Moose Forge

Gas Forges

My first propane forge

My new forge - coming soon!

A forge typically uses propane or natural gas as the fuel. One common, efficient design uses a cylindrical forge chamber and a burner tube mounted at a right angle to the body. The chamber is typically lined with refractory materials, preferably a hard castable refractory ceramic. The burner mixes fuel and air which are ignited at the tip, which protrudes a short way into the chamber lining. The air pressure, and therefore heat, can be increased with a mechanical blower or by taking advantage of the Venturi Effect.

The Venturi effect is an example of Bernoulli's principle, in the case of fluid flow through a tube or pipe with a constriction in it. The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to conservation of energy: the gain in kinetic energy is supplied by a drop in pressure or a pressure gradient force. The effect is named after Giovanni Battista Venturi, (1746–1822), an Italian physicist.

Gas forges vary in size and construction, from large forges using a big burner with a blower or several atmospheric burners to forges built out of a coffee can utilizing a cheap, simple propane torch. A small forge can even be carved out of a single soft firebrick.

The primary advantage of a gas forge is ease of use, particularly for a novice. A gas forge is simple to operate compared to coal forges, and the fire produced is clean and consistent. They are less versatile, as the fire cannot be reshaped to accommodate large or unusually shaped pieces;. It is also difficult to heat a small section of a piece. A common misconception is that gas forges cannot produce enough heat to enable forge-welding, but a well designed gas forge is hot enough for any task.

What about natural gas and Propane?

Blacksmiths today now have access to gas-fired forges and furnaces as well as coal and coke forges to heat the iron. Gas forges offer the convenience of not having to worry about where to buy good smithing coal. Gas forges are not as hot as coal forges and take longer to heat the iron to a forging temperature. In all cases the lower heat value of gas means longer heat times and more oxidation. However the size and capacity of the gas forge allows a much larger number of straight un-worked, or nearly straight bars to be placed in the fire at one time, and therefore can heat more un-worked bars over a longer period of time than the coal forge. This last point is the reason why a business needing forgings is more likely to have a gas forge than a coal forge. On the other hand the coal forge is still king when higher heats on larger and heavier bars are needed, and fewer bars are to be heated for work, and for heating work of more complex shape which cannot be placed inside the limited interior area of the gas forge. Each type of forge (coal or gas) has its advantages and disadvantages, and this is why each shop must choose what type of setup works best in their situation. Many shops employ both gas and coal forges and use them each for specific tasks such as-coal for heavy bars and gas for large numbers of small work.

Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. In the United States, it is readily available practically anywhere since most gas grills run off refillable propane tanks. Natural gas is available in many areas as it is piped into your house for heating, cooking, etc. If you don't know whether or not you have natural gas available, you probably don't.

The lower temperature and slower heating associated with the gas forge is actually helpful to most beginner smiths and those with poor fire skills because, a cheap gas forge will not heat the iron to a sizzling white heat- suddenly destroying the iron. Instead the iron will waste away (slowly burning) in the fire over a long period of time, but the inexperienced smith need not worry about suddenly destroying his iron by accidentally leaving it in the fire too long. On the other hand...

Some gas forges CAN get hot enough to forge weld!

There are some homemade and custom designed gas forges that can reach this higher heat. If the reader is going the gas forge route, I recommend visiting Ron Reil's website to see how to design the hotter custom-made forges at http://ronreil.abana.org/design1.shtml . Ron has compiled a large collection of designs both of his own and those sent to him by friends. Lots of designs of burners, insulation, most are inexpensive. These guys keep adding more stuff.

Special fluxes needed for fire welding with gas forges.

Since gas forges will take longer to heat iron, more oxidation will develop during the extended heating period. Special fluxes are used to deal with the additional scaling which results from this oxidation.

Gee Mom, look what else I've found!

Wisdom of my father: "It takes more of a man to walk away from a fight than to stay and fight."