Plasma Gases and Their Uses

How to Choose the Best Gas for Your Plasma Torch

There are five main types of plasma gases used in CNC plasma cutting systems: compressed air, N2 (nitrogen), O2 (oxygen), H35 (argon-hydrogen), and F5 (hydrogen-nitrogen). Choosing which plasma gas is right for your operation depends on a number of factors including the material being cut, cut quality, material thickness, consumable life-span, and cost of production.

Compressed Air is the most commonly used and the most versatile gas for lower current plasma cutting and works well for most metals from gauge thickness to 1 inch. Compressed air can also be used for plasma gouging on carbon steel.  However a concern with air plasma is the weldability of the cut edge. Some nitriding and oxidation of the cut surface occurs with air plasma; this can cause porosity in welds. For versatility, good speed, low dross levels, and parts life up to 600 starts, air is a good option for many shops
Nitrogen is often used for higher current plasma systems and for cutting materials up to 3 inches thick, although for anything over an inch thick consider using argon-hydrogen. It is the best choice if you cut a lot of aluminum and stainless and the cut quality and parts life is excellent (over 1000 starts is normal). It produces excellent quality cuts on most materials.
Oxygen is used when the highest quality mechanized cuts are desired on carbon steel up to 1 -1/4 inch thick. The cut face is smooth, and dross is easy to remove. Oxygen can also be used on stainless steel and aluminum, but it produces a rougher cut face. Oxygen plasma gas reacts with carbon steel to produce a finer spray of molten metal, each droplet having a lower surface tension. This molten spray is more easily ejected from the kerf. The disadvantage of oxygen is the cost of the gas and the consumable parts life. However state-of-the-art oxygen plasma systems use inert starting gases (such as nitrogen) with oxygen plasma to achieve similar parts life to nitrogen or air systems. These systems may have parts life in the 800-1500-start range. Increased consumable and gas costs are usually offset by a decrease in expensive secondary operations to remove dross and straighten beveled parts.
Argon-Hydrogen mixtures are generally used for cutting stainless steel and aluminum cutting (>1/2″). The mixture typically used is 35% Hydrogen: 65% Argon (H-35). They produce a clean, high quality cut face. Argon-Hydrogen is required for mechanized cutting of any material more than 3 inches thick. This mixture also provides an excellent gas for plasma gouging on all materials. Argon hydrogen is the hottest burning plasma gas and provides the maximum cutting capability. Some jagged dross may occur along the bottom edge. The disadvantage of this combination is its expense.

F5 (5% hydrogen 95% nitrogren) is used primarily for cutting stainless steel.  F5 provides fast, oxide-free cuts, however the hydrogen gas introduces a lot of heat into the material. As a result, more dross forms, and cut parts often need cleaning before they can proceed to welding or painting. Using F5 also can also be expensive.