Can’t decide which gas to use for plasma cutting? Don’t sweat it—this post will help you make an informed choice.
There are five main options for which gas to use when it comes to CNC or handheld plasma cutting. These are:
- Compressed air
- Nitrogen (N2)
- Oxygen (O2)
- Hydrogen-nitrogen (F5)
- Argon-nitrogen (H35)
These gases have pros, cons, different costs, and are intended to cut various materials. Below, we will explore each of these gases, in turn, to determine which one works for what jobs.
Plasma Cutter Basics
For the uninitiated, a plasma cutter runs a charge through a concentrated jet of gas. The gas feeds into a torch nozzle attached to a CNC plasma cutting machine for precise cutting or a handheld nozzle for freehand.
The gas is fired at extremely high pressure against the surface of whatever metal needs cutting. The metal must be conductive, as an electric current is passed through the gas jet and connects with it. The electric arc works with the gas to transform it from a gas into plasma – the fourth state of matter.
Plasma is extremely hot (up to around 25,000 degrees Celsius) and cuts through the intended metal surface by essentially obliterating the material. A coating air jet, a secondary gas, removes any dross formed during cutting, leaving a smooth and clean cut.
Plasma cutters are intended solely for cutting metals (as mentioned above), making them a popular tool amongst engineers and artists. As a handheld tool, they are significantly more accurate and cleaner than a flame-cutting torch and faster to work with. However, the type of gas needed will depend on what metal needs to be cut and how thick it is.
Types of Plasma Cutter Gases
The industry standard of most plasma cutters is either compressed air, oxygen, or nitrogen. These are the most popular, but two others – Hydrogen-nitrogen and Argon-nitrogen- have their pros and cons to consider.
Compressed Air
This is the most common of all the gases used in plasma cutting. Compressed air is turned into plasma with a lower current than other gases and is ideal for high-quality cuts in aluminum and mild stainless steel.
Compressed air is typically used to cut through materials no thicker than an inch. It is also the cheapest and most freely available of all gases, as it is available from almost any source.
The cons of using compressed are that its cutting area is affected by high degrees of oxidation. This will affect the surface’s weldability post-cut, so you must clean it after completing the cutting process. It can also lead to porosity in welds and weakening joints, but you can avoid that by using a high-quality weld wire.
Finally, plasma cutters using compressed air will need either a separate air compressor or a built-in compression tank.
Nitrogen (N2)
Nitrogen is ideal for high-current plasma cutters due to the volatile reaction nitrogen has when turned into plasma. This intensity makes it great for cutting metals up to three inches thick, such as stainless steel or aluminum. You can also use it with argon.
The best secondary gas to use with nitrogen is carbon dioxide (CO2), which will help improve the cutting speed and lengthen the life of your plasma cutter. However, it will also increase the cost of the cut, as you will need a second set of gas cylinders to provide the CO2 input. Nitrogen gas is more costly than compressed air or oxygen, making thicker cuts more expensive.
However, the costs are offset by nitrogen’s excellent cut quality, as limited oxidation will occur along cut lines.
Oxygen (O2)
When working on a tight deadline, oxygen is an ideal gas for plasma cutting. This gas provides the fastest cutting speed without sacrificing cut quality. Oxygen is used to cut carbon steel up to 1.25 inches in thickness whenever a high-quality cut is required.
Using oxygen on carbon steel will create a fine spray of molten metal. Each droplet in this spray has a low surface tension, making it disperse quickly and cleanly. This is due to the high oxidation caused by using oxygen, reducing the surface metal to nothing. The fine spray makes the cut much neater, as any remaining metal is expelled away from the cutting edge as kerf.
You can use oxygen to cut stainless steel and aluminum. However, the cutting edge will be much rougher due to the less reactive nature of these metals.
Regardless of the metal, the lifespan of consumable parts when using oxygen is shorter than with other gases. Oxygen gas is more expensive than compressed air, but it does not need a secondary gas as it will naturally expel dross. This also reduces post-welding costs as the surfaces will not need cleaning or treating as they do with other gases.
Hydrogen-Nitrogen (F5)
A mixture of 5% hydrogen and 95% nitrogen is an ideal gas for plasma cutting through stainless steel. Due to the lack of available oxygen, hydrogen-nitrogen cuts will be free of any oxide, keeping them strong.
However, hydrogen-nitrogen mixed gases burn at a very high temperature, meaning that cuts will form more dross. This dross will harden at the bottom of any cuts and must be removed afterward and cleaned before you can use the piece.
Hydrogen-nitrogen is naturally a more expensive mix to use when cutting and must also move at a slower cutting speed. This combination makes it great for stainless steel cutting without a tight deadline, but it will always cost more than available counterparts.
Argon-Hydrogen (H35)
When working with stainless steel or aluminum, a mixture of argon and hydrogen is an ideal gas for plasma cutting. The ideal ratio for creating argon-hydrogen is 65% argon to 35% hydrogen. This is because it provides the hottest plasma-burning gas and will provide near-perfect, clean cuts in stainless or aluminum. However, H35 should never be used for cutting through mild steel, as it will not provide a clean cut, instead melting it into a rough slag.
Argon-hydrogen is most used to cut material more than three inches thick but less than six inches. It can also be used for plasma gouging on any material you need but will leave a jagged line of dross along the lower edge of the material. This dross line will need post-cut cleaning to make it workable, potentially incurring additional time or monetary costs.
To reduce the chances of ragged edges, you should use argon-hydrogen with nitrogen as a shielding gas, but this will also increase the cutting costs.
Conclusion
Plasma cutting is a fantastic tool for cutting metals such as mild steel, stainless steel, and aluminum. In many cases, it can be cheap and quick, but this will depend on factors such as the thickness of a given material. So long as you consider these factors, finding the ideal gas to use in any cutting job is simple.
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