[TheForge] FAQ

[Jerry Frost]

Drats! How are we ever going to have a debate?

Diffusers are flame shapers, my old Johnson 133a has them. In the Johnson, 
the A:F mix is manifolded to four burner nozzles near the bottom of the 
firebox. The nozzles are flat rectangular flares that cause the flame to fan 
across the bottom of the forge.

With a blower driving the flame you can make the nozzles all kinds of 
shapes. I've seen pics of needle flames, broad short cones and vortices. 
While it isn't impossible to make these things work with naturally aspirated 
burners it's trickier. Guns are positive pressure and naturally aspirated 
are negative pressure devices. So, if somebody tells you naturally aspirated 
burners suck you can tell them their gun burners blow. <grin>

Pick a simple conical diffuser for instance. This is just an exagerated 
version of the burner flares being used to enhance N/A burners. An 
exagerated cone diffuser will increase the draw of the burner exponentially, 
making it harder to get a proper burn. On top of that an increase (flare) 
greater than 1:12 makes turbulence that makes tuning a lot harder.

Most naturally aspirated burners with diffusers are purpose built. A Fisher 
burner being a perfect example. The Fisher burner was designed to make a 
very hot close flame over a wide area. It's tube is tapered over it's entire 
length from the throat to a point just below the nozzle where the body 
enlarges well more than the 1:12 ratio. Then it's capped by a perforated 
dome. The flame of a Fisher burner is (as I recall) only about 1/2" high, 
intense blue with little feathering. It spreads across the entire dome in a 
very uniform way.

There's a burner diffuser in use that's been mentioned here a few times in 
conjunction with gun burners. It's a bunch of burner nozzles in an array 
made by drilling or casting a grid of small holes in a block. A burner block 
maybe? A:F is fed into the block under pressure and it makes a wide even 
"wall" of flame in the forge.

Anyway, gun burners handle different diffusers better than naturally 
aspirated burners do.

Frosty
-------------------------------
If it ain't forged
it ain't real.
Wrought iron is.
The FrostWorks

Meadow Lakes, AK.

http://www.artmetalradio.com/

From: "Mike Porter" <michael.a.porter at comcast.net>


> Well, I'm not sure there's anything here to disagree with. When discussing
> dragon's breath, I'm referring to the end result exiting the forge. That 
> is
> not the same as the high velocity flame entering the equipment from a
> naturally aspirated burner. I like to design forges and furnaces so that
> that furious little flame is pretty well spent and puny by the time it 
> exits
> :-) Tell us more about diffusers please; greedy minds want to know.
> Mikey
> P.S. "Pandora's Tums...catchy. Now all I need is a text to go with it :)
>