Technical Gases

The most common industrial gases are oxygen, nitrogen, carbon dioxide and argon. In addition to these four main gases, there are dozens of other specialty gases that play an important role in industry. For example, hydrogen is used in fuel cells and engines, and helium is used in many cryogenic processes. Chlorine and bromine are used in water and wastewater treatment, while ammonia is essential for fertiliser production.

This article discusses the industrial gases argon, helium, nitrogen, carbon dioxide and oxygen. A distinction is also made between inert and protective gases, as their effect in the production press is very different.

Argon as shielding gas

Argon, like helium and xenon, is a noble gas and a very inert gas. For this reason, argon is used as a protective gas in industry. Argon is a very common element and occurs naturally in the Earth's atmosphere. With a concentration of almost one percent, argon is the third most abundant gas in the air we breathe, after nitrogen and oxygen. Because of this high concentration, this noble gas is chemically extracted directly from the air.

As argon does not form chemical compounds, it is an excellent shielding gas and is used in MIG and TIG welding, among other applications. In this process, argon displaces the ambient breathing air, preventing the oxygen in the air from reacting with the molten metal in the weld pool.

Argon is less expensive to purchase than helium because it is relatively easy to distill from the atmosphere.

Helium as an inert gas

A helium atom consists of two protons, two neutrons and two electrons. The electrons are located in the same, closed electron shell. The completely filled electron shell means that helium behaves very non-reactive. So far, no chemical compound containing helium has been discovered.

Even under extreme conditions, helium does not form any compounds with other elements. This inertness makes helium an excellent intert gas for industry. For example, during welding or laser cutting, helium displaces the ambient air and thus prevents chemical reactions between the heated metal and the oxygen contained in the air.

Nitrogen as an inert gas

Nitrogen is a colourless, odourless and tasteless gas that makes up 78 per cent of the volume of the Earth's atmosphere. Nitrogen is non-toxic, but in high concentrations it can be lethal (suffocation) to living things.

Nitrogen is an inert gas and can therefore be used as a shielding gas for welding and laser cutting. Nitrogen is also used in many other industrial applications. It is used as a coolant and as a protective gas in food packaging. Nitrogen compounds can be found in fertilisers and explosives. Nitrogen is used in nitriding to harden the surface of steel.

Nitrogen can be extracted directly from breathing air by chemical processes. Because of its abundance and worldwide availability, nitrogen is much cheaper than helium, argon or other shielding gases.

Nitrogen displaces oxygen in breathing air and prevents oxidation of molten metal during thermal processing. Welds made with shielding gases are much higher quality and more durable. In laser cutting, nitrogen prevents the formation of scale and slag and improves the quality of laser parts at the cut edges.

Nitrogen for laser cutting

Rime uses fusion cutting. The nitrogen used is ideal for cutting sheet metal without oxidation. Theoretically, an argon-helium mixture could also be used, but the price of nitrogen is about 40% lower than that of inert gases. The decision in favour of nitrogen is therefore also of an economic nature, in order to be able to offer laser cutting at reasonable prices.

Because nitrogen, like inert gases, does not form chemical compounds with the metal, the workpiece edges are very clean and rarely need to be reworked. This fact makes laser processing an economical sheet metal processing method despite the high nitrogen consumption.

Carbon dioxide - An inert gas becomes active

Carbon dioxide is often used as a protective gas and also shields our food, among other things. For welding, CO₂ can be used in combination with argon or helium. However, it is very important to note that carbon dioxide loses its protective gas character at higher temperatures and becomes an active gas.

This means that carbon dioxide reacts with the weld pool and carbon accumulates in the liquid metal. The enrichment is quite desirable in this welding process, as it can increase the hardness. The degree of this effect can be controlled by the amount of CO₂ in the shielding gas.

The problem with oxygen

With a volume share of 20%, oxygen is the second most common gas in our atmosphere and by far the most common element on our planet. This gas is very reactive and forms compounds with the majority of other elements. However, oxygen only develops its decomposing effect on iron and steel in combination with water. Through diffusion processes, water removes ions from the iron, which then enables the oxygen to attack the iron effectively.

The situation is different with welding, laser cutting or other thermal processing methods. Due to the enormously high temperatures, the oxygen can react with the metal even without the help of water. For this reason, the area where there is liquid metal must be shielded from the air by inert gases.

Oxygen, a steel pest

In a humid environment, oxygen attacks unalloyed or low-alloy steels and decomposes the surface of the material through oxidation processes. If this process is not counteracted, it continues. This leads to pitting and ultimately to the complete decomposition of the material.

Oxygen can also be introduced into the material during the processing of steel. This can happen during welding and laser cutting if not enough attention is paid to the use of protective gases (inert gases). An inert gas, such as nitrogen, prevents oxygen molecules from the surrounding air from entering the molten material. If the oxygen is not shielded, rust will form at the weld, which can make the welded structure unstable.

The reactive property of oxygen can also have a positive influence on steel production. If there is too much sulphur or phosphorus in the molten steel, then these elements can be burnt off with the help of oxygen. Oxygen is also important during refining (reduction of the carbon content).

In steel processing, oxygen is also used as an active gas. During flame cutting, oxygen is blown into the processing area instead of a protective gas in order to achieve a significantly higher temperature. This allows thicker material thicknesses to be processed. After cutting, however, the cut edges must be cleaned of slag and scale.