RayG
3rd Nov 2011, 04:58 PM
Hi All,
Here are three LPG burners, the first two are normally aspirated, the last one (most recent) is forced air.
The design is pretty simple, you have a LPG cylinder with an adjustable regulator, the one I use is a standard CIG (BOC) 0-400kpa, mostly I run in the range 0-150 kPa...
A gas jet, which can be as simple as a brass tube with a small hole pointing down the pipe, I've used gas tips so I can play with nozzle sizes, TWECO 14, I think from memory.
The next thing is a means of adjusting the mixture, this is just a series of slots that are covered with a sliding tube.
If you are running the burner in free air, then you need a flare on the end to reduce the gas velocity to less than the flame velocity, otherwise it will blow itself out, once the burner is inside the furnace, that problem goes away. A temporary flare of sheet metal is easy enough to make anyway.
Ok that's the basics.
This is the first one, normally aspirated, gas jet directed straight down the pipe, and sliding mixture adjustment.
http://www.backsaw.net/pics/Casting/DSCN0930.JPG
http://www.backsaw.net/pics/Casting/DSCN0931.JPG
The extra sliding section, was an experiment to see if the position of the gas jet relative to the air inlet section ending made any difference.. as a burner it worked fine, but struggled with larger bronze pours, so onto the second generation..
This one has a flared section for the air inlet, and the gas entry point is where we expect the air velocity to be the highest, just at the end of the flare (remember bernouilli)
http://www.backsaw.net/pics/Casting/DSCN0940.JPG
http://www.backsaw.net/pics/Casting/DSCN0932.JPG
http://www.backsaw.net/pics/Casting/DSCN0933.JPG
This is the best normally aspirated burner yet, we can melt 1 kilo of bronze in 7 minutes. The secret is more air and more gas. Unfortunately we couldn't get to cast iron temperatures, for that we need... more air more gas... so the next one is forced air.
Initially we used a vacuum cleaner (make sure you connect to the correct outlet), and ran that off a variac, it worked fine, but was very noisy, and way too big for the job. We melted zirconia fibre blanket with that cranked up, so I got a spa air blower, the kind that you use to put bubbles in your hot tub... (my hot tub goes to 1400C :) ) Big plus was that it's completely silent. and small.
Going to forced air, meant that I had to bring the gas in from the side, not ideal, but, I thought a quick shut-off valve would be a handy addition, so it quickly got over-engineered.
http://www.backsaw.net/pics/Casting/DSCN0935.JPG
http://www.backsaw.net/pics/Casting/DSCN0936.JPG
http://www.backsaw.net/pics/Casting/DSCN0934.JPG
The other upgrade for this burner, was to get some titanium tubing, going to cast iron temperatures was a problem with the steel tubing on the previous burners.
So it ended up over-engineered and you could make the same thing much simpler.
The blower speed is still controlled by a variac and the fuel/air ratio is a combination of gas pressure and blower speed.
The burner tuning is done by observing the flame colour as you adjust the mixture.
A rich mixture has a green tinge to it.
A neutral mixture is a nice clean blue long cone.
A lean mixture is a blue with short cone and reddish tinge.
This is a picture of one of the earlier normally aspirated burners, being tested, note the flare.
http://www.backsaw.net/pics/Casting/21062009796.jpg
Regards
Ray
Here are three LPG burners, the first two are normally aspirated, the last one (most recent) is forced air.
The design is pretty simple, you have a LPG cylinder with an adjustable regulator, the one I use is a standard CIG (BOC) 0-400kpa, mostly I run in the range 0-150 kPa...
A gas jet, which can be as simple as a brass tube with a small hole pointing down the pipe, I've used gas tips so I can play with nozzle sizes, TWECO 14, I think from memory.
The next thing is a means of adjusting the mixture, this is just a series of slots that are covered with a sliding tube.
If you are running the burner in free air, then you need a flare on the end to reduce the gas velocity to less than the flame velocity, otherwise it will blow itself out, once the burner is inside the furnace, that problem goes away. A temporary flare of sheet metal is easy enough to make anyway.
Ok that's the basics.
This is the first one, normally aspirated, gas jet directed straight down the pipe, and sliding mixture adjustment.
http://www.backsaw.net/pics/Casting/DSCN0930.JPG
http://www.backsaw.net/pics/Casting/DSCN0931.JPG
The extra sliding section, was an experiment to see if the position of the gas jet relative to the air inlet section ending made any difference.. as a burner it worked fine, but struggled with larger bronze pours, so onto the second generation..
This one has a flared section for the air inlet, and the gas entry point is where we expect the air velocity to be the highest, just at the end of the flare (remember bernouilli)
http://www.backsaw.net/pics/Casting/DSCN0940.JPG
http://www.backsaw.net/pics/Casting/DSCN0932.JPG
http://www.backsaw.net/pics/Casting/DSCN0933.JPG
This is the best normally aspirated burner yet, we can melt 1 kilo of bronze in 7 minutes. The secret is more air and more gas. Unfortunately we couldn't get to cast iron temperatures, for that we need... more air more gas... so the next one is forced air.
Initially we used a vacuum cleaner (make sure you connect to the correct outlet), and ran that off a variac, it worked fine, but was very noisy, and way too big for the job. We melted zirconia fibre blanket with that cranked up, so I got a spa air blower, the kind that you use to put bubbles in your hot tub... (my hot tub goes to 1400C :) ) Big plus was that it's completely silent. and small.
Going to forced air, meant that I had to bring the gas in from the side, not ideal, but, I thought a quick shut-off valve would be a handy addition, so it quickly got over-engineered.
http://www.backsaw.net/pics/Casting/DSCN0935.JPG
http://www.backsaw.net/pics/Casting/DSCN0936.JPG
http://www.backsaw.net/pics/Casting/DSCN0934.JPG
The other upgrade for this burner, was to get some titanium tubing, going to cast iron temperatures was a problem with the steel tubing on the previous burners.
So it ended up over-engineered and you could make the same thing much simpler.
The blower speed is still controlled by a variac and the fuel/air ratio is a combination of gas pressure and blower speed.
The burner tuning is done by observing the flame colour as you adjust the mixture.
A rich mixture has a green tinge to it.
A neutral mixture is a nice clean blue long cone.
A lean mixture is a blue with short cone and reddish tinge.
This is a picture of one of the earlier normally aspirated burners, being tested, note the flare.
http://www.backsaw.net/pics/Casting/21062009796.jpg
Regards
Ray