Blacksmithing is both a hobby and a useful skill. I initially planned to forge knives, but smaller projects are easier when first learning.
Making a Propane Forge Burner
A venturi propane burner is a great way to get started blacksmithing or operating a metal foundry. Propane burners and forges, when made correctly, are very easy to start. Propane is readily available at many stores due to its frequent use for grills. A proper propane burner can be built using many plumbing parts available at a local hardware store, and will get much hotter than a bernzomatic hand torch.
Fire and Combustion Basics
First, you need to understand a little bit about fire and combustion. All fire needs three things to burn:
Different components can work better or worse, giving different results. Increasing oxygen will increase the speed in which the fuel burns. This will ultimately increase the temperature you are able to reach in a forge or foundry.
As an example, an oxy-acetylene torch supplies 100% oxygen into the reaction, and is thus able to burn hot enough to melt and cut most metals. A coal forge uses coal as the fuel, and ambient air/oxygen, usually from an electric fan, hand cranked blower, or billows.
Propane forges can use a venturi burner, or a forced air burner. Here, we will learn about venturi burners.
What Is a Venturi Forge Burner?
A venturi forge burner is a device made to entrain larger amounts of oxygen into the combustion process inside a forge or foundry. The increased oxygen will speed the rate in which the propane will burn and allow for more complete combustion. More complete combustion and faster burning propane means higher temperatures, hot enough to be able to forge iron and steel. Venturi burners are popular because they do not require electricity to operate, and have few, if any, moving parts, making them very reliable. Generally, the only moving part during operation would be a choke.
How a Venturi Burner Works Using Bernoulli's Principle
Instead of using a blower to increase the speed amount of oxygen, a venturi burner utilizes a scientific principle called Bernoulli's principle. Bernoulli's principle states that as fluid and gas speed increases, the pressure decreases. This doesn't sound too important to blacksmithing, but a venturi burner is built around this principle.
Ambient air contains about 21% oxygen in most circumstances. Instead of increasing the concentration of oxygen(as in the oxy-acetylene example), we are going to increase the volume of air available to burn. The propane will provide the fuel needed for this reaction. The heat will be started with a spark or lighter, and then continued by continually feeding oxygen and fuel into the reaction.
Principles of a Venturi Forge Burner
A venturi burner works by ejecting propane through a venturi into a pipe into a combustion process, creating heat. Since the propane is being ejected at a high speed, it will not immediately disperse into the air, but can be directed, similar to how a stream of water from a garden hose can be directed. If this stream of propane is directed into a venturi, and through a tube, it will accelerate. This will also decrease the pressure inside the tube.
Remember Bernoulli's principle: As gas and water speed increases, pressure decreases. This decrease pressure creates a relative vacuum, causing ambient air (and oxygen) to rush into the venturi and into the tube with the propane. At the end of the tube is the flame, which will quickly burn due to the increased oxygen levels and readily available propane. A burner flare at the end of the tube will help keep the flame contained and directed towards what blacksmith piece on which you are working.
Parts of a Venturi Propane Burner
A venturi burner for blacksmithing and in metal foundries contains four basic parts:
- Propane Ejector
- Venturi Head
- Burner Flare (recommended)
The propane ejector's job is to force propane into a smaller area, causing it to eject out as a thin stream into the venturi. Propane ejectors come in many shapes, sizes, and designs. In this application, a thin, directable jet should be used.
Three common propane ejectors for a forge burner:
- Propane Orifice 0.030 minimum
- TWECO MIG tapered contact tip 0.030 minimum
- Capped Brass Nipple pipe with hole drilled (starts at #68 and work your way larger)
Remember, larger is not always better!
The venturi head is what gives the environment to use Bernoulli's principle to increase airflow into your burner. Venturi heads can be made from plumbing parts, particularly a Tee, or a reducing Tee. Larry Zoeller from Zoeller Forge specifically recommends a "Ward reducing tee." You may have some difficulty sourcing these, as there are a few different styles of reducing tees, and this style is less common. They can be purchased directly from him at the burner parts page, but his whole site is very useful. A regular Tee with a reducer coupling can also be used, but will not be as good as the Ward Tee.
However, instead of purchasing a plumbing part to make into a venturi head, consider purchasing something designed to be a venturi head from the start.
Optimal tube length is going to be different for every application. What I would recommend is to purchase two or three pieces of black iron tubes of about 10 inches to use. One will be used to find optimal tube length, while the other will be the final tube. Run your completed venturi burner with a 10 inch tube, and then cut it down by an inch, and try it again.
Ensure you allow time for your forge to come to full temperature when testing each tube length. As you learn about how your forge works at a particular temperature, you can try cutting down you tube shorter to see how it performs. Use the second or third tube as a final piece. Black iron is cheap, so don't worry too much about ruining a tube.
Burner flares are optional, but recommended. Burner flares are the last half of the venturi to slow down the flow. However, you don't want too large of a flare. A gradual 12 to 15 degrees increase in diameter over an inch (2.54 cm) should be optimal.
Tips for Beginning Blacksmiths
Venturi forge burners are a great choice for beginning blacksmiths. They have few moving parts, and can be made from parts available at any big box store. While it can be easy to get caught up in making the "perfect" choice, getting started is going to be the biggest hurdle. Make something and move forward.
Do not slow down becoming a maker of things. Becoming a maker is a process, and making a propane forge burner is not a permanent decision that cannot be changed and improved upon. The important thing is to get started!
Start making decisions and progress, which can then be refined once you get more experience in this craft. Make it happen, gain experience, and make choices to advance the skills you have to make things in the future.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Devin Gustus
Burhan Mani on April 14, 2021: