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I picked up my new burners yesterday after work and did some testing, not real happy with the results....

 

Firstly I couldn't get it lit outside the forge except if the gas was barely open and the choke almost closed, open the gas or the choke and the flame just runs out.

Stuck it in my existing forge and then it stays lit at least, flame is blue, which I think is not correct?

Played around a bit and the best I got it was turning the gas feed way down on the regulator, in that state the choke works exactly like a volume control, and I could get the noise down to acceptable levels and the forge does get hot.....but not great.

Also, same as with my original burners there's cold, dark circle right below the burner.

I'm a bit stumped, only ideas I have now is to try and get 0.6mm and 1mm MIG nozzles and try them instead of the current .8mm

 

I got some proper fire bricks and will be building a new forge for these burners, plan on it having a slightly higher roof and the burners will come in at an angle on the top edge instead of straight up in the center, but I can't spend the money on that if I'm not happy with the burners.

Any advice would be appreciated.

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17 hours ago, Jerrod Miller said:

I have found that tapered MIG tips (like this one) certainly helped my burners.  

Mine are the screw-in type so they won't work with the design....

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I spoke to my friend who built the burners, he's not a burner expert, just a very good machinist and fabricator, explained what was happening and his first suggestion was a large nozzle.

Took me a minute, but I agree that's the first step.

 

I got the fire bricks so I NEED to get building.....

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6 hours ago, Gerhard Gerber said:

Mine are the screw-in type so they won't work with the design....

They make them for both male and female.  That was just the clearest picture of the taper I could find in a quick search.  

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I could only get 1.2mm nozzles, the burner seems to run better in general but no matter how I adjusted it the steel didn't get to forging heat.

The dead spot on the forge floor is almost double the size and there are tiny flames on the floor, unburnt gas I assume........still can't get it to stay lit outside the forge.

Swapped to the older burners and had the forge up to heat in a few minutes.

The 0.6mm nozzles have much smaller thread, I think that's the next step so more work for my machinist friend.

 

I have more money into these burners than the first forge, burners and regulator included :wacko:

 

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  • 3 weeks later...

Now I don't know anymore, fit the 0.6mm mig tips and no joy, still can't get them to burn outside the forge except with the choke completely closed, open the choke slightly and the flame runs out.

Seems like a better result inside the forge, but I have to believe if they don't work outside, they're not really working yet.

 

Wasn't expecting this, price wise I'd have been better off importing burners from South Africa :wacko:

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Posted (edited)

Try building a simple enclosure for the burner.  A box of bricks will do for the experiment.  Venturi burners often need the bit of back pressure to burn properly.  I'm not the expert on Venturi's, but I believe I've seen this question before.  It will only cost you a bit of time to try it.

 

Have you got a picture of the burner?

 

Geoff

Edited by Geoff Keyes
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On 6/8/2020 at 7:30 PM, Geoff Keyes said:

  Venturi burners often need the bit of back pressure to burn properly.  

 

Have you got a picture of the burner?

 

Geoff

First time I hear that, but it does make me feel a bit better :)
My experience is limited to two sets of burners, both worked outside the forge so I thought that was like a minimum requirement...
I'll post some pics as soon as I touch ground again (day job) and make a bit more effort to tune in the .6mm jets

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  • 2 weeks later...

So here are the long promised pics, my last effort was to add the elbow to get a longer down pipe, still could not get them to burn outside the forge, and inside the forge I got it tuned to burn steadily, eventually, but it's a piss poor little flame.  I've considered halving one of the pipes, but because they don't burn outside the forge I can't see the point.
Hopefully the photos make the basic construction clear, I currently have the 0.6mm nozzles installed, the initial 1.2mm and 0.8mm nozzles also in picture.

My tool-up-or-die efforts of late have been expensive and unsuccessful, I've paid my buddy for his work, but I'm stumped by this problem.
Hoping for some brilliant insights, but for the mean time the burners are on a heap with the equally unsuccessful platen I tried to build :wacko:

IMG_20200624_162906[1].jpg

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I'd try it without the nut/washer flange piece, then try adjusting how far the MIG tip sits into the flare, from deep down in to out of the flare.  Also try various pressures and flow rates throughout.  

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It would be nice to see the position of the gas jet relative to the end of the long threaded nipple with everything assembled.

 

Looking at the photo, it seems that with the brass sleeve-thing inserted into the threaded nipple with enough sticking out at the back end to get the hose on, the jet will be somewhere close to flush with the end of the threaded nipple? I suspect that'll cause all kinds of turbulence right where you don't want it. 

 

I think you probably want the full length of the mig tip exposed to allow air to be drawn relatively smoothly into the low-pressure zone created by the gas coming out of the jet.

 

Once you've got it something like, there are plenty of adjustments available with that design.

 

If the installed burner is similar to the right-hand one in the first pic, there's a very long length (in total) of pipe on it plus an elbow. A screwed 90-degree elbow is usually considered to be equivalent to "about" 30 pipe diameters in terms of pressure loss IIRC. I think the left-hand one in the top pic is probably pretty close to convention at "about" 8 pipe diameters. The one on the right looks to be equivalent to perhaps 40-50 diameters. 

