue sticks out. Can blow air in the tube and it flows out lots of nozzles.  Judging by all the spheres I might have over-vibrated.  Frosty by adding all of the nozzelet length I wonder if I should have used a shorter than 6” mixing tube?, 

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In an effort to make the perfect Frosty burner, and because of my repeated failures at getting a tip perfectly centered in the "T" I decided to try and make a jig to make it fool proof and repeatable. What I ended up with was a 3/4 nipple and a slug of the correct diameter to fit inside the nipple and then drill a through hole all the way through the slug. (Pictures to follow). I did this with the taps also. Shown below are the completed pieces. The one on the left has the slug welded to the nipple and a 21/64 hole drilled the length of the slug. I have a friend with a lathe that makes short work of the machine work. The two on the right are the taps. Again the nipple and slugs were machined to the correct tolerances. For me the inside of the nipples were machined to .83 and the slugs to .82. Then the top of the slugs were drilled and tapped to accept a 3/8 X 1 1/2 bolt to use to turn the slug when complete. The bottom of the slug was drilled to accept the taps one for 1/8 NPT and one for the size of your mag tip. Then a couple of 1/4 X 1/4 set screws to hold in the taps. 

Very simple to use, even with a hand drill you get perfectly centered holes every time.

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This one shows the drill slug all the way in place.

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This one shows the slug pulled back a ways to show how it automatically centers the hole  with no chance for the bit to wander!

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This one shows the tap in place.

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