make a gas forge run fuel rich?

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I have a new twin burner propane forge (venturi) I'm new to forging so need some advice.
I want to run the forge fuel rich sometimes.

Quoting Ed Caffrey from a few years back - "...ideal for bladesmithing. The flames burning outside the forge indicates that there is a fuel rich environment, what we often call a "carburizing" flame. It happens when the combustion has consumed all the oxygen inside the forge chamber, and the excess fuel comes outside the forge and gets its oxygen for the surrounding atmosphere. This type of environment minimizes scale, and makes for a much better forging, and forge welding environment."

Quoting Kevin Cashen - "The carburizing flame is rich in fuel and uses up any free oxygen in the forge so that there is a noticeable flame coming out the door of the forge as the unburned fuel combines with the outside oxygen. This leaves no oxygen to interfere with my welds."

so the question, is there anything I need to be aware of or careful about? Anything special about the dragon's breath?

thank you

 

[Stacy E. Apelt - Bladesmith]

If a forge is running properly, it will have a certain amount of dragon's breath. Except for avoiding singeing your beard, there is no concern over it.

What you want is just a little of flame outside the forge. A roaring jet engine appearance with two feet of billowing orange flame shooting out means there is way too much gas being pumped into the forge.

The way you control the chamber atmosphere on a venturi burner is by controlling the air. You choke the burner where the air enters. There is usually a round plate that can be moved to partially close the opening. On a blown burner, you can control both the air and the gas. Most folks tune the burners to get about 3-6" of dragons breath. If you are a purist, a forge with a just barely perceptible dragons breath is perfectly tuned.

Note - Look at the forge running in the dark, or at least in low light, to see how much flame is outside the port. It may not be fully visible in bright light.

 

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thanks for this
my hybrid burners have a choke built in so I'm good to go.

 

[stezann]

What Stacy said!

You can play with the dragon breath, and have a rough idea just approaching with your finger in front of the burner air inlet port...you'll see immediatly the flame changing.
It is not necessary actually closing the port, also placing something, disrupting the air path close to the port makes for fine tuning.

Any of theese regulations should be done when the forge is already well soaked at the working temperature range; if the forge is still cold it is too soon to make fine athmosphere regulations.

 

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Any of these regulations should be done when the forge is already well soaked at the working temperature range; if the forge is still cold it is too soon to make fine athmosphere regulations.

very good, thanks for the tip

 

[Salem Straub]

The more fuel rich your fire is, the more CO it produces, so be sure to ventilate your forging area well.

 

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The more fuel rich your fire is, the more CO it produces, so be sure to ventilate your forging area well.

my "shop" is a 2 car garage and I generally wheel the forge outside so all the neighbors can see
but thanks for the advice, I'll be aware of the CO