Plasma cutting is a powerful yet simple process during which an electric arc is sent through a gas passing through a copper nozzle's constricted opening. The extreme heat that is created elevates the gas's temperature, converting it to the fourth state of matter called plasma. The plasma's electrical conductivity causes the arc to transfer to the workpiece, and the high-speed gas cuts the metal effortlessly.
Of course, the material must be conductive, meaning a plasma cutter works on carbon steel, stainless steel, aluminum, copper, brass, and cast iron. The dense stream slices through these metals, and the gas is also directed around the perimeter of the cutting area to shield the cut from contamination.
As you can see, the plasma cutter gas is a relatively crucial component in the plasma-cutting process. However, you must know which gases are suitable to guarantee the best performance and results. You'll need to choose a gas that matches up with the type of metal you're cutting. It will most times be a single gas, although you'll require a special combination of gases on occasion.
Plasma cutter gas types
The most common plasma cutter gases include air, hydrogen, oxygen, nitrogen, and argon. All five of these work relatively well on thinner sheets of metal, one-half inch or less, but when the plate thickness increases, fabricators typically use a combination of these gases to improve production.
In addition to the metal's thickness, its chemical characteristics and the cut's dimensions will factor into the plasma cutter gas selection process.
Here is a detailed look at each plasma cutter gas:
The most commonly used plasma cutter gas type is air. Highly versatile and inexpensive, compressed air works well for lower current cutting and on most metals—mild steel, stainless steel, and aluminum--from gauge sizes to one-inch thickness.
One of the primary advantages of compressed air is that it is inexpensive to purchase and store. You can use it as either the main gas or secondary fuel source, and it doesn't leave behind any particles as it cuts through metal.
PrimeWeld's CUT50DP plasma cutter uses an electrical current and non-hazardous compressed air to cut through stainless steel, alloy steel, mild steel, copper, and aluminum. A pilot arc improves the plasma arc's ability to transfer to the workpiece, allowing it to cut through rough, painted, rusty surfaces efficiently while producing minimal slag.
Another compressed air option is PrimeWeld's CUT50D Air Inverter portable plasma cutter. Inverter plasma cutters allow for a high-frequency arc start that jump-starts the plasma before jumping the gap from the torch tip to the work surface. Inverters are smaller and lighter than transformers meaning the entire machine is light-weight and portable.
One downside to using compressed air is that it can leave an oxidized cut area that might affect welding the cut's edge.
Oxygen has become the go-to gas for cutting mild steel because it offers clean cuts and faster cutting speeds on carbon steels up to a 1 ¼" thickness. While it isn't recommended for cutting stainless steel or aluminum, you can count on high-quality cuts with a smooth face and dross (mineral waste formed on the surface of molten metal) that's easy to remove from the kerf (the slit made by cutting with a saw) when you use oxygen with carbon steel. And oxygen works effectively in combination with other secondary fuels.
Some of the disadvantages of oxygen include its cost and the shortened life of the consumables. It doesn't work on shiny surfaces, making it ineffective on stainless steel and aluminum projects.
Nitrogen is often chosen as the plasma cutter gas for higher current systems and cutting materials up to 3" thick. It produces quality cuts on most materials, including stainless and mild steel and aluminum. For thicker metals, however, it's better to use nitrogen with air as a secondary gas. Also, consider carbon dioxide as a secondary gas if you want to increase the cutting speed and get a better finish.
Nitrogen is abundant and available in the atmosphere, making it an inexpensive choice. By itself, it's most effective on smooth and shiny thin sheets. However, you can use it with several secondary gases, such as air, carbon dioxide, and argon, for thicker material.
Argon is a rare, inert gas, making it relatively expensive but unreactive with the metals it's cutting. Using argon gas improves the stability of the arc and prevents atmospheric contamination of welding pools. While its high kinetic energy makes it an effective gas for plasma cutting, it can't work alone because of its low conductivity. As a result, argon must be paired with an appropriate secondary gas.
Along with being an excellent thermal conductor, hydrogen has the properties needed to quickly cool hot metal surfaces. For these reasons, hydrogen is ideal for cutting aluminum and stainless steel. However, although it has excellent conductivity, its low atomic weight prevents it from having high kinetic energy. Just like argon, it must combine with other gases to produce a high-intensity plasma flame.
Because they have contrasting properties, combining hydrogen and argon creates an outstanding plasma-cutting flame. With a standard mix of 65% argon and 35% hydrogen, it produces the hottest plasma cutting flame and some of the cleanest cuts. Typically used for cutting stainless steel and aluminum, the argon-hydrogen mixture is required for cutting material over 3" thick. It is also an ideal mixture for gouging practically any material.
The nitrogen-water plasma cutter gas mixture uses nitrogen as the main gas and water as the secondary (shield) gas. The energy produced from the plasma gas splits the torch's water into its two components--hydrogen and oxygen. The hydrogen isolates the cutting zone from contamination, leaving a clean cut free of dross and oxides.
Since it is converted into its essential components, the water does not require disposal. The water also helps reduce fume and nitrogen oxide emissions. This affordable plasma cutter gas mixture produces a glossy finish on aluminum and stainless steel.
PrimeWeld plasma cutters and multi-process units
PrimeWeld's top-of-the-line CUT60 Dual Voltage Plasma Cutter is a versatile machine appropriate for industrial settings or in a home workshop.
At the same time, the CT-520DP Pilot Arc Plasma Cutter Combo and CT-520D Plasma Cutter/Stick Welder Combo feature a high-quality plasma cutter teamed up with a TIG and stick welder. And our plasma cutters work with a variety of gases.