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I was unable to upload some of the photos that might have clarified things a bit, also I forgot to mention the following:

- Been testing with one burner and I've shortened the drilled out threaded rod that the brass bit goes into, so the nozzle is outside the threaded rod.

-  With this modification I'm able to adjust the position of the mig tip from right inside the down pipe to almost above rim of the venturi with no improvement.

 

What is the ideal position?

 

8 hours ago, timgunn said:

Looking at the photo, it seems that with the brass sleeve-thing inserted into the threaded nipple with enough sticking out at the back end to get the hose on, the jet will be somewhere close to flush with the end of the threaded nipple? I suspect that'll cause all kinds of turbulence right where you don't want it. 

 

Do you think it might help to grind off the threads and smooth out the lower part of the threaded rod? I filed down the inside of the pipe and smoothed out that joint as much as possible.

 

13 hours ago, Jerrod Miller said:

I'd try it without the nut/washer flange piece, then try adjusting how far the MIG tip sits into the flare, from deep down in to out of the flare.  Also try various pressures and flow rates throughout.  

 

Best results have been with the choke down to about the position in the last photo.  I'll admit, I tried to be systematic with the tests, but I have a very simple adjustable regulator, no flow sensor, and there was some frustration after 4 testing sessions burning lots of gas and no results......frustration is not the friend of logic.

IIRC the result with the choke all the way up sounds like a pulse jet engine.

 

8 hours ago, timgunn said:

If the installed burner is similar to the right-hand one in the first pic, there's a very long length (in total) of pipe on it plus an elbow. A screwed 90-degree elbow is usually considered to be equivalent to "about" 30 pipe diameters in terms of pressure loss IIRC. I think the left-hand one in the top pic is probably pretty close to convention at "about" 8 pipe diameters. The one on the right looks to be equivalent to perhaps 40-50 diameters. 

 

This sounds important but you just went way over my head.......:P

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The length of the burner tube matters. There is a pressure loss (resistance to flow)  associated with the length of the pipe and the flowrate. The maths gets pretty complex pretty quickly. 

 

The gas issuing from the jet generates a low-pressure zone around the gas stream that draws air in. The gas and air mix with the gas slowing down and the overall gas/air mixture retaining the momentum of the original gas flow. This effectively results in a (very) small overpressure that drives the turbulent mixture along the burner tube towards the forge. "Some" length of burner tube is necessary to get adequate mixing, but the longer the tube is, the greater the pressure loss along the tube. "About" 8 pipe diameters seems to be the length that most of the homebuilt NA burner designers have found works best. Elbows and other fittings offer a restriction to flow that can be expressed (for "simplicity", though that is a relative term) as an equivalent length of pipe.

 

The combination of pipe lengths and the elbow looks, to my strictly inexpert eye, to be equivalent to about 5 or 6 times the "works best" value.

 

The (fuel) gas pressure is so high that the gas will flow regardless. The extra resistance to flow will therefore affect the airflow almost exclusively, reducing the amount of air relative to fuel.

 

Going to a smaller gas jet should help to get the mixture back towards a "good" mixture.

 

If the resistance to flow in your long pipe is high, the mixture speed will be relatively slow. The mixture needs to move towards the forge faster than the flame-front can move through the mixture in the opposite direction. If the flamefront moves faster through the mixture, the flame will run back down the burner tube until it runs out of mixture to burn (somewhere near the gas jet, where the gas and air have not had the time/distance to form a flammable mixture). The flame will go out, mixture will start to flow. After a time, it will reach the hot forge chamber and ignite, whereupon the process will repeat. I am guessing this may be the pulse jet effect you mention. 

 

 

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Gerhard, how long are your pipes and what is the inside diameter?

Gary LT

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I had a bit of an epiphany this weekend, put back my old improvised burners to get some forging working done, and realised  the one thing I haven't tried is shorter pipes.....

Thank you @timgunn for taking the time to explain, my English 2nd language finally caught up and now I have something to work with.

25mm pipe, there's a slight lip from the thread, ID measures 22mm but it should be 23mm cleaned up, so 184mm which is just more than half of the current length. The pipes are cheap so I can afford to play around a bit.
I'm a bit obsessed with the blade I'm working on ATM but I'll make time this week for some more tuning.

 

Thank you all very much!

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Hi Gerhard, I’m certainly no expert however I have had some success recently with a Venturi burner. My set up used 1” black pipe, 8” long attached to this cast Venturi. You’ll see the fitting in the Venturi that the mig tip attaches to so it sits around halfway in the flare. The other end is a 2” flare. The mig tip is a 1.2mm. I run it around 7psi and it gets HOT. 57A068CE-4E23-4BBC-B13E-2CB17F31929D.jpeg

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So "about 8 pipe diameters" didn't work, still can't get it to burn outside the forge, and inside the forge the pulse jet effect is now permanent, couldn't tune it to burn evenly, noisier than ever.

Do I go shorter in small steps?

 

I'm starting to think there's something inherently wrong with the design, but it's a very close copy of the best burner I've seen in action, only real difference being that one used (what I think is called) a welding reducer for the venturi part.

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