Depending on the type of material to be processed, the gas choice is crucial for process efficiency. Hence, the right choice of gas affects the speed and quality of the process and equipment life and operating costs. This guide will explain the combinations, characteristics, and benefits of the different plasma and shielding gases.
The gases used in plasma torches can be divided into plasma and shielding gases. Plasma gases are the gases which the plasma cutter or plasma cutting machineuses to produce the plasma stream. Accordingly, shielding gases, are used for cooling, focusing and protecting the nozzle.
A mixture of argon and hydrogen is ideal for cutting thick aluminium or stainless steel components. However, it is not recommended for mild steel. The shielding gas is usually pure nitrogen. Hence, this solution, on the one hand, guarantees high quality on the other hand it is quite expensive.
Furthermore, the addition of nitrogen to the argon/hydrogen mixture can increase productivity and quality when machining high alloy steels.
Nitrogen plasma is characterised by high cutting speed and long service life of consumables. Therefore, it is best suited for the process of thin workpieces. Additionally, air is the optimal shielding gas for nitrogen plasma.
Although the use of CO2 as an auxiliary gas is a more expensive solution, it increases the cut quality and speed as well as the life of consumables. Moreover, as an alternative to nitrogen, water can be used as a shielding gas to ensure a very high-quality cut on aluminium and stainless steel.
Besides, in the case of a nitrogen-hydrogen mixture, the addition of hydrogen reduces the surface oxidation that occurs when pure nitrogen is used.
A prevalent gas used in plasma torches is atmospheric air. This natural, freely available mixture of nitrogen, oxygen and trace gases characterises with by its availability, low price and high cutting quality and processing speed. Although the air has no cost, it is vital to consider the need for a suitable compression and filtration system to keep the air free of moisture, oil and contaminants. Therefore, operators often use the air as a shielding gas in this solution.
Oxygen plasma is excellent for machining mild steel – it offers a high cutting speed and excellent quality. However, it is not recommended for cutting aluminium or stainless steel. The disadvantages are relatively high costs and reduced equipment life (recently improved with modern systems). The shielding gas used with oxygen is atmospheric air.
Below we present a table summarising the most important information about plasma gases.
| plasma gas | shielding gas | recommended application | advantages and disadvantages |
|---|---|---|---|
| argon/hydrogen | nitrogen nitrogen/hydrogen | stainless steel aluminium with greater thicknesses | +high-quality cuts for thicknesses above 127 mm -high cost |
| nitrogen | atmospheric air carbon dioxide water | mild steel stainless steel aluminium | +speed, quality and durability of parts. +excellent quality when used with water and water table -not recommended for thicker parts (<127 mm) |
| atmospheric air | atmospheric air | mild steel stainless steel aluminium | +excellent quality/price ratio -oxidation/nitriding of the cutting surface |
| oxygen | atmospheric air | mild steel | +excellent cutting quality and high speed for thin workpieces -not recommended for hard steels and aluminium high cost |
The vast majority of plasma cutter users use atmospheric air. Therfore, this gas is the most commonly used because of its availability and price. Accordingly, one-off purchase of, e.g. a screw compressor solves the problem and contributes to plasma cutting of excellent quality.
The article is based on:
Cięcie plazmowe [Plasma cutting], Linde Gas, 2019. [Accessed: 29.06.2019].
Baran, K. Cięcie plazmą. Wpływ stosowanych gazów na jakość procesu, Projektowanie i Konstrukcje inżynierskie, 2015. [Plasma cutting. Influence of applied gases on process quality, Engineering Design and Construction, 2015]. [Accessed: 29.06.2019]. Available online: link [Polish]
Engineering Design and Construction, 2015]. [Accessed: 29.06.2019]. Available online: link [Polish]
Gas selection guide for plasma cutting aluminum, stainless steel, and mild steel. [Accessed: 29.06.2019]. Available online: link
Produkcja metalowa [Metal production], Air Product and Chemicals Inc., 1996–2019. [Accessed: 29.06.2019